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Incidence and predictors of major complications from contemporary catheter ablation to treat cardiac arrhythmias Marius Bohnen, BSc, William G. Stevenson, MD, FHRS, Usha B. Tedrow, MD, MSc, FHRS, Gregory F. Michaud, MD, FHRS, Roy M. John, MD, PhD, FHRS, Laurence M. Epstein, MD, FHRS, Christine M. Albert, MD, MPH, Bruce A. Koplan, MD, MPH, FHRS From the Cardiac Arrhythmia Service, Cardiovascular Division, Department of Medicine, Brigham and Women’s Hospital, Boston, Massachusetts. BACKGROUND Updated understanding of the risks of catheter ablation is important because techniques have evolved for procedures treating non–life-threatening as well as potentially lethal arrhythmias. OBJECTIVE This prospective study sought to assess the incidence and predictors of major complications from contemporary catheter ablation procedures at a high-volume center. METHODS Over a 2-year period, 1,676 consecutive ablation procedures were prospectively evaluated for major complications throughout 30 days postprocedure. Predictors of major complications were determined in a multivariate analysis adjusted for demographics, clinical variables, ablation type, and procedural factors. RESULTS Rates of major complications differed between procedure types, ranging from 0.8% for supraventricular tachycardia, 3.4% for idiopathic ventricular tachycardia (VT), 5.2% for atrial fibrillation (AF), and 6.0% for VT associated with structural heart disease (SHD). Ablation type (ablation for AF [odds ratio (OR) 5.53, 95% confidence interval (CI) 1.81 to 16.83], for VT with SHD [OR 8.61, 95% CI 2.37 to 31.31], or for idiopathic VT [OR 5.93, 95% CI 1.40 to 25.05] all referenced to supraventricular tachycar- Introduction Reported catheter ablation complication rates vary considerably, depending on the type of procedure.1–7 A better understanding of the procedural risk is important for selecting patients for ablation. In addition, because several reports on procedural complications have been published many years ago and technology to improve safety has advanced, prior results may be outdated. Knowledge of the contemporary major complication rates for catheter ablation is a necessity in the current health policy climate, as professional organizations and regulatory entities weigh risk and benefits, relative value, and consider health care quality issues. We sought to determine the incidence and predictors Drs. Koplan, Tedrow, Michaud, Epstein, and John serve as consultants to and receive research support from St. Jude Medical. Dr. Epstein serves as a consultant to Medtronic, General Electric, and Bard Medical and receives research support from Medtronic. Dr. Tedrow receives research support from Biosense Webster/Johnson & Johnson. Address reprint requests and correspondence: Dr. Bruce A. Koplan, Brigham and Women’s Hospital, 75 Francis Street, Boston, MA 02115. E-mail address: [email protected]. (Received April 14, 2011; accepted May 19, 2011.) dia ablation), and serum creatinine level ⬎1.5 mg/dl (OR 2.48, 95% CI 1.07 to 5.76) were associated with increased adjusted risk of major complications, whereas age, gender, body mass index, international normalized ratio level, hypertension, coronary artery disease, diabetes, and prior cerebrovascular accident were not associated with increased risk. CONCLUSION In a large cohort of contemporary catheter ablation, major complication rates ranged between 0.8% and 6.0% depending on the ablation procedure performed. Aside from ablation type, renal insufficiency was the only independent predictor of a major complication. KEYWORDS Atrial fibrillation; Catheter ablation; Outcomes; Quality of care ABBREVIATIONS AF ⫽ atrial fibrillation; AVNRT ⫽ atrioventricular nodal reentrant tachycardia; CVA ⫽ cerebrovascular accident; LV ⫽ left ventricle; SHD ⫽ structural heart disease; SVT ⫽ supraventricular tachycardia; VT ⫽ ventricular tachycardia (Heart Rhythm 2011;8:1661–1666) © 2011 Heart Rhythm Society. All rights reserved. of major complications from contemporary catheter ablation procedures at a high-volume center. Methods In this prospective study, all patients undergoing catheter ablation at our institution were enrolled in an electronic