Comparative study of electrophysiological and Holter monitoring data in estimating sinoatrial function. Significance of intrinsic heart rate in disclosing autonomic sinus node dysfunction.

To study the diagnostic possibilities and mechanisms involved in sinus node dysfunction (SND), 26 patients with sick sinus syndrome were evaluated by basic electrophysiological tests before and after autonomic blockade, and by Holter monitoring. Based on intrinsic heart rate (IHR), two groups, a normal and a pathologic one, were separated. With Holter recordings, significant differences were manifested in minimal heart rate during sleeping and also in sinus cycles averaged for 24 h between the two groups. In patients with pathological IHR (n = 9) abnormal intrinsic rhythmicity were verified by electrophysiological means, while we found positive ECGs referring to sinoatrial dysfunction during the first 24 h of rhythm recording. The group of normal IHR (n = 17) covers patients with intrinsic SND (intrinsic SA block, 3/17 patients) and patients (14/17) where the electrophysiologic properties of the pacemaker cells were normal: normal intrinsic recovery time, gradual return to the stable intrinsic sinus cycle length in the postpacing secondary cycles, biphasic postextrasystolic patterns with a well-estimated intrinsic sinoatrial conduction time. Repeated Holter recording (total 26 X 24 h) revealed severe bradycardia (2 cases), SA block (4 cases), SA arrest (2 cases), tachybradyarrhythmia (1 case). Electrophysiological studies have a low diagnostic value in autonomic SND; repeated rhythm monitoring is obviously the best complementary method for appreciating the role and significance of autonomic tone in sick sinus syndrome.