Mechanical remodeling of the left atrium after loss of atrioventricular synchrony - A long-term study in humans

Background-Tachycardia-mediated mechanical remodeling of the atrium is cons idered central to the pathogenesis of thromboembolism associated with chron ic atrial fibrillation. Whether atrial mechanical remodeling also occurs in response to atrial stretch induced by chronic asynchronous ventricular pac ing in patients with permanent pacemakers is unknown. Methods and Results-The study design was a prospective randomized compariso n between 21 patients paced chronically in the VVI mode and 11 patients pac ed chronically in the DDD mode for 3 months. Left atrial appendage (LAA) fu nction and the presence of spontaneous echo contrast (SEC) were determined with transesophageal echocardiography (TEE) within 24 hours of pacemaker im plantation and after 3 months. The VVI patients were then programmed to DDD and underwent a third TEE after DDD pacing for an additional 3 months. Aft er chronic VVI pacing, LAA velocity decreased from 82.4+/-29.0 to 42.1+/-25 .4 cm/s (P<0.01), LAA fractional area change decreased from 74.9+/-17.2% to 49.8+/-22.0% (P<0.01), and 4 patients (19%) developed left atrial SEC (P<0 .05), With the reestablishment of chronic AV synchrony, LAA velocity increa sed to 61.6+/-18.5 cm/s (P<0.01), LAA fractional area change increased to 7 6.4+/-18.1% (P<0.01), and SEC resolved. in the 11 patients undergoing chron ic DDD pacing, no significant changes in LAA velocity (baseline, 86.0+/-28. 8 cm/s versus 3 months, 79.6+/-14.9 cm/s) or LAA fractional area change (ba seline, 76.2+/-19.3% versus 72.5+/-15.7%) were demonstrated, and SEC did no t develop. Conclusions-Chronic loss of AV synchrony induced by VVI pacing is associate d with mechanical remodeling of the left atrium, which may reverse after th e reestablishment of AV synchrony with DDD pacing, This process may be part ly responsible for the higher incidence of thromboembolism observed in pati ents undergoing VVI pacing compared with AV sequential pacing.