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 h igher in patients with single-chamber ventricular demand (VVI) pacemak ers than. in patients with dual-chamber (DDD) pacemakers. However, dat a on left atrial appendage flow velocity in pacing patients are limite d. To investigate the influence of the pacing mode on the left atrial appendage flow velocity, we studied 19 patients with permanent DDD pac emakers and measured the left atrial appendage flow velocity by transe sophageal echocardiography at baseline (during DDD pacing) and after s witching to VVI pacing. The indications for pacemaker implantation wer e second- and third-degree atrioventricular block (AVB group, n = 11) and sick sinus syndrome (SSS group, n = 8). Compared with the DDD paci ng mode, there was a significant decrease in the left atrial appendage flow velocity during WI pacing in both the SSS group (43 +/- 14 vs 23 +/- 7 cm/sec, P < 0.05) and the AVB group (59 +/- 18 us 41 +/- 18 cm/ sec, P < 0.05). In eight patients with persistent retrograde ventricul oatrial conduction during VVI pacing, the left atrial appendage flow v elocity was markedly decreased (from 43 +/- 16 to 25 +/- 9 cm/sec, P < 0.05). In five (63%) of the eight patients, left atrial appendage flo w velocity was less than 25 cm/sec. A reduction in left atrial appenda ge flow velocity when switching from DDD to VVI pacing may account for an increased risk of thrombus formation, in the left atrial appendage tan increased thromboembolic risk in patients in, sinus rhythm with V VI pacemakers).