Diaphragm transplantation; a preliminary report on an experimental form of permanent myocardial assistance

Comparison of three methods of electrical stimulation for converting skeletal muscle to a fatigue resistant power source suitable for cardiac assistance

Twelve dogs were sorted into 3 equal groups, and the in-situ right latissimus dorsi muscle of each dog was stimulated via its motor nerve for a period of 6 weeks. The resulting isotonic contractions were used to pump fluid in an implanted, 2-chambered, compressible pouch system. Three methods of electrical stimulation were used: (a) continuous 2 sec-1 single pulses that caused muscle twitching, (b) a 250 msec train of pulses (36 sec-1) that caused tetanic muscle contractions and was repeated every 2 sec for 15 min followed by a 15 min period of rest, and (c) alternating 15 min periods of the above 2 stimulation methods to cause alternating twitch and tetanic contractions. The 2 sec-1 twitch stimulation and the combined twitch/tetanic stimulation methods resulted in a 100% conversion to fatigue-resistant fibers within 6 weeks. Standardized muscle function tests were performed weekly. With the twitch stimulation (Method 1), the time to fatigue increased from 9 to 116 min (p less than 0.001), but fluid pumping ability of the muscle decreased substantially from 0.25 to 0.14 liters min-1 (p less than 0.05). With the intermittent tetanic stimulation (Method 2), the fatigue resistance increased only slightly from 7 to 11 minutes (p = NS), and pumping ability was unchanged. With the combined (twitch-tetanic) stimulation (Method 3), the time to fatigue increased from 9 to 107 min (p less than 0.001), and the pumping ability did not significantly change from 0.20 to 0.22 liters min-1 (p = NS). These results suggest that a combined electrical stimulation method which produces both twitches and tetanic contractions can achieve rapid fiber conversion and increased fatigue resistance without loss of muscle strength.

Paced latissimus dorsi used for dynamic cardiomyoplasty of left ventricular aneurysms

Two patients are described, each with a large left ventricular aneurysm and severe coronary artery disease, and each with an ejection fraction lower than 30% and in congestive heart failure. In both, the left latissimus dorsi (LD) muscle was used in the repair of the ventricular aneurysm because preoperative studies demonstrated that there was concomitant coronary artery disease, and there was a strong suggestion that resection of the entire aneurysm would seriously compromise the residual ventricular capacity. One patient had an 18-year history of coronary occlusion with two infarctions. A large, calcified ventricular aneurysm developed, and despite vigorous medical treatment, intractable congestive heart failure and angina persisted. The diffuse coronary artery disease made this patient a poor candidate for bypass grafting. The other patient sustained an acute myocardial infarction 5 months prior to operation. The left anterior descending coronary artery was totally occluded, and a large apical aneurysm developed along with an akinetic anterior wall and septum. After his heart attack, the patient had progressive dyspnea on exertion. Following operation in both patients, the transpositioned LD, then a component in the repair of the left ventricular wall, was electrically trained to synchronously contract with each systole, driven by a standard dual-chamber cardiac pacemaker. Steady improvement and a return to normal activities were observed in both patients. There was an indication of improved ejection fraction with synchronous contraction of the skeletal muscle.