Beneficial effects of cardiomyoplasty have been documented and the use of this technique in the treatment of dilated cardiomyopathy have been suggested. This study was undertaken to evaluate the contracting and fatigue characteristics of normal and conditioned Latissimus Dorsi and the effectiveness of stimulated preconditioned skeletal muscle flaps wrapped around the heart to restore ventricular contractility in presence of myocardial dysfunction. Thirteen adult mongrel dogs were studied after burst stimulation of left Latissimus Dosi for six to eight weeks. In seven animals, conditioned muscles were compared with unconditioned contralateral controls by isometric force development. Normal and transformed muscles exhibited the same optimum pacing parameters (burst frequencies from 5o Hz up, train duration from 150 ms up). Conditioned muscles showed a smaller force (-27%) and a longer contraction time (+32%). Fatigue curves of unconditioned muscles under different duty cycles showed marked initial decrease and inversely proportional stable values of force after some minutes with equal final tension time indexes (18 ± 2 KgF. seg/min). Conditioned Latissimus Dorsi maintained stable force during prolonged stimulation under same conditions with a greater tension time index (68 ± 6 KgF. seg/min). The other six animals were submited to cardiomyoplasty; hemodynamic and echocardiographic evaluation were performed after induction of myocardial dysfunction by betablockers administration and volume loading. With synchronous pulse train stimulation increases of cardiac index by an average of 36 ± 4% (p<0.01) were observed, associated with a decrease of pulmonary wedge pressure. Ejection fraction augmentation of 51 ± 3% above the control was also documented in same conditions (p<0.01), even when muscle flap was wrapped only around the left ventricle. In conclusion, this study reveals that skeletal muscles are capable to maintain steady-state work similarly to the myocardium with a power dependent of their aerobic capacity. It also suggests the occurrency of muscle adaptive transformation, increasing its steady-state work capacity, with chronic pulse train stimulation. In addition, cardiomyoplasty may be an alternative method of treatment for irreversible cardiomyopathy, including when muscle flap may wrapp only partially the heart.
cardiomyoplasty; circulatory support; myocardial insufficiency; skeletal muscle stimulation