Background: Catheter ablation of atrial fibrillation (AF) is an increasingly popular therapeutic option for symptomatic patients who have failed multiple antiarrhythmic medications. Patients of higher body mass index often fail direct current cardioversion. The role of body mass index (BMI) on the success of AF ablation is not well understood. 
Methods: We prospectively studied 893 patients who underwent AF ablation at the Cleveland Clinic Foundation between 1999 and 2003. Patients were divided into four classes based on their BMI: Class I (≤ 25); Class II (25.1-30); Class III (30.1-35) and Class IV (>35). They were compared for baseline demographic and clinical characteristics. Any recurrence of AF after 3 months of ablation was considered as failure. All classes were followed for at least 12 months and rates of failure were compared. 
Results: Based on their BMI, 25% of patients were assigned to class I, 37% in class II, 21% in class III and 16% in class IV. Patients of higher classification (class III or IV) were more likely to be male (p<0.001),  diabetic (p<0.001), smokers (p=0.002), with coronary artery disease (=0.018), echocardiographic evidence of left atrial enlargement (p=0.015) and longstanding AF (p=0.007). We found a significant correlation between long-term (one-year) AF recurrence after catheter ablation and BMI classification with recurrence rates of 5.2% in class I, 7.5% in class II, 14.1% in class III and 8.4% in class IV (p=0.01). The short-term recurrence rates of 12.7% in class I, 19.1% in class II, 23.0% in class III and 17.4% in class IV did not achieve statistical significance (p=0.05) .

Conclusion: Obesity is significantly associated with long-term AF recurrence after catheter ablation. Higher incidence of systemic inflammation, smoking & left atrial enlargement possibly contribute to higher failure rates in this sub-group of patients.