Diaphragm pacing: histopathological changes in the phrenic nerve following long-term electrical stimulation

Phrenic nerves were obtained at autopsy from 7 patients with chronic ventilatory insufficiency. One or both nerves had been subjected to electrical stimulation to pace the diaphragm for about 2 months to 4 years. Sections of the nerves made from above, at the level of, and below the site of application of the cuff electrode were studied microscopically. In most specimens, focal areas of demyelination were seen ranging from severity from swelling and fragmentation of isolated fibers to focal myelin destruction with phagocytic activity and total removal of myelin with fibrosis. Some axone loss was seen. The fact that the nerves from 2 patients, each stimulated for about 2 years, showed no changes suggests that injury to the nerve was not caused by the electrical stimuli but rather was secondary to the technique of application and fixation of the cuff electrode to the nerve.