BORDEAUX, FRANCE. It is well-established that permanent or long-lasting, persistent atrial fibrillation (AF) is significantly more difficult to cure with catheter ablation than is paroxysmal (intermittent) atrial fibrillation. Paroxysmal AF is usually triggered by rogue P-cells located in the pulmonary veins; thus, electrically isolating the veins from the left atrium is often enough to terminate the arrhythmia permanently (pulmonary vein isolation [PVI] procedure). However, once episodes become long-lasting and no longer subject to spontaneous self-conversion (persistent or permanent AF), then it becomes much more difficult to cure the arrhythmia with catheter ablation. This is due to the fact that triggers are now also active outside the pulmonary veins and substantial substrate modification has likely taken place as well. Thus, although a standard PVI (segmental or circumferential) is still the starting point, it is necessary to also perform electrogram-based ablation and linear ablation in order to achieve a reasonable degree of success.
It is becoming increasingly clear that the demand for catheter ablations is increasing substantially faster than the capacity to provide them. This is especially true when it comes to persistent and permanent AF where exceptional skill and longer procedure times are required to ensure success. A team of researchers from Hopital Cardiologique du Haut-Leveque and Lund University in Sweden now reports that a standard surface electrocardiogram (ECG) taken prior to an ablation can provide a surprisingly accurate indication as to whether the procedure is likely to be successful or not.
Their study involved 90 patients (average age of 57 years, 84% men) with long-lasting, persistent AF defined as continuous afib lasting longer than one month and resistant to either electrical or pharmaceutical conversion. The majority (75%) of the patients had no structural heart disease, so would be classified as lone afibbers. All patients underwent a standard segmental PVI plus whatever other ablations were necessary to terminate the arrhythmia. Overall success, measured as being afib-free without antiarrhythmics, was 84%; however, an average of 1.8 procedures per patient was required to achieve this. Prior to starting the actual ablation, all patients had a standard ECG in which particular attention was paid to the AF cycle length (AFCL) observed at lead V1. This cycle length was found to correlate well with cycle lengths measured inside the heart at the right and left atrial appendages.
The researchers noted that the pre-ablation AFCL was a good indicator of whether or not afib would be terminated by the ablation procedures. Thus, the average pre-procedure AFCL among patients whose arrhythmia terminated was 154.3 milliseconds (corresponding to 389 atrial contractions per minute) as compared to only 131.7 ms (corresponding to 456 atrial contractions per minute) in those whose arrhythmia did not terminate. This difference was highly significant.
It was also clear that patients with a smaller left atrial diameter (47 mm vs 54 mm) and a shorter duration of persistent afib (22 months vs 60 months) had a significantly better chance of termination. However, the only independent predictor of termination success was a long AFCL.
Eighteen months after the last ablation, 84% of patients were in normal sinus rhythm (NSR) without the use of antiarrhythmics. At one year, 93% of patients with an AFCL greater than 142 ms were in NSR as compared to only 68% among those with a cycle length less than 142 ms. Also at one year, 95% of patients who had been in persistent afib for less than 21 months were in NSR as compared to only 72% of those who had longer-standing afib.
The authors conclude that measuring the AFCL with a standard ECG prior to deciding on treatment is useful for predicting which patients are most likely to benefit from an ablation. They also suggest that patients with long-standing, persistent (permanent) afib should wait no longer than 2 years before being referred for an electrophysiology study and possible ablation.
Matsuo. S, et al. Clinical predictors of termination and clinical outcome of catheter ablation for persistent atrial fibrillation. Journal of the American College of Cardiology, Vol. 54, No. 9, August 25, 2009, pp. 788-95
Wilber, DJ. Pursuing sinus rhythm in patients with persistent atrial fibrillation: when is it too late? Journal of the American College of Cardiology, Vol. 54, No. 9, August 25, 2009, pp. 796-98
Editor's comment: This study resulted in two important findings. Firstly, afibbers whose episodes change from paroxysmal to persistent or permanent should get in line for a possible ablation as soon as possible and those already in permanent afib should delay as little as possible in order to improve their chances of a successful outcome. Secondly, a measurement of AFCL on a standard surface ECG will give a good indication of whether an ablation procedure is likely to be successful in the case of permanent afib. Put another way, if the AFCL is below 142 ms then as many as 4 procedures may be required.