Spectral analysis of small-amplitude electrical activity in the cold potassium-arrested heart

Recent reports have suggested that small-amplitude electrical activity may persist following the administration of potassium cardioplegia. This report confirms the presence of small-amplitude electrical activity in the potassium-arrested heart and describes a canine model that may be used to measure microvolt plunge-electrode potentials during ischemic arrest. Thirty-one adult mongrel dogs were placed on cardiopulmonary bypass and underwent 90 minutes of ischemic arrest. The heart was arrested with 10 ml per kilogram of body weight of crystalloid cardioplegia (20 mEq of KCl/L) at 4 degrees C. Core temperature was maintained at 26 degrees C and myocardial temperature, within a range of 8 degrees to 10 degrees C with topical ice-slush saline solution. Cardioplegic solution, 10 ml/kg, was reinfused every 30 minutes during the 90 minutes of ischemia. Electrical activity and transmural temperature were continuously monitored over the anterior surface of the left ventricle with specially designed plunge electrodes. Visual electrical and mechanical activity ceased in each animal after the infusion of cardioplegic solution, and was associated with an isoelectric electrocardiogram. However, microvolt (10(-6)V) small-amplitude electrical activity was recorded at a myocardial temperature of 10 degrees C in each animal during ischemic arrest, and the activity from 6 animals was stored on magnetic tape. Spectral analysis of electrical activity during cardioplegic arrest indicated that the fundamental frequency of small-amplitude electrical activity was in the range of 3.25 Hz. These data confirm the presence of small-amplitude electrical activity in the cardioplegia-arrested heart at 10 degrees C.