Optimization of pacing parameters for conditioned latissimus dorsi muscle in cardiomyoplasty

Synchronous paced contractions of latissimus dorsi muscle pedicle (LDM) around the heart improve ventricular function in dynamic cardiomyoplasty. To optimize assistance and prolong pacemaker battery life, the LDM should be stimulated with the lowest energy pacing parameters (PP) that will produce maximal muscle contraction. Muscle fractional shortening (FS) and duration of contraction (CT) were studied in conditioned, fatigue-resistant LDM of six goats. Fractional shortening and CT were determined at increasing amplitude, (A, 1-6v); pulse width, (PW, 60-450μsec); and frequency, (F, 5-130 Hz). Maximal rate of contraction was determined by pacing at higher rates. Maximal FS plateaued after V, 2.4 ± .6v; PW, 125 ± 47 μsec; and F, 36 ± 9 Hz. Mean CT for all PP was significantly longer (p ≤ 0.001) than the burst length (185 msec). Increasing F resulted in CT, which peaked at 460 ± 59 msec. Increasing rate of contraction demonstrated that over 87 beats per minute the muscle fails to achieve complete relaxation, and, therefore, maximal FS.