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1 0 2 Catheter Ablation of Supraventricular and Ventricular Arrhythmias Luz-Maria Rodriguez, Carl Timmermans, and Hein J.J. Wellens Historical Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2139 Indications for Catheter Ablation of Tachycardias. . . . 2140 Key Points • Catheter ablation has become the first truly curative treatment for many supraventricular and some ventricular tachycardias. • The success rate for anteroseptal and midseptal accessory pathways ranges between 95% and 100%, but the risk of creating a more complete atrioventricular (AV) block in patients with midseptal accessory pathways is not negligible. The recurrence rate after ablation of accessory pathways is low, and if necessary, the patient can be reablated with a high success rate. Patients should be followed for at least 6 months after ablation. • Catheter ablation in patients with AV nodal reentrant tachycardia (AVNRT) has been very successful in curing patients. • The success rate for catheter ablation for common atrial flutter ranges between 65% and 98%. There is a risk of recurrence of ablated atrial flutter of 10% to 55%. • In general, catheter ablation for atrial tachycardia is effective and safe. • In ablation procedures to treat atrial fibrillation, ostial pulmonary vein isolation is reported to result in a success rate of 70% to 80%. Potential complications include pulmonary vein stenosis and esophageal injury with or without atrioesophageal fistula. • Atrioventricular nodal ablation followed by pacemaker implantation is limited to patents in whom catheter ablation cannot cure the supraventricular arrhythmia, such as left atrial flutter, multifocal atrial tachycardia, and some atrial fibrillation. It is an accepted modality in patients with atrial fibrillation with a very rapid ventricular response that cannot be controlled with antiarrhythmic medication, external and internal cardioversion, and perhaps the atrial implantable defibrillator. Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2158 • Catheter ablation of ventricular tachycardia (VT) is much more modest in its success as compared to results in patients with supraventricular tachycardias (SVTs). In idiopathic VT, however, catheter ablation is a curative technique and should be offered early in the treatment of symptomatic patients. • Primary idiopathic ventricular fibrillation is characterized by dominant triggers from the distal Purkinje system. The triggers can be eliminated by focal energy delivery. Historical Aspects In 1967, programmed electrical stimulation of the heart was introduced into clinical cardiology independently by Durrer and coworkers1 in Amsterdam and by Coumel et al.2 in Paris. Programmed electrical stimulation of the heart has revolutionized our methods of diagnosis and treatment of cardiac arrhythmias.3 It resulted not only in the ability to localize the site of origin of the arrhythmia but also in better understanding of arrhythmia mechanisms, better interpretation of the arrhythmia electrocardiogram, and the development of new treatment modalities like antitachycardia pacing4 and surgical5 or catheter ablation to cure or control cardiac arrhythmias.6,7 In 1986, the first successful clinical arrhythmia ablation using radiofrequency current was reported.8 Early experience in ablation of supraventricular arrhythmias had variable results. With evolving understanding of the anatomy of the heart and the introduction of a new radiofrequency (RF) ablation catheter with a large (4 mm) distal electrode, the success rate improved dramatically.9,10 To date, catheter ablation has become the first truly curative treatment for many supraventricular and some ventricular tachycardias.11 The catheter ablation procedure should be preceded by a careful analysis of the 12-lead arrhythmia electrocardiogram 213 9 CAR102.indd 2139 11/24/2006 10:52:49 AM 214 0 chapter and an electrophysiologic study. The electrophysiologic study should consist of a systematic analysis of the arrhythmia by recording and measuring a variety of electrophysiologic parameters during the basal state and by evaluating the response to programmed electrical stimulation. Programmed electrical stimulation of the heart not only gives important information about the electrophysiologic properties of the atrioventricular (AV) node, the His-Purkinje system, the atria, and the ventricles, but also facilitates studying the mechanism and localizing the site of origin or pathway of an arrhythmia. How the electrophysiologic study and the subsequent catheter ablative procedure should be conducted will depend on the specific arrhythmia of the patient. Indications for Catheter Ablation of Tachycardias The efficacy and the safety profile of catheter ablation have resulted in the indications listed in Table 102.1.12 The approaches to the different types of supraventricular and ventricular tachycardias are discussed separately. 10 2 Catheter Ablation of Supraventricular Tachycardias Accessory Pathways As also discussed in Chapter 93 on preexcitation, an accessory atrioventricular pathway is a connection between the atrium and the ventricle crossing the AV groove on the left or right side of the heart. Originally, accessory AV connections were divided into those located on the right or left free wall, and the posteroseptal, anteroseptal, and midseptal region. Use of catheter ablation requires a more precise localization of the accessory pathways in the AV groove (Fig. 102.1). Free wall accessory pathways are subdivided in a posterior, lateral, and anterior localization. Posteroseptal accessory pathways may also be found in the wall of the coronary sinus and in some cases in the middle cardiac vein.13 Anteroseptal accessory pathways are those pathways located above the His bundle, and the midseptal pathways are those located in the midseptal area.14,15 The midseptum is the region located superior to the ostium of the coronary sinus but below the His bundle (Fig. 102.2). It is important to stress that accessory pathways may be conducting in both direc- TABLE 102.1. Indications for catheter ablation of supraventricular arrhythmias according to the American College of Cardiology (ACC)/ American Heart Association (AHA)/European Society of Cardiology (ESC) Guidelines12 Arrhythmia Classification Level of evidence Accessory pathways WPW syndrome (preexcitation symptomatic arrhythmias, well-tolerated I B WPW syndrome (with AF and rapid-conduction or poorly tolerated AVRT) I B AVRT, poorly tolerated (concealed accessory pathway) I B Single or frequent AVRT episode(s) (concealed accessory pathway) IIa B Preexcitation, asymptomatic IIa B AV nodal reentry tachycardia (AVNRT) Recurrent AVNRT I B AVNRT with frequent episodes in patients who desired complete control of arrhythmias I B Infrequent, well-tolerated AVNRT I B Focal atrial tachycardia (AT) Asymptomatic or symptomatic incessant AT(s) I B Nonsustained and asymptomatic AT III B Atrial flutter (AFL) First episode and well-tolerated AFL IIa B Recurrent and well-tolerated AFL I B Poorly tolerated AFL I B AFL appearing after use of class IC agents or amiodarone for the treatment of AF I B Symptomatic non-CTI dependent AFL after failed antiarrhythmic drugs therapy IIa B Supraventricular tachycardia after repaired congenital heart disease Focal AT or scar macro reentry tachycardia I C Classification I: Evidence for/and/or general agreement that the procedure or treatment is useful and effective II: There is confl icting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure or treatment IIa: Weight of evidence is in favor of the procedure or treatment III: There is evidence and/or general agreement that the procedure or treatment is not useful/effective and in some cases may be harmful Level A: (highest) derived from multiple randomized clinical studies Level B: (intermediate) data are on the basis of a limited number of randomized trials, nonrandomized studies, or observational registries Level C: (lowest): primary basis for the recommendation was expert consensus AVRT, atrial ventricular reentry tachycardia; CTI, cavotricuspid isthmus; WPW, Wolff-Parkinson-White syndrome. CAR102.indd 2140 11/24/2006 10:52:49 AM 2141 c a t h e t e r a b l a t i o n o f s u p r av e n t r i c u l a r a n d v e n t r i c u l a r a r r h y t h m i a s His bundle 1 anterior 2 perinodal 3 posterior CS AVN FIGURE 102.1. The location of accessory pathways along the tricuspid and mitral annulus. AS, anteroseptal; CS, coronary sinus; LA, left anterior; LL, left lateral; LP, left posterior; LPS, left posteroseptal; RA, right anterior; RL, right lateral; RP, right posterior; RPS, right posteroseptal. ostium FIGURE 102.2. The location of the three types of midseptal accessory pathways (anterior, perinodal, posterior) in the space between the ostium of the coronary sinus (CS) inferiorly, and the His bundle superiorly. AVN, atrioventricular node. tions (anterogradely and retrogradely), or only anterogradely, or only retrogradely. The latter pathway is called a “concealed” pathway. Concealed pathways are of two types, the rapidly and the