A morphological control for ventricular pathology in man: a morphometric and morphologic assessment of LV myofibres in secundum ASD.

Ethical considerations preclude the biopsy of normal human myocardium. As a consequence, morphological investigations of diseased human heart muscle are hampered by a lack of suitable normal control tissue. The left ventricular (LV) myocardium of patients with isolated secundum atrial septal defect (ASD) is considered to be normal. This study was designed to investigate the possibility that the fine-structure of LV myofibres in hearts with ASD could be used as normal controls for myofibre pathomorphology. Wedge biopsies from the LV of four adults undergoing elective surgery for the repair of ASD were examined by light and electron microscopy. Bivariant myofibre morphometry showed that the LV myocardium of one specimen was 'normal' while three specimens exhibited varying degrees of hypertrophy. There was a correlation between the diameter (FD) and morphology of individual myofibres within and between specimens. In general, myofibres with FD less than 25 microns were similar in fine-structural appearance to those described as morphologically normal in animal models whereas those with FD greater than 25 microns exhibited hypertrophic features that increased in 'severity' with increase in myofibre size. It is proposed that although the LV myocardium in ASD may be mildly hypertrophied, myofibres with FD less than 25 microns are probably normal and may be used as fine-structural controls for myofibre pathomorphology in hearts suspected of disease.