Autonomic and electrocardiographic changes in cardioinhibitory syncope

Area of Science:

• Cardiology
• Autonomic Nervous System Physiology
• Neurally Mediated Syncope

Background:

• Cardioinhibitory syncope (CS) is a neurally mediated condition characterized by bradycardia or asystole.
• Understanding the autonomic nervous system's role in CS is crucial for diagnosis and management.

Purpose of the Study:

• To investigate changes in blood pressure, heart rate variability (HRV), and ECG patterns before and after syncope with asystole in CS patients.
• To elucidate the autonomic shift preceding and during CS-induced asystole.

Main Methods:

• Thirty-five patients with CS and a matched control group underwent 60-degree head-up tilt testing with nitroglycerin.
• Continuous monitoring of blood pressure, HRV, and ECG was performed throughout the procedure.

Main Results:

• Syncope with asystole occurred after an average tilt duration of 1082 seconds.
• Asystole, lasting a median of 21.3 seconds, was preceded by sinus rhythm, junctional rhythm, or AV block.
• Prior to syncope, patients exhibited increased sympathetic tone (higher total and low-frequency HRV) followed by a shift to vagal dominance (lower high-frequency HRV) and PR-interval shortening.

Conclusions:

• The findings indicate a marked accentuation of sympathetic tone followed by a sudden shift to vagal dominance preceding syncope in CS.
• The asystole observed in CS is predominantly accompanied by vagally induced, benign arrhythmias.