slowly conducting one. To perform an ablation procedure, catheters are inserted through both femoral veins or the subclavian vein and positioned in the heart under fluoroscopy. A quadripolar catheter is placed in the high right atrium, the His bundle, and the right ventricular apex. A multipolar catheter is placed in the coronary sinus. Finally, the ablation catheter is positioned at the site of the accessory pathway as determined during the electrophysiologic study. In general, two fluoroscopic views, the left anterior oblique (LAO) and the right anterior oblique (RAO) projection, are used to position the ablation catheter in the accessory pathway region. In patients with a left-sided accessory pathway, the usual approach is to insert the ablation catheter into the femoral artery, retrogradely advance the catheter across the aortic valve, followed by positioning under the mitral annulus (Fig. 102.3). Mapping of the left AV groove to obtain specific electrograms, indicating the exact localization of the accessory pathway, is performed before attempting ablation. This requires a careful manipulation of the ablation catheter under the mitral annulus and a good understanding and interpretation of the recorded electrograms. This approach is used when the ventricular insertion of the accessory pathway is the target of ablation. If the atrial insertion of the accessory pathway needs to be ablated, the ablation catheter should be positioned on the mitral annulus. Some centers prefer a transseptal catheterization to ablate left-sided accessory pathways, and in those patients, ablative FIGURE 102.3. Figure illustrating the right anterior oblique (RAO) projection (A) of catheters positioned in the coronary sinus (CS), the high right atrium (HRA), the His bundle, and right ventricle (RV). The tip of the radiofrequency (RF) ablation catheter is located under the mitral valve in the left lateral region. The same catheters in the left anterior oblique projection (LAO) (B). Ablation Procedure CAR102.indd 2141 11/24/2006 10:52:50 AM 214 2 chapter energy is delivered at the atrial insertion of the accessory pathway. The catheter inserted in the coronary sinus anatomically marks the AV groove and helps in mapping leftsided accessory pathways. In patients with right-sided accessory pathways, the procedure is performed using either the femoral or subclavian approach. The ablation catheter is carefully advanced most of the time over and sometimes under the tricuspid annulus to obtain the optimal electrograms indicating the exact location of the accessory pathway. Posteroseptal accessory pathways are located in the posteroseptal space (right and left) just outside and below the coronary sinus ostium. Some accessory pathways can also be located within the coronary sinus or in one of its branches (e.g., middle cardiac vein). Therefore, mapping of the posteroseptal space should also include the first centimeters of the coronary sinus and its posterior branches.13 Because of the vicinity of the conduction system (right bundle for anteroseptal accessory pathways; His bundle and AV node for midseptal accessory pathways), mapping of these regions should carefully and precisely be performed before delivering ablative energy. This is to avoid complications such as right bundle branch block or complete AV block, which may require permanent pacemaker implantation. Optimal Ablation Site Several electrophysiologic criteria are used to localize the optimal site to deliver ablative energy.16–19 During preexcited rhythms the following parameters are used to localize the ventricular insertion of an accessory pathway: the local AV interval, the earliest ventricular activation compared to the delta wave, and the recording of an accessory pathway potential (Fig. 102.4). Certain morphologies of the unipolar electrogram and an early intrinsic deflection of the unipolar A I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 HRA HIS AV RF RFU1 RFU2 B 95-2286 95-2286 A-V = –20 ms 99512 A V AP 200 mm/sec FIGURE 102.4. (A) Upper part: The 12-lead electrocardiogram (ECG) in a patient with a left lateral accessory pathway. Lower part: endocardial recordings recorded from the high right atrium (HRA), His bundle, and the tip of the RF ablation catheter with the bipolar (RF) and corresponding unipolar recordings (RFU1, RFU2). Note that the bipolar electrogram of the RF catheter located at the successful ablation site shows an accessory pathway (AP) potential, and an AV interval of −20 ms. Furthermore, the unipolar RFU1 shows a PQS pattern. (B) After successful ablation preexcitation and the AP potential have disappeared, the AV interval recorded from the tip of the RF catheter ablation has lengthened to 100 ms. CAR102.indd 2142 10 2 I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 97-0153 99518 RFd RF1 RF2 25 mm/sec start FIGURE 102.5. The 12-lead ECG, the bipolar (RF) and the unipolar (RFUI, RFU2) electrograms during RF ablation in a patient with an anterogradely conducting left lateral accessory pathway. Note the disappearance of preexcitation immediately after RF energy application (*). recording relative to the delta wave onset may also indicate an optimal ablation site.18 The atrial insertion of an accessory pathway is usually localized by identifying the site of the shortest ventriculoatrial (VA) interval during ventricular pacing or during circus movement tachycardia or by recording an accessory pathway potential. In general, the following criteria are considered to select the optimal site for delivering ablative energy in preexcited rhythms: the presence of an accessory pathway potential, the onset of a local ventriculogram preceding the delta wave by 5 to 20 ms, a local AV interval less than 40 ms, and a PQS morphology in the unipolar recordings.18,19 In patients with a concealed accessory pathway, the ablation site of the atrial insertion is indicated by the shortest VA interval.20 If the ablation catheter has good tissue contact and the previously mentioned criteria are present, the loss of preexcitation or retrograde conduction should occur within seconds after delivering ablative energy. Disappearance of preexcitation within 10 seconds is a good predictor for long-term success (Fig. 102.5). After the interruption of accessory pathway conduction and after a waiting period of 30 minutes, the electrophysiologic study is repeated under isoproterenol administration (1 to 3 μg/kg) to ensure permanent interruption of the accessory pathway and to exclude other possible supraventricular tachycardia mechanisms. Success Rate of Ablation of Accessory Pathways The long-term success of catheter ablation depends on the correct localization of the accessory pathway and the experience of the operator. The success rate for left free wall accessory pathways is currently as high as 95% to 99%.7 The success rate for right free wall and posteroseptal accessory pathways is less than for left free wall accessory pathways and ranges between 90% and 93%. This is due to less good catheter stability (right free wall accessory pathways) and to 11/24/2006 10:52:50 AM c a t h e t e r a b l a t i o n o f s u p r av e n t r i c u l a r a n d v e n t r i c u l a r a r r h y t h m i a s rate. Based on this information, patients should be followed for 6 months after ablation. the complexity of the posteroseptal space (posteroseptal accessory pathways) where the accessory pathways may have an anatomic epicardial insertion with widespread branching, making complete ablation difficult. The success rate for anteroseptal and midseptal accessory pathways ranges between 95% and 100%, but the risk of creating complete AV block in patients with midseptal accessory pathway is not negligible. The success rate for a Mahaim-type accessory pathway (a decrementally conducting pathway inserting into the right ventricle) has also been reported as high as 90% to 100%.21 Recording of a Mahaim potential on the tricuspid annulus is a good indicator for a successful ablation (Fig. 102.6). Finally, in patients with circus movement tachycardia, using a slowly conducting accessory pathway for ventriculoatrial conduction, the success rate is as high as 95% to 100%.22 Complications of Accessory Pathway Ablation The risk of radiofrequency catheter ablation is related to the location of the accessory pathway. As previously mentioned, ablation of a midseptal accessory pathway carries the risk of complete AV block. In posteroseptal epicardially located accessory pathways, where the ablation has to be performed from the coronary sinus, there is a risk of damage to the coronary artery or perforation of the venous system leading to cardiac tamponade.13 A Multicentre European Survey25 reported on the complications of radiofrequency catheter ablation in 2222 patients with accessory pathways. Fourteen patients (0.63%) developed complete AV block, 16 patients (0.72%) had a cardiac perforation with or without tamponade, and 12 patients developed a clinically significant pericardial effusion. In three patients, death was thought to be related to the procedure. However, it is important to mention that this study