VARIABLE-FREQUENCY TRAIN STIMULATION OF CANINE LATISSIMUS-DORSI MUSCLE DURING SHORTENING CONTRACTIONS

In cardiomyoplasty, the latissimus dorsi muscle (LDM) is wrapped aroun d the heart ventricles and electrically activated with a constant-freq uency train (CFT). This study tested the hypotheses that increased mec hanical performance from the LDM could be achieved by activating the m uscle with variable-frequency trains (VFTs) of shorter duration or con taining fewer stimulus pulses than the CFT now used. The mechanical pe rformance of the canine LDM (n = 7) during shortening contractions was measured while the muscle was stimulated with 5- and 6-pulse CFTs (of duration 132 and 165 ms, respectively) and 5- and 6-pulse VFTs (of du ration 104 and 143 ms, respectively) that were designed to take advant age of the catchlike property of skeletal muscle. Measurements were ma de from fresh and fatigued muscles. For the fresh muscles, the VFTs el icited significantly greater peak power than did the 6-pulse CFT. When the muscles were fatigued, VFT stimulation significantly improved bot h the peak and mean power produced compared with stimulation by CFTs. These results show that stimulation of the LDM with shorter duration V FTs is potentially useful for application in cardiomyoplasty.