Increased digitalis-like immunoreactive substances in patients with hypertrophic cardiomyopathy

Aims Although increased digitalis-like immunoreactive substances have been found in cases of hypertension and heart failure, no information is availab le about digitalis-like immunoreactive substances in patients with hypertro phic cardiomyopathy. We investigated digitalis-like immunoreactive substanc es in the plasma and biopsied specimens of patients with hypertrophic cardi omyopathy. Methods and Results In 40 patients with hypertrophic cardiomyopathy (27 wit h the non-obstructive type and 13 with the obstructive type), the plasma co ncentration of digitalis-like immunoreactive substances was studied by fluo rescence polarization immunoassay. Right ventricular endomyocardial biopsy specimens were analysed immunohistochemically, using a monoclonal antibody against digoxin. An increase in digitalis-like immunoreactive substances of more than 0.2 ng. ml(-1) in plasma was found in six of 27 patients with no n-obstructive hypertrophic cardiomyopathy (22.2%) and five of 13 with obstr uctive hypertrophic cardiomyopathy (38.4%). Under light microscopy, positiv e staining against the antibody was observed hyperogeneously on some cardio cytes. In non-obstructive hypertrophic cardiomyopathy, digitalis-like immun oreactive substances in the plasma correlated with the left atrial dimensio n and inversely with the cardiac index. In obstructive hypertrophic cardiom yopathy, plasma and myocardial digitalis-like immunoreactive substances wer e positively correlated; they also correlated with left ventricular end-dia stolic pressures. Under electron microscopy, digitalislike immunoreactive s ubstances were detected at the sarcolemma in the free wall, T-tubules, inte rcalated discs and Z-bands of cardiocytes. Conclusions Increased digitalis-like immunoreactive substances in plasma an d cardiocytes, which may have been caused by pressure and/or volume overloa d, were found in patients with hypertrophic cardiomyopathy. Digitalis-like immunoreactive substances may act on the sarcolemma of cardiocytes and be t ransported into the cytoplasm. (C) 2000 The European Society of Cardiology.