database at the time of their procedure that included demographic and procedural information, along with all complications through 30 days of follow-up. All procedures from January 2009 through January 1, 2011, were analyzed. Procedures were classified as either ablation for atrial fibrillation (AF), supraventricular tachycardia (SVT) other than AF, ventricular tachycardia (VT) associated with structural heart disease (SHD), or idiopathic VT. The study was reviewed and approved by our institutional review board. Anticoagulation and postprocedural management Patients on long-term anticoagulation therapy were managed with either a bridging strategy with intravenous heparin/subcutaneous enoxaparin or remained on coumadin 1547-5271/$ -see front matter © 2011 Heart Rhythm Society. All rights reserved. doi:10.1016/j.hrthm.2011.05.017 1662 Heart Rhythm, Vol 8, No 11, November 2011 through their procedure with a targeted international normalized ratio (INR) of 2.0 to 3.0. During left heart procedures, intravenous heparin was administered to maintain the activated clotting time over 350 seconds for AF and over 250 seconds for all other ablations. All patients were assessed for complications before hospital discharge. Patients also received written and verbal instructions to contact the operating physician regarding any complications or unplanned outside hospital visits. Patients were routinely evaluated at our outpatient arrhythmia clinic postprocedure. When follow-up in our clinic could not be scheduled because of logistical issues, information about complication follow-up was obtained from patients per their written discharge instructions and/or outside following physician. Definition of outcomes A major complication was defined as an adverse event related to the procedure requiring intervention for treatment, causing long-term disability, or resulting in prolonged hospitalization.7,8 An intervention was counted if it involved an invasive procedure (e.g., vascular surgery, pericardiocentesis, thrombin injection) or blood transfusion. Adverse events that only required outpatient drug administration was not considered a major complication. Arrhythmia recurrence requiring medical or invasive management was not counted as a complication. All complications were reviewed, with the members of the arrhythmia service in a morbidity and mortality meeting and classified as major or minor. Only major complications were included in our current analysis. Table 1 Statistical analysis Our analysis included all patients entering the electrophysiology laboratory for catheter ablation, regardless of whether ablation was performed. Continuous variables are summarized as mean ⫾ SD, categorical variables as absolute frequency (percentage). For univariate analysis, an independent t test was used for continuous variables and a 2 or Fisher exact test for categorical variables. Analysis of variance (ANOVA) was used to compare multiple means. To adjust for differences between groups, multivariate analysis was performed creating a binary logistic regression model. All tests were 2-sided, and a P value of ⬍0.05 was considered statistically significant. Statistical analysis was done with SPSS version 18.0 (SPSS Inc., Chicago, IL). Results Patient and procedural characteristics During the 2-year period, 1,676 consecutive ablation procedures were performed. Table 1 displays baseline demographics. The average age was in the 6th decade, with approximately one-third of the cohort being female. About one-third of the cohort had a body mass index (BMI) ⱖ30. There was a reasonable representation of comorbidities, including coronary artery disease (22.1%), diabetes (15.4%), and abnormal renal function, reflected by elevated serum creatinine levels of ⬎1.5 mg/dl (6.4%). Procedures types are also displayed in Table 1. The most common ablation was for AF (46.8%), with 57.1% parox- Baseline demographics (n ⫽ 1,676 ablations) Characteristic Total SVT n ⫽ 524 AF N ⫽ 784 VT with SHD n ⫽ 250 Idiopathic VT n ⫽ 118 Age (y) Age ⱖ 70 Female Weight (kg) BMI BMI categories ⬍25 25–29.9 ⱖ30 LVEF (%) LVEF ⱕ30% Medical history Hypertension Coronary artery disease Diabetes mellitus Prior CVA Laboratory values INR INR ⱖ2.0 Creatinine (mg/dl) Creatinine ⬎1.5 mg/dl Procedure types SVT ablation AF ablation VT ablation with SHD VT ablation, idiopathic Procedural factors Access ⱖ4 sheaths 57.6 ⫾ 14.4 19.0% 34.0% 88.0 ⫾ 20.4 28.7 ⫾ 5.9 54.9 ⫾ 18.2 21.2% 45.2% 81 ⫾ 20.8 27.3 ⫾ 6.1 59.1 ⫾ 10.7 15.8% 28.4% 93.1 ⫾ 19.3 29.6 ⫾ 5.6 62.6 ⫾ 13.0 31.7% 19.7% 87.5 ⫾ 19.1 28.7 ⫾ 6.1 48.8 ⫾ 13.0 4.25% 50.4% 84.4 ⫾ 18.8 28.3 ⫾ 5.9 27.6% 38.4% 33.8% 53.1 ⫾ 13.8 12.9% 41.1% 32.4% 26.5% 56.4 ⫾ 10.6 5.5% 18.1% 42.9% 38.9% 57.5 ⫾ 8.8 4.5% 29.3% 36.9% 33.7% 31.5 ⫾ 13.9 63.1% 28.2% 38.5% 33.3% 54.7 ⫾ 11.4 5.9% 47.5% 22.1% 15.4% 5.6% 42.65% 15.7% 15.1% 4.4% 51.7% 16.1% 12.9% 4.8% 53.0% 60.6% 28.1% 12.4% 30.3% 10.1% 6.7% 1.7% 1.7 ⫾ 0.7 34.2% 1.04 ⫾ 0.5 6.4% 1.4 ⫾ 0.6 18.9% 1.04 ⫾ 0.8 6.8% 2.1 ⫾ 0.6 59.3% 1.0 ⫾ 0.3 3.3% 1.3 ⫾ 0.3 3.6% 1.2 ⫾ 0.6 16.9% 18.5% 71.8% 49.4% 1.1 ⫾ 0.1 0% 0.9 ⫾ 0.2 2.5% 31.3% 46.8% 14.9% 7.1% 49.5% 39.5% Data displayed as mean ⫾ SD or percentage. AF ⫽ atrial fibrillation; BMI ⫽ body mass index; CVA ⫽ cerebrovascular accident; INR ⫽ international normalized ratio; LVEF ⫽ left ventricular ejection fraction; SHD ⫽ structural heart disease; SVT ⫽ supraventricular tachycardia; VT ⫽ ventricular tachycardia. Bohnen et al Complications From Contemporary Catheter Ablation ysmal and 42.9% persistent. SVT ablation occurred in 31.3%, of which 26.5% were atrioventricular nodal reentrant tachycardia (AVNRT), 14.3% accessory pathways, 11.5% atrial tachycardia, and 42% right atrial flutter. VT ablations, either in the presence or absence of SHD, comprised 22.0% of the cohort. Epicardial access was obtained in 21.3% of VT ablations with SHD. Patient and procedure characteristics varied among different procedure types. SVT or idiopathic VT ablation patients were younger (55 ⫾ 18 years and 48 ⫾ 13 years, respectively) than patients undergoing an AF ablation (59 ⫾ 11 years) or an ablation for VT in the setting of SHD (63 ⫾ 13 years, P ⬍ .01). Prior ablation had occurred in 432 (30.1%) patients. A transseptal approach occurred in 14.7% of SVT, 10.1% of idiopathic VT, 14.5% of other VT, and all AF procedures, except 1, which was aborted prematurely for anatomic reasons. Transseptal puncture utilized intracardiac ultrasound in 85.6% of cases. Epicardial access was obtained mainly in VT ablation, except for 2 cases of an accessory pathway and 1 case of atrial tachycardia. A therapeutic INR level on the day of the procedure occurred in 34.2% of patients. Among the 1026 (61.3%) procedures with the patient being on long-term anticoagulation therapy, 827 (49.3%) patients continued warfarin (INR 2.2 ⫾ 0.5) throughout their procedure, whereas 198 (11.8%) used a bridging strategy with intravenous heparin or subcutaneous enoxaparin (INR 1.4 ⫾ 0.3). Incidence of major complications Major complication rates by procedure type are displayed in Table 2. In our entire cohort, a major complication occurred in 64 of 1,676 (3.8%) of procedures. The rate was lowest for SVT (0.8%), and highest for AF (5.2%) and VT ablations in with SHD (6.0%, P ⬍ .01). In SVT, excluding AF, in which left heart access was obtained (n ⫽ 76) the rate was 1.3% (n ⫽ 1 psuedoaneurysm in a retrograde aortic approach). Table 2 1663 Most complications (35 of 64, 54.7%) occurred on the procedure day (22 of 64, 31.1% intraoperatively). Postprocedural complications were diagnosed at a mean of 4.4 ⫾ 5.6 days, including 2 late pericardial effusions on postprocedural day 5 and 6. Two (0.1%) patients suffered procedure-related death. One resulted from intraprocedural embolic stroke during AF ablation. Postmortem examination revealed an interatrial septum aneurysm containing chronic thrombus, which was not seen in the preprocedural TEE. In a second patient with severe cardiomyopathy and peripheral vascular disease, who underwent urgent ablation for ischemic VT, death resulted from complications of retroperitoneal bleed. The most common major complications were related to femoral access (1.4%). Pericardial effusion occurred in 1.3%, with tamponade in 0.7%. Each of these complications was least common in SVT ablation. Access complications occurred more frequently after ablations for AF and VT with SHD than SVT (P ⫽ .022 and P ⫽ .016, respectively). All (14 of 14) perforations in AF ablations were managed