Stimulated Preconditioned Skeletal Muscle Cardiomyoplasty

Skeletal muscle grafts can be used to mechanically assist the failing heart. In 13 mongrel dogs, latissimus dorsi muscle was preconditioned in situ for 6–8 weeks. Biopsy samples of the muscles were obtained for histochemical analysis. In seven dogs, muscle force and fatigue were compared in conditioned and contralateral unconditioned (controls) muscles. In six dogs, latissimus dorsi cardiomyoplasty was performed in propranolol-induced acute heart failure, and its effects were evaluated by hemodynamic and echocardiographic parameters. Muscle conditioning was responsible for latissimus dorsi transformation to a muscle with predominantly fatigue-resistant type I fibers. Conditioned muscles developed less initial force (−27±6%) and a longer contraction time (+32±4%) (p < 0.05) but did not show fatigue for less than 15 minutes. With synchronous pulse-train stimulation of the muscle flap, cardiac output increased from 1.4±0.1 (mean+SD) to 2.0±0.2 1/min (p < 0.05), pulmonary wedge pressure decreased from 16.3±0.9 to 12.1±1.4 mm Hg (p < 0.05), and left ventricular end-diastolic pressure decreased from 18± 2.0 to 13.5 ±1.4 mm Hg (p <0.05). Echocardiographically derived ejection fraction increased from 39.3±2.4% to 59.6±2.9% (p < 0.05), and fractional shortening increased from 15.4±1.1% to 26.3±1.7% (p < 0.05). Thus, chronic stimulation of skeletal muscles induces fiber transformation and increases resistance to fatigue and force development. Cardiomyoplasty, on the other hand, improves ventricular function in the presence of acute heart failure. This surgical technique represents an alternative method of treatment for advanced myocardial failure.