analyzed retrospective data from an early period (1987–1992) of radiofrequency catheter ablation. Calkins et al.26 in a prospective study found a similar incidence of the same complications in the period 1992–1995. In children and adolescents, the American Society of Pediatric Electrophysiology27 reported 3.2% of complications after radiofrequency catheter ablation of supraventricular tachycardias in 4135 patients. The complications were complete AV block, cardiac perforation, pericardial effusion, cerebral emboli, and pneumothorax. A multivariate analysis showed three independent factors for recognizing patients with a high probability Recurrence of Conduction of Accessory Pathways In our institution, the incidence of reappearance of conduction through an accessory pathway after catheter ablation is around 8%. The time of recurrence of accessory pathway conduction ranged from 3 hours to 3 months.23 These figures are in agreement with other studies reporting a recurrence rate of 8% to 12% after a time delay of 4 to 7 months.24 Several variables have been reported to be predictors for recurrence of conduction over an accessory pathway: the presence of multiple accessory pathways, a high number of radiofrequency applications, young age,24 and a right-sided location.23 In general, the overall recurrence rate is low, and if necessary, the patient can be reablated with a high success I II III aVR aVL aVF V1 V2 V3 HBEP HBED 96-0419 V4 V5 V6 AF PF Mahaim 214 3 A RB M A M RF RB RB RB HBED HBEF RVA 100 mm/sec FIGURE 102.6. An electrophysiologic study in a patient with a preexcited tachycardia with atrioventricular conduction over an atriofascicular (Mahaim) fiber, and ventriculoatrial conduction over the His-AV node pathway. Note the presence of a Mahaim potential CAR102.indd 2143 (M) recorded with the tip of the RF catheter where successful ablation was performed. RB, right bundle; HBED, distal His bundle electrogram; HBEF, proximal His bundle electrogram. 11/24/2006 10:52:50 AM 214 4 chapter 10 2 tion. In the early days of catheter ablation, two approaches were suggested: the anterior approach to interrupt the fast pathway, and the posterior approach to block the slow pathway. These approaches were named anterior and posterior based on the location of the fast and slow pathway in the triangle of Koch. The fast pathway is located close to the His bundle, in the anterior part of the triangle of Koch, and the slow pathway is situated in the posterior part of this triangle (Fig. 102.7). Currently, fast pathway ablation is seldom used in view of the high risk of complete AV block (5% to 10%) because of the proximity of the ablation site to the compact AV node and proximal His bundle.31 Slow Pathway Ablation Procedure FIGURE 102.7. The triangle of Koch, composed of the tendon of Todaro (TT) superiorly and the tricuspid valve (TV) inferiorly. The coronary sinus ostium forms the base and the His bundle the apical part. The numbers in the triangle represent the three approaches to perform RF ablation of AV nodal reentrant tachycardia: 1, anterior; 2, midseptal; and 3, posterior. of developing a complication: the experience of the operator, the presence of right-sided accessory pathways, and a body weight of less than 15 kg. Also in this survey four deaths (0.11%) were reported. In the early days of catheter ablation, the fluoroscopy time was an important concern for eventual complications. To date, with more experience, procedure and fluoroscopy times have shortened, thereby reducing the risk of complications due to radiation. Atrioventricular Nodal Reentrant Tachycardia Catheter ablation in patients suffering from AV nodal reentrant tachycardia (AVNRT) has been quite successful in curing patients.28–33 It has become the treatment of choice when the patient is symptomatic with this arrhythmia, not responding to or not willing to take antiarrhythmic medica- FIGURE 102.8. The catheter position used for ablation of AV nodal reentrant tachycardia in two fluoroscopic views: (A) right anterior oblique view; (B) left anterior oblique view. CS, coronary sinus; CSO, CAR102.indd 2144 Two techniques have been used to ablate the slow pathway: the anatomic technique 30,32 and the electrophysiologic technique.28,29 In the anatomic technique, fluoroscopic landmarks are used to guide the positioning of the ablation catheter. Using the posterior approach, the ablation catheter is positioned in the posterior third of Koch’s triangle (Fig. 102.8). An atrial/ventricular (A/V) ratio of 0.5 or <1 in the electrogram recorded with the tip of the ablation catheter is required prior to the delivery of energy. A successful radiofrequency application is frequently associated with the appearance of a short episode of an accelerated junctional rhythm. After each application, conduction over the slow pathway and inducibility of AVNRT should be assessed. If this posterior approach is unsuccessful, the catheter is carefully moved to the midseptal region where ablative energy is again delivered. When using the electrophysiologic technique, ablation is performed based on specific electrograms representing slow pathway conduction. Two distinct morphologies of slow pathway potentials have been described. Jackman et al.28 described a sharp spikelike potential preceded by a lower frequency, lower amplitude atrial potential during sinus rhythm. The slow pathway potential usually follows the atrial potential after 10 to 40 ms. The slow pathway potential is recorded in the vicinity of the coronary sinus ostium, near the tricuspid annulus. coronary sinus ostium; HRA, high right atrium; RF, radiofrequency catheter; RV, right ventricle. 11/24/2006 10:52:50 AM c a t h e t e r a b l a t i o n o f s u p r av e n t r i c u l a r a n d v e n t r i c u l a r a r r h y t h m i a s Another type of slow pathway potential was described by Haïssaguerre et al.29 This is a low-amplitude, low-frequency signal, and it follows the atrial electrogram and is recorded in the midseptal area. Acute success of AVNRT ablation ranges from 90% to 100%.28,32 Few patients (1% in our laboratory) experience a recurrence of the arrhythmia and require a second procedure. The risk of AV block using the posterior approach is low (1%) compared to the anterior approach (5% to 10%).26,33 Other complications, like venous thrombosis and pericardial effusion, can occur but, in general, the risk of the procedure is low because no arterial catheterization is required. Right Atrial Common Flutter The most frequent form of atrial flutter, the so-called common or typical atrial flutter, occurs in the right atrium and may rotate in a counterclockwise (CCW) or clockwise (CW) manner.34,35 Nonfluoroscopic mapping36 and the use of multiple endocardial electrograms37 have identified the circuit of the right atrial common flutter. The CCW atrial flutter is a broad band of peri-tricuspid activation that enters the isthmus [the atrial tissue between the inferior vena cava (IVC) orifice and the tricuspid annulus (TA)], slows in its medial part, ascends the atrial septum, reaches the root of the superior vena cava, usually crosses anteriorly and rarely, fuses around it to descend the free wall. The CW atrial flutter, while running in the opposite direction, shares the same circuit with the same endocardial borders as the CCW atrial flutter. On the 12-lead ECG, the common atrial flutter shows the so-called sawtooth appearance. Ablation Procedure An atrial flutter ablation procedure usually requires the insertion of the following catheters: a duodecapolar catheter for detailed mapping of the lateral right atrial wall and the IVC-TA isthmus, and multipolar catheters to record the activation of the coronary sinus ostium–TA isthmus, the His bundle, and the coronary sinus. During the electrophysiologic study, the atrial flutter is induced and the type of isthmus conduction evaluated.38 Thereafter, an ablation catheter is positioned in the right atrial isthmus. The LAO and RAO views are used to guide ablation, either using fluoroscopy or a three-dimensional mapping system (Fig. 102.9). Two approaches have been described to ablate common atrial flutter: the anatomic approach39–42 and the electrophysiologic approach.43 The anatomic approach uses fluoroscopic landmarks to localize the right atrial isthmus, and the electrophysiologic approach targets areas with critical isthmus conduction determined on the basis of concealed entrainment or the presence of double potentials.43 Two isthmi have been described 38: the posterior isthmus (IVC-TA), which includes the space between the IVC and the TA (IVC-TA), and the septal (TA-CS) isthmus, which is the space between the TA (at the level of the posterior margin of the coronary sinus ostium) to the posteroapical margin of the coronary sinus ostium (CS) or to the eustachian ridge. In patients without atrial conduction between the coronary sinus ostium and the eustachian ridge, ablation of the septal isthmus produces complete conduction block from the TA to the coronary sinus ostium and to the IVC, eliminating both CCW CAR102.indd 2145 214 5 and CW atrial flutter.38 A linear ablation is performed