BOSTON, MASSACHUSETTS. Success rates for pulmonary vein isolation (PVI) vary widely and depend primarily on the skill and experience of the electrophysiologist (EP) performing the ablation. In order to ensure optimum results it is common practice to measure the electrical potential between the pulmonary veins and the left atrium outside of the ablation rings after completing the procedure. If potentials are still present, thus indicating incomplete isolation, the ablation is continued until no potentials are evident. At this point, some EPs consider the procedure complete, while others do a "final check" by trying to induce afib by rapid burst pacing of the atrium often accompanied by infusion of isoproterenol, a drug capable of inducing atrial fibrillation. If AF can be induced, then further ablation is carried out, if necessary on the left atrium wall and roof, the superior vena cava, etc. Only when AF can no longer be induced is the procedure deemed complete. Unfortunately, the lack of inducibility does not ensure long-term freedom from afib recurrence; thus, the search continues for a method to predict long-term success before the ablation procedure is terminated.
A group of researchers from Harvard Medical School and McGill University now report that trying to induce AF by administering an external shock (as done in electrocardioversion) to the ablatee after burst pacing and isoproterenol infusion may help in determining the need for further ablation, or the continued use of antiarrhythmics, in order to achieve long-term success. The study included 116 patients who underwent PVIs guided by electroanatomical mapping (CARTO, Pappone method). For 17 of the patients it was their second procedure. Following PV isolation, AF could be induced in 19 patients (16%) with burst pacing with or without isoproterenol. Nine of these patients were rendered non-inducible through further ablation. Burst pacing induced atrial tachycardia in 26 patients, 20 of whom were successfully ablated for this arrhythmia. Subsequent to the burst pacing, 81 patients in whom AF could not be induced were given a 30 J external shock timed to the peak of the R wave (most vulnerable time for initiation of AF). Among these patients, 16 went into afib, while in the remaining 65 (80%) afib could not be induced.
After an average follow-up of 16 months, 54% of ablatees in whom AF could be induced either by burst pacing or shock had experienced recurrent AF vs. only 21% among non-inducible patients. Comparing only those who were non-inducible by burst pacing and underwent subsequent shock, the recurrence rate at one year was 60% in patients who went into afib after the shock vs. only 18% in those who did not. The researchers conclude that administering a shock at the end of the procedure to ablatees who were non-inducible by burst pacing (with or without isoproterenol) may help to guide post-procedure management so as to reduce the incidence of recurrence. They also note that besides inducibility, mitral regurgitation was also associated with a poorer long-term success. Experiencing paroxysmal (intermittent) afib was, however, associated with a significantly better long-term prognosis than having persistent or permanent afib.
Wylie, JV, et al. Inducibility of atrial fibrillation with a synchronized external low energy shock post-pulmonary vein isolation predicts recurrent atrial fibrillation. Journal of Cardiovascular Electrophysiology [Epub ahead of press]
Ilkhanoff, L and Goldberger, JL. Recurrent atrial fibrillation after ablation. Journal of Cardiovascular Electrophysiology [Epub ahead of press] (editorial comment)
Editor's comment: This study clearly demonstrates that equating complete isolation of the pulmonary veins at the end of the procedure with long-term success is not realistic. Thus, results of studies using this endpoint as proof of the capability of new catheters, robot-assisted systems, etc. should be taken with a very large grain of salt indeed.