TAIPEI, TAIWAN. There is emerging evidence that pre-ablation left atrium size, C-reactive protein level, and left atrium voltage are important predictors of the success of catheter ablation for atrial fibrillation (AF). Now a group of researchers at the Taipei Veterans General Hospital reports that stroke risk, as measured using the CHADS2 score, is also an important predictor of ablation outcome. The CHADS2 score assigns 1 point each for congestive heart failure, hypertension, age over 75 years and diabetes, and 2 points for a history of stroke or TIA (transient ischemic attack).

The Taipei study involved 247 paroxysmal afibbers (178 men and 69 women) with an average age of 53 years and an average AF duration of about 4 years. The participants were divided into three groups according to their CHADS2 score. Group 1 (123 patients) had a score of 0, group 2 (87 patients) a score of 1–2 (average of 1.24), and group 3 (37 patients) a score of 3–6 (average of 3.60). The members of group 3 were clearly a great deal sicker than those of group 1 with 95% having hypertension, 89% having diabetes, and 54% having suffered a previous stroke or TIA.

All participants underwent an electrophysiological study with electroanatomical mapping (NavX system) in sinus rhythm and subsequent ablation. Left atrial voltages were significantly higher in group 1 (2.08 mV) than in group 2 (1.80 mV) and group 3 (1.06 mV). Total left atrial activation times (P-wave durations) were significantly shorter in group 1 (93.4 ms) than in group 2 (101.9 ms) and group 3 (112.2 ms). The lower voltages and longer activation times in group 3 are consistent with increased fibrosis and advanced structural and electrical remodeling of the left atrium. The researchers also noted that the average left atrial diameter in group 3 (42 mm) was significantly larger than in group 1 (37 mm).

The ablation procedure involved the creation of circumferential lesions around the left and right pulmonary vein ostia as well as focal ablation of non-pulmonary vein triggers in about 10% of patients. All received antiarrhythmic drugs for 8 weeks following the procedure. Thirty-one patients who continued to take the drugs beyond 8 weeks were excluded from the study. At the end of a 17-month follow-up period, 87% of the remaining patients in group 1 were in normal sinus rhythm as compared to 72% in group 2, and 54% in group 3. After adjusting for possible confounding variables, the group 3 participants were 6 times more likely to experience recurrence than were those in group 1.

The Taiwanese researchers conclude that a high CHADS2 score is associated with unfavorable left atrial substrate properties and a poor outcome of catheter ablation for paroxysmal AF.
Chao, TF, et al. Associations among the CHADS2 score, atrial substrate properties, and outcome of catheter ablation in patients with paroxysmal atrial fibrillation. Heart Rhythm, Vol. 8, 2011, pp. 1155-59

Editor's comment: This study confirms that the presence of comorbid conditions, notably hypertension, diabetes and congestive heart failure, markedly reduces the chance of a successful ablation, as does an enlarged left atrium and the presence of fibrosis as indicated by lower left atrial voltages and longer activation times.