Correspondence

Transesophageal Echocardiography before Cardioversion

N Engl J Med 1993; 329:577-578August 19, 1993

Article

To the Editor:

In the March 18 issue of the Journal, Manning et al.1 admirably advocate early cardioversion for atrial fibrillation without prolonged anticoagulation beforehand, if the possibility of atrial thrombi can first be excluded by transesophageal echocardiography. Although we are in full agreement with the concept of a strategy guided by transesophageal echocardiography for the management of anticoagulation and the screening of patients before cardioversion, several issues raised by this study deserve comment.

The study cohort was very heterogeneous with regard to the anticoagulant regimen and the type of cardioversion used. Twenty of the 78 patients (26 percent) who underwent successful cardioversion received only intravenous heparin for 24 hours after cardioversion rather than the conventional four weeks of warfarin. Although no embolic events were reported in this subgroup, this practice should not be misconstrued by clinical cardiologists as being safe if atrial thrombi can be ruled out by transesophageal echocardiography. Investigations into the mechanisms of thromboembolism in atrial fibrillation support the use of anticoagulation at the time of cardioversion and afterward in all patients with atrial fibrillation, even in the absence of thrombus. The function of the left atrial appendage may be impaired and spontaneous echocardiographic contrast of the left atrium (a marker of thromboembolic risk) may be increased immediately after cardioversion, representing a potential risk of thromboembolism2. In support of this hypothesis, a study in a larger series with a design similar to that of Manning et al.1 reported one embolic event after cardioversion in a total of 156 patients; this patient had no thrombus identified by transesophageal echocardiography before cardioversion and therefore did not undergo anticoagulation. Moreover, a transesophageal echocardiogram obtained after the embolic event documented a new thrombus in the left atrial appendage with increased spontaneous echocardiographic contrast3.

With respect to the mode of cardioversion, 47 patients underwent pharmacologic cardioversion, whereas only 31 underwent electrical cardioversion. Previous studies have reported similar incidences of embolic events after either type of cardioversion; however, there may be different mechanisms of post-cardioversion thromboembolism, necessitating more or less conservative anticoagulation strategies. Therefore, a more homogeneous study population with regard to the anticoagulation regimen and type of cardioversion may be more illustrative. Furthermore, the relatively small number of patients with mitral-valve disease (n = 2) probably reflects the exclusion of patients who underwent long-term anticoagulation and would in turn introduce a selection bias in favor of a lower-risk population undergoing cardioversion.

Finally, the number of patients studied (78 patients underwent successful cardioversion) was less than the 100 patients needed for an embolic event, assuming a conservative embolic-event rate of 1.0 percent. Consequently, a larger sample is required to determine the potential benefit of this strategy. The Assessment of Cardioversion Utilizing Transesophageal Echocardiography trial is a controlled, prospective, randomized multicenter trial designed to test the hypothesis that a management strategy for anticoagulation guided by transesophageal echocardiography that allows early cardioversion will be safer, more convenient, and less costly than the conventional approach to management as described by Laupacis et al.4. We therefore find this study intriguing, yet would agree with the suggestion of Manning et al. and of Daniel (also in the March 18 issue)5 that we await the results of randomized trials.

Richard A. Grimm, D.O.
Ian W. Black, M.B., B.S.
Allan L. Klein, M.D.
Cleveland Clinic Foundation, Cleveland, OH 44106

5 References

1. 1

   Manning WJ, Silverman DI, Gordon SPF, Krumholz HM, Douglas PS. Cardioversion from atrial fibrillation without prolonged anticoagulation with use of transesophageal echocardiography to exclude the presence of atrial thrombi. N Engl J Med 1993;328:750-755
   Full Text | Web of Science | Medline

2. 2

   Grimm RA, Stewart WJ, Maloney JD, et al. Impact of electrical cardioversion of atrial fibrillation on left atrial appendage function and smoke: characterization by simultaneous transesophageal echocardiography. J Am Coll Cardiol (in press).
   

