Sinus node pacemaker shift: a phenomenon induced by premature atrial stimulation in man?

The aim of this study was to investigate whether premature atrial stimulation is able to induce a shifting of the sinus node pacemaker. For this purpose we compared, in 18 patients, the curve of sinus node function obtained with Strauss' method with that resulting from the scanning, with premature atrial stimulation, of the first returning cycle following a single premature induced atrial beat. We found that the length of the compensatory phase (zone I) evaluated on the curve resulting from the scanning of the first returning cycle following the single premature induced atrial beat was shorter (15%) than that observed with the original Strauss method. In addition, an inverse relationship between the shortening of the compensatory zone and the estimated sinoatrial conduction time was observed. This result could be accounted for by one of the following explanations: 1) a change in the sinoatrial conduction or in the sinus pacemaker automaticity; 2) sinus node reentry; 3) sinus node pacemaker shift. Even if there is no direct evidence either to prove or to exclude one or more of these explanations, sinus node pacemaker shift seems to be the most convincing explanation.