BACKGROUND: Syncope is a sudden transient loss of consciousness and postural tone caused by cerebral hypoperfusion. The most common form is vasovagal syncope (VVS). Presyncopal progressive early hypotension in older VVS patients is caused by reduced cardiac output (CO); younger patients have reduced systemic vascular resistance (SVR). Using a priori criteria for reduced CO ( downward arrowCO) and SVR ( downward arrowSVR), we studied 48 recurrent young fainters comparing subgroups of VVS with VVS- downward arrowCO, VVS- downward arrowSVR, and both VVS- downward arrowCO& downward arrowSVR. METHODS AND RESULTS: Subjects were studied supine and during 70-degrere upright tilt with a Finometer to continuously measure blood pressure, CO, and SVR and impedance plethysmography to estimate thoracic, splanchnic, pelvic, and calf blood volumes, blood flows, and vascular resistances and electrocardiogram to measure heart rate and rhythm. Central blood volume was decreased in all VVS compared to control. VVS- downward arrowCO was associated with decreased splanchnic blood flow and increased splanchnic blood pooling compared to control. Seventy-five percent of VVS patients had reduced SVR, including 23% who also had reduced CO. Many VVS- downward arrowSVR increased CO during tilt, with no difference in splanchnic pooling, caused by significant increases in splanchnic blood flow and reduced splanchnic resistance. VVS- downward arrowCO& downward arrowSVR patients had splanchnic pooling comparable to VVS- downward arrowCO patients, but SVR comparable to VVS- downward arrowSVR. Splanchnic vasodilation was reduced, compared to VVS- downward arrowSVR, and venomotor properties were similar to control. Combined splanchnic pooling and reduced SVR produced the earliest faints among the VVS groups. CONCLUSIONS: Both downward arrowCO and downward arrowSVR occur in young VVS patients. downward arrowSVR is predominant in VVS and is caused by impaired splanchnic vasoconstriction.
Stewart, J., Medow, M., Sutton, R., Visintainer, P., Jardine, D., & Wieling, W. (2017). Mechanisms of Vasovagal Syncope in the Young: Reduced Systemic Vascular Resistance Versus Reduced Cardiac Output. Journal of the American Heart Association, 6 (1), e004417. https://doi.org/10.1161/JAHA.116.004417
Originally published in Journal of the American Heart Association 2017;6:e004417. The original material can be found here.
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