Ultrastructural alterations during ischemia and reperfusion in human hearts during cardiac surgery

Abstract

Needle biopsies taken from human hearts during cardiac surgery were investigated with the electron microscope. Cardiac tissue obtained before induction of ischemia was compared with tissue removed at the end of the ischemic period during total cardiopulmonary bypass with mild cardiac hypothermia and elective cardiac arrest (cardioplegia) and with tissue obtained after onset of coronary reperfusion. Ischemia led to changes in mitochondrial, nuclear, and vascular structures. The mitochondrial changes consisted of: loss of dense matrix granules, clearing of the matrix, fragmentation of cristae, appearance of amorphous densities, vacuolation and formation of myelin figures. The nuclear changes were: swelling of the nucleus, margination of chromatin, clumping of chromatin and, later, shrinkage of the nucleus. Study of reperfused tissue showed that amorphous densities, vacuolation and formation of myelin figures in mitochondria and nuclear shrinkage are probably irreversible. A good correlation was found between the duration of ischemia and the degree of ultrastructural damage. The degree of damage and the recovery upon reperfusion also correlated well. Full reversibility of ischemic changes was noted up to 40 min of ischemia. Between 40 and 60 min a number of cells appeared irreversibly damaged. The proportion of irreversibly damaged cells increased markedly with ischemia times exceeding 60 min.