Changes in the proportion of types I and III collagen in the left ventricular wall of patients with post-irradiative pericarditis.

Pericardiectomy for post-irradiative constrictive pericarditis achieves poor results because of the extensive damage to the heart and pericardium caused by ionizing radiation. The extracellular structural protein, collagen, is responsible for the functional integrity of the myocardium and allows reversible interdigitation and the transmission of force between contracting myocytes. Collagen concentration and composition were examined in the cardiac tissue of three patients undergoing pericardiectomy and post-irradiative pericarditis. Normal heart tissue was taken at autopsy from patients without cardiac disease and acted as controls. Total collagen concentration (mean(s.e.m.)) was significantly increased in the ventricular tissue of patients with post-irradiative pericarditis compared with that of the controls (119.8(16.6) versus 50.4(5.2) mg/g dry weight, P<0.01). Although there was an increase in concentration of both type I and III collagen, a disproportional increase in type I was observed. The proportion of type III collagen was lower in patients with post-irradiative pericarditis than in the control group (33(2.6)% versus 38.2(3.7)%, P<0.05). The results of the present study suggest that this marked alteration in collagen concentration and proportion may contribute to the impaired diastolic distensibility of the ventricles seen in this group of patients.