[Effects of digitalis on the parameters of sinus function in sick sinus syndrome. Evaluation using a multiprogrammable permanent atrial pacemaker with temporary inhibition].

A non invasive electrophysiological study was performed in eight patients with sick sinus syndrome using a multiprogrammable AAI pacemaker (Medtronic Spectrax Sxt) with temporary pacing inhibition. We measured the corrected sinus node recovery time and sino-atrial conduction time (Narula method) before and after digoxin administration (acutely iv and orally for 10 days). Digitalis lengthened both the corrected sinus node recovery time and the sino-atrial conduction time; in particular, after the long-term oral treatment sinus function worsened markedly. The prolongation of the sino-atrial conduction time seems to be related to an indirect effect of the drug, since its disappears after atropine administration. Our results suggest that patients with the sick sinus syndrome need permanent pacing when long-term treatment with digitalis is requested; the pacemaker we used permits a non-invasive long-term evaluation of sinus function in such patients.