A NEW STIMULATION PROTOCOL FOR CARDIAC ASSIST USING THE LATISSIMUS-DORSI MUSCLE

When treating severe cardiac failure with dynamic cardiomyoplasty, kno wledge about the optimal way of stimulating the latissimus dorsi (LD) muscle is of obvious importance. We evaluated a new stimulation protoc ol in four goats using in situ electrical stimulation of the left LD m uscle. Stimulation was started using a burst of two pulses with an int erpulse interval of 100 msec for 50 bursts/min. The number of pulses w as increased every 2 weeks concomitant with a decrease in interpulse i nterval. This resulted after 12 weeks in 60 bursts/min using bursts of six pulses with an interpulse interval of 20 msec after 12 weeks. For ce measurements, which were done every 2 weeks, showed an early decrea se in contraction and relaxation speed as reflected in the ripple (= i nterstimulus amplitude/peak force amplitude measured at 10 Hz). Fatigu e resistance increased significantly within 4 weeks of conditioning as indicated by preservation of force, positive dF/dt, and negative dF/d t. Full preservation of these variables was seen even during a 1-hour fatigue test at the end of the conditioning period. Skeletal muscle en zyme activity as an indicator of muscle damage showed a significant ri se in creatine kinase enzyme activity only on the first day following the start of LD stimulation. LD muscle biopsies revealed almost comple te transformation to type I muscle fibers with a significant increase in capillary/fiber ratio when compared to the nonstimulated LD muscle. However, some biopsies, in particular near the electrodes, did show s ome signs of skeletal muscle damage. Contraction characteristics of th e fully transformed LD muscles were tested by increasing the number of bursts of six pulses from 50/min to 100/min. Interpulse intervals of 20 and 33 msec were used. These tests revealed that maximal force, pos itive dF/dt, and negative dF/dt was reached with 50 bursts/min using a six pulse burst with interpulse intervals of 20 msec.