Left ventricular assistance in dogs using a skeletal muscle powered device for diastolic augmentation

A pulse train stimulator was developed for skeletal muscle stimulation synchronous to the myocardium. Left ventricle contraction was augmented by a stimulated rectus abdominis muscle pedicle grafted into the left ventricular wall. A miniaturized and programmable stimulator was built. The stimulation parameters for this device were optimized and the configuration of a skeletal muscle powered assist device for cardiac assistance was investigated in acute canine experiments. A hydraulic balloon preparation was used to characterize stimulation parameters and to compare rectus abdominis, latissimus dorsi and pectoralis major muscles as power sources. Assist devices evaluated included a left ventricle apico-aortic conduit with a central pumping chamber and an extra-aortic balloon pump. The pumping chambers were either wrapped by the rectus abdominis and latissimus dorsi pedicles, or placed deep into the pectoralis major. The optimal stimulation parameters were pulse trains of 200 msec duration containing pulses 240 mu wide at a frequency of 35 pulses/second. There was no fatigue over a ten hour period despite stimulation at a rate of 120 contractions/minute. Muscle dissection and selection were determinants of fatigability. However, counter-pulsation was possible regardless of the muscle selected. The most efficient device was an extra-aortic balloon pump. There was a consistent increase in subendocardial viability index (DPTI/TTI). The advantages in using a skeletal muscle power source for diastolic rather than systolic assistance were established.