Scanning electron microscopy of the human myocardium.

Owing to the impossibility of fixation, in the human being, by means of perfusion in vivo and the rare availability of fresh comparatively intact hearts resected at transplantation, the possibility was explored of using post-mortem material in instances where the autopsies were performed within 2 hours of demise of the patients. Four cases were examined: 2 normal adult hearts and 2 hearts of hypertensive patients in the stage of decompensation. The hearts were fixed by means of perfusion with 2.5% glutaraldehyde in phosphate buffer, pH 7.4. Contiguous blocks were taken for light microscopy (LM) and scanning electron microscopy (SEM) from the left ventricular free wall of all 4 cases and of the impulse conducting system of the heart in the 2 normal hearts. The SEM material was processed by the osmium-thiocarbohydrazide-osmium method (O-T-O). There was good correlation between the LM and SEM findings. The left ventricular blocks were sectioned in the transverse axis and SEM showed a step-wise transection of the myofibrils. Z and M bands, mitochondria and myofilaments were identified a ultrastructural magnifications. The difference in vascularity between normal and hypertensive myocardium and the presence of para-arterial fibrosis in the latter were demonstrated by SEM. The SEM study of the impulse conducting system of the heart included the sinoatrial (SA) and atrioventricular (AV) nodes and the penetrating portion of the atrioventricular (AV) bundle of His. Characteristic pacemaker or "P" cells were identified in the nodes.