Morphometric observations of the effects of normothermic ischemic arrest on dog myocardial ultrastructure

The design of the experiment was to examine, using stereological techniques, ultrastructural changes in the left ventricular myocardium of dog hearts exposed to cardiopulmonary bypass with normothermic ischemic arrest. Normothermic ischemic arrest was induced in dogs by cross-clamping the aorta proximal to the brachiocephalic artery for 1 h, after which the hearts were perfused with fixative. For control purposes after achieving cardiopulmonary bypass, the aortas of dogs were cross-clamped proximal to the brachiocephalic artery, and the hearts were immediately perfused with fixative. Normothermic ischemic arrest was associated with a loss of glycogen stores, disrupted sarcoplasmic reticulum and T-tubules, and vacuolization and decrease in matrix density of mitochondria. Stereological measurements showed that the percent volume of myofibrils, mitochondria, T-system, and SR declined significantly following normothermic ischemic arrest. It was also found that although the membrane area of SR and T-system per unit myofibrillar volume remained constant in controls and ischemic hearts, that the membrane area of SR per unit SR volume and the membrane area of the T-system per unit volume of T-system significantly increased in ischemic hearts suggesting vesiculation of these organelles.