Vagal tone, significance of electrophysiologic findings and clinical course in symptomatic sinus node dysfunction

The relation of hypersensitive carotid sinus syndrome (HCSR) to sick sinus syndrome (SSS) is not clear; vagal role, relevance of electrophysiological testing, and the natural course of both syndromes are ill defined. In 186 symptomatic patients, resting heart rate (HR), carotid sinus pressure results (CSP), and corrected sinus node recovery time (CSRT) were determined before and after atropine (A). According to test results 102 patients had HCSR (group I), 33 had HCSR + SSS (group II), 30 patients had isolated SSS (group III) and 20 served as control (group IV). HR below 60 b.p.m. in groups I to III and lower than controls (p < 0.01) rose after A by approximately 31 per cent in groups I to IV. This indicates predominant vagal tone, and establishes that rate response to A is unreliable as a diagnostic test for groups I and III. CSP normalized after A but CSRT remained unchanged (p > 0.05), which implies increased vagal tone in HCSR but destructive affection of the SA node in SSS. Bradycardia, S-A block, supraventricular tachyarrhythmias and the combination of dizziness and syncope served as diagnostic clues for HCSR or SSS in a limited number of patients. CSP and CSRT separated HCSR from SSS but failed to predict syncope in groups I to III (p > 0.05) and thereby cannot aid the indication for pacer application. SSS test results remained unchanged over 16 months showing an unfavorable prognosis. We conclude that HCSR and SSS, although frequently occurring together, are entities made separate by specific testing, which, however, fails to aid in therapeutic decision-making. Vagal tone plays but one role in HCSR and SSS and electrophysiologic pathology of SSS does not improve in its course.