Holter monitoring in the complex analysis of sinus node dysfunction.

To study the diagnostic possibility and the mechanisms involved in sinus node dysfunction, 23 patients with sick sinus syndrome were evaluated by the basic electrophysiological method (recovery times, secondary postpacing phases, sinoatrial conduction times) before and after pharmacologic autonomic blockade with i.v. propranolol 0.2 mg/kg and atropine 0.04 mg/kg, and by continuous rhythm monitoring. Patient groups of normal (I) and pathological (II) intrinsic heart rate (IHR) were compared. In group I (no. 15) prolonged recovery time (2/15), postpacing sinoatrial-block (1/15) and chaotic postextrasystolic patterns (5/15) ceased after autonomic blockade; we obtained normal intrinsic recovery time, gradual return to the stable intrinsic sinus cycle length in the secondary phase, and a normal intrinsic sinoatrial conduction time. In group II (no. 8) during the control study only 50% of patients had pathological electrophysiological parameters before, and 100% after the drug test (no gradual postpacing return to the intrinsic heart rate, abnormal recovery times, abnormal sinoatrial conduction times or chaotic postextrasystolic patterns). Holter monitoring revealed significant differences between the minimal heart rate during sleeping (group I: 48 +/- 10 bpm, mean +/- SD group II: 32 +/- 4 bpm, probability less than 0.001) as well as in the average sinus cycle length for 24 hours (group I: 848 +/- 88 ms, group II: 1254 +/- 136 ms, P less than 0.001) with a very characteristic histogram. In the patients with pharmacologically and electrophysiologically documented abnormal intrinsic rhythmicity (group II), the first 24 hour Holter monitoring revealed positive ECGs for sinus node dysfunction. In patients with normal intrinsic electrophysiological sinus node properties (group I) repeated continuous rhythm recordings revealed severe sinus bradycardia (1 patient), sinoatrial-block (1 patient), tachybrady syndrome (1 patient) and sinus-arrest (2 patients, up to 29 120 ms in waking period). These findings suggest that 1) IHR is the best and simplest diagnostic method of intrinsic sinus node dysfunction (in patients of abnormal low IHR we found positive electrophysiological and Holter parameters), and 2) in autonomic sinus node dysfunction electrophysiological parameters are essentially negative showing normal intrinsic sinus node function; in these patients systematically repeated Holter monitoring is the most valuable diagnostic method.