Comparison of the effects of left ventricular distention during cardioplegic-induced ischemic arrest and ventricular fibrillation

To evaluate the role of left ventricular distention in the pathophysiology of myocardial injury during cardiac surgery, 40 isolated, perfused feline hearts were subjected to 1 hour of either hypothermic potassium arrest (groups 1, 2 and 3) or 1 hour of hypothermic ventricular fibrillation (groups 4 and 5). During this period, intracavitary left ventricular pressure was maintained at 0 mm Hg in groups 1 and 4, at 30 mm Hg in groups 2 and 5 and at 45 mm Hg in group 3. After either reperfusion or defibrillation, myocardial gas tensions, left ventricular function, coronary blood flow, the ratio of endocardial to epicardial blood flow, and myocardial water content were measured to evaluate the degree of myocardial injury incurred. In addition, structural changes in the myocardium were assessed using light and electron microscopy. No differences in these parameters were seen in hearts that underwent ischemic arrest, regardless of the presence or absence of significant left ventricular distention. In fibrillating hearts, however, dilatation decreased ventricular performance, impaired subendocardial blood flow and elevated myocardial CO ₂ tensions. These results suggest that left ventricular distention per se is not harmful during periods of ischemia. During periods of ventricular fibrillation, however, distention produces impaired subendocardial blood flow, resulting in increased ischemia and decreased recovery of ventricular performance.