Importance of adaptive stimulation of the latissimus dorsi muscle in cardiomyoplasty

During cardiac synchronized latissimus dorsi (LD) stimulation, adaptive duration (AD) allows the pulse train length to be set as a percentage of the cardiac cycle. The LD contraction duration adjusts to variations in heart rate (HR). The effects of AD on LD work output and blood flow (BF) were investigated in nine dogs that underwent skeletal muscle ventricle (SMV) construction. The SMVs were stimulated according to the cardiomyoplasty protocol. BF and the pressure increase (ΔP) generated during SMV contraction were monitored biweekly for 3 months. SMV contraction time increased significantly after training (P<0.0001). The trained SMV could only partially contract at duration settings of 25% and 30%. Before training, the increase in mean pressure and BF during 35% AD increased proportionally with increasing HR. After training, BF and mean pressure decreased with increasing HR because of reduced peak pressure generation during partial SMV contractions. When duration was fixed at 200 msec, BF increased with HR to 80 bpm but decreased with additional increases in HR. At high rates and fixed duration, inadequate relaxation between contractions resulted in inefficient muscle performance and reduced BF. AD did not impair BF and allowed the appropriate autoregulatory response to occur in the trained and untrained LD so that the supply-to-demand ratio did not become compromised over a large range of HR.