[Sick sinus syndrome: comparative study of atrial and ventricular stimulation tests].

Subjects with a ventriculo-atrial block and normal sinus function exhibit acceleration of the sinus rhythm during incremental right ventricular pacing; this acceleration is nor observed or is hardly visible in patients with sinus node dysfunction. Incremental right ventricular pacing up to 150/min was performed in 16 patients with ventriculo-atrial block (Group A) referred for investigation of sinus node dysfunction and the results compared with the classical tests of atrial pacing (Strauss'graph, atrio-sino-atrial conduction time, sinus node recovery time). The same tests were carried out in 19 patients without sinus node dysfunction (Group B). In the latter group, sinus rhythm exceeded 80/min during right ventricular pacing at 150/min and the rate increased with respect to the basal rhythm was always greater than 10/min. In Group A premature atrial pacing gave abnormal results in 4 cases, sinus node recovery times were abnormal in 15 cases, and rapid right ventricular pacing abnormal in all cases (sinus rhythm less than 80/min and/or rate increase of less than 10/min). There was no relation between the increased sinus node recovery time and the degree of rate increase during rapid ventricular pacing. Incremental right ventricular pacing, therefore, seems to be a new method of investigating sinus node function but complementary studies are required to determine its limitations, the exact mechanism and to try to widen its application to subjects without ventriculo-atrial block.