Published Online
on October 13, 2003

A more recent version of this article appeared on October 21, 2003

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Submitted on March 28, 2003
Revised on July 22, 2003
Accepted on July 22, 2003

Reversal of Atrial Mechanical Dysfunction After Cardioversion of Atrial Fibrillation. Implications for the Mechanisms of Tachycardia-Mediated Atrial Cardiomyopathy

Prashanthan Sanders MBBS, Joseph B. Morton MBBS, Peter M. Kistler MBBS, Jitendra K. Vohra MD, Jonathan M. Kalman MBBS, PhD, and Paul B. Sparks MBBS, PhD^*

From the Department of Cardiology, Royal Melbourne Hospital, and the Department of Medicine, University of Melbourne, Melbourne, Australia.

^* To whom correspondence should be addressed. E-mail: paul.sparks{at}mh.org.au.

Background--Atrial mechanical "stunning" develops after cardioversion of atrial fibrillation (AF) and is implicated in the genesis of thromboembolic complications. However, the mechanisms responsible for this phenomenon are poorly understood. Whether atrial mechanical dysfunction caused by AF can be reversed by pacing at increased rates or by pharmacological agents is unknown.

Methods and Results--Twenty-six patients with AF undergoing cardioversion were dichotomized prospectively on the basis of the duration of arrhythmia as short-duration (1 to 6 months) or long-duration (3 years) AF. Left atrial appendage emptying velocities (LAAEVs) and spontaneous echocardiographic contrast (LASEC) were assessed by transesophageal echocardiography during AF, after reversion to sinus rhythm, during atrial pacing at cycle lengths of 750 to 250 ms, after a postpacing pause, and with isoproterenol. In patients with short-duration AF, LAAEV decreased (42.0±2.7 to 18.5±2.0 cm/s; P<0.0001) and LASEC increased (0.9±0.3 to 2.2±0.3; P<0.01) with termination of AF; pacing increased LAAEV (48.3±4.1 cm/s; P<0.0001) and decreased LASEC (1.5±0.3; P<0.01); isoproterenol increased LAAEV (73.3±7.8 cm/s; P<0.0001) and decreased LASEC (0.3±0.2; P<0.01); and the postpacing pause increased LAAEV (68.3±3.8 cm/s; P<0.0001). In contrast, patients with long-duration AF demonstrated a significantly attenuated response of atrial mechanical function at each time point. With termination of AF, LAAEV decreased (19.1±2.6 to 8.2±1.0 cm/s; P=0.003) and LASEC increased (2.0±0.2 to 3.3±0.2; P<0.01); pacing increased LAAEV (18.4±2.7 cm/s; P<0.0001) and decreased LASEC (2.3±0.2; P<0.01); isoproterenol increased LAAEV (26.1±3.9 cm/s; P=NS to equivalent atrial rate) and decreased LASEC (1.0±0.3; P<0.01); and the postpacing pause increased LAAEV (27.2±2.4 cm/s; P=0.007).

Conclusions--Atrial pacing at increased rates and isoproterenol can reverse atrial mechanical stunning associated with short-duration AF. In contrast, long-duration AF is associated with an attenuated response to these maneuvers. These findings suggest a functional contractile apparatus in the mechanically remodeled atrium caused by AF; however, with longer durations of AF, additional factors may determine atrial mechanical function.

Key words: arrhythmia • atrium • cardioversion • echocardiography • remodeling

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