Jin-Bae Kim, et al. Delivery of impulses was guided by impedance control. A bidirectional isthmus block was demonstrated by pacing technique which was performed at coronary sinus ostium and the low lateral right atrium. The line of block was re- evaluated 30 min after the catheter ablation. Electrical cardioversion of persistent AF Electrical cardioversion was performed after 4-6 weeks of anticoagulation with warfarin or when LA thrombi were not seen on the transesophageal echocardiography. R wave synchronized direct current (DC) shock with a monophasic or biphasic waveform was delivered during sedation in- duced by intravenous pentothal sodium (1.5 mg/kg). One defibrillator pad, with a 10-cm diameter, was placed at the second intercostal space on the right side parasternally and the other was placed at a left-sided lateral position along the midaxillary line. The cardioversion procedure started with 100 J (biphasic) or 200 J (monophasic), followed by 200 J and 300 J, until the restoration of sinus rhythm. Data collection and follow-up Demographic, clinical and procedural variables were col- lected retrospectively by review of the medical records. All patients in both groups were instructed to continue the anti- arrhythmic medications. Most patients received warfarin to maintain an International Normalized Ratio of 2.0-3.0 for at least one month after the ablation. In some patients who had no indications for systemic anticoagulation, warfarin was changed to aspirin 100 mg daily after 1-2 months of anticoagulation. All patients had regular follow-up with standard 12 lead electrocardiogram (ECG) in the out-patient clinic every 2-4 months or Holter monitoring if the patient was symptomatic. Patients with palpitations or symptoms suggestive of atrial fibrillation or atrial flutter underwent am- bulatory 24-hour Holter monitoring. Recurrent atrial fibril- lation was diagnosed when documented by ECG or Holter monitoring. Patients were instructed to obtain an ECG at the nearest hospital in cases where symptomatic palpitation developed. Patients were followed for a mean period of 55.7+/-43.0 months (up to 7 years) after catheter ablation or electrical cardioversion. The follow-up end point was recur- rence of atrial fibrillation or flutter. Statistical analysis Continuous variables are expressed as mean±SD, and cate- gorical variables as percents. The unpaired Student t-test and χ2 analysis were used to compare continuous and cate- gorical variables, respectively. The 95% confidence interval (CI) was determined on the basis of the normal distribution of variables. Kaplan-Meier estimates were used to deter- mine overall survival and event-free survival for both groups. Comparison between the groups was performed using the log-rank test. Cox regression hazard analysis was used to identify independent correlates of long-term event-free sur- vival. All analyses were performed using SPSS software version 11.5 (SPSS Inc., Chicago, IL, USA). RESULTS Clinical characteristics of patients The baseline characteristics of both groups of patients are listed in Table 1. When compared with the cardioversion group, the hybrid group included more patients with diabe- tes (28.1% vs. 9.1%; p=0.018). However, there was no dif- ference in age, gender, body mass index, or valvular heart disease. No significant difference was found with regard to the periprocedural medications such as antiarrhythmics, an- giotensin converting enzyme inhibitors/angiotensin recep- tor blockers, beta blockers and calcium channel blockers between the two groups. The pre-procedural echocardio- graphic parameters showed that the left ventricular dimen- sion and left ventricular systolic function were within nor- mal range and there was no difference between the groups. The left atrial size, measured by the anterior-posterior dis- tance in the parasternal long axis view, was not statistically different; patients with more than 44 mm left atrial anteri- or-posterior diameter were more common in the hybrid group, but the difference was not statistically significant (53.1% vs. 48.5%, p=0.68). Catheter ablation of atrial flutter and electrical cardioversion Four patients (12.5%) in the hybrid group presented with atypical atrial flutter on the 12 lead ECG and showed clock- wise atrial activation sequences. Atypical atrial flutter was treated with the catheter ablation procedure. It was cavo-tri- cuspid isthmus (CTI) dependent and successfully ablated with CTI block; 28 patients (87.5%) had common atrial flutter and all atrial flutters were cavo-tricuspid isthmus de- pendent as proven by entrapment mapping and terminated by CTI block. The mean cycle length of the atrial flutter on the electrophysiological studies was 325.8+/-127.6 ms. All patients achieved complete bidirectional isthmus block and 78 Yonsei Med J http://www.eymj.org Volume 53 Number 1 January 2012