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How To Differentiate Right Ventricular Outflow Tract Tachycardia from Arrhythmogenic Right Ventricular Cardiomyopathy? C. WOLPERT, C. ECHTERNACH, C. VELTMANN, R. SCHIMPF, M. BORGGREFE Introduction Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a disease characterised by partial replacement of myocardial tissue by fibrofatty tissue. Ventricular tachycardia may originate from the diseased areas and cause haemodynamically non-tolerated ventricular tachycardia, syncope, or sudden death already in young patients. Time of first diagnosis is usually before the age of 40 and not infrequently already in adolescence. The aetiology of ARVC varies and there are different hypotheses as to how ARVC develops [1, 2]. Among affected patients, there is a predominance of males and early reports suggested that in some cases the disease may be familial. Moreover, a number of different gene mutations in desmosomes have been identified, such as mutations in cytoskeletal proteins, plakoglobin, and desmoplakin, and both autosomaldominant and autosomal-recessive modes of inheritance have been reported. In some patients disease is also manifested in the left ventricle [3, 4]. Right ventricular outflow tract (RVOT) tachycardia is a benign condition. In the absence of structural heart disease, it is considered to be primary electrical defect that results in ventricular extra beats, salvos, or sustained tachycardias mainly from the right ventricular outflow tract, but also infrequently from other regions in the right ventricle, above the pulmonary valve or the sinus valsalva. A variety of mechanisms have been suggested, including cAMP-triggered activity through late after-depolarisation. RVOT tachycardia is also mainly observed in young patients, predominantly females, and often 1st Department of Medicine-Cardiology, University Hospital Mannheim, Faculty of Clinical Medicine of the University of Heidelberg, Mannheim, Germany 346 C. Wolpert et al. becomes symptomatic already in young adults. When confronted with a patient with left bundle-branch-block tachycardia with inferior axis, a diagnosis of idiopathic RVOT tachycardia can be made only after exclusion of ARVC. The differential diagnosis of ARVC is based on the criteria of the Task Force of the Working Group Myocardial and Pericardial Disease of the European Societ y of Cardiolog y and of the Scient ific Council on Cardiomyopathies of the International Society and Federation of Cardiology. Classification is based on electrocardiographic patterns of depolarisation and repolarisation, echocardiography, endomyocardial biopsy findings, magnetic resonance imaging results, arrhythmia history, and other criteria [5]. However, clinical presentation alone does not allow a diagnosis to be made in the majority of patients. To differentiate between ARVC and RVOT tachycardia is a clinical challenge, and an intense work up is essential to making the correct therapeutic decision. Electrocardiogram in Sinus Rhythm There are different signs in the surface ECG of patients with arrhythmogenic right ventricular cardiomyopathy, most strikingly, the T-wave inversion and an epsilon-wave in lead V1 or V2. In addition, a localised increase of the QRS duration of > 110 ms in leads V1–V3 or positive late potentials are signs for a potential ARVC [1, 6, 7]. However, they are not observed in every patient and especially not during early stages of the disease. Although patients with a normal ECG at rest are less likely to suffer from ARVC, in the studies of Niroomand [6] and O’Donnell [7], repolarisation abnormalities in the precordial leads varied between the two studies from 66% to 52% in patients with ARVC, and from 23% to 6% in patients with RVOT tachycardia. The ECGs of patients with ARVC often display an incomplete right bundle-branch block or T-wave inversion in the right precordial leads, sometimes also until V4, V5. In Niroomand’s study, T-wave inversion was seen in 13/15 patients (87%), while 14% of patients displayed epsilon waves [6]. O’Donnell observed positive late potentials on the signal-averaged electrogram in 78% of patients with ARVC and in none of the patients with idiopathic RVOT tachycardia. Electrocardiogram During Ventricular Tachycardia In patients with ARVC, the ventricular tachycardia (VT) shows a pattern of left bundle-branch block. The QRS axis is shifted to the right when the VT originates in the pulmonary infundibulum. The axis may also be shifted to the extreme left when the VT arises from the diaphragmatic wall or is locat- ARVC and Idiopathic Ventricular Tachycardia 347 ed in the right ventricular apex or close to the tricuspid annulus [1, 2]. In patients with ARVC, the upstroke of the QRS complex seems to have some ‘slurring’ and a slew rate that is less steep. The QRS complex also appears broader. In the study by Niroomand et al., the axis during VT in ARVC was inferior in 48%, intermediate in 27%, and left/superior in 20% of patients. In contrast, in patients with idiopathic RVOT tachycardia, it was inferior in 90% and intermediate or superior in only 5% [6]. The most common clinical presentation of RVOT tachycardia is a frequent, nonsustained repetition of uniform, monomorphic VT alternating with periods of sinus rhythm. Isolated ventricular extra systoles present the same morphologic pattern as observed in tachycardia. The cycle length of sustained ventricular tachycardia commonly ranges from 140 to 180 bpm [8, 9]. Transthoracic Echocardiography The structural major abnormalities in ARVC can be detected by echocardiography, but minor abnormalities are seen only by magnetic resonance imaging (MRI). The signs of the disease are dilation of the right ventricle, the presence of aneurysm during diastole, and dyskinetic areas in the inferobasal region. Therefore, if there is any doubt about the diagnosis after transthoracic echocardiography, the patient should undergo cardiac MRI. Nuclear Magnetic Resonance Imaging Patients with right ventricular tachycardia should undergo MRI before intervention in order to detect aneurysms, intramyocardial fat, or advanced wall thickening before catheter ablation, if not distinct on echocardiography or right ventricular ventriculography [10]. Electrophysiological Study Electrophysiological studies (EPSs) may help to differentiate RVOT tachycardia due to ARVC from idiopathic RVOT-VT. In the setting of ARVC, the signals of the endocardial electrograms may be significantly altered in terms of activation delay, fragmentation, amplitude decrease, or dense scarring. These features are not likely to be found in idiopathic RVOT tachycardia patients. Some investigators have analysed the endocardial electrograms by using an electroanatomical mapping tool. Using this approach, Boulos et al. found a significant difference between patients with ARVC and those with idiopathic RVOT tachycardia [11]. They also compared the duration and amplitude of 348 C. Wolpert et al. the electrogram between normal probands, patients with RVOT-VT, and patients with an ARVC, and could demonstrate that while there was no difference between normal probands and patients with an idiopathic RVOT-VT, there was a very large difference compared to ARVC patients [11]. Areas with a strong disposition to fibrofatty degeneration and therefore areas to look for fragmentation or scarring are the RVOT, the subtricuspidal base of the ventricle, and the RV-apex. Another indicator for VT in structural heart disease is repetitive inducibility by programmed stimulation and the presence of a critical coupling interval. O’Donnell found that, in contrast to idiopathic RVOT-VT patients (3%), VT was induced by extra stimulation in 82% of pat ients w ith ARVC which indicates a re-ent rant mechanism [6]. Furthermore, in that study, in patients with idiopathic RVOT tachycardia there was usually only one morphology in premature beats or VT, whereas 71% of patients with ARVC presented from one to six morphologies characteristic of inducible tachycardia. Therefore, in the presence of VT pleomorphism an ARVC should be suspected. Finally, the study also noted that fragmented diastolic electrograms occurred in 82% of patients with ARVC [6]. Inducibility maybe facilitated by infusion of isoproterenol in both clinical entities and is therefore not a criterion to discriminate between the two diseases. Triggering Factors for VT and Symptoms Idiopathic ventricular tachycardia from the RVOT and VT in ARVC are difficult to discriminate based on circumstances of onset, because sustained tachycardia and salvos tend to be induced by stress, catecholamines, or physical exercise in both cases [1, 2, 6]. However, there is a difference in symptoms in terms of severity for the overall population. Whereas syncope is more frequent in ARVC and cardiac arrest does practically not occur in idiopathic RVOT-VT, in idiopathic VT there are more mild to moderate palpitations and dizziness due to bradycardia with bigeminus and resulting peripheral pulse deficit. In ARVC, intensive physical activity or extreme anxiety is known to cause fast and recurrent VT with a considerable risk of sudden death. Therefore, it should be absolutely avoided in those patients [1]. Conclusions The diagnosis of an idiopathic RVOT-VT is made by exclusion of ARVC or any other structural heart disease. If there are no signs of RV myocardial changes, such as dilatation, dyskinesia, hypokinesia, or aneurysms and wall thickening, and there are no electrocardiographic signs of ARVC, the patient ARVC and Idiopathic Ventricular Tachycardia 349 most likely has an idiopathic RVOT-VT. However, especially in families with a history of sudden death, close follow-up may be useful. When enough minor or major criteria are met, the patient should be risk-stratified and treatment options should be tailored to the individual, taking into consideration the risks and benefits. In some younger patients with, e.g. syncope and one other minor criterion and RVOT-VT, this decision is often very difficult and will probably remain difficult. Genetic testing should be performed in all patients with a family history in order to detect relatives at risk. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Fontaine G, Fontaliran F, Hébert JL et al (1999) Arrhythmogenic right ventricular dysplasia. Annu Rev Med 50:17–35 Corrado D, Fontaine G, Marcus FI et al (2000) Arrhythmogenic right ventricular dysplasia/cardiomyopathy: need for an international registry. Circulation 101:E101-E106 Paul M, Schulze-Bahr E, Breithardt G et al (2003) Genetics of arrhythmogenic right ventricular cardiomyoapthy-status quo and future perspectives. Z Kardiol 92:128–136 Gerull B, Heuser A, Wichter T et al (2004) Mutations in the desmosomal protein plakophilin-2 are common in arrhythmogenic right ventricular cardiomyopathy. Nat Genet 36:1162–1164 McKenna WJ, Thiene G, Nava A et al (1994) Diagnosis of arrhythmogenic right ventricular cardiomyopathy. Task force of the working group on myocardial and precardial disease of the European Society of Cardiology and the scientific council on cardiomyopathies of the International Society and Federation of Cardiology. Br Heart J 71:215–218 Niroomand F, Carbucicchio C, Tondo C et al (2002) Electrophysiological characteristics and outcome in patients with idiopathic right ventricular arrhythmia compared with arrythmogenic right ventricular dysplasia. Heart 87:41–47 O’Donnell D, Cox D, Bourke J et al (2003) Clinical and electrophysiological differences between patients with arrhythmogenic right ventricular dysplasia and right ventricular outflow tract tachycardia. Eur Heart J 24:801–810 Altemose G, Buxton A (1999) Idiopathic ventricular Tachycardia. Annu Rev Med 50:159–177 Farzaneh-Far A, Lerman B (2005) Idiopathic ventricular outflow tract tachycardia. Heart 91:136–138 Carlson MD, White RD, Trohman RG et al (1994) Right ventricular outflow tract ventricular tachycardia: detection of previously unrecognised anatomic abnormalities using cine magnetic resonance imaging. J Am Coll Cardiol 24:720–727 Boulos M, Lashevsky I, Gepstein (2005) Usefulness of electroanatomical mapping to differentiate between right ventricular outflow tract tachycardia and arrhythmogenic right ventricular dysplasia. Am J Cardiol 95:935–940