Ultrastructural changes in myocardium during mild hypothermic retrograde blood cardioplegia

Uniformity of myocardial protection during retrograde blood cardioplegia is still a controversial area. We conducted a study on electron microscopic c hanges in the myocardium during mild hypothermic retrograde cardioplegia (3 1-32 degrees C) in 12 patients undergoing coronary artery bypass grafting. Biopsies for electron microscopy were taken from the right and left ventric ular myocardium before and at the end of aortic cross-clamping and after 15 min reperfusion. The intercellular junctions, intracellular and extracellu lar oedema, mitochondria, capillaries, nuclei and myofibrils were analysed separately in each specimen, using a semiquantative method with scoring fro m 0 (unchanged) to 3 (severe changes), and the total scores were correlated with the severity of right and left coronary artery disease and with ischa emia time during aortic cross-clamping. Mild to moderate ultrastructural ch anges occurred in the myocardium during the cardiopolegia, most typically m yofibrillar injury and oedema. These changes increased during aortic cross- clamping and reperfusion, especially in the right ventricle. The total ultr astructural score for the right ventricle correlated negatively with the se verity of right coronary artery disease at the end of cross-clamping. No su ch correlation was found in the left ventricle. Apart from one case of peri operative myocardial infarction, the clinical outcome was unproblematic. My ocardial structure thus was by and large well preserved during mild hypothe rmic retrograde blood cardioplegia, with the right ventricle seemingly some what less protected than the left.