Pathological aspects of transcutaneous cardiac pacing.

Although electrical energy has the potential to produce myocardial injury, the risk of tissue damage from transcutaneous cardiac pacing is largely unknown. This study reports the anatomical findings of a canine transcutaneous stimulation study. Ten dogs had 100-mA, 20-msec (pulse duration), transcutaneous impulses delivered across the thorax for 30 minutes at a rate of 80 stimuli per minute. Seventy-two hours later the animals were sacrificed, and the heart, lungs, and tissues of the chest wall were examined for pathological changes. Gross and microscopic lesions consistent with electrically induced myocardial damage were found in all hearts examined. These lesions included myocardial pallor and focal myofibril coagulation necrosis in the right ventricular outflow tract and perivascular microinfarcts in the posterior left ventricular myocardium. These lesions were not extensive; less than 5% of the right ventricular free wall and less than 1% of the left ventricular posterior wall were involved. Lesions of this extent would not be expected to cause clinically detectable changes in cardiovascular status. Short-term use of transcutaneous pacing appears to be safe. Determination of the potential for clinically significant injury with long-term use requires further study.