Timing and magnitude of prestretch strongly affect cardiac muscle tension development (545.2)

Abstract

Ectopic ventricular pacing leads to regional myocardial prestretch. In‐vivo studies suggest that the timing of prestretch determines the effect on pump function and can lead to regional wall remodeling. Here we measure the direct effects of prestretch timing on the magnitude of tension development in isolated cardiac muscle. The effects of prestretch were simulated using excised murine right ventricular papillary muscles. A servo motor was used to impose precisely timed stretches, while a force transducer measured force output and strain was monitored using a CCD camera and topical markers. A critical stretch timing interval was observed to statistically increase peak tension by as much as 500%, while shortening during this interval inhibited peak tension significantly by as much as 40%. A simple model consisting of experimentally obtained time varying elastance and the force‐velocity relation could not completely explain the results. An estimate of shortening deactivation was measured by performing quick stretches to dissociate crossbridges. The results showed that the timing of shortening deactivation could explain the remaining differences between the model and the experimental results. These evaluations have led us to the conclusion that prestretches performed at slow physiologic velocities cause alterations in twitch kinetics that cannot be explained solely by time varying elastance.