Vagal Cardiovascular Reflexes in Young Persons with Syncope

Abstract

Objective: To study the neurocardiologic reflexes in young persons who have fainted under conditions of emotional stress.

Design: Case-control study.

Setting: Clinical neurophysiology laboratory in Haifa, Israel.

Patients: Sixty persons (41 women and 19 men), 15 to 17 years old, who were referred for study because of syncope related to an emotionally distressing event. Forty aged-matched, healthy volunteers drawn from the same population served as controls.

Measurements: Resting electrocardiogram, inspiratory-expiratory difference in heart rate during deep breathing, heart rate response to the Valsalva maneuver, and blood pressure during motionless standing for 5 minutes.

Results: Although individual results were within widely accepted limits of normal, patients with syncope as a group had higher vagal autonomic tone than did controls. This manifested as a slower heart rate at rest (mean, 67.8 beats/min compared with 73.2 beats/min; P = 0.005), a higher inspiratory-expiratory difference in heart rate (mean, 44.1 beats/min compared with 37.9 beats/min; P = 0.001), and a higher Valsalva ratio (1.91 compared with 1.72; P < 0.0001). No significant difference was found in the PR and QT_c (QT interval corrected for rate) intervals of the electrocardiogram or in the blood pressure response to standing.

Conclusion: Many young persons who faint under conditions of emotional distress do so because a relatively high vagal tone predisposes them to the cardioinhibitory component of the syncope. Age-related physiologic reduction in vagal cardiac responses may explain the lower incidence of this type of syncope with increasing age.