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CLINICAL STUDY

Enhanced reflex response to baroreceptor deactivation in subjects with tilt-Induced syncope

Mariavittoria Pitzalis, MD, PhD^*,*, Gianfranco Parati, MD, Francesco Massari, MD^||, Pietro Guida, MSc^*, Marco Di Rienzo, Eng, MSc^¶, Brian Rizzon, MD^*, Paolo Castiglioni, Eng, MSc^¶, Massimo Iacoviello, MD^*, Filippo Mastropasqua, MD^|| and Paolo Rizzon, MD^*

^* Institute of Cardiology, University of Bari, Bari, Italy
Innovative Technologies for Signal Detection and Processing Center, University of Bari, Bari, Italy
Department of Clinical Medicine, Prevention, and Applied Biotechnologies, University of Milano-Bicocca, Milan, Italy
II Cardiology Unit, S. Luca Hospital, Istituto Auxologico Italiano, Milan, Italy
^|| Cardiology, "Salvatore Maugeri" Foundation, IRCCS, Cassano, Italy
^¶ LaRC, Bioengineering Center, Don Gnocchi Foundation, Milan, Italy

Manuscript received July 13, 2002; revised manuscript received December 4, 2002, accepted December 12, 2002.

^* Reprint requests and correspondence: Dr. Maria Vittoria Pitzalis, Institute of Cardiology, University of Bari, Piazza Giulio Cesare 11, 70124 Bari, Italy.
mariavittoria.pitzalis{at}cardio.uniba.it

OBJECTIVES: We sought to evaluate whether changes in resting baroreflex control of heart rate are a distinctive feature of healthy subjects with a history of syncope prone to a positive tilt-test response.

BACKGROUND: The mechanisms involved in the pathogenesis of vasovagal syncope (VVS) are still poorly understood; in particular, the contribution of arterial baroreflex control of heart rate is matter of discussion.

METHODS: A passive tilt-table test was performed in 312 consecutive, otherwise healthy subjects (age 36 ± 15 years) with unexplained syncope and 100 control subjects. At baseline, spontaneous baroreflex sensitivity (BRS; ms/mm Hg) and the baroreflex effectiveness index (BEI) were assessed using the sequence method.

RESULTS: The study population showed normal baroreflex function. Tilt-induced VVS in 94 subjects who were younger than both the tilt-negative and control subjects (30 ± 14, 38 ± 15, and 37 ± 14 years, respectively; p = 0.00005) showed greater BRS (17.4 ± 9.8, 13.2 ± 7.9, and 12.8 ± 8.2 ms/mm Hg, respectively; p = 0.0001), but had a similar BEI (0.59 ± 0.18, 0.56 ± 0.19, and 0.58 ± 0.2, respectively; p = NS). On Cox multivariate analysis, the occurrence of VVS during tilt was inversely related to age (hazard ratio 0.97; p = 0.0004) and directly related to the BRS slope of sequences, implying a baroreceptor deactivation (hazard ratio 1.05; p = 0.02), but not of sequences characterized by arterial baroreceptor stimulation.

CONCLUSIONS: Subjects with tilt-induced VVS showed greater resting BRS but had a normal BEI. The enhanced reflex tachycardic response to arterial baroreceptor deactivation at rest may represent a characteristic feature of subjects prone to tilt-induced VVS.

Abbreviations and Acronyms   BEI = baroreflex effectiveness index   BRS = baroreflex sensitivity   BRS-down = baroreflex sensitivity for sequences with reduction in systolic arterial pressure and shortening of the pulse interval   BRS-up = baroreflex sensitivity for sequences with increase in systolic arterial pressure and lengthening of the pulse interval   SAP = systolic arterial pressure   VASIS = VAsovagal Syncope International Study   VVS = vasovagal syncope

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