First Human Experience With Pulmonary Vein Isolation Using a Through-the-Balloon Circumferential Ultrasound Ablation System for Recurrent Atrial Fibrillation
Background—Standard mapping and ablation of focal sources of atrial fibrillation are associated with very long procedure times and low efficacy. An anatomic approach to complete pulmonary vein isolation could overcome these limitations.
Methods and Results—Fifteen patients with atrial fibrillation refractory to medication underwent circumferential isolation of the pulmonary veins by using a novel catheter, with an ultrasound transducer (8-MHz) mounted near the tip, in a saline-filled balloon. Twelve atrial foci and/or atrial fibrillation triggers were identified in 9 patients (pulmonary vein locations: left upper, 3; right upper, 6; right middle, 1; right lower, 1; and left inferior, 1). In 5 patients, lesions were placed in the absence of any mapped triggers. Irrespective of trigger mapping, circumferential isolation of both upper pulmonary veins was attempted in all patients. The lower pulmonary veins were ablated when sinus rhythm activation mapping revealed evidence of a sleeve of atrial muscle in the vein. The median number of lesions per patient required to isolate 1 pulmonary vein was 4 (range, 1 to 29). After ablation, no evidence of narrowing was seen with repeat venography or follow-up computed tomography scan. After a mean follow-up of 35±6 weeks, 5 patients had recurrence of atrial fibrillation. Three responded to drugs that were previously ineffective, and 2 remained in atrial fibrillation.
Conclusions—This novel ultrasound ablation system can successfully isolate multiple pulmonary veins. At early follow-up, this approach seems to be effective in preventing recurrent atrial fibrillation in a significant number of patients.
Recently, several groups1 2 3 showed that, in the majority of patients with paroxysmal and persistent atrial fibrillation, the premature atrial beats that initiate atrial fibrillation originate from the pulmonary veins. However, ablating these triggers using standard radiofrequency catheter technology has proven to be a significant technical challenge, and pulmonary vein stenosis has been reported. We present our preliminary results using a through-the-balloon circumferential ultrasound ablation technique to isolate the pulmonary veins in patients with paroxysmal and persistent atrial fibrillation.
The study population consisted of 15 patients enrolled consecutively who had markedly symptomatic atrial fibrillation resistant to ≥2 antiarrhythmic drugs and who had at least monthly episodes. Patients enrolled in the study were asked to sign an informed consent form that was approved by the hospital ethics committee. Antiarrhythmic drugs were discontinued 5 half-lives before the procedure was performed.
The oral anticoagulant warfarin was discontinued in every patient 2 days before the procedure. In each patient, instrumentation consisted of a 16-electrode catheter, with 8 distal electrodes positioned in the coronary sinus and an additional 8 electrodes floating in the junction of the high right atrium and superior vena cava. A bipolar recording catheter was also advanced in the esophagus to obtain electrograms from the posterior left atrium. In addition, an octapolar recording catheter (Boston Scientific EP Technology) was placed in the pulmonary vein, via transseptal access, to complete mapping of the atrial premature contraction foci and to confirm complete conduction block at the junction of the left atrium and pulmonary vein. Atrial ectopic beats were induced with an isoproterenol infusion. Patients in atrial fibrillation were cardioverted to sinus rhythm.
During the ablation procedure, an infusion of heparin was maintained to achieve an activation coagulation time >250 seconds. Ablation using the ultrasound balloon system was performed in both upper pulmonary veins and in every other pulmonary vein ostium that had a sleeve of atrial muscle (vein spikes), ectopic activity, and a diameter >5 mm. The ablation system (Atrionix, Inc) consists of a 0.035-inch diameter luminal catheter with a distal balloon (maximum diameter, 2.2 cm) housing a centrally located ultrasound transducer (Figure 1⇓). The system is advanced over a guidewire into the target pulmonary vein.
Ablation system performance and tissue heating were monitored and confirmed by thermocouples on the balloon and the ultrasound transducer. The ablation time was 2 minutes; this was followed by an additional minute before the balloon was deflated. A contrast venogram was obtained through a 12F sheath, and the ultrasound balloon ablation system was then placed into the vein over a guidewire (Figure 1⇑). Pulmonary vein size was assessed with a spiral computed tomography (CT) scan before the procedure and by the angiography performed during the procedure.
After every ablation with a temperature >55°C, entry block into the pulmonary vein was confirmed by repositioning the octapolar catheter in the vein. A venogram of the ablated pulmonary vein was repeated to exclude acute thrombosis or stenosis. After the procedure, the patients were placed on anticoagulant therapy (warfarin) and observed with a Holter monitor for 48 hours and with an event recorder for the first month. Holter monitoring was repeated at 3, 6, and 12 months. Event recorder monitoring was repeated if patients experienced a recurrence of symptoms. In addition, patients also underwent spiral CT scans with contrast 3 months after ablation.
Fifteen patients were included in the initial experience with the Atrionix through-the-balloon circumferential ultrasound vein ablation system. Their mean age was 59±10 years (range, 30 to 69 years). Nine patients were female, and 6 were male. Thirteen patients had paroxysmal atrial fibrillation, and 2 patients had atrial fibrillation that required cardioversion for termination. All patients were highly symptomatic. Nine patients had no known structural heart disease, 4 patients had a history of hypertension, 1 patient had reduced ventricular function (ejection fraction of 40%), and 1 patient had a history of valvular heart disease. All 15 patients had failed antiarrhythmic drug therapy.
Premature Atrial Contraction Mapping
Mapping of the triggering beats and the initiation of atrial fibrillation was possible in 9 of the 15 patients (60%). A total of 12 atrial foci were observed, 3 of them originating in the left superior pulmonary vein, 1 in the right inferior pulmonary vein, 1 in the right middle pulmonary vein, and the remaining 6 in the right superior pulmonary vein. In 1 patient, a right atrial tachycardia was noted, but mapping and ablation were not pursued. In 5 patients, no spontaneous premature atrial contractions were recorded.
Pulmonary Vein Ablation
In each patient, ablation of the right superior, left superior, and left inferior pulmonary veins was performed. All left inferior pulmonary veins showed vein spikes, but only 1 of the right inferior pulmonary veins showed firing and vein spikes. Nine right inferior pulmonary veins did not have vein spikes, and the remaining 5 right inferior veins were too small to receive ablation with the system. In 1 patient, all 4 pulmonary veins were ablated. A mean of 14.7±12.6 (range, 3 to 39) ultrasound energy applications were delivered per patient, and there was a median of 4 (range, 1 to 29) applications per vein. The postablation vein angiogram revealed no acute thrombosis or stenosis. In 2 patients, the right superior and left inferior pulmonary vein ostia were larger than the maximum diameter of the current balloon (2.6 and 3.0 cm, respectively). In the patient with a large left inferior pulmonary vein, final isolation of the vein was obtained with radiofrequency ablation lesions. An interface temperature >55°C was seen in 179 of the 208 ultrasound applications (86%). The mean procedure time was 224±89 minutes (range, 135 to 360 minutes). The mean fluoroscopic time was 62±39 minutes (range, 37 to 120 minutes).
One periprocedural cerebellar embolic stroke occurred in a patient with daily paroxysms of atrial fibrillation. No evidence of clot or pulmonary vein thrombosis was seen after the procedure on either a transesophageal echogram or MRI scan. Three additional complications that did not require intervention were seen. In 1 patient, ST segment elevation in the inferior leads, most likely secondary to coronary spasm triggered by air embolism, was observed. This resolved spontaneously within 1 minute. This patient had a 95% proximal right coronary artery lesion. In another patient, the pericardial space was entered with the transseptal needle. On withdrawal of the needle, no evidence of pericardial fluid accumulation was noted, and the procedure was continued with no hemodynamic compromise. In the third patient, phrenic nerve paralysis was documented after ablation in an anterior branch of the right superior pulmonary vein. Partial return of phrenic nerve function was documented at the 3-month follow-up.
After a mean follow-up of 35±6 weeks, 4 patients (27%) had a reoccurrence of atrial fibrillation. Two other patients appeared to have short bursts of atrial tachycardia. Overall, 9 patients remained in sinus rhythm off drugs (60%), and 6 patients had atrial tachycardia (2 patients; 13%) or atrial fibrillation recurrence (4 patients; 27%). Four of the 6 who did not remain in sinus rhythm responded to drugs that were previously ineffective, and the remaining 2 patients continued to have atrial fibrillation that was unresponsive to drugs. Recurrence of atrial fibrillation were seen in patients with ostial foci (3 patients), with a vein ostium larger than the balloon (1 patient), and with foci outside the pulmonary vein (right atrial tachycardia, 1 patient; ligament of Marshall, 1 patient). No patient had any symptoms suggestive of pulmonary vein stenosis. In all 15 patients, the spiral CT scan performed 3 months after the procedure showed no evidence of pulmonary vein stenosis (Figure 1⇑) in the veins receiving ablation with the ultrasound system only. The left inferior pulmonary vein isolated with radiofrequency energy showed mild to moderate narrowing, without any evidence of pulmonary hypertension.
Radiofrequency catheter ablation targeting the site responsible for triggering atrial fibrillation has resulted in a cure of atrial fibrillation in 50% to 70% of patients.1 2 3 However, most patients require multiple procedures, along with many days of inpatient monitoring before and after the procedure, to capture elusive atrial ectopy. Therefore, because the pulmonary veins seem to be a crucial source of triggers of atrial fibrillation, present mapping and ablation techniques seem to have significant limitations. Given the difficulty in precisely locating and ablating these triggers, an alternative approach that simply seeks to isolate electrically the pulmonary veins from the left atrium seems logical. This novel, over-the-wire catheter, which integrates a cylindrical ultrasound transducer within a saline-filled balloon, seemed to be an effective way to perform anatomical ablation of the pulmonary veins. In our preliminary experience, electrical isolation (Figure 2⇓), as determined by an absence of any activation in the pulmonary veins in sinus rhythm, was achieved in all but 1 of the pulmonary veins targeted. Ultrasound does not rely on extensive heating on the vein surface, and heat is not conducted to the cardiac tissue as it is with radiofrequency. This may partially account for the absence of any clinical or radiographic evidence of pulmonary vein stenosis in our patients.
Despite the promising early results, there are limitations to both this initial study and the present technology itself. Electrical isolation of >1 pulmonary vein in all patients seems safe and supports the empirical approach to pulmonary vein isolation. However, whether all lesions were needed to prevent clinical arrhythmia is unclear. It is possible that limiting ablation to fewer veins may reduce the risk of complications such as embolic stroke.
In larger pulmonary vein orifices, it was difficult to achieve adequate heating. Finally, it was at times challenging to place the catheter in all pulmonary veins at the proximal portion. Therefore, foci at the most proximal lip of a pulmonary vein may not be ablated successfully.
We report the preliminary use in patients of a through-the-balloon ultrasound ablation catheter for circumferential isolation of the pulmonary veins. With this system, empirical electrical isolation of the pulmonary veins seems feasible; this promising approach may prevent the recurrence of atrial fibrillation. If catheter design limitations are addressed, isolation using through-the-balloon ultrasound could add significantly to the tools available for treating patients with drug-refractory atrial fibrillation.
The study was supported in part by a grant from Atrionix, Palo Alto, Calif.
Dr Lesh is a coinventor of the Atrionix device used in this study; he is also a member of the board of trustees for Atrionix, Inc.
- Received June 12, 2000.
- Revision received August 22, 2000.
- Accepted August 13, 2000.
- Copyright © 2000 by American Heart Association