Carotid sinus massage has its primary effect on the heart by increasing which autonomic input?

• A. Increased sympathetic activity
• B. Increased parasympathetic activity
• C. Decreased parasympathetic activity
• D. No effect on autonomic input

Answer: (B)

Stimulation of the carotid sinus triggers a baroreceptor reflex that increases parasympathetic (vagal) input to the heart. The enhanced vagal tone slows the sinus node firing and slows conduction through the AV node, producing bradycardia. This is why carotid sinus massage predominantly increases parasympathetic influence on the heart. Increased sympathetic input would raise heart rate, and decreasing parasympathetic input or having no autonomic change wouldn’t produce the same bradycardic effect.