Abnormalities in Cardiac Mechanics and Autonomic Function in People With Syncope Using Pulse Wave Doppler Echocardiography – A Pilot Study

Background: Vasovagal syncope is a type of reflex syncope characterised by a transient loss of consciousness and postural tone due to temporary, self-limiting global cerebral hypoperfusion. Syncope is broadly classified into four categories: reflex (neurally mediated), orthostatic hypotension, cardiac arrhythmias, and structural cardiac causes. This study aimed to evaluate the extent of reduction in cardiac output and stroke volume associated with syncope. Methods: A prospective observational case-control study of 21 participants, comprising 11 males (52.3%) and 10 females (47.7%), who underwent head-up tilt table (HUTT) testing and echocardiographic evaluation for syncope at Kasturba Medical College Hospital, Manipal, India, between July 2023 and April 2024. Participants were categorised into syncope and non-syncope groups based on HUTT outcomes. Results: Of the 21 participants, 5 developed syncope during the HUTT test, while 16 did not. Participants with syncope demonstrated a significant reduction in cardiac output and stroke volume, associated with a decrease in blood pressure (<90/50 mmHg). Systemic vascular resistance increased significantly during the syncope stage, likely due to baroreflex-mediated vasoconstriction in the splanchnic and skeletal muscle vascular beds. Conclusion: The findings suggest that a reduction in cardiac output secondary to hypotension is the primary determinant of syncope. An increase in systemic vascular resistance appears to act as a compensatory mechanism to prevent a further decline in cardiac output. The combined use of HUTT and echocardiography is valuable in assessing cardiac mechanics during syncope.