Neuromuscular function of the latissimus dorsi muscle in goats after dynamic cardiomyoplasty.

Skeletal muscle deterioration is emerging as a limitation to long-term cardiac assist by dynamic cardiomyoplasty. Chronic electrical stimulation of in situ skeletal muscle showed that ischemia, decreased muscle preload, muscle overuse, and chronic electrical stimulation are factors for muscle deterioration. Transposition around the heart has been associated with signs of muscle denervation after chronic electrical stimulation. To evaluate latissimus dorsi muscle neuromuscular function after longterm dynamic cardiomyoplasty, we performed neuromuscular functional analysis and histology on the latissimus dorsi muscle and thoracodorsal nerve of six normal goats and six goats after 6 months of dynamic cardiomyoplasty. Electromyographic analysis showed positive sharp waves and fibrillation potentials in the latissimus dorsi of three goats from the dynamic cardiomyoplasty group. Conduction velocity of the thoracodorsal nerve of goats from the dynamic cardiomyoplasty group (58.32+/-9.80 m/s) was reduced compared to the goats from the control group (71.48+/-5.71 m/s, P = 0.02). Histologic changes in skeletal muscle were compatible with denervation. Loss of myelin sheaths, collapse of endoneurial connective tissue, and solitary foci of axonophagia and myelinophagia further documented severe injury to the thoracodorsal nerve in goats from the dynamic cardiomyoplasty group. The latissimus dorsi muscle wrap was denervated after long-term dynamic cardiomyoplasty. Traction on the neurovascular pedicle at each contraction of the transposed muscle may induce afferent axonal injury of the thoracodorsal nerve resulting in diminished muscular function.

Fluoroscopic determination of latissimus dorsi muscle shortening fraction after dynamic cardiomyoplasty.

Optimization of the skeletal muscle contraction during cardiac assist is important to achieve maximal cardiac assist and yet avoid overstimulation that may injure skeletal muscle. Dynamic cardiomyoplasty suffers from lack of an objective, reproducible, and accurate technique to measure skeletal muscle shortening fraction after wrap and training of the muscle. A recruitment curve is considered the best way to select the proper stimulation level to achieve supramaximal contraction without overstimulating the muscle. A fluoroscopic technique of determining latissimus dorsi recruitment curve was evaluated in five goats undergoing dynamic cardiomyoplasty with an anterior cardio-subcutaneous wrap. Two pairs of stainless steel targets (0.5 and 1 cm of diameter) were implanted on each side of the muscle wrap. One pair of sonomicrometer crystals was also implanted. Displacement of the targets was measured under fluoroscopy at five different stimulation levels. Correlation coefficients between targets on the inside surface of the wrap and the sonomicrometer crystals, and targets on the outside surface of the wrap and the sonomicrometer crystals were 0.71 (P < 0.05) and 0.60 (P < 0.05), respectively. Targets on the inside surface of the wrap were more accurate than targets on the outside surface of the wrap for measurement of skeletal muscle shortening fraction and establishment of a recruitment curve. Adverse effects from the targets were not observed.

A mechanical evaluation of the resistance of various interfragmentary wire configurations to torsion.

Fourteen interfragmentary orthopedic wire configurations were tested in torsion using a transverse fracture polyvinylchloride pipe model. These models included single and double Kirschner pins with and without orthopedic wire added to the configuration. The orthopedic wire was applied in either an encircling, figure-of-eight (skewer pin), or cruciate pattern. Double Kirschner pins were applied in a mono- or biplanar fashion. An external fixator model was also tested. Stiffness, yield load, safe load, and energy of absorption were measured and calculated for each model. Orthopedic wire added to any configuration increased stiffness. All single pin configurations with orthopedic wire and the external fixator had the highest stiffness. Two Kirschner pins had a higher torsional yield load and safe load than single pin configurations with or without orthopedic wire. The external fixator model had the highest torsional yield load, safe load and energy of absorption of all configurations tested. However, the external fixator was only significantly different in safe load from the 900 biplanar configurations with wire and the cross pin configuration with encircling wire. The 900 biplanar configurations with wire and the cross pin configuration with encircling wire were equally as effective as the external fixator model in yield load and energy of absorption.