The term “stunning” is used to describe the mechanical dysfunction of the left atrium that occurs after conversion of atrial fibrillation to sinus rhythm. This phenomenon has been implicated in the development of embolic events after cardioversion of atrial fibrillation. Studies have shown that electric remodeling can occur in only seven minutes of atrial fibrillation and can be sufficient to promote subsequent episodes of atrial fibrillation. Whether stunning develops after a brief episode of atrial fibrillation is unknown. Sparks and colleagues studied the effect of a brief duration of atrial fibrillation on the mechanical function of the left atrium and the left atrial appendage in patients with underlying structural heart disease. The authors also attempted to determine the risk of embolic events.

The study included 24 patients with significant structural heart disease, including a low ejection fraction and an increased atrial diameter. These patients were undergoing implantation of a ventricular implantable cardioverter defibrillator when the study was performed. Transesophageal echocardiography was used to evaluate the left atrium and the atrial appendage before, during and after the induction of atrial fibrillation.

Left atrial function and left atrial appendage function were assessed at six junctures: (1) when the heart was in sinus rhythm one minute before induction of atrial fibrillation; (2) after induction of atrial fibrillation at one minute; (3) after induction of atrial fibrillation at 10 minutes; (4) immediately after reversion of atrial fibrillation to sinus rhythm; (5) when the heart was in sinus rhythm five minutes after reversion; and (6) when the heart was in sinus rhythm 10 minutes after reversion of atrial fibrillation. The arrhythmia continued for 15 minutes, at which time it was allowed to resolve spontaneously. If spontaneous resolution did not occur by 20 minutes, a sinus rhythm was reestablished electrically. Spontaneous echo contrast was evaluated at the six time points.

During atrial fibrillation, changes in velocities within the left atrium and the atrial appendage were observed, but velocities returned to baseline immediately after converting to sinus rhythm. No significant change in left atrial function was seen immediately after the termination of atrial fibrillation.

The authors conclude that a 15- to 20-minute period of atrial fibrillation is not associated with left atrial stunning, even in patients with underlying heart disease. The findings suggest that patients with short runs of atrial fibrillation that spontaneously convert to sinus rhythm do not require anticoagulation therapy to reduce the risk of embolic stroke.