in one of the previously mentioned isthmi, either by applying pointby-point radiofrequency energy or cryothermia, or by dragging the catheter during the radiofrequency application. Regardless of the approach used, the end point for successful ablation is the noninducibility of atrial flutter after completion of the ablation line and the demonstration of a bidirectional isthmus conduction block and the presence of double potentials in the cavotricuspid isthmus.41 Before ablation, pacing from the ostium of the coronary sinus results in the propagation of the atrial impulse in a clockwise direction to the IVC-TA isthmus and the lateral right atrium, and in a counterclockwise direction to the septum and the high right atrium. This pacing maneuver creates a collision of the atrial wave fronts in the lateral right atrium (Fig. 102.10A). In contrast, during pacing from the right lateral wall, the atrial impulse propagates in counterclockwise direction along the ICV-TA isthmus and in a clockwise direction to the high right atrium and septum (Fig. 102.10B). After completion of the ablation during bidirectional isthmus block, pacing from the coronary sinus ostium results in a single atrial wave front descending along the lateral right atrium (Fig. 102.10C). Pacing from the right lateral wall results in a single atrial wave front ascending the high right atrium and descending through the atrial septum (Fig. 102.10D). Finally, pacing is repeated under isoproterenol perfusion44 to confirm the noninducibility of atrial flutter and bidirectional isthmus conduction block. Using this methodology, the acute success rate of catheter ablation for common atrial flutter ranges between 65% and 98%.38–43 In a number of patients with atrial fibrillation, the arrhythmia may organize into atrial flutter while treating these patients with class III45 or class IC46,47 antiarrhythmic drugs. Catheter ablation of the right atrial isthmus may significantly reduce the incidence of atrial fibrillation in these patients.45–47 After ablation, these patients should continue to take the medication that changed atrial fibrillation into atrial flutter. Catheter ablation of the septal isthmus has a (small) risk of complete AV block. Other complications are similar to those reported for right-sided radiofrequency catheter ablation procedures. Recurrences of Right Atrial Common Flutter A high recurrence rate (10% to 55%) has been reported if noninducibility of atrial flutter alone is used as a criterion for successful ablation.40,48,49 The recurrence rate is lower (6% to 9%) in patients with bidirectional isthmus conduction block compared to patients with unidirectional isthmus conduction block or bidirectional isthmus conduction delay at the end of the procedure.50 In our hospital, isoproterenol is used to evaluate resumption of conduction after right atrial isthmus ablation.44 In some patients, isoproterenol infusion can unmask an apparent bidirectional isthmus conduction block, necessitating a new ablative procedure in the isthmus to create complete isthmus block. Left Atrial Flutter At the present time, two different types of left atrial flutter have been recognized. Spontaneous atrial flutter and atrial 11/24/2006 10:52:51 AM 214 6 chapter AP 10 2 LAO CS Halo His Halo CS His Cryo Cryo A B TV SVC His Halo IVC Halo CS His TV PS CS IVC SVC C flutters occurring after ablation of atrial fibrillation. Recently, by mapping the spontaneous atrial flutter with the CARTOTM Biosense system, electrical silent areas or zones of block in the left atrium were demonstrated.51 Different types of reentrant circuits could be delineated: (1) single-loop reentrant circuits, mainly rotating around the mitral annulus (Fig. 102.11); (2) multiple-loop circuits rotating around a silent area or around a zone of block anchored in one of the pulmonary veins; and (3) small reentry circuits localized in the left atrial septum, fossa ovalis, or one of the pulmonary veins.51 Termination of the perimitral flutter circuits can be obtained by deploying a line of ablation between the mitral annulus and the superior right or left pulmonary veins, or by connecting the mitral annulus and one of the silent zones. The peripulmonary vein circuits can be ablated by joining the pulmonary vein to the mitral annulus. Ablation of atrial flutters with small reentry circuits should be performed at the area of the slow conduction. The chronic success rate in this type CAR102.indd 2146 FIGURE 102.9. The catheter positions for ablation of a common atrial flutter in the right anterior (A), and the left anterior oblique view (B). A duodecapolar catheter (Halo) is positioned around the tricuspid annulus in such a way that the proximal poles (bipolar 20–19 and 18–17) are septally located, and the distal part (bipolar 1–2 and 3–4) covers the posterior isthmus region. The rest of the catheter covers the lateral wall of the right atrium. The ablation catheter (Cryo) is positioned in the posterior isthmus. A quadripolar catheter is located in the His bundle region, and a decapolar catheter inserted in the coronary sinus (CS) records left atrial activation. (C) The delineation of the cavotricuspidal isthmus for ablation using the NavX system in the anteroposterior (AP) and bottom view in the same patient. White spots with numbers represent the number and location of the ablation applications. In this example, cryoablation was used during the procedure. of atrial flutter is around 75%. Atrial flutter after linear ablation for atrial fibrillation has been reported to be as high as 7% (Fig. 102.12).52 Recompletion of the previous ablation line is necessary to treat this type of atrial flutter. Catheter Ablation of “Incisional Tachycardia” Atrial arrhythmias are a frequent clinical problem after surgical correction of congenital heart disease. Hemodynamic impairment and pressure overload, together with the presence of surgical scars and prosthetic material, may result in an arrhythmogenic combination of fi xed artificial obstacles and electrophysiologic abnormalities that cause scar flutters or macroreentrant incisional tachycardia.53 These tachycardias can occur after correction of atrial septal defects and after corrective surgery for complex anomalies, such as the Mustard, Senning, or Fontan procedures. They may also occur following right or superior atrial incisions during 11/24/2006 10:52:51 AM 2147 c a t h e t e r a b l a t i o n o f s u p r av e n t r i c u l a r a n d v e n t r i c u l a r a r r h y t h m i a s I III HBEd HBEp H1920 H1718 H1516 H1314 H1112 H0910 H0708 H0506 H0304 H0102 CS78 CS56 CS34 CS12 CRYO 011425 A B C D E 200 mm/sec 200 mm/sec lead III is shown. Intracardiac electrograms are recorded from the FIGURE 102.10. (A,B) Atrial pacing during sinus rhythm before His bundle area. H1.2 to H19.20 indicate 10 bipoles of the duodeablation. (A) Pacing at the coronary sinus ostium. (B) Pacing at the capolar (Halo) catheter positioned around the tricuspid annulus, and low lateral right atrium. Note a dual wave front of right atrial activaCS1.2 to CS7.8 represent four bipoles of a decapolar catheter placed tion with bidirectional conduction, which collides in H.9.10. (C,D) in the coronary sinus (CS). (E) Sinus rhythm with the presence also Bidirectional conduction block with the presence of double potenof double potential. tials in the cavotricuspid isthmus. (C) Pacing at the coronary sinus ostium. (D) Pacing at the low lateral right atrium. The surface ECG mitral valve surgery. The electrocardiogram (ECG) pattern of these scar flutters or “incisional tachycardia” is variable; the rate is often slightly below the lower limit usually accepted for common atrial flutter. The localization and the size of the scar may vary from patient to patient. Endocardial mapping of the entire reentrant circuit is sometimes difficult or impossible (especially after the Mustard and Senning procedures). Catheter ablation in these patients is targeted to areas forming a critical part (isthmus) of the circuit, identified on the basis of electrogram timing, fragmentation,54 or entrainment techniques.53 Using the entrainment technique, Kalman et al.53 reported an acute success of 83%. Seventytwo percent of the patients had a long-term clinical improvement and 50% of these patients were asymptomatic and did not require medical therapy after a mean follow-up period of 17 months. In some patients, the critical isthmus of conduction cannot be localized. In these cases, areas in proximity to anatomic or surgical barriers showing concealed entrainment with local return intervals equal to the cycle length of the tachycardia are targeted for ablation.55–58 In the study of Kalman et al., reentry was more often found around the atriotomy than around the septal patch of the atrial septal defect repair. We and other authors have reported isthmusdependent common atrial flutter in most of these patients.57,59 With new mapping techniques, like the three-dimensional, nonfluoroscopic mapping (CARTO) system, the scar can be more precisely located and the ablation site can be better directed and verified (Fig. 102.13). 