Cardiac involvement in secondary haemochromatosis: a catheter biopsy study and analysis of myocardium.

Although high blood transfusion regimens have improved the life expectancy of the patient with Thalassemia Major, cardiac failure and arrhythmias remain a cause of early death. It is not certain whether the massive myocardial iron deposition found in such patients is preventable by intensive chelation therapy. This study evaluates endomyocardial biopsy as a method of assessing myocardial iron deposition. Of four patients with clinical and biochemical evidence of severe haemochromatosis, only one had a myocardial iron content comparable to that found in severe haemochromatotic myocardium. The one patient with cardiac failure had an endomyocardial iron content within the normal range. Studies of the iron distribution in haemochromatotic myocardium demonstrate that the subendocardial myocardium contains only half the iron content of the subepicardial layer, and there is a large sampling variation. It is concluded that catheter endomyocardial biopsy is an insensitive method of determining early myocardial deposition because of the location of iron and the variability of the sampling. Studies of the nature of the myocardial iron protein with CM32 cation exchange resin chromatography show that there is a large increase in the haemosiderin: ferritin ratio (5:1) in iron overload myocardium as compared with the normal heart (2:1). Similar results have been observed in the liver with iron overload, where the increase in hepatic haemosiderin was associated with greater lysosomal fragility. It is possible that myocardial cell damage may also occur by the rupture of iron engorged lysosomes.