Variable-frequency train stimulation of canine latissimus dorsi muscle during shortening contractions

In cardiomyoplasty, the latissimus dorsi muscle (LDM) is wrapped around the heart ventricles and electrically activated with a constant-frequency train (CFT). This study tested the hypotheses that increased mechanical performance from the LDM could be achieved by activating the muscle with variable-frequency trains (VFTs) of shorter duration or containing fewer stimulus pulses than the CFT now used. The mechanical performance 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 duration 104 and 143 ms, respectively) that were designed to take advantage of the catchlike property of skeletal muscle. Measurements were made from fresh and fatigued muscles. For the fresh muscles, the VFTs elicited significantly greater peak power than did the 6-pulse CFT. When the muscles were fatigued, VFT stimulation significantly improved both the peak and mean power produced compared with stimulation by CFTs. These results show that stimulation of the LDM with shorter duration VFTs is potentially useful for application in cardiomyoplasty.