397 ms FIGURE 102.11. An example of a clockwise perimitral flutter (cycle length, 400 ms) bounded by an anterior silent area (gray color) in the left anterior oblique (LAO) (A) projection. The posteroanterior (PA) view (B) shows a zone of block anchored in the left pulmonary vein (LPV) and a posterior silent area with bystander activation proceeding superiorly and inferiorly, colliding on its right lateral aspect. Radiofrequency ablation was performed to connect the mitral annulus to the anterior silent area. Solid arrows, circuit loop(s); dotted arrows, passive activation; double line, zone of block; RPV, right pulmonary vein. CAR102.indd 2147 y+ 7 ms LPV RPV SA RFC Mitral SA Left anterior oblique Posteroanterior 11/24/2006 10:52:51 AM 214 8 chapter 35 ms 10 2 I V1 II V2 RUPV LUPV –210 ms aVR V4 aVL V5 aVF A FIGURE 102.12. (A) Left atrial electroanatomic map of a patient with a “gap-related” left atrial flutter recorded during the tachycardia in the LAO projection. Color bars indicate the local activation time relative to the reference catheter. Gray color represents the scars caused by prior RF ablation. The arrhythmia revealed a circle (arrows) traveling around the left pulmonary veins, traveling up left * V3 III LLPV * * * V6 B before the left pulmonary veins and down the posterior left atrial wall, passing a gap with slow conduction in the ablation line encircling the left pulmonary veins. The red points show the gap in the ablation line. (B) The 12-lead during tachycardia showing positive flutter waves in the inferior leads and V1 (stars). Right atrium: activation maps y+ A 012219 I II III B H1718 H1516 aVR x+ H1314 H1112 H0910 aVL aVF L V2 213 ms Left posterior oblique view y+ H0102 CS910 CS78 CS56 V3 V4 V5 V6 25 mm/sec AFL (240 ms) R CS H0708 H0506 H0304 V1 D x+ 1.63 cm 0 ms z+ CS34 CS12 RF CS 200 mm/sec Conventional mapping (170 ms) FIGURE 102.13. An example of an atrial arrhythmia in a patient with patch closure of an atrial septal defect after excision of a left atrial myxoma. (A) Atrial flutter with positive flutter waves in lead II and negative in lead III. (B) Counterclockwise atrial activation along the tricuspid annulus (TA). The bipolar CS 9–10 is not activated in tandem with the halo catheter, and double potentials, as a CAR102.indd 2148 C I 012219 III HBEd HBEp H1920 TA Left anterior oblique-caudal view result of a previous ablation attempt, were recorded on the cavotricuspid isthmus (bipolar RF). These fi ndings suggest a bystander counterclockwise activation along the TA. (C) Confi rms reentry around the septal scar. (D) Bystander activation around the TA via two wave fronts. These two wave fronts collide in the posterior isthmus which was previously successfully ablated. 11/24/2006 10:52:52 AM 214 9 c a t h e t e r a b l a t i o n o f s u p r av e n t r i c u l a r a n d v e n t r i c u l a r a r r h y t h m i a s Atrial Tachycardia As shown in Chapter 91 on supraventricular tachycardias, the P wave axis and width can be very helpful in localizing the likely site of origin of atrial tachycardia. Atrial tachycardia can be classified according to its mechanism into automatic, triggered activity and reentry. As pointed out in Chapter 91, supraventricular tachycardias may be paroxysmal or incessant. Results from a metaanalysis study show that the clinical and electrophysiologic characteristics of atrial tachycardia may vary between different age groups.60 This study demonstrated that pediatric patients have more often automatic and incessant forms, whereas the adult patients present more often the nonautomatic forms with a paroxysmal pattern.60 Furthermore, right-sided atrial tachycardia and multifocal atrial tachycardia were more common in adults. It is important to know that in patients with incessant atrial tachycardia the inability to control the ventricular rate may result in a dilated (tachycardia-induced) cardiomyopathy. In these patients, catheter ablation of the site of abnormal impulse formation leads to cure of the arrhythmia and regression of pump failure.61,62 Atrial tachycardia can originate in the right or in the left atrium. The localization in the right atrium includes the crista terminalis, the right atrial appendage, the intraatrial septum (Fig. 102.14) around the tricuspid valve, and the coronary sinus ostium. In a few patients, the site of origin of the atrial tachycardia can be localized in the sinus node area (sinoatrial node reentrant). Atrial tachycardia originating from the left atrium is more commonly located in the ostia of the pulmonary veins and less frequently located in the free wall and the atrial appendage. Rarely, atrial tachycardia may be found in the Marshall ligament and may be the trigger of atrial fibrillation (Fig. 102.15).63 A B A BLATION PROCEDURE Currently, two techniques are used to localize the site of origin of atrial tachycardia: the technique using multielectrode catheters and the three-dimensional, nonfluoroscopic mapping (CARTO, EnSiteTM) system; or a combination of both techniques (Figs. 102.14 and 102.15). The left atrial tachycardia is approached by the transseptal technique. The electrophysiologic criteria used to localize the site of origin are the earliest atrial activation time preceding the surface ECG P wave, an optimal pace map, and concealed entrainment. Catheter ablation of focal atrial tachycardia has a high success (99%) and low recurrence rate (4%).64 Chen et al.64 found that the presence of a right-sided atrial tachycardia was the only independent predictor of successful catheter ablation. Although the left atrium is easily accessed using the transseptal technique, left-sided mapping may be more difficult than right-sided mapping. In general, catheter ablation for atrial tachycardia is effective and safe. No procedurerelated complications have been reported. Atrial Fibrillation To date, catheter ablation of atrial fibrillation has been shown to be most effective in patients with symptomatic paroxysmal atrial fibrillation resistant to antiarrhythmic drugs. Strategies aimed at treating atrial fibrillation are trigger elimination and substrate modification. C D RA septum 02.2397 I II III aVR aVL 02.2397 I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 aVF HISD V1 HISP LA septum 02.2397 y+ 45 ms –77 ms z+ CS910 V2 LA RA x+ His CS78 V3 CS34 V5 CS12 V6 CARTO 10 mm/mV 25 mm/s 1.50 cm –5 10 mm/mV 200 mm/s FIGURE 102.14. The 12-lead ECG (A) of a patient with a focal atrial tachycardia. Mapping of the right (RA) and left atrium (LA) showed the earliest activation in the inferior part of the left side of the atrial septum (B,C). The electroanatomic mapping during atrial tachycardia confi rmed this location (D). Color bars indicate the CAR102.indd 2149 CS TV CS56 V4 MV –20 200 mm/s local activation time relative to the reference catheter. Ablation from the left septum stopped the tachycardia. CS, coronary sinus; HISD, HISP, His bundle electrograms distal and proximal; TV, tricuspid valve. 11/24/2006 10:52:52 AM 215 0 chapter A 10 2 B y+ y+ LSVP –125 ms –125 ms LSPV LMPV x + LA R z+ His LIPV MV L LIPV x+ TV RA CS 2.00 cm 2.00 cm C I 010892 II III aVR aVL aVF V1 V2 V3 V4 V5 V6 25 mm/sec D I 010892 III HBEd HBEp H1920 H1718 H1516 H1314 H1112 H0910 H0708 H0506 H0304 H0102 CSd CSm CSp RF * 200 mm/sec 510 ms * FIGURE 102.15. Left (LA) and right atrium (RA) electroanatomic map during atrial tachycardia in the posterior-anterior (A) and LAO (B) views. Color bars indicate the local activation time relative to the reference catheter. Earliest activation (red color) occurs in the posterolateral region close to the atrioventricular groove with activation spreading gradually from that region over the entire LA. Right atrial activation occurs through a superior connection (Bachmann’s bundle) activating the left septum and the rest of the RA from superior to inferior. This activation is blocked in a bidirectional manner in the cavotricuspidal isthmus, as a result of a previous RF ablation. Red dots indicate radiofrequency applications. CS, coronary sinus; LIPV, left inferior pulmonary vein; LMPV, left intermediate pulmonary vein; LSPV, left superior pulmonary vein; MV, mitral valve; TV, tricuspid valve. (C) The 12-lead ECG shows isoelectric p waves in lead I and aVL and positive in the inferior and precordial leads with 2 : 1 atrioventricular conduction. (D) Endocardial recordings during atrial tachycardia of the RA and LA. The cycle length of the tachycardia is 320 ms. Note the Marshall potential (*) preceding the atrial electrograms recorded with mapping/ ablation RF catheter, positioned between the LSPV and the CS. From top to bottom, ECG leads I and III; bipolar intracardiac recordings from distal (HBEd) and proximal (HBEp) His bundle; high septal (H 1920), lateral (H1516), and low (H0102) RA obtained from a duodecapolar catheter positioned around the tricuspid annulus; distal (CSd), medial (CSm), and proximal (CSp). T RIGGER ELIMINATION As demonstrated by Haïssaguerre et al.,65 the majority of the triggers for atrial fibrillation originate from the pulmonary veins, but they may also be found in other areas, for example, the left atrium, Marshall