The hemodynamic and atrial electrophysiologic consequences of chronic left atrial volume overload in a controllable canine model.

Abstract

OBJECTIVE: The purpose of this study was to determine the effects of chronic left atrial volume overload on atrial anatomy, hemodynamics, and electrophysiology using a titratable left ventriculoatrial shunt in a canine model. METHODS: Canines (n&#xa0;=&#xa0;16) underwent implantation of a shunt between the left ventricle and the left atrium. Sham animals (n&#xa0;=&#xa0;8) underwent a median sternotomy without a shunt. Atrial activation times and effective refractory periods were determined using 250-bipolar epicardial electrodes. Biatrial pressures, systemic pressures, left atrial and left ventricle diameters and volumes, atrial fibrillation inducibility, and durations were recorded at the initial and at 6-month terminal study. RESULTS: Baseline shunt fraction was 46%&#xa0;&#xb1;&#xa0;8%. The left atrial pressure increased from 9.7&#xa0;&#xb1;&#xa0;3.5&#xa0;mm Hg to 13.8&#xa0;&#xb1;&#xa0;4&#xa0;mm Hg (P&#xa0;<&#xa0;.001). At the terminal study, the left atrial diameter increased from a baseline of 2.9&#xa0;&#xb1;&#xa0;0.05&#xa0;cm to 4.1&#xa0;&#xb1;&#xa0;0.6&#xa0;cm&#xa0;(P&#xa0;<&#xa0;.001) and left ventricular ejection fraction decreased from 64%&#xa0;&#xb1;&#xa0;1.5% to 54%&#xa0;&#xb1;&#xa0;2.7% (P&#xa0;<&#xa0;.001). Induced atrial fibrillation duration (median, range) was 95&#xa0;seconds (0-7200) compared with 0&#xa0;seconds (0-40) in the sham group (P&#xa0;=&#xa0;.02). The total activation time was longer in the shunt group compared with the sham group (72&#xa0;&#xb1;&#xa0;11&#xa0;ms vs 62&#xa0;&#xb1;&#xa0;3&#xa0;ms, P&#xa0;=&#xa0;.003). The right atrial and not left atrial effective refractory periods were shorter in the shunt compared with the sham group (right atrial effective refractory period: 156&#xa0;&#xb1;&#xa0;11&#xa0;ms vs 141&#xa0;&#xb1;&#xa0;11&#xa0;ms, P&#xa0;=&#xa0;.005; left atrial effective refractory period: 142&#xa0;&#xb1;&#xa0;23&#xa0;ms vs 133&#xa0;&#xb1;&#xa0;11&#xa0;ms, P&#xa0;=&#xa0;.35). CONCLUSIONS: This canine model of mitral regurgitation reproduced the mechanical and electrical remodeling seen in clinical mitral regurgitation. Left atrial size increased, with a corresponding decrease in left ventricle systolic function, and an increased atrial activation times, lower effective refractory periods, and increased atrial fibrillation inducibility. This model provides a means to understand the remodeling by which mitral regurgitation causes atrial fibrillation.