3. 3

   Black IW, Grimm RA, Walsh WF, et al. Risk factors for atrial thrombus and stroke in 156 patients undergoing electrical cardioversion: a multicenter transesophageal echocardiographic study. J Am Coll Cardiol 1993;21:Suppl A:28A-28A abstract.
   CrossRef

4. 4

   Laupacis A, Albers G, Dunn M, Feinberg W. Antithrombotic therapy in atrial fibrillation. Chest 1992;102:Suppl:426S-433S
   CrossRef | Web of Science | Medline

5. 5

   Daniel WG. Should transesophageal echocardiography be used to guide cardioversion? N Engl J Med 1993;328:803-804
   Full Text | Web of Science | Medline

Author/Editor Response

The authors reply:

To the Editor: We agree with both Grimm et al. and Daniel that our study had insufficient power to demonstrate the benefit of an approach guided by transesophageal echocardiography, as compared with the conventional practice of giving systemic anticoagulation for three to four weeks before cardioversion, for patients with atrial fibrillation of unknown or prolonged (more than two days) duration. As we stated, such a randomized trial, if the embolic risk is assumed to be 1.2 percent with conventional therapy and 0.6 percent with cardioversion guided by negative transesophageal echocardiography, would require more than 6000 patients. Before such a large and costly trial is undertaken, preliminary studies like ours need to be performed. Our study did demonstrate that such an approach based on the results of transesophageal echocardiography is reasonable and safe. The allocation of resources to conduct large, randomized studies such as the multicenter Assessment of Cardioversion Utilizing Transesophageal Echocardiography trial can now be justified.

We also agree that our findings should not be misconstrued as indicating that 24 hours of heparin therapy after cardioversion is sufficient to avert embolic events, nor can cardioversion guided by transesophageal echocardiography without systemic anticoagulation be advocated. Although no embolic events occurred in our series, the number of hospitalized patients who received either anticoagulation alone or no systemic anticoagulation was too small to draw any conclusions.

We continue to advocate therapeutic anticoagulation before transesophageal echocardiography and for three to four weeks after cardioversion. To our knowledge, there have been no reports in the literature of embolic events in patients with atrial fibrillation who undergo cardioversion with this regimen. There have been isolated reports of systemic emboli after negative transesophageal echocardiography. These have been limited to instances in which patients have not undergone therapeutic anticoagulation either after imaging or during the pericardioversion period1. Anticoagulation is needed for several weeks after cardioversion because of the delay in the return of atrial mechanical function,2 as well as for prophylaxis in the event of reversion to atrial fibrillation. Some patients, however, are thought to be at high risk for bleeding complications related to anticoagulation. For these patients, we continue to believe that cardioversion guided by the results of transesophageal echocardiography is preferable to “blind” cardioversion. Patients who receive no anticoagulation should undergo immediate electrical cardioversion if the possibility of a thrombus has been excluded. If a thrombus is identified, then the risks and benefits of systemic anticoagulation need to be further assessed.

Warren J. Manning, M.D.
Beth Israel Hospital, Boston, MA 02215

David I. Silverman, M.D.
University of Connecticut Health Center, Farmington, CT 06032

Pamela S. Douglas, M.D.
Beth Israel Hospital, Boston, MA 02215

2 References

1. 1

   Ewy GA. Optimal technique for electrical cardioversion of atrial fibrillation. Circulation 1992;86:1645-1647
   Web of Science | Medline

2. 2

   Manning WJ, Leeman DE, Gotch PJ, Come PC. Pulsed Doppler evaluation of atrial mechanical function after electrical cardioversion of atrial fibrillation. J Am Coll Cardiol 1989;13:617-623
   CrossRef | Web of Science | Medline

Citing Articles (3)

Citing Articles

1. 1

   Waldemar E. Wysokinski, Naser Ammash, Folakemi Sobande, Henna Kalsi, David Hodge, Robert D. McBane. (2010) Predicting left atrial thrombi in atrial fibrillation. American Heart Journal 159:4, 665-671
   CrossRef

2. 2

   John A Kastor, Magdi M Saba. 2009. Cardiac Arrhythmias. .
   CrossRef

3. 3

   Richard A. Grimm, William J. Stewart, James D. Maloney, Gerald I. Cohen, Gregory L. Pearce, Eranesto E. Salcedo, Allan L. Klein. (1993) Impact of electrical cardioversion for atrial fibrillation on left atrial appendage function and spontaneous echo contrast: Characterization by simultaneous transesophageal echocardiography. Journal of the American College of Cardiology 22:5, 1359-1366
   CrossRef