ligament,65 coronary sinus, and superior vena cava.66 In the first 45 patients studied by Haïssaguerre et al., a single focus of atrial ectopy was identified in 29 patients, two foci were identified in nine patients, and three or four foci were identified in seven patients. Focal ablation, inside the pulmonary vein(s), was performed in this population. This approach has been abandoned due to the high recurrence rate67 and the occurrence of pulmonary vein stenosis with or without pulmonary hypertension.68 Therefore, other approaches were developed, for example, ostial isolation of the arrhythmogenic pulmonary vein(s) 67 or empirical isolation of all four pulmonary veins69 (one by one pulmonary vein isolation or encircling two by two pulmonary veins). Ostial pulmonary vein CAR102.indd 2150 11/24/2006 10:52:53 AM c a t h e t e r a b l a t i o n o f s u p r av e n t r i c u l a r a n d v e n t r i c u l a r a r r h y t h m i a s 2151 C I RSPV Lasso LSPV Lasso 03.1945 17 18 II V1 220 HRA D His CS 200 RSPV12 RSPV34 A 200 140 110 140 90 100 RSPV56 RSPV78 Cryo RSPV910 LSPV LSPV12 Lasso 310 220 200 200 310 220 200 200 Lipv LSPV34 LSPV56 CS B LSPV78 LSPV910 100 mm/s FIGURE 102.16. This is an example of mapping of the pulmonary veins (PVs) using circular catheters (Lasso) in a patient with paroxysmal atrial fibrillation who underwent PV isolation with cryothermia. (A) Fluoroscopy view in anterior-posterior projection showing two Lasso catheters in the right superior (RSPV) and left superior PV (LSPV), the coronary sinus (CS) and the His bundle catheters. (B) Lasso catheter and the cryoablation catheter in the LSPV; a isolation can be performed either by recording the pulmonary vein potential electrograms using circular mapping catheters with fluoroscopy guidance (Fig. 102.16) or, empirically, using a three-dimensional mapping system (Fig. 102.17).69,70 The chronic outcome using these two approaches is reported to range between 70% and 80%. The procedure end points, when pulmonary vein potentials are used to guide ablation, are shown in Figures 102.18 and 102.19. Although the incidence of pulmonary vein stenosis has decreased when a more ostial ablation is performed, the development of new complications has emerged, for example, esophageal injury with or without an atrioesophageal fistula.71 Therefore, other ablative energies for ablation of atrial fibrillation (see New Ablative Energy Sources, below) need to be considered. SUBSTRATE MODIFICATION In patients with chronic atrial fibrillation (persistent and permanent), the substrate (all conditions responsible for the continuation of the arrhythmia, e.g., areas of fragmentation, wave front curvature, sink-source relationship, etc.) is essential for the maintenance of the arrhythmia. At the present time, two techniques are used to modify the substrate. One technique encircles the right and left pulmonary veins two by two and connects the two superior pulmonary veins with a posterior line (Fig. 102.20).70 A second technique consists of delivering focal applications at the sites of fragmented electrograms in both atria during atrial fibrillation (Fig. 102.21).72 However, complications may occur with the first technique, such as pulmonary vein stenosis and atrioesophageal fistula.71 The latter is due to the vicinity of the esophagus to the left pulmonary veins and to the thickness of the CAR102.indd 2151 decapolar catheter is inserted in the LIPV (recording/pacing). (C) Initiation of a paroxysm of atrial fibrillation by a PV extrasystole (arrow). Note the earliest rapid and irregular activation in the RSPV in comparison to the LSPV or in the right atrium (HRA D). From top to bottom: leads I, II, V1, high right atrium (HRA D), circular mapping of the ostium (from 12 to 910) of the RSPV and LSPV. posterior wall of the left atrium (3 mm). A longer follow-up is needed to evaluate the impact of substrate modification on the arrhythmia burden in patients with chronic atrial fibrillation. FIGURE 102.17. This figure shows an example of an isochronal activation map during coronary sinus pacing after anatomically isolation of all four pulmonary veins. Color coding represents activation times. The earliest activation is located at the pacing site (red color). Note the abrupt color change from shades of yellow or green to purple (latest activation). The latest activation is around the PVs. Red dots represent RF applications. LA, left atrium; LLUP, left lower PV; LUPV, left upper PV; RLPV, right lower PV; RUPV, right upper PV. 11/24/2006 10:52:54 AM 215 2 chapter 04.0268 19 20 21 10 2 22 I II V1 HBED CS34 LSPV12 LSPV34 LSPV56 FIGURE 102.18. An example of entrance block between the left atrium and the left superior pulmonary vein (LSPV) after isolation with cryoablation. During coronary sinus (CS) pacing the left atrium and the PV potentials are dissociated (arrows). From top to bottom: leads I, II, and V1, HBED, His bundle electrogram distal, circumferential mapping from the ostium of the LSPV (LSPV12 to LSPV910). Cryo, cryocatheter. LSPV78 LSPV910 Cryo 50 mm/s Catheter Ablation of the Atrioventricular Junction Currently, AV junctional ablation followed by pacemaker implantation is limited to patients in whom catheter ablation cannot cure the supraventricular arrhythmia (such as in left atrial flutter, multifocal atrial tachycardia, and atrial fibrillation). It is an accepted treatment for symptomatic patients with atrial fibrillation in whom the arrhythmia and the ventricular response cannot be controlled by the currently existing treatment modalities, like antiarrhythmic drugs, external or internal cardioversion, and the implantable atrial defibrillator.73 Atrioventricular junctional ablation results in complete heart block and requires chronic pacing. For successful ablation, the catheter is positioned across the tricuspid valve to record a high atrial, small His bundle and small ventricular deflection. The success rate of this technique is close to 100%. On rare occasions, interruption of conduction over the AV node–His-Purkinje system cannot be achieved from the right side, and a left-sided approach is necessary. Modification or partial, instead of complete, AV nodal conduction74 has a moderate long-term success rate; therefore, complete interruption of the AV junction and pacemaker implantation is preferred in patients with rapid, uncontrollable ventricular rates. The best site for ventricular pacing in these patients is currently being studied, following reports of detrimental effects of right ventricular apical pacing. RUPV LAA LUPV I III 020147 L910 LLPV RLPV L78 L56 L34 R L12 CS78 MA CS56 CS34 Cryo 50 mm/sec FIGURE 102.19. This figure demonstrates the loss of PV potential of the left superior pulmonary vein (L) during coronary sinus pacing (CS) during cryoapplication. From top to bottom: leads I and III, circumferential recordings of the ostium of the left superior PV (L12 to L910), left atrial electrograms recording from several sites from the CS (CS78 to CS34). CAR102.indd 2152 FIGURE 102.20. Posterior-anterior view of an electroanatomic reconstruction of the left atrium, including the pulmonary veins (PV). Dark red dots represent ablation lines. A circumferential lesion was placed around the left and right PVs >5 mm from the orifices. In addition, two linear lesions were placed, one connecting the circular lesions in the posterior wall and one connecting the left circular lesion with the mitral valve (MV) (so-called left atrial isthmus). 11/24/2006 10:52:54 AM 215 3 c a t h e t e r a b l a t i o n o f s u p r av e n t r i c u l a r a n d v e n t r i c u l a r a r r h y t h m i a s 2.45 mV Bipolar 1-Map > 21 Tip 0.12 mV L R ABL ABL V4 420 410 420 410 370 400 CS d CS 3–4 FIGURE 102.21. A biatrial map (mesh presentation) in the anterior-posterior view. The arrow points to the electrogram recorded from the inferolateral (Inf lat) aspect of the right atrium. Note the short cycle length and fragmented atrial electrogram in this area (90 ms). RF application at this site terminated atrial fibrillation. CS 5–6 220 200 210 190 210 190 200 190 220 190 200 CS 7–8 CS P 90 Inf lat 1-2 Inf lat 3-4 Catheter Ablation of Ventricular Tachycardia Sustained monomorphic ventricular tachycardia (VT) is in 75% of cases associated with ischemic heart disease. In the remaining patients, cardiomyopathy (dilated or hypertrophied), valvular heart disease, and arrhythmogenic right ventricular dysplasia/cardiomyopathy are among the underlying cardiac causes. Sustained monomorphic VT may also occur in the absence of any other cardiac abnormality and is then called idiopathic. As discussed in Chapter 96, the 12-lead ECG during VT may be of help in identifying the etiology and the site of origin of the arrhythmia. Therefore, an effort should always be made to obtain a 12-lead ECG during VT.75 An electrophysiologic study is performed to analyze the number of VTs, their morphology, their site of origin, using mapping and entrainment techniques, and (in ischemic VT) the critical zone of slow conduction in the reentry circuit. In comparison to the outcome of catheter ablation in the patients with supraventricular