successfully with percutaneous drainage (even with INR therapeutic at the procedure). In contrast, 4 of 4 patients suffering a perforation during ablation for VT with SHD developed tamponade and subsequently required surgical revision. Two AF procedures were aborted because of pericardial contrast during transseptal puncture. These patients, however, did not develop a pericardial effusion and did not meet criteria to be classified as major complication. There were 11 (0.7%) thromboembolic events: 10 strokes and 1 peripheral embolus. Thromboembolic events were higher in AF ablation than SVT (P ⫽ .017). For other ablation types, thromboembolic rates did not differ from SVT ablation. Of all thromboembolic events, only 3 (27.3%) were clinically evident before the patient leaving the procedure room. Two patients experienced a postablation bleeding complication, Major complications from catheter ablation procedures Type of major complication Total n ⫽ 1,676 SVT n ⫽ 524 AF n ⫽ 784 VT with SHD n ⫽ 249 Idiopathic VT n ⫽ 119 Death Perforation Tamponade Pericardial effusion Thromboembolic event Stroke/TIA Systemic embolus Access complication Retroperitoneal bleed Groin hematoma Pseudoaneurysm AV fistula Other complications Deep vein thrombosis Aspiration pneumonia Pulmonary edema Conduction system damage Genitourinary trauma Major complication rate 2 21 12 9 11 10 1 23 5 9 7 2 9 1 3 2 1 2 64 0 1 0 1 0 0 0 2 0 0 2 0 1 0 0 1 0 0 4 1 14 7 7 8 7 1 14 4 6 3 1 5 0 3 0 1 1 41 1 4 4 0 2 2 0 5 1 3 1 1 3 1 0 1 0 1 15 0 2 1 1 1 1 0 1 0 0 1 0 0 0 0 0 0 0 4 (0.1) (1.3) (0.7) (0.5) (0.7) (0.6) (0.1) (1.4) (0.3) (0.5) (0.4) (0.1) (0.5) (0.1) (0.2) (0.1) (0.1) (0.1) (3.8) (0.2) (0.2) (0.4) (0.4) (0.2) (0.2) (0.8) Data displayed as absolute frequency (percentage). AV ⫽ atrioventricular; TIA ⫽ transient ischemic attack; other abbreviations as in Table 1. (0.1) (1.8) (0.9) (0.9) (1.0) (0.9) (0.1) (1.8) (0.5) (0.8) (0.4) (0.1) (0.6) (0.4) (0.1) (0.1) (5.2) (0.4) (1.4) (1.4) (0.8) (0.8) (2.0) (0.4) (1.2) (0.4) (0.4) (1.2) (0.4) (0.4) (0.4) (6.0) (1.7) (0.8) (0.8) (0.8) (0.8) (0.8) (0.8) (3.4) 1664 Heart Rhythm, Vol 8, No 11, November 2011 Table 3 Univariate predictors of major complications from catheter ablation (n ⫽ 1,676) Characteristic Age Age ⱖ70 y Female Weight (kg) BMI BMI categories ⬍25 25–29.9 ⱖ30 LVEF (%) LVEF ⱕ30% Medical history Hypertension Coronary artery disease Diabetes mellitus Prior CVA Laboratory values INR INR ⱖ2.0 Creatinine (mg/dl) Creatinine ⬎1.5 mg/dl Procedure types SVT ablation AF ablation* VT ablation with SHD* VT ablation, idiopathic* Procedural factors Access ⱖ4 sheaths Complication n ⫽ 64 None n ⫽ 1,614 60.6 ⫾ 13.9 26.6% 31.3% 86.5 ⫾ 21.6 28.7 ⫾ 6.4 57.5 ⫾ 14.4 18.7% 34.1% 88.1 ⫾ 20.3 28.7 ⫾ 5.9 .44 .11 .64 .75 .79 30.2% 33.3% 36.5% 52.2 ⫾ 15.2 15.1% 27.1% 38.6% 34.3% 53.1 ⫾ 13.8 12.2% .72 57.8% 5.1% 18.8% 12.5% 47.1% 3.5% 15.3% 5.3% .09 .14 .45 .02 1.9 ⫾ 0.7 50.0% 1.14 ⫾ 0.6 14.1% 1.7 ⫾ 0.7 33.6% 1.03 ⫾ 0.5 6.1% .04 .01 .05 .01 6.3% 64.1% 23.4% 6.3% 32.3% 46.1% 14.5% 7.1% ⬍.01 ⬍.01 .06 65.6% 48.9% .01 P .33 .30 Data shown as mean ⫾ SD or percentage. Abbreviations as in Table 1. *Reference ⫽ non-AF SVT ablation. prompting temporary discontinuation of anticoagulation, which was followed by a major thromboembolic complication in the setting of a subtherapeutic INR. Other major complications included aspiration pneumonia (3), and 1 traumatic urinary catheter event leading to acute renal failure that eventually resolved. There was 1 case of conduction system damage necessitating permanent pacing that occurred during AF ablation when ablation was performed in the coronary sinus os. There was no case of atrioventricular block in 524 SVT ablations, of which 169 were AVNRT. Similarly, there were no significant pulmonary vein stenosis or atrioesophageal fistulas after AF ablation. Because of the large component of major complications occupied by access complications, we also performed subanalysis to evaluate predictors of this particular complication group. In a multivariate model controlling for the type of procedure, serum creatinine ⬎1.5 mg/dl was shown to be a predictor for access complications as well (odds ratio [OR] 4.0, 95% confidence interval [CI] 1.4 to 11.9, P ⫽ .012). Discussion