Abstract 13369: Impact of Single-Site Versus Multi-Site Pacing on the Contraction-Relaxation Relationship in a Canine Model of Atrioventricular Block
Background: It has been reported that biventricular pacing (BiV) is superior or equal to LV only, and that both are superior to right ventricular pacing (RVA) pacing, in terms of contractile performance and work. Several reports have also shown that LV relaxation is superior during BiV and LV pacing compared to RVA pacing. Previous efforts have evaluated the impact of a change in preload or afterload during one cardiac cycle on the contraction-relaxation (CR) paradigm. The current study is designed to determine if acute transients changes in both pre and afterload alter the CR relationship.
Methods: Anesthetized canines (n=8) were studied acutely with epicardial pacing leads on the right atrium, right ventricular apex and left ventricular apex following catheter ablation of the AV node. LV function was evaluated with a conductance catheter for PV relations. Beat-to-beat data collected during vena-caval occlusion (VCO) were analyzed for changes in LV dP/dtmax and Ravg, a model independent parameter of LV relaxation. Assessment of LV relaxation during VCOs is problematic, as the number of datapoints available to model tau may become insufficient for accurate measurement of this variable. Ravg was calculated as the change in end-systolic pressure (Pes) from dPdtmin to 5 mmHg above the next cycle's end-diastolic pressure divided by the time difference between these two points.
Analysis: The relationship between dP/dtmax and Ravg was evaluated with linear regression. All datasets (n=24) were associated with r values between .93 and .99.
Results: RVA pacing was associated with a greater dP/dttmax-Ravg slope (1.28 ± 0.43) compared with LVA (0.90 ± 0.23) and BiV (0.98 ± 0.27), p < 0.05. Pacing mode did not influence the rate of drop in Pes.
Conclusion: While RVA pacing is known to decrease the rate of LV relaxation, this is the first time that pacing mode has been shown to impact LV relaxation in a linear manner across a large change in preload and afterload. This suggests that LV relaxation may be more load insensitive than previously believed.
- © 2011 by American Heart Association, Inc.