tachycardias, the success rate in patients with VT is more modest. Catheter Ablation of Idiopathic Ventricular Tachycardia Idiopathic VT usually originates from the right ventricular outflow tract, and is in or close to the specific conduction system of the left ventricle. In a small series of patients, idiopathic VT has been found to originate in the root of the aorta and pulmonary artery. In the left ventricle, most idiopathic VTs are localized in the inferoposterior aspect of the septum in or close to the left posterior fascicle.76 Rarely, VTs are localized in or close to the anterior fascicle.77 The ECG characteristics of left ventricular idiopathic VT are discussed in Chapter 96. Ventricular tachycardias originating in the right ventricular outflow tract typically have a left bundle branch blocklike configuration with an intermediate or vertical QRS axis CAR102.indd 2153 210 200 in the extremity leads (Fig. 102.22). The mechanism of this VT is considered to be triggered activity. These VTs are frequently exercise related and catecholamine sensitive, and can be terminated by intravenous adenosine or beta-blocker A I B 92364 II III aVR aVL aVF V1 V2 V3 V4 V5 V6 92102 400 ms FIGURE 102.22. A typical example of an idiopathic right ventricular outflow tract tachycardia. (A) Note the vertical axis and the left bundle branch block-like shape of the QRS complex. (B) An optimal match between the clinically recorded 12-lead ECG and the ECG recorded during pacing on the septal site of the right ventricular outflow tract. 11/24/2006 10:52:55 AM 215 4 chapter administration. Recently, we reported that in patients with idiopathic left bundle branch block–shaped VT, the origin of the arrhythmia may be in the root of the pulmonary artery.78 The QRS shape of these VTs did not much differ from those originated in the right ventricular outflow tract (RVOT). The VTs arising in the inferoposterior aspect of the septum of the left ventricle have a right bundle branch block-like configuration and a left or northwest QRS axis (Fig. 102.23). These VTs can frequently be initiated by programmed electrical stimulation and terminated by intravenous verapamil.76 The mechanism of these VTs is probably microreentry in the left posterior fascicle. Mapping of these VTs consists of localizing the earliest ventricular endocardial activation during VT. Additionally, an optimal pace map (with the 12-lead ECG showing an identical QRS morphology during ventricular pacing as the QRS during spontaneous VT) (Fig. 102.22B) is required. Furthermore, recording of a fascicular potential can be useful in selecting successful sites in idiopathic VT originating from the inferoposterior aspect of the left ventricle79 (Fig. 102.24). In our experience,80 catheter ablation of the right ventricular outflow tract VT successfully eliminated the arrhythmia in 29 out of 35 patients (83%) and in 12 out of 13 VT (92%) from the left ventricle. After a mean follow-up period of 30 months, A B I I 10 2 93-2038 93871 I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 RF HBE CS d 100 mm/sec FIGURE 102.24. The 12-lead ECG of an idiopathic left ventricular tachycardia having a right bundle branch block–like morphology and left axis. Note the very sharp potential (the posterior fascicle) preceding the QRS complex in the endocardial recording from the radiofrequency ablation catheter (RF). CS d, distal coronary sinus; HBE, His bundle electrogram; RF, radiofrequency catheter. V1 V1 II V2 II V2 III III V3 V3 aVR V4 aVR V4 V5 aVL V5 aVL aVF V6 aVF V6 400 ms FIGURE 102.23. (A) The 12-lead ECG of a patient with an idiopathic ventricular tachycardia originating in the left ventricle in the inferoposterior aspect of the septum close to the posterior fascicle. Note that the ventricular tachycardia has a right bundle branch block–like configuration and a left axis deviation. (B) The 12-lead ECG of an idiopathic ventricular tachycardia originating more anteriorly in the apicoseptal aspect of the left ventricle. That ventricular tachycardia shows a right bundle branch block–like configuration and a northwest QRS axis. CAR102.indd 2154 there were four recurrences (14%) in patients with RVOT VT and none in patients with left ventricular VT. Unsuccessful ablation of right and left VT was characterized by more than one VT morphology and the presence of a delta wave-like beginning of the QRS (Fig. 102.25), suggesting an epicardial origin, and a pace map showing a correlation in fewer than 11 out of the 12 ECG leads. Other series of RVOT and left ventricular VT have shown similar success rate and rare complications.81,82 In patients who cannot be ablated from the right ventricle, specific characteristics of the QRS complex during VT may point to an origin in the left ventricular outflow tract or aortic root.83 In idiopathic VT, catheter ablation is a curative technique, and therefore, should be offered early in the treatment of symptomatic patients. Catheter Ablation of Postinfarction Ventricular Tachycardia Monomorphic VT due to the presence of scar tissue, most often after myocardial infarction, is commonly based on a reentry mechanism.11 Interruption of the reentry circuit by catheter ablation requires identification of an essential part of the reentry circuit. A reentry circuit varies in size, configuration, and location (subendocardial, midmyocardial, subepicardial). The region where the wave front emerges from the circuit is termed the exit site. The region proximal 11/24/2006 10:52:55 AM 215 5 c a t h e t e r a b l a t i o n o f s u p r av e n t r i c u l a r a n d v e n t r i c u l a r a r r h y t h m i a s A I II III V1 V2 V3 B I II 94579 V1 V2 III V3 aVR V4 aVL V5 aVR V4 aVL V5 aVF aVF V6 V6 400 ms 931381 FIGURE 102.25. Example of a patient in whom RF catheter ablation failed. (A) The 12-lead ECG during sinus rhythm. (B) The 12-lead ECG during ventricular tachycardia with a left bundle branch block–like morphology and right axis. Note the slow (delta wavelike) beginning of the QRS complex. tion, all inducible stable VT were targeted. Ten of 52 patients died (19%) and 16 patients (31%) had VT recurrences. In general, the long-term success ranges from 45% to 75%.85–90 In the majority of the patients reported in those studies and also in our patients, antiarrhythmic drugs were continued. A new approach that allows better localization of the reentry circuit(s) has been described to treat patients with multiple unstable VT morphologies.91 This approach consists of localizing the area of scarred tissue, and the regions of residual “viable” myocardium in the scar during sinus rhythm using the CARTO system (voltage mapping) (Fig. 102.28). The success rate using this approach varies from 70% to 88%. The success rate in postinfarction VT may be improved by using new ablative sources (cryotechnology) that can produce deeper lesions in case of calcified and fibrotic scars. In postinfarction patients who, after implantable cardioverter-defibrillator (ICD) implant require frequent shocks, catheter ablation may substantially reduce the number of shocks. Additionally, in patients who present with an electrical storm after an acute myocardial infarction, and in whom antiarrhythmic drugs and sedation failed to control the arrhythmia, catheter ablation of the triggering ventricular premature beats may be a bailout therapy.92 An uncommon form of VT that can be cured by catheter ablation is the Outer loop Exit CAR102.indd 2155 Proximal to the exit consists of a central and a proximal part (Fig. 102.26). After the wave front emerges from the exit, it propagates through a loop, back to the proximal region of the circuit. The outer loop is a broad pathway along the margin of the scar.11 Identification of the central part of the reentry circuit, which in general, exhibits slow conduction, is of importance to obtain successful ablation. If the zone of slow conduction is not too broad, a single ablation may terminate the VT. However, in some cases a broad portion of the reentry circuit has to be interrupted by a series of energy applications in a manner similar to that used for ablation of atrial flutter.84 Stevenson et al.11 have proposed criteria to identify the central part (slow conduction zone) of the reentry circuit. These criteria include the presence of a mid-diastolic potential, and the demonstration of concealed entrainment (Fig. 102.27). The strategy in these patients varies from center to center. Some centers advocate ablating all inducible stable VTs.11,85,86 Other groups87,88 prefer only to target the clinically stable one. In our institution, we prefer to target only the clinical VT(s). Sixty-one patients underwent catheter ablation in our institution. Successful ablation was obtained in 79%. After a mean follow-up period of 20 ± 10 months, 11 patients had a VT recurrence and 10 patients died (four patients from pump failure, three from sudden cardiac death, and three from noncardiac death).89 Our results are comparable to those reported by Stevenson et al.11 In their popula- Central Inner loop A B Outer loop FIGURE 102.26. The parts of a reentry circuit with an inner loop (A) and a broad outer loop (B) in scarred myocardium. 