Variable interbeat intervals caused no change in force in canine preparations and a nonsignificant decrease in rabbit trabeculae, with higher preload increasing the impact of prebeat duration.
The impact of beat-to-beat variability on cardiac contractility is species-dependent and becomes more prominent with higher preload in rabbit trabeculae.
We investigate the effect of beat-to-beat variability on cardiac contractility. Cardiac trabeculae were isolated from the right ventricle of rabbits and beagle dogs and stimulated to isometrically contract, alternating between fixed steady state versus variable interbeat intervals. Trabeculae were stimulated at physiologically relevant frequencies for each species (dog 1 and 4 Hz; rabbit 2 and 4 Hz) intercalating fixed periods with 40% variability. A subset of the trabeculae (at 90% of optimal length) was stretched prior to stimulation between 5 and 13% and stimulated at the same frequencies with a fixed versus 40% variation. Fixed rate response at the same base frequency was measured before and after each variable period and the average force reported. In canine preparations no change in force was observed as a result of the imposed variability in beat-to-beat duration. In the rabbit, we observed a nonsignificant decrease in force between fixed and variable pacing at both 2 and 4 Hz (n = 8) when 40% variability was introduced. When a 5% and 13% stretch was applied, the correlation coefficient sharply increased, indicating a more prominent impact of the prebeat duration on the following cycle with higher preload.
Torres et al. (Sat,) conducted a other in Cardiac contractility. Variable interbeat intervals vs. Fixed steady state interbeat intervals was evaluated on Average force (contractile strength). Variable interbeat intervals caused no change in force in canine preparations and a nonsignificant decrease in rabbit trabeculae, with higher preload increasing the impact of prebeat duration.