Ultrasound Ablation for Recurrent Atrial Fibrillation
Abstract & Commentary
Synopsis: Results with the ultrasound ablation catheter are promising and this ablation system allows isolation of pulmonary vein ectopic foci in a significant proportion of patients.
Source: Natale A, et al. Circulation 2000;102:1879-1882.
Natale and associates report on the use of a new ultrasound ablation catheter for pulmonary vein isolation in patients with recurrent paroxysmal atrial fibrillation. The ablation system consists of a 0.035 in diameter luminal catheter with a distal balloon, which houses an ultrasound transducer. A guide wire is used for placement of the ablation catheter in the target pulmonary vein using a transseptal approach. Delivery of ultrasound produces tissue heating and, when successful, circumferential electrical isolation.
Data from 15 patients are included in this report. These patients all had markedly symptomatic atrial fibrillation that had been resistant to two or more antiarrhythmic drugs. The patients ranged in age from 30 to 69 years with a mean age of 59 ± 10 years. In 13 patients, only paroxysmal atrial fibrillation had been observed while in two patients atrial fibrillation episodes had required cardioversion. Nine patients had no known structural heart disease, four patients had a history of hypertension, one patient had reduced ventricular function, and one patient had valvular heart disease. Mapping of atrial premature contraction foci was performed using an octapolar recording catheter placed in the pulmonary veins. A site of origin for triggering beats that initiated atrial fibrillation was identified in nine of the 15 patients. In these nine patients, 12 atrial foci were observed. In five patients, no spontaneous premature contractions were recorded and in one patient a right atrial tachycardia was noted but was not mapped or ablated during this procedure. In the nine patients who underwent ablation, ablation was performed in the right superior, left superior, and left inferior pulmonary veins. In five patients, however, the right inferior veins were too small to accept the balloon ultrasound ablation catheter. A median of four ultrasound applications were required to isolate each vein. In one patient, in whom the target pulmonary vein was larger than the ablation balloon, radiofrequency lesions were used to complete the ablation. The ultrasound applications produced an adequate interface temperature of greater than 55oC in 86% of lesions. Four of the nine patients had significant complications. One patient suffered a peri-procedural embolic stroke, one patient developed transient ST segment elevation, one patient had entry into the pericardial space by the transseptal needle, and one patient developed phrenic nerve paralysis that only partially resolved after three months. During a follow-up of 35 ± 6 weeks, nine patients remained in sinus rhythm off drugs, four patients had atrial fibrillation recurrence, and two patients had atrial tachycardia. Four of the six who suffered recurrences responded to drugs that had previously been ineffective. Natale et al concluded that these results with the ultrasound ablation catheter are promising and that this ablation system allows isolation of pulmonary vein ectopic foci in a significant proportion of patients.
Comment by John P. DiMarco, MD, PhD
The observation by Haissaguerre and his colleagues that ectopy originating in the pulmonary vein sites was frequent precursor of paroxysmal atrial fibrillation has led to widespread interest in the development of new approaches for electrically isolating the pulmonary veins. Circumferential ablation at or near the ostia is difficult to achieve with currently available radiofrequency ablation catheters and several different devices that produce circumferential lesions more rapidly are now in clinical trials. The ultrasound ablation catheter has the advantage that one system allows the pulmonary vein to be occluded and visualized. Another potential advantage is that this catheter should produce uniform heating around the edge of the balloon, which is in direct contact with the entire circumference of the vein. As might be expected in an initial clinical trial, the overall results in this study are not overwhelming. Since only nine patients underwent ablation, it appears that the success rate in those undergoing ablation is less than the rate based on "intention-to-treat" quoted by Natale et al. Five of the nine patients with ectopic foci appear to have experienced recurrences while recurrence was noted in only one of six who did not undergo the ablation procedure. However, these are merely the first pilot results with a new device in an exciting area. As new tools are developed for electrophysiologists who produce electrical isolation of the pulmonary veins with a low rate of complications and a short procedure time, we can expect to see a revolution in the way patients with paroxysmal atrial fibrillation are handled.
Reference
1. Haissaguerre M, et al. N Engl J Med 1998;339:659-666.
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