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An insight into the autonomic and haemodynamic mechanisms underlying reflex syncope in children and adolescents: a multiparametric analysis

Published online by Cambridge University Press:  23 June 2014

Sérgio Laranjo ,
Cristiano Tavares ,
Mário Oliveira ,
Conceição Trigo ,
Fátima Pinto  and
Isabel Rocha
Sérgio Laranjo*
Affiliation:
Institute of Physiology and Cardiovascular Autonomic Lab, Faculty of Medicine of Lisbon, Lisbon, Portugal Department of Pediatric Cardiology, Santa Marta Hospital, Lisbon, Portugal
Cristiano Tavares
Affiliation:
Institute of Physiology and Cardiovascular Autonomic Lab, Faculty of Medicine of Lisbon, Lisbon, Portugal
Mário Oliveira
Affiliation:
Institute of Physiology and Cardiovascular Autonomic Lab, Faculty of Medicine of Lisbon, Lisbon, Portugal
Conceição Trigo
Affiliation:
Department of Pediatric Cardiology, Santa Marta Hospital, Lisbon, Portugal
Fátima Pinto
Affiliation:
Department of Pediatric Cardiology, Santa Marta Hospital, Lisbon, Portugal
Isabel Rocha
Affiliation:
Institute of Physiology and Cardiovascular Autonomic Lab, Faculty of Medicine of Lisbon, Lisbon, Portugal
*
Correspondence to: Dr S. Laranjo, MD, Cardiovascular Autonomic Function Lab, Instituto de Fisiologia, Faculdade de Medicina de Lisboa, Lisbon, Portugal. Tel: (+351) 217 999 435; E-mail: [email protected]
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Abstract

Around 15% of children and adolescents experience at least one episode of syncope until adulthood. Excluding cardiac disease, the majority of syncopes are of reflex origin and benign in nature. In this situation, a tilt test is conducted to reproduce symptoms and to evaluate cardiovascular adaptations to orthostatism, but its mechanisms are not yet well defined. Here, we investigated haemodynamics and autonomic activity during tilt in young patients. Patients (n=113) with unexplained syncope were enrolled. Tilt followed a standard protocol without provocative agents. A positive response (fainters) was defined as a sudden development of syncope or presyncope associated with hypotension, bradycardia, or both. Haemodynamic parameters, autonomic activity, and baroreflex sensibility were evaluated. Data were analysed on baseline; immediately after tilting; on tilt adaptation; before fainting or before tilt-down for non-fainters; and on tilt-down. A total of 45 patients experienced syncope after a mean time of 18 minutes. During tilting up, fainters showed lower blood pressure and peripheral resistance values, which decreased progressively with time together with baroreflex sensibility. Sympathetic tone increased massively along time till syncope. No changes in cardiac output and heart rate were observed. Results show a strong effort of the autonomic nervous system to adapt to orthostatic stress through different magnitudes of sympathetic output, which was maximal before syncope without apparent modifications of parasympathetic tone. These changes suggest an imbalance between both branches of the autonomic nervous system, not enabling a time-progressive adaptation and leading the subject to faint.

Keywords

Reflex syncopetilt testsympathetic reserveautonomic nervous systembaroreflex
Type
Original Articles
Information
Cardiology in the Young , Volume 25 , Issue 4 , April 2015 , pp. 647 - 654
Copyright
© Cambridge University Press 2014 

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