Abstracts: ASAIO Cardiac Abstracts
LOAD DEPENDENCE OF CARDIAC OUTPUT IN BIVENTRICULAR PACING: LEFT VENTRICULAR VOLUME OVERLOAD IN PIGS
Previous work from our laboratory has shown that optimization of biventricular pacing (BiVP) is load dependent. Cardiac output (CO) was maximized with a ventricular-ventricular (V-V) delay of +40 ms (RV-first pacing) during RV pressure overload. We hypothesized that a model of LV volume overload (LVVO) would also have specific timing requirements during BiVP for optimization of CO.
Following median sternotomy in six anesthetized pigs, complete heart block was induced by ethanol ablation. Bipolar leads were placed on the RA, anterior RV, and obtuse margin of the LV. An ultrasonic flow probe was placed on the aorta. A conduit was grafted from the LV to the LA to simulate LVVO. An ultrasonic flow probe was placed around the conduit to measure flow that averaged 50% of CO. During atrial tracking DDD, BiVP was initiated. Atrioventricular delay (AVD) was varied between 60 and 270 ms in 30 ms increments for 20-second intervals. After determining optimum AVD, V-V delay was varied in 20 ms increments from +80 to -80 ms for 20-second intervals.
V-V delays had no significant effect on CO with the graft clamped (Control). With the graft unclamped, however, there was a statistically significant (p<0.0001 by repeated measures analysis of variance) trend toward higher CO with RV-first pacing.
RV-first pacing in swine significantly increased CO during acute LVVO but not during the control state. Understanding load specific pacing requirements will facilitate development of perioperative temporary BiVP for acute heart failure.Copyright © 2005 by the American Society for Artificial Internal Organs