Myocardial ischaemia in constrictive pericarditis--a morphometric and electron microscopical study.

Left ventricular biopsies, taken during pericardiectomy, were morphometrically and morphologically examined to determine the pathology of the myocardium in constrictive pericarditis (CP). To serve as a normal control a similar appraisal was made of tissue from the left ventricle of a patient undergoing atrial septal repair. Morphometrically, mean cross-fibre diameters at the position of the nucleus in atrial septal defect (ASD) and CP hearts were within a range previously reported as normal. In hearts from patients with CP, the range of individual myocardial fibre diameters was extended. Ultrastructurally the myocardium in ASD appeared normal. In CP, myofibres could be divided into two groups: (a) small and morphologically normal; and (b) large and oedematous. Oedematous fibres contained abnormal nuclei and sarcoplasmic organelles and myofibrillar dissolution was a prominent feature in many cells. These pathological features are among those previously used to characterize myofibre ischaemia. In CP, prolonged cardiac compression is thought to predispose the heart to atrophy due to its inability to function properly (disuse atrophy). The results of this study suggest that in CP, myocardial ischaemia is a more important factor in the aetiology of myocardial dysfunction than is atrophy which arises from enforced cardiac disuse.