Influence of Cardiac Pacing Mode on Left Atrial Appendage Flow Velocity: Implication to Systemic Embolism During VVI Pacing.

Previous studies have shown that the incidence of thromboembolism is higher in patients with single-chamber ventricular demand (VVI) pacemakers than in patients with dual-chamber (DDD) pacemakers. However, data on left atrial appendage flow velocity in pacing patients are limited. To investigate the influence of the pacing mode on the left atrial appendage flow velocity, we studied 19 patients with permanent DDD pacemakers and measured the left atrial appendage flow velocity by transesophageal echocardiography at baseline (during DDD pacing) and after switching to VVI pacing. The indications for pacemaker implantation were second- and third-degree atrioventricular block (AVB group, n = 11) and sick sinus syndrome (SSS group, n = 8). Compared with the DDD pacing mode, there was a significant decrease in the left atrial appendage flow velocity during VVI pacing in both the SSS group (43 +/- 14 vs 23 +/- 7 cm/sec, P < 0.05) and the AVB group (59 +/- 18 vs 41 +/- 18 cm/sec, P < 0.05). In eight patients with persistent retrograde ventriculoatrial conduction during VVI pacing, the left atrial appendage flow velocity was markedly decreased (from 43 +/- 16 to 25 +/- 9 cm/sec, P < 0.05). In five (63%) of the eight patients, left atrial appendage flow velocity was less than 25 cm/sec. A reduction in left atrial appendage flow velocity when switching from DDD to VVI pacing may account for an increased risk of thrombus formation in the left atrial appendage (an increased thromboembolic risk in patients in sinus rhythm with VVI pacemakers).