Altered Autonomic Mechanisms in the Sick Sinus Syndrome and Diurnal Variations in the Parameters of Sinus Node Function : Symposium on Sinus Node Function and Its Abnormality

Abstract

Listen

Translate article

The role of two divisions of autonomic nervous system was investigated and the variations of the sinus cycle length after autonomic blockade (the intrinsic cycle length, ICL) and the sinus node recovery time (SNRT) were tested in 26 patients with symptomatic sinus bradycardia. Three groups of patients were recognized from the responses of sinus rate to autonomic blocking with propranolol followed by atropine, comparing with the healthy controls. In 9 patients (group A) with normal responses to cholinergic and beta-adrenergic blockades, reactions to the autonomic stimulations with barorefiexe and Valsalva maneuver and to isoproterenol were all normal. Reduced automaticity of sinus node and normal autonomic regulation are conceivable in these patients. In some of this group, sinoatrial disease was evident from abnormal ICL. In other I 7 patients with reduced response to atropine, reactions to the autonomic stimulations and to isoproterenol were blunted. With propranolol, enhanced prolongation of sinus cycle length was observed in 7 patients (group BI) and normal or reduced response in 10 (group BII). Severe clinical symptoms were more prevalent in group BI and BII patients than group A and SNRT and ICL was abnormal in most of Group B. Sinoatrial disease is evident in these patients, and reduced cholinergic control and partial beta-adrenergic compensation in group BI and disturbed regulation by both of cholinergic and beta-adrenergic system in group BII are suggested. Difference between ICL at 4 pm and O am was more than 200 msec in 8 and exceeded 300 msec in 5 of I 7 patients whose ICL were determined twice. Measurement of SNRT was repeated more than three times at O, 6 and 10 am and 4 and 10 pm in I 8 patients. SNRT fluctuated more than 2 seconds in 10 and the ratio of the longest SNRT to the shortest was 2 or more in 7 patients. We conclude that different and altered autonomic mechanisms exist in the patients with the sick sinus syndrome. Sinus node automaticity free from autonomic influence is fluctuating and the clinical parameters of sinus node function are non-reproducible in some of the sick sinus patients.