Embolic Risk Post Ablation

Abstract & Commentary

By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.

Synopsis: Discontinuation of anticoagulation 3-6 months after successful atrial fibrillation ablation is reasonable in low-risk patients.

Source: Oral H, et al. Risk of Thromboembolic Events after Percutaneous Left Atrial Radiofrequency Ablation of Atrial Fibrillation. Circulation. 2006;114:759-765.

In this study, oral and colleagues from the University of Michigan reviewed their experience with stroke and systemic thromboembolic events associated with percutaneous catheter ablation procedures for atrial fibrillation (AF). Oral et al reviewed data from 755 consecutive patients with paroxysmal or persistent (here called chronic) atrial fibrillation who underwent left atrial catheter ablation between January 2003 and July 2005. The population was mostly middle aged (55 ± 11 years) and included 577 men and 178 women. The AF pattern was paroxysmal in 490 patients and persistent in 265 patients. During their initial evaluation, the following risk factors for stroke were identified: congestive heart failure, hypertension, age greater than 65, diabetes mellitus, and prior stroke or transient ischemic attack (TIA).

All patients received low molecular weight heparin injections for 5 days prior to the procedure. Patients with persistent atrial fibrillation or with a history of either a stroke or a documented left atrial thrombus underwent a transesophageal echocardiogram in the 24 hours before the ablation attempt. During left atrial mapping and ablation, heparin was administered to maintain an activated clotting time between 300 and 350 seconds. Once the ablation catheters and sheaths had been removed and hemostasis achieved, intravenous heparin was restarted and maintained overnight. Low molecular weight heparin at a dose of 0.5 mg/kg twice per day was then continued during warfarin treatment until the INR was ≥ to 2.0. All patients continued warfarin for at least 3 months after the procedure, with a desired INR of 2.0 to 3.0. In patients without risk factors, warfarin was discontinued at this point, and these patients were advised to take aspirin chronically. Patients with risk factors were advised to continue warfarin.

In the entire group, 411 patients (56%) had one or more risk factors for stroke, with hypertension being the most commonly identified risk factor. The remaining 344 patients (44%) had no risk factors. In the entire group, 32 (4%) had a history of congestive heart failure, 325 (43%) had a history of hypertension, 126 (17%) were over age 65, 55 (7%) had diabetes, and 34 (5%) had a prior stroke or TIA. Thromboembolic events were observed in 7 of 755 patients (0.9%) within 30 days of their ablation procedure. One event occurred with 6 hours of the procedure, 3 occurred one to 7 days after the procedure, and the remaining 3 occurred one to 2 weeks after the procedure. Six of the 7 patients with an early thromboembolic event had one or more risk factors for stroke. All patients with early events were between ages 51 and 67. In 5 of these 7 patients, deficits completely resolved. There were only 2 thromboembolic events beyond 30 days after the procedure. Both occurred in men, aged 40 and 55, with persistent AF. One of these patients had hypertension and diabetes, whereas the other had no risk factors. Both of the latter patients had therapeutic INRs at the time of their event. AF was present at the time of 5 of 7 early events and one of 2 late events.

At a median of 4 months after the ablation procedure, anticoagulation was discontinued in 203 of 256 (79%) patients who remained in sinus rhythm and did not have risk factors for stroke. Among the 266 patients who remained in sinus rhythm and had more than one risk factor, anticoagulation was discontinued in 180 (68%), at a median of 5 months after the procedure. Two hundred thirty-three patients had recurrent AF or atrial flutter after ablation, and 218 of these (94%) were continued on warfarin. There were 2 major bleeding complications in this series. Both occurred in patients being treated with warfarin who also had recurrent AF.

Oral et al conclude that their data suggest that discontinuation of warfarin 3 to 6 months after left atrial catheter ablation in patients without baseline risk factors for stroke is reasonable.

Commentary

Stroke is the most feared adverse consequence of atrial fibrillation. Since left atrial catheter ablation was first introduced as a potential treatment for atrial fibrillation, the procedure has been shown to be effective in preventing or reducing the burden of recurrent arrhythmia in selected populations. However, the frequency of stroke, as a complication of the procedure itself, and the long-term effects of left atrial catheter ablation on stroke incidence have not been well characterized. In this paper, Oral et al showed that the acute stroke rate with left atrial catheter ablation is reasonably low. They also show that the intermediate-term stroke rate is low if the procedure is effective in eliminating arrhythmia at least in low or intermediate risk patients.

It has been estimated that there are over 2 million people in the United States who have some form of atrial fibrillation. The majority of these patients are elderly, and many have several other risk factors for stroke. As admitted by Oral et al, much more experience will be needed before we will know if left atrial catheter procedures are effective and safe in these higher risk populations.