Abstract

The serum-digoxin level was measured by radio-immunoassay (Immutope) on 245 patients in a coronary care unit. Cardiac arrhythmias were assumed to be digoxin-induced if they disappeared after the drug had been stopped. Patients who had received digitoxin or spironolactone were excluded. The results indicated a normal digoxin range of 1.52 +/- 0.2 ng/ml and a toxic one of 2.78 +/- 0.38 ng/ml. First degree A-V block, atrial ectopic beats and ventricular ectopics with variable coupling intervals were frequently associated with serum-digoxin levels of 1.5-2.5 ng/ml, while higher grade A-V block, atrial tachycardia, bigeminy and atrial tachycardia with block were more frequent with higher serum-digoxin levels (greater than 3.0 ng/ml). Atrial arrhythmias were especially frequent with serum levels above 3.0 ng/ml. This suggests different sensitivities of atrial and ventricular myocardium. Atrial arrhythmias thus in general indicate a higher degree of toxicity at high serum levels, while ventricular ectopic beats occur both with high serum levels and also with increased digoxin sensitivity of the ventricles.