Heart rate and force-frequency effects on diastolic function of the left ventricle in exercising dogs

Abstract

Background: Previous studies from our laboratory have shown pronounced augmentation of the force-frequency relation on myocardial contraction during exercise, but the influence of this effect on diastole has not been investigated. Methods and Results: Accordingly, the effect of changing heart rate on left ventricular (LV) relaxation, filling dynamics, and pressure- volume relations during exercise was studied in eight conscious dogs. The exercise heart rate was slowed from 208±21 (SD) to 163±11 beats per minute by injection of a specific sinus node inhibitor (UL-FS 49, or zatebradine, 0.6 mg/kg) during continuous exercise. Heart rate was then abruptly restored to the predrug level by atrial pacing during continued exercise. LV volume was calculated by use of implanted ultrasonic crystals, and LV pressure was determined with an implanted micromanometer. Comparing conditions after pacing back to a heart rate of 210 beats per minute with those obtained when the heart rate was slowed by atrial pacing, LV dP/dt(max) was increased by 27% at the higher rate (P