Under investigation in this study were the role of vagal tone in symptomatic sinus node dysfunction and the relationship between hypersensitive carotid sinus reflex (HCSR) and sick sinus syndrome (SSS). In 168 symptomatic patients (pts) resting heart rate (HR), maximal corrected sinus node recovery time (CSRTmax) and maximal carotid sinus pressure results (CSPmax) were determined before and after Atropine, 1 mg i.v. (A). According to test results, 103 pts had HCSR (1), 33 had HCSR + SSS (II), 30 pts had isolated SSS (III) and 20 pts with normal test results served as controls (IV). Mean age was the same in groups I--IV (p greater than 0.05). Groups I--III had a HR less than or equal to 60 bpm, rising 31% after A in groups I--IV, but absolute values were below those in group IV. In groups I--III CSP normalized after A and CSRT remained unchanged (p greater than 0.05). We conclude that increased vagal tone plays but one role in groups I--III and the combination HCSR + SSS seems rather frequent. Specific testing clearly separated HCSR from SSS.
