Left atrial mechanical function after brief duration atrial fibrillation.

OBJECTIVES: This study examined the effect of brief duration atrial fibrillation on left atrial and left atrial appendage mechanical function in humans with structural heart disease.
BACKGROUND: Left atrial dysfunction and the development of spontaneous echo contrast (SEC) may follow the cardioversion of atrial fibrillation (AF) to sinus rhythm. This phenomenon has been termed "stunning" and is implicated in the development of atrial thrombus and embolic stroke. The effects of brief duration AF on left atrial mechanical function in humans are unknown.
METHODS: Twenty-four patients (23 men, aged 59.1+/-12.7 years) with significant structural heart disease (ejection fraction 31.2+/-9.0%, left atrial diameter 4.9+/-0.4 cm) undergoing implantation of a ventricular cardiodefibrillator underwent transesophageal echocardiography to evaluate left atrial appendage emptying velocities (LAAeV) and SEC before, during and after a 15-min period of AF induced by rapid right atrial pacing. Atrial fibrillation was then permitted to terminate spontaneously within 5 min or was reverted with an endocardial direct current shock. Velocities and SEC were assessed in sinus rhythm pre-AF, during AF and immediately, 5 and 10 min after reversion to sinus rhythm.
RESULTS: Atrial fibrillation terminated spontaneously in 10 patients after 16.1+/-1.0 min. Endocardial direct current (DC) cardioversion of 10.4+/-6.4 J was required in 14 patients after AF lasting 20 min. Mean LAAeV pre-AF (50.0 +/- 17.5 cm/s) was not significantly different to LAAeV immediately (52.8 +/- 16.7 cm/s), 5 min (54.3 +/- 16.4 cm/s) or 10 min (53.7 +/- 15.7 cm/s) after reversion to sinus rhythm. Atrial stunning defined as a reduction in LAAeV of >20% was not observed in any patient. Fourteen of 24 patients (58%) developed SEC during AF, which resolved within 30 s of AF termination. There were no significant differences between LAAeV in those patients reverting with DC shock (pre-AF 50.6+/-16.2 cm/s vs. immediately post-AF 54.7+/-16.6 cm/s) or in those patients with spontaneous reversion (pre-AF 48.9+/-20.2 cm/s vs. immediately post-AF 49.8+/-17.3 cm/s).
CONCLUSIONS: Significant left atrial stunning was not observed after brief duration AF in humans with structural heart disease. Transient left atrial SEC develops in a significant proportion of these patients during AF but resolves rapidly on reversion to sinus rhythm. These findings suggest that the risk of thromboembolism may be low after brief duration AF that terminates either spontaneously or with an endocardial DC shock even in patients with significant structural heart disease. These findings have important implications for recipients of implantable devices that are capable of atrial defibrillation in response to AF.