11/24/2006 10:52:56 AM 215 6 chapter 99520/1 10 2 aVF I 99-1344 II III aVR aVL aVF V1 V2 V3 V4 V5 V6 V1 HISd V2 HISp V3 RV V4 RFd 99-1344 I II III aVR aVL 99520/2 25 mm/sec V5 D V6 25 mm/sec A B I 99-1344 II III aVR aVL aVF V1 V2 V3 V4 V5 V6 HISd 99520/4 470 470 S-QRS = 270 450 HISp RV RFd 100 mm/sec PPI = 450 Eg-QRS = 270 C A start FIGURE 102.27. (A) The 12-lead ECG during ventricular tachycardia in a patient with an old inferoposterior infarction. The ventricular tachycardia shows a left bundle branch block–like morphology with QR complexes in lead II, III, and aVF. (B) Sinus rhythm with incomplete left bundle branch block. (C) Ventricular pacing in the infarcted area by way of the RF ablation catheter. Pacing is performed 20 ms faster than the ventricular tachycardia rate (fi rst four QRS complexes). Note that the morphology of the QRS during ventricular pacing is identical to that during ventricular tachycardia indicating concealed entrainment. The pacing spike-QRS (S-QRS) interval is 270 ms and is equal to the mid-diastolic electrogram-QRS interval (Eg-QRS). The postpacing interval (PPI) is the same as the pacing cycle length (450 ms). This suggests that the RF catheter is located in the zone of slow conduction. (D) RF ablation at the site shown in C terminates the ventricular tachycardia within 3 seconds. Note the appearance of complete left bundle branch block after VT ablation. This was due to catheter manipulation in the left ventricle. B C VT1 y+ PM 010985 Blpolar voltage ≥1.50 mV VT2 VT PM VT I II Exit VT1 III aVR ≤0.50 mV aVL aVF LV V1 V2 V3 V4 V5 1.46 cm V6 25 mm/sec 25 mm/sec Exit VT2 25 mm/sec 25 mm/sec (amplitude >1.5 mV); gray, dense scar (amplitude <0.5 mV) and range FIGURE 102.28. (A) A bipolar voltage map during sinus rhythm of between purple and red; border zone (signals amplitudes between the left ventricle (LV) in a posterior-anterior view of a patient with 0.5 and 1.5 mV). The 12-lead ECG during VT and pace map (B,C) an old inferoposterolateral infarction. The patient had two different directed the linear ablation. Arrows indicate the site where the exit ventricular tachycardias: VT1 with a left bundle branch block morpoint of the VTs was found. Linear lesions (red dark dots) were phology and left axis, VT2 with right bundle branch block morpholextended from dense scar and cross-border zone. ogy and northwest QRS axis. Color range indicates the ventricular electrogram amplitude (mV). Purple represents normal myocardium CAR102.indd 2156 11/24/2006 10:52:56 AM c a t h e t e r a b l a t i o n o f s u p r av e n t r i c u l a r a n d v e n t r i c u l a r a r r h y t h m i a s so-called bundle branch reentry VT.93 These VTs are observed in patients with extensive interventricular septal damage leading to conduction disturbances in the bundle branches and the septum (as in patients with ischemic or dilated cardiomyopathy after aortic valve replacement, myotonic dystrophy, and following chest trauma). The reentrant circuit in this type of VT may utilize one bundle branch as an anterograde limb of the circuit with after transseptal conduction retrograde conduction over the other bundle branch. These VTs, therefore, may show a left or a right bundle branch block-like morphology.94 They can be cured by ablating one of the bundle branches. Another possibility is that the reentry circuit uses the anterior fascicle and posterior fascicle of the left bundle branch. This is called “interfascicular” VT. In the latter situation, the VT shows a right bundle branch block-like configuration with right or left axis deviation.95 Catheter ablation of one of the fascicles can cure this type of VT. The results of catheter ablation of VT in patients with right ventricular dysplasia are frequently disappointing in the long term because of the progressive nature of the disease. Only a limited number of cases of VT ablation in patients with hypertrophic96 and dilated cardiomyopathy have been reported. In some patients with small and circumscribed subepicardial reentry circuits, like patients with cardiomyopathy secondary to Chagas’ disease or inferior wall myocardial infarction, epicardial catheter ablation has shown favorable results.97 Catheter Ablation of Ventricular Fibrillation Recently, catheter ablation of idiopathic ventricular fibrillation has been described in 27 patients. The initiating beat of ventricular fibrillation had an identical electrocardiographic morphology and coupling interval compared to the preceding isolated premature beats typically noted in the aftermath of resuscitation. The initiating ventricular premature beats were preceded by distal Purkinje activity in the majority of the patients and originated predominantly in the septum of the left ventricle. Interestingly, these triggers were also found in the right ventricle and were also preceded by Purkinje activity. After a mean follow-up 215 7 of 24 months, 89% of the patients had no recurrence of ventricular fibrillation as confirmed by the defibrillator memory. Primary idiopathic ventricular fibrillation is characterized by dominant triggers from the distal Purkinje system. The triggers can be eliminated by focal energy delivery.98 Larger series of patients and longer follow-up are needed to confirm the efficacy of catheter ablation of this type of arrhythmia. New Ablative Energy Sources While the vast majority of arrhythmia substrates can be successfully ablated using radiofrequency energy, this energy source has its limitations. For example, radiofrequency ablation may induce complete AV block when ablating focal tachycardia or accessory pathways close to the conduction system, or perforation of the coronary sinus if the accessory pathway is located in this anatomic structure. As mentioned in the section on ablation of atrial fibrillation, radiofrequency energy may produce pulmonary vein stenosis in patients undergoing ablation of paroxysmal atrial fibrillation. Pulmonary vein stenosis may lead to life-threatening pulmonary hypertension or hemorrhage.99 Furthermore, radiofrequency energy produces pain when ablating the cavotricuspidal isthmus,100 the coronary sinus, and the atria. Because radiofrequency energy produces endocardial disruption, cardiac perforation may occur. Another potential hazard of radiofrequency energy is the occurrence of a fistula between the left atrium and the esophagus.71 This complication may develop 3 weeks after radiofrequency ablation. It has become vital, therefore, to study other energy sources that could avoid these disadvantages. Table 102.2 compares current catheterbased systems that can be applied to treat cardiac arrhythmias with especial emphasis on the treatment of atrial fibrillation. We and other investigators have demonstrated that in contrast to radiofrequency energy, cryoablation does not produce acute or chronic pulmonary vein stenosis,101 is painless,100 and less thrombogenic.102 Furthermore, we have recently demonstrated that the long-term results of catheterbased cryoablation for supraventricular and ventricular arrhythmias are comparable to those reported with radiofrequency energy.103 TABLE 102.2. Comparison between radiofrequency (RF) and new ablative energy sources Clinical experience Endothelial disruption (e.g., PV stenosis) Thrombogenicity Mapping capability Ability to create transmural lesion Lesion size Perforation rate CAR102.indd 2157 RF Cryothermia Ultrasound Laser Microwave +++ Increased ++ Minimal + Increased + Increased + Increased High Yes Requires optimal contact + Low Low Yes Requires optimal contact (cryoadherence) + Very Low Medium No Requires optimal contact ++ Low High No Excellent, contact forgiving +++ High High No Excellent, contact forgiving +++ High 11/24/2006 10:52:57 AM 215 8 chapter 10 2 Summary During the past 15 years, catheter ablation developed into an effective and safe curative treatment for patients with different types of supraventricular arrhythmias including paroxysmal atrial fibrillation. This is also true in patients with idiopathic ventricular tachycardia and patients with bundle branch reentrant ventricular tachycardia. The technique, therefore, should be considered early in the therapy of these arrhythmias. Catheter ablation provides palliative treatment in patients with recurrent episodes of spontaneous welltolerated postinfarction VT. In atrial fibrillation ablation, new catheter designs, new ablative energy sources, and better understanding of how to define and localize the substrate are needed to improve results and to expand the indications for other subsets of atrial fibrillation (persistent, permanent). Catheter ablation should be restricted to centers where an experienced clinical electrophysiologist performs these often complicated and time-consuming procedures. References 1. Durrer D, Schoo L, Schuilenburg RM, Wellens HJJ. The role of premature beats in the initiation and termination of supraventricular tachycardia in the Wolff-Parkinson-White syndrome. Circulation 1967;36:644–662. 2. Coumel Ph, Cabrol C, Fabiato A, Gourgon R, Slama R. 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