Acute electrophysiological effects of cardiac glycosides on sinus node function and ventricular repolarization under clinical conditions

The influence of digoxin, digitoxin and g-strophanthin (ouabain) on the sinus node function (recovery time, sinoatrial conduction time, PP-interval) and on ventricular repolarisation (corrected QT interval and QT during permanent atrial stimulation) was studied in 101 patients (36 with sick sinus syndrome-SSS, 34 with ischaemic heart disease-IHD, and 31 control patients without cardiac disease). Digoxin caused marked prolongation of sinoatrial conduction time (in SSS and in control patients), digitoxin prolonged the PP interval (in IHD and SSS patients); digitoxin and ouabain shortened the QTcorr in SSS patients, ouabain shortened also QT during atrial pacing. The results do not point to specific indication of individual glycosides in sinus node function disturbances. Under certain clinical prerequisites, however, digitoxin can be recommended in ventricular ectopic contractions caused by prolonged or inhomogeneous repolarisation, and also the capacity of ouabain to shorten the repolarisation time deserves attention.