Enzyme Activities in Endomyocardial Biopsy Samples from Patients with Cardiomyopathy

Abstract

Endomyocardial biopsy is now an established and safe technique for obtaining samples of fresh ventricular myocardial tissue. Histopathological examination of biopsy samples from patients with suspected cardiomyopathy has improved the accuracy of the clinical diagnosis in approximately 10% of the cases [7], but limitations are still present since, particularly in congestive cardiomyopathy (COCM), the histological findings may not be specific [10], although myocarditis can be excluded. Similarly, in hypertrophic cardiomyopathy (HOCM) histological examination may not confirm the diagnosis as the diseased area may not have been sampled [10]. Highly sensitive enzyme assays already exist for other tissues and it has now been shown that these techniques can be applied to very small myocardial biopsy samples. Comparison of enzyme activities in patients with valvar heart disease and either good or poor left ventricular function has shown that when ventricular function is impaired calcium dependant adenosine triphosphatase (ATPase) activity is strikingly reduced and the activity of lactate dehydrogenase significantly increased [11]. Similarly, in the congestive cardiomyopathies left ventricular tissue showed reduced levels of mitochondrial and myofibrillar enzymes but high levels of lactate dehydrogenase. It has been suggested that defective mitochondrial function is characteristic of both poor left ventricular function, secondary to valvar heart disease, and of congestive cardiomyopathy, and that the increased levels of lactate dehydrogenase reflect a compensatory response [12].