Electroplegia: an alternative to blood cardioplegia for arresting the heart during conventional (on-pump) cardiac operation

Abstract

Background. Aortic cross-clamping is contraindicated in patients with severe atherosclerosis of the ascending aorta, and administration of chemical cardioplegia may be cumbersome in these patients. In this study, we demonstrate an alternative method of achieving cardioplegia by electrical stimulation of the vagus nerve. Methods. In anesthetized canines, the left anterior descending coronary artery was reversibly ligated for 90 minutes, followed by cardiopulmonary bypass (CPB) and randomization to three groups (n = 8 each): (1) BCP group: 1 hour of intermittent hypothermic (4°C) blood cardioplegia infusion; (2) CPB group: 1 hour of CPB alone; (3) EP group (group receiving electroplegia): 1 hour of intermittent vagal stimulation (total of 60 20-second electrical stimuli at 40 Hz, 6 to 10 V) with adjunctive pyridostigmine (0.5 mg/kg), verapamil (50 μg/kg), and propranolol (80 μg/kg) to potentiate hyperpolarization and suppress ectopic escape beats. Results. The EP group achieved consistent intervals of arrest with 3.8 ± 1.2 escape beats per 20-second stimulation period. After 2 hours of reperfusion off CPB, the left anterior descending coronary artery segmental shortening was reduced from baseline in all groups, but the segmental shortening recovered to a greater extent in the EP group than in either the CPB or BCP group (2.4% ± 1.4% versus −1.3% ± 1.3% versus −4.0% ± 0.8%, p < 0.05). Infarct size (TTC stain, percentage of area at risk) was comparable among groups (EP: 20.9% ± 4.7%; CPB: 29.6% ± 3.2%; BCP: 25.1% ± 5.7%). Postischemic left anterior descending coronary artery endothelial function (percent maximum relaxation to acetylcholine) was depressed in the EP group (68.6% ± 7.6% versus 102.3% ± 6.4%, p < 0.05), but was comparable versus nonischemic circumflex function in the BCP group (77.1% ± 11.9% versus 100.4% ± 10.0%, p = 0.15) and the CPB group (93.8% ± 6.6% versus 93.3% ± 6.6%). Conclusions. Electroplegia achieves elective intermittent cardiac arrest, avoids hypothermia, chemical cardioplegia, and aortic cross-clamping, with physiological outcomes comparable to blood cardioplegia.