Atrial Thrombi in Atrial Flutter

Abstract & Commentary

Synopsis: Patients with pure atrial flutter do not require anticoagulation prior to ablation or cardioversion, but patients with concomitant paroxysmal atrial fibrillation do.

Source: Schmidt H, et al. J Am Coll Cardiol. 2001; 308:778-784.

Current guidelines do not recommend routine anticoagulation prior to cardioversion of atrial flutter.1 However, the large, randomized, atrial fibrillation trials included some patients with atrial flutter and suggested that they benefited from anticoagulation as well. Also, observational studies have shown left atrial thrombi in patients with atrial flutter and left atrial stunning after cardioversion of atrial flutter. Thus, Schmidt and colleagues from the University of Bonn, Germany, studied 139 patients with atrial flutter undergoing 202 electrophysiologic studies by transesophageal echocardiography. After echocardiography, all patients were put on effective anticoagulation therapy and the electrophysiologic study was performed < 24 h. In 122 patients, radiofrequency catheter ablation was performed; 64 had overdrive suppression, and 16 had electrical cardioversion. Anticoagulation was stopped 24 hours after the procedure, except in 38 of the 69 patients who had a history of paroxysmal atrial fibrillation; in whom coumadin was continued. Also, 11 patients with pure atrial flutter were continued on coumadin for other reasons. The patients were followed for 1 month for subsequent events.

Transesophageal echocardiography demonstrated atrial thrombi in 2 patients (1%). No postprocedure thromboembolic complications were observed. A thrombogenic milieu, as defined by the presence of thrombus or dense spontaneous echo contrast, was found in 15 patients (7%). A left ventricular ejection fraction < 40%, diabetes, and systemic hypertension were significant correlates of a thrombogenic milieu; and all 15 patients had at least 1 of these factors, 10 had 2 of them. Also, 7 of the 15 had an ejection fraction < 40%. In addition, both of the patients with left atrial thrombi identified had heart failure and paroxysmal atrial fibrillation. Schmidt et al concluded that this study supported the current guidelines that patients with pure atrial flutter do not require anticoagulation prior to ablation or cardioversion, but patients with concomitant paroxysmal atrial fibrillation do. Also, in patients with heart failure/poor left ventricular function, diabetes or hypertension, anticoagulation should be considered since these parameters indicate a higher likelihood of atrial thrombi.

Comment by Michael H. Crawford, MD

The role of warfarin anticoagulation in patients with atrial flutter remains controversial. Part of the reason for this is that there are few patients with lone atrial flutter and even fewer studies of them. Even this study, which focused on patients with atrial flutter, was contaminated by paroxysmal atrial fibrillation in about half the patients. Also, patients with atrial flutter often have other problems that predispose them to thromboembolic events such as heart failure. These other factors could not be avoided in this study either. Despite these caveats, left atrial thrombus was rare by transesophageal echo in their patients. Thus, their conclusion that routine anticoagulation for weeks before and after cardioversion is not necessary seems correct and is in agreement with published guidelines.

A key issue is who with atrial flutter should receive standard anticoagulation? Schmidt et al suggest that patients with paroxysmal atrial fibrillation in addition to atrial flutter should. This is an axiomatic conclusion since more than half of their patients in this category were on chronic warfarin therapy, which was continued. They imply that patients with heart failure or ejection fraction < 40% should be since this is a traditional risk factor for thromboemboli and both their patients with left atrial thrombi on echocardiography had heart failure. Although diabetes and hypertension also predicted thrombi or dense spontaneous echo contrast, their high prevalence in the population makes these conditions less useful as indicators for standard anticoagulation. Thus, this study does not adequately address this issue.

This study does demonstrate that a strategy of periprocedure anticoagulation with transesophageal echo guidance for cardioversion or ablation of atrial flutter is safe, as has been shown for atrial fibrillation. However, given the low incidence of thrombi and the complete lack of complications, it could be argued that echo guidance is unnecessary, especially if selected higher risk patients are given standard anticoagulation. Unfortunately, a study of 139 patients is not large enough to make firm conclusions about these alternative strategies.

Reference

1. Lanpacis A, et al. Chest. 1998;114:579S-589S.

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