Main findings This study provides an update on the incidence of major complications of cardiac catheter ablation at a high-volume center. Our analysis showed that catheter ablation in general is associated with a low risk, but that complication rates vary by as much as a 5- to 8-fold between various types of ablation procedures. Whereas the existence of this difference is not surprising, the magnitude of the difference is notable and could be useful when weighing the risks and benefits of different types of procedures. Among several patient and procedural characteristics, serum creatinine level of ⬎1.5 mg/dl was associated with major complications in general and more specifically with access complications. Incidence of major complications by type of procedure When comparing our results with previous literature, it seems that complication rates for SVT ablations have diminished over time. The Multicenter European Radiofrequency Survey (MERFS)1 reported complication rates for SVT ablations during the years 1987 until 1992 ranging from 3.2% (atrioventricular junction ablations) to 8.0% (AVNRT ablations), with a 5.1% incidence of complete heart block in the latter subgroup. For 1992 to 1995, Calkins et al3 reported for ablations of accessory pathways, AVNRT, and atrioventricular junction a complication rate of 3%, and 0.3% periprocedural death. The incidence of complete heart block had further decreased, being 1.0% at that time. In 1997 a NAPSE survey2 from 68 centers revealed major complication rates of 0.6% to 5.0% for various SVT procedures. In our SVT group, the complication rate was 0.8% without a procedure-reTable 4 Multivariate predictors of major complications from catheter ablation (n ⫽ 1,626) Univariate analysis Characteristic Odds ratio 95% CI P In univariate analysis, patients with major complications were roughly twice as likely to have a prior history of a cerebrovascular accident (CVA), elevated serum creatinine, and higher INR levels (Table 3). Furthermore, more complex types of ablation procedures were associated with a higher complication rate. Age ⱖ70 y Female gender BMI ⱖ30 LVEF ⱕ30% Hypertension Coronary artery disease Diabetes mellitus Prior CVA INR ⱖ2.0 Creatinine ⬎1.5 mg/dl AF ablation* VT ablation, VT with SHD* VT ablation, idiopathic VT* Access ⱖ4 sheaths 1.26 1.23 0.98 0.75 1.26 0.97 1.02 2.1 1.73 2.48 5.53 8.61 5.93 1.25 0.70–2.42 0.69–2.18 0.57–1.69 0.29–1.95 0.73–2.15 0.48–1.96 0.51–2.07 0.91–4.68 0.91–3.26 1.07–5.76 1.81–16.83 2.37–31.31 1.40–25.02 0.70–2.24 .49 .48 .94 .55 .40 .93 .95 .08 .09 .03 ⬍.01 ⬍.01 .02 .44 Multivariate analysis Multivariate analysis adjusted for all variables from our univariate analysis (Table 4). In this analysis, only procedure type (SVT as reference) and baseline serum creatinine were independent predictors, whereas age, gender, BMI, INR level, number of sheaths, and other comorbidities were not predictive. Abbreviations as in Table 1. *Reference is non-AF SVT ablation. Bohnen et al Complications From Contemporary Catheter Ablation 1665 Thromboembolic events lated death and without a case of complete heart block, indicating a further decreased risk. It is worth noting that surveys mentioned earlier were retrospective, voluntary, and did not include demographics or an adjusted analysis. Complications from AF ablations were reported in a 1995– 2002 worldwide voluntary survey4 showing a major complication rate of 6.0%, and updated from 2003–2006, reporting a rate of 4.5%.9 Other single-center studies conducted during the years from 2005–2008 showed major complications ranging from 3.9%10 to 5.0%.11 A multicenter Italian study from 2005– 2006 showed a major complication rate of 3.9%.12 In our cohort, we found a similar major complication rate of 5.2% for AF ablation procedures. The slightly higher complication rate at our institution may be explained by different patient populations and a different definition of outcomes to some of the mentioned studies. As established by Cappato et al,9 the rate of major complications does not seem to decrease with more experience. Scant data exist on idiopathic VT ablation safety.13–15 Most studies are too small to allow reliable conclusions, or did not primarily focus on complications. We found a rate of major complications of 3.4%. Furthermore, there does not seem to be a significant difference between right heart (3.2%) and left heart (3.5%) idiopathic VT ablations. Major complication rates for ablation procedures of VT with SHD vary widely up to 15%.16 The MERFS study (1987), which did not distinguish between SHD and idiopathic VT, showed a rate of 7.5%.1 More recently, multicenter trials of VT ablation in patients with advanced structural heart disease found complication rates of 5% to 8%,5,17 with a 3% procedure-related mortality. In our cohort of VT in SHD, the complication rate was relatively low (6.0%) with only 1 (0.4%) death. It is notable that advanced pump failure therapies such as ventricular assist devices were available at our institution. Thus, it seems that the safety of VT ablations has increased further despite the sick patient population. Complications related to the site of vascular access are the most common major complication, but generally do not lead to longterm disability or mortality. AF and VT with SHD procedures had a higher incidence of femoral access complications than SVT procedures, presumably related to the different needs for anticoagulation and vascular access. For SVT ablation, the major access complication rate was 0.4%, consistent with other studies, ranging from 0 to 0.3%.1,2 Regarding AF ablations, the published literature reports access complications from about 1%20,21 up to 14% of cases,25 but comparability is impaired by the several different definitions of outcome used. Our rate of 1.8% was based on the definition suggested in previously published guidelines,19,23 which still leaves room for interpretation. Patients undergoing a VT ablation experience an access complication rate of 0.7% to 4.7%.14,24 In our study, the incidence ranged from 0.8% to 2.0%, being higher for ablations for VT with SHD. Cardiac perforation Predictors of major complications The overall incidence of cardiac perforation was 1.3%, with the risk being higher in AF (1.8%) and VT with SHD (1.4%) than in SVT ablations (0.2%). This may be explained by longer catheter manipulation time, delivery of more lesions, and greater anticoagulation. The MERFS study1 reported for SVT ablations a rate of 0.1% to 1.3%, similar to results by Calkins et al3 of 0.6%. In previous studies assessing the risk of perforation during left atrial ablation, the incidence of perforation was 2.4%18 and 2.9%.19 The AF survey reported a 1.2% incidence,4 the updated survey a 1.3% incidence of perforation.9 Regarding ablation for VT with SHD, a multicenter study reported a 2.7% perforation rate.5 We have previously published a 1% rate.20 It is thought that atrial perforation is higher than in the ventricles. However, we could not find a significantly increased risk in AF versus VT with SHD or idiopathic VT. Ventricular perforation more frequently led to tamponade and cardiac surgery. An explanation may be the higher ventricular systolic pressure, making it less likely for the bleeding to stop. In our study, thromboembolic events occurred exclusively in complex ablation procedures (AF and VT), where left heart access occurred. Although sporadic thromboembolic events have been reported for SVT ablations, the incidence is generally very low (approximately 0.5%).1,3 For AF, Oral et al21 found a risk of thromboembolic events of 1.1%. Scherr et al22 and the worldwide AF survey reported a 1.4% and 0.94%9 incidence of CVA. In our series, the thromboembolic event rates were 1.0% of AF ablations, consistent with previous studies. For both types of VT ablations, the rate of thromboembolic events was 0.8%, which is lower than reported in a previous study (2.7%)5 and estimated in a consensus document (1.3%).7 An important problem often encountered in clinical practice is the management of patients with bleeding complications who at the same time are at increased risk for a thromboembolic event in the periprocedural period. Two of our patients had a bleeding complication before their major thromboembolic event, emphasizing the challenge of managing these situations. Vascular access complications Identification of impaired renal function as a predictor of adverse events in cardiac procedures, as was the case in our study, has been demonstrated in previous literature.25–28 This may result from a higher prevalence of cardiovascular risk factors in these patients, but also from enhanced atherogenesis due to factors associated with renal dysfunction itself,29 such as inflammation and oxidative stress. Additionally, an elevated serum creatinine level is a validated predictor for adverse outcomes after general surgery,30 coronary artery bypass graft,31 and percutaneous coronary intervention.32 Prior studies have investigated risk factors for major complications from AF ablation procedures. These predictors included advanced age ⬎70 years, female gender, presence of coronary artery disease, and history of congestive heart failure.10 –12,33 However, studies specifically focusing on these patient populations failed to show an increased risk.32–36 Similarly, we did not find an association between major complications and these or other patient factors. None of these studies investigated the impact of impaired renal 1666 function on the risk of catheter ablation. Furthermore, the safety of ablation with therapeutic INR has also been demonstrated in previous literature.24 Study limitations First, our study represents a single-center experience; however, procedures were performed by multiple primary operators with varied backgrounds. Second, the setting of this study was a large tertiary referral center with possibly more complex and ill patients. Hopefully, adjustment for confounding factors helps to address this issue. Another potential limitation is the possibility of missed complications from patients referred from longer distances. In these patients, follow-up was often obtained through referring physician correspondence or telephone follow-up. In total, follow-up was obtained in 96% of the entire cohort, and all patients were given written instructions to notify the operating physician of any complications postdischarge. In addition, because major complications are considered and the majority occurred in a short time span, it is unlikely that a significant number of major complications was missed. Intracardiac ultrasound was used in 86% of transseptal procedures. This may be a limitation to the extent that other centers may have different use of this technology. Finally, a larger cohort may provide a greater statistical power, and may allow for more clinical variables to be adjusted for in order to increase the chance of controlling for all possible confounders, especially when analyzing rare outcomes. It is also possible that more complex procedures with higher event rates could have a greater influence on the results. Conclusion In the contemporary practice of catheter ablation, major complications rates vary from 0.8% to 6.0% depending on procedure type and patient factors. A preprocedural serum creatinine level of ⬎1.5 mg/dl identifies patients at higher risk for a major complication and for access complications, regardless of the type of ablation procedure. Our findings could be used to weigh the risks and benefits of a planned procedure. These results may also assist with planning further studies of the safety and outcomes of ablation. References 1. Hindricks G. The Multicentre European Radiofrequency Survey (MERFS): complications of radiofrequency catheter ablation of arrhythmias. Eur Heart J 1993;14:1644 –1653. 2. Scheinman MM, Huang S. The 1998 NASPE prospective catheter ablation registry. Pacing Clin Electrophysiol 2000;23:1020 –1028. 3. Calkins H, Yong P, Miller J, Olshansky B, Carlson M. Catheter ablation of accessory pathways, atrioventricular nodal reentrant tachycardia, and the atrioventricular junction: final results of a prospective, multicenter clinical trial. Circulation 1999;99:262–270. 4. Cappato R, Calkins H, Chen S, et al. Worldwide survey on the methods, efficacy, and safety of catheter ablation for human atrial fibrillation. Circulation 2005;111:1100 –1105. 5. Calkins H, Epstein A, Packer D, et al. Catheter ablation of ventricular tachycardia in patients with structural heart disease using cooled radiofrequency energy: results of a prospective multicenter study. J Am Coll Cardiol 2000;35:1905–1914. 6. 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