Abstract 19247: Biventricular and Left Ventricular Pacing Reduces Stroke Work in Ventricles With Preserved Function Due to Non-Uniform Work Distribution
Purpose: Pacing therapy for heart failure (HF) patients with narrow QRS has gained increasing interest. We investigated the responses to biventricular (BV) and left ventricular lateral wall (LV) pacing in hearts with intact LV function and no electrical conduction delay.
Methods: In 6 anesthetized dogs with micromanometers we measured dimension changes with sonomicrometry in 4 circumferential segments. Peak intersegmental time delay (ITD) was measured between onset R in intramyocardial electromyograms. Stroke volume (SV) was calculated from an aortic flowmeter and stroke work (SW) from pressure-volume loops. Regional work was defined as the area of the pressure-segment length loops. Measurements were performed during baseline, BV pacing and LV pacing.
Results: LV pacing increased ITD from 11±4.8ms (mean±SD) to 30±7.6ms (p<.01), indicating electrical dyssynchrony. BV pacing increased ITD to 17±6.7ms, p<.05. LV- and BV pacing decreased SV by 10 ± 8% (p<.05) and 5±7 % (n.s.) and SW by 28±13% (p<.01) and 17±14% (p<.05), respectively. LV pacing caused a marked redistribution of segmental work (fig. 1) and pre-ejection deformation (fig. 2). LV pacing and to a lesser degree BV pacing caused marked pre-ejection shortening in the early-activated lateral wall and reduced segmental work. There was pre-systolic lengthening in the late activated septal myocardium, and during LV pacing this resulted in increased segmental work in the septum (Fig.2).
Conclusion: In hearts with intact LV function and normal electrical conduction, LV pacing reduced stroke work and stroke volume, and there were similar trends with BV pacing. These responses were attributed to non-uniform distribution of segmental work with reduced work in the early-activated lateral wall. Clinical studies should be done to determine if a similar mechanism may attenuate responses to pacing therapy in patients with LV failure and narrow QRS.
- © 2010 by American Heart Association, Inc.