Ventricular fibrillation during cardiopulmonary bypass: long-term effects on myocardial morphology and function

Mongrel dogs were subjected to hypothermic (28 degrees to 30 degrees C) cardiopulmonary bypass with hemodilution by 50%. In two groups of 8 dogs each, ventricular fibrillation was induced for 60 and 90 minutes, respectively, while the dogs were on bypass. A group of 6 dogs with the heart beating but nonworking served as control. Seven weeks after operation, hemodynamic measurements were made in the survivors (6 in each group) and the heart was fixed by perfusion with glutaraldehyde. Multiple transmural samples were taken from both ventricles. Light microscopy revealed solitary left ventricular scars (0.5 to 3 mm wide) in 2 hearts each from Groups 2 and 3. None of the hearts exhibited diffuse subendocardial fibrosis indicative of healed ischemic injury. All animals were hemodynamically normal. We conclude that in the nonhypertrophied heart, ventricular fibrillation up to 90 minutes with continuous bypass-sustained coronary perfusion (perfusion pressure at or above 70 mm Hg) offers protection from permanent myocardial injury.