Subclinical Stroke in AF Ablation

Abstract & Commentary

By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville

Source: Siklody CH, et al. Incidence of asymptomatic intracranial embolic events after pulmonary vein isolation. Comparison of different atrial fibrillation ablation technologies in a multicenter study. J Am Coll Cardiol 2011;58:681-688.

In this study, Siklody and her colleagues from three large and experienced atrial fibrillation (AF) ablation centers performed cerebral magnetic resonance imaging before and after AF ablation using three different catheter technologies. Patients were eligible for inclusion if they had symptomatic drug-resistant AF and were referred for a catheter ablation. Patients with longstanding persistent AF, patients in whom left atrial ablation other than pulmonary vein isolation, and those with contraindications to cerebral magnetic resonance imaging (MRI) were excluded. Three different ablation catheter technologies were evaluated in the study. These included conventional irrigated radiofrequency (RF) ablation catheters (either CoolPath Duo or Thero-Cool), an Arctic Front cryoballoon ablation catheter, or a multielectrode duty-cycled phased RF pulmonary vein ablation catheter (Medtronic Ablation Frontiers). Ablations were performed by operators at the individual institutions with expertise in these respective techniques. Standard RF ablation procedures were performed at all three centers, cryoballoon ablations in one center and phased RF pulmonary vein catheter ablations in two centers.

All three of these catheters are available for routine clinical use in Europe. Recommended techniques were used in each. For conventional pulmonary vein isolation with externally irrigated catheters, a double transseptal technique was used. The cryoballoon pulmonary vein isolation procedure used a single transseptal puncture. For phased RF pulmonary vein isolation using a multielectrode catheter, a single transseptal approach was also used.

Patients were treated before the procedure with 4 weeks of oral anticoagulation. Anticoagulation was reduced or stopped two to three days before ablation and bridging with low molecular weight heparin was permitted if necessary. Patients underwent a transesophageal echocardiogram on the day before ablation to rule out left atrial thrombi. During the procedure, intravenous unfractionated heparin was administered immediately after the first transseptal access. Anticoagulation was resumed after the procedure with heparin bridging if necessary until the INR was greater than 2.5.

A systematic neurologic exam was performed on admission, the day after the procedure, and 4-5 days after the procedure. Cerebral MRI was performed 1 day before and 1-2 days after ablation using a 1.5-T unit. Two experienced radiologists blinded to the ablation technique analyzed all MRI scans. A third radiologist was used in cases of disagreement.

The study included 74 patients. There were slightly more patients with persistent AF in the externally irrigated RF group. Left atrial size and thromboembolic risk profiles were similar between the groups. Seventeen of the 74 patients presented in AF, and AF was noted during the procedure in another 10 patients. Twenty-three patients underwent electrical DC cardioversions during the procedure. These characteristics were evenly distributed in all three groups. All pulmonary veins were successfully isolated with all three techniques. Procedural and fluoroscopy times were longest in the externally irrigated RF group, intermediate in the cryoballoon group, and shortest in the pulmonary vein ablation catheter group.

No patient had new neurologic symptoms after the procedure and standard neurological examination in all patients were normal before and after ablation. Chronic lesions on the baseline MRI before ablation were noted in six patients in the externally irrigated RF group, two in the cryoablation group, and one in the pulmonary vein catheter ablation group. After the procedure, MRI revealed new ischemic lesions in 2 of 27 (7.4%) patients in the externally irrigated RF group, in 1 of 23 (4.3%) in the cryoballoon group, and in 9 of 24 (37.5%) in the pulmonary vein ablation catheter group. In the latter group, these patients presented with a median of three acute lesions on postprocedure MRI. The increased incidence of new ischemic lesions in the pulmonary vein ablation catheter group was statistically significant. The new lesions could be distributed over both hemispheres, but were preferentially located in the vertebrobasilar territory. The median lesion size was 5.5 mm. There was no difference in the details of procedural anticoagulation that could be related to the finding of new emboli.

The authors conclude that pulmonary vein isolation applied with the multielectrode duty-cycled phased RF ablation catheter used in this study is associated with an increased incidence of intracranial emboli that are fortunately subclinical. Further studies to clarify the causes and clinical significance of these embolic lesions should be performed.

Commentary

Until recently, no ablation catheter was approved specifically for pulmonary vein isolation during AF ablation procedures. Now several externally irrigated RF ablation catheters and a cryoballoon system have been approved for use in the United States and the multielectrode phased RF system is available in Europe. The trials that led to these device approvals were relatively small and focused primarily on early and intermediate term efficacy and secondly on procedural safety. Routine cerebral MRI imaging was not included in the design of these trials.

Most surveys on the results of pulmonary vein isolation in AF patients show a per-procedural stroke rate of 0.5%-2%. This number is based on clinically manifest events. However, several small single-center reports, and now this three-center report, have shown that routine cerebral MRI imaging after the procedure can detect clinically silent new lesions. The current report suggests that the rate of these events may differ based on the catheter technology used. Although we don't now know the long-term significance of these lesions in individual patients, we must assume that they may have subtle adverse effects during follow-up.

The data presented here strongly argue that routine MRI imaging should be an additional feature included in protocols designed to evaluate new catheter technologies. Catheter associated with higher rates of new lesion formation should probably not be approvable.