ELECTROPHYSIOLOGICAL ABNORMALITIES OF THE ATRIAL MUSCLE IN PATIENTS WITH SINUS NODE DYSFUNCTION WITHOUT TACHYARRHYTHMIAS

The duration and the number of fragmented deflections of the right atrial electrograms were assessed and quantitatively measured in 74 patients who underwent endocardial catheter mapping during sinus rhythm. The bipolar electrograms were recorded at 12 sites in the right atrium. An abnormal atrial electrogram was defined as a duration of 100 ms or longer, and/or 8 or more fragmented deflections, according to our previous criteria. The patients were divided into two groups. The control group consisted of 41 age-matched patients with normal sinus node function and without paroxysmal atrial fibrillation. The study group comprised 33 patients with sinus node dysfunction but without tachyarrhythmias. Abnormal atrial electrograms were observed in 8 (19.5%) control patients, and in 16 (48.5%) sinus node dysfunction patients; p < 0.02. The total number of abnormal electrograms was 14 (2.89%) of 483 atrial electrograms in controls, and 36 (9.38%) of 384 in the study group; p < 0.0002. The mean duration (75.6 +/- 17) and the mean number of fragmented deflections (4.1 +/- 2) of the total atrial electrograms in the sinus node dysfunction group was significantly greater than that in controls (70.9 +/- 11 and 3.6 +/- 1, respectively); p < 0.01. The mean number of abnormal electrograms per patient in the study group (1.06 +/- 1.8) was significantly higher than that in the control group (0.3 +/- 0.8); p < 0.05. These data suggest that: (1) there is a significantly greater electrophysiological abnormality of the atrial muscle in patients with sinus node dysfunction but without paroxysmal atrial fibrillation than in age-matched controls, and (2) not only the sinus node but also the atrial muscle is electrophysiologically altered in patients with sinus node dysfunction but without tachyarrhythmias.