Myocardial injury from transthoracic defibrillator countershock.

Myocardial damage resulting from transthoracic administration of direct current with cardiac defilbrillators present in clinical use was studied in 66 dogs. Electrodes were applied to the thoracic skin. All direct current discharges were delivered via a commercially available defilbrillator. Most of the animals received ten consecutive discharges with a dial setting of 400 watt-seconds. Animals were killed from 3 to 14 days after receiving the discharges. Myocarial necrosis was produced in most of the animals. The lesions were characterized by sharply localized areas of muscle necrosis that progressed to fibrous scars. Mineralization of damaged muscle and florid proliferation of large mononuclear cells were striking features of the lesions.