The safety of induced ventricular fibrillation during cardiopulmonary bypass in nonhypertrophied hearts

The effect of electrically maintained ventricular fibrillation on the nonhypertrophied canine heart during normothermic cardiopulmonary bypass was studied. Twenty dogs underwent ventricular fibrillation (7 volt, AC) for 60 min, at which time they were either killed immediately (groups I and III) or taken off bypass for 1 hr (groups II and IV). No differences occurred in the measured parameters of ischemic injury between those animals subjected to a hemodilution priming agent (groups I and II) and those having fresh, autologous blood as the priming agent (Group III and IV). Subendocardial blood flow was equal to or greater than subepicardial blood flow in all groups in the control state, in the bearing, nonworking heart, after 5 and 60 min of ventricular fibrillation, and 60 min after cessation of cardiopulmonary bypass (groups II and IV). Transmural left ventricular bipolar action potential amplitude and local myocardial activation times were unchanged following 60 min of ventricular fibrillation. No difference occurred in the level of subendocardial ATP (4.67 ± 0.25 μmoles/g) and subepicardial ATP (4.74 ± 0.17 μmoles/g). Subendocardial creatine phosphate levels (10.92 ± 0.34 μmoles/g) were unchanged from control levels (11.08 ± 0.76 μmoles/g). However, subepicardial creatine phosphate increased to 13.11 ± 0.56 μmoles/g. The serum CPK MB isoenzyme level was zero in all control samples and every 15 min thereafter in all experiments. The left ventricular free wall, papillary muscles, and ventricular septum showed no histologic evidence of ischemic injury on hematoxylin and eosin, phosphotungstic acid, hematoxylin, or succinic dehydrogenase enzyme stains. Although the deleterious effects of ventricular fibrillation on the hypertrophied left ventricle are well documented, this study demonstrates that induced ventricular fibrillation is a safe modality to employ during cardiopulmonary bypass of the nonhypertrophied heart.