Digoxin Concentrations in the Serum and Myocardium of Digitalised Patients*

Abstract

Summary: In an attempt to evaluate the serum digoxin concentration as a guide to digitalis treatment, serum and myocardial concentrations were measured in 27 patients undergoing cardiac surgery. Myocardial samples were taken from the right atrium immediately prior to institution of cardiopulmonary bypass; blood was taken in the previous 1–2 hours. Digoxin was extracted from the myocardial sample using a methanol/ water technique, which allowed a yield of 95%± 7%. Digoxin estimations were carried out using radioimmunoassay, with antibody raised in rabbits to a digoxinbovine serum albumin conjugate. No digoxin activity was found in the myocardium of six patients who were not being treated with the drug. In the 21 patients under treatment with digoxin, serum concentration averaged 1.2 ng/ml (range 0.64-2.3) and myocardial concentration averaged 76.5 ng/g (range 30–175). The ratio of myocardial to serum concentration averaged 70:1 (range 25:1 to 128:1) with standard deviation (SD) 28:1. The ratios of myocardial digoxin concentration to serum digoxin concentration exhibited a normal distribution in that 67% of the patients fell within ± 1 SD and 95% of the patients fell within ± 2 SD of the mean. Serious post-operative ventricular arrhythmias were noted in three of four patients with myocardial digoxin concentrations over 100ng/g but in only two of 23 patients with myocardial concentrations less than 100 ng/g.