Absence of increased systemic vascular resistance during syncopal episodes in patients with tilt-positive neurocardiogenic syncope

Shira Perl, Shimon Weitzman, Alexander Battler, Amos Katz

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Background: The purpose of this study was to elucidate the mechanism of syncope in patients with neurocardiogenic syncope (NCS) by measuring hemodynamic parameters continuously during a head-up tilt (HUT) test. Methods: Twenty-three adults (mean age 22.6 ± 9.8, range 15-62) participated in the study: 16 with a history of syncope suggesting NCS and 7 healthy volunteers who served as controls. The subjects underwent a 45-minute 60°tilt test. Heart rate and blood pressure were monitored continuously. The stroke volume was measured every minute by noninvasive impedance cardiography, and systemic vascular resistance was calculated from these measurements. The test was terminated when syncope occurred or after