LONDON, UNITED KINGDOM. It is becoming clear that long-standing persistent (permanent) atrial fibrillation (AF) is a different entity than paroxysmal (intermittent) AF. The main difference being that the heart tissue (substrate) in persistent afibbers is more abnormal because it has undergone more extensive electrical and structural remodeling resulting in a greater degree of left atrial enlargement and hypertrophic cardiomyopathy (thickening of the heart muscle). Not surprisingly, success rates for ablation of persistent and long-standing persistent AF are consequently very much lower than the success rates for paroxysmal AF.

Electrophysiologist at the University College Hospital now report that left atrial size is a crucial determinator of ablation outcome in persistent afibbers. Their study involved 191 patients with persistent AF, the majority (88%) of which had been in AF for at least a year prior to undergoing their first ablation. The average age of the patients was 58 years, 79% were male, average left atrial diameter (parasternal long-axis view) was 47 mm, prevalence of coronary artery disease was 11%, and 7% had been diagnosed with hypertrophic cardiomyopathy.

All study participants underwent an initial circumferential pulmonary vein isolation (PVI) procedure using a 3D mapping system (CARTO or NavX) and a 3.5-mm irrigated tip ablation catheter. In addition, linear ablation in the left atrium roof (in 71% of procedures) or mitral isthmus (in 44% of procedures), and ablation of complex fractionated electrograms (in 42% of procedures) were performed at the discretion of the operator. After a mean follow-up of 13.5 months (excluding recurrences during a 3-month blanking period), 32% of patients were in normal sinus rhythm.

Follow-up ablations were carried out in 101 patients – 48 had two procedures, 17 had three, 1 had four, and 1 had five procedures. After a mean follow-up of 13 months from the last procedure, 47% of patients were in normal sinus rhythm without the use of antiarrhythmics, while another 17% remained free of AF with the aid of previously ineffective antiarrhythmics, resulting in an overall success rate of 64%.

The outcome was found to be highly dependent on left atrial size with patients with a LA diameter less than 43 mm having an estimated success rate (freedom from AF with or without antiarrhythmics) of 91% at year 1 and year 2 after their final ablation. Corresponding numbers for the 127 patients whose LA diameter exceeded 43 mm were 54% at year 1 and 51% at year 2. A steady decline in favourable outcome was noted as LA diameter increased from 43 mm to 46 mm, but no further decline was observed above 46 mm. The final outcome in patients with a LA diameter greater than 43 mm was also markedly poorer in patients with hypertrophic cardiomyopathy.

The researchers conclude that left atrial size is the major determinant of procedural success in ablation for persistent, especially long-standing persistent, AF. They found no correlation between outcome and the presence or absence of coronary heart disease, low ventricular ejection fraction, prior TIA or stroke, dilated cardiomyopathy, hypertension or diabetes. Nor did they observe any effect of age or gender on outcome.

McCready, JW, Chow, AW, et al. Predictors of recurrence following radiofrequency ablation for persistent atrial fibrillation. Europace, Vol. 13, 2011, pp. 355-61

Editor's comment: There is considerable evidence that long AF episodes results in atrial enlargement. In view of the findings of this study, it would appear that persistent afibbers should arrange for an ablation before their left atrial diameter exceeds 43 mm.