SYNCHRONOUSLY STIMULATED SKELETAL-MUSCLE GRAFT FOR MYOCARDIAL REPAIR - AN EXPERIMENTAL-STUDY

Abstract

The feasibility of augmentation of impaired myocadium with synchronously paced skeletal muscle grafts was studied. The short contractile period of skeletal muscle required development of a new stimulator to ensure that the pedicle graft contraction would simulate that of the myocardium. In 4 dogs each, rectus and diaphragmatic muscles were wrapped around a ballooon and electrically stimulated in synchrony with the ECG, varying stimulation currents and frequency of discharge during systole. For this purpose, a prototype hybrid stimulator was developed which senses the cardiac R wave and modulates the electrical output to the skeletal muscle by delivering a train of impulses of varying frequencies within the systolic intervals. The contraction characteristics in response to such stimulation were similar in rectus and diaphragmatic muscles, but the former developed higher maximum tensions because of the greater muscle bulk. Square-wave output was found to be more effective than sine-wave stimulation, and a single stimulating electrical pulse of 40 ms duration produced a maximum tension of 60 mm Hg lasting for 120 ms, whereas a train of 4 pulses with a 320 ms period was able to achieve a maximum tension of 100 mm Hg lasting nearly 400 ms, the latter approximating that of the myocardium. In 6 other dogs, the rectus muscle pedicle graft was used to replace a segment of the left ventricle (25.5% .+-. 2.1% of left ventricular mass) excised under cardiopulmonary bypass. Left ventricular isometric contraction was studied using a left ventricular balloon with stimulators turned on and off. Significant augmentations of left ventricular maximum tension (+19.3% .+-. 2.5%, P < 0.001, paired t test) and left ventricular contractility (+38.3% .+-. 9.4%, P < 0.001) were achieved when the skeletal muscle grafts were stimulated. Thus, in this preliminary study, skeletal muscle graft properly oriented and stimulated is able to augment the left ventricular isometric contractile function after significant loss of left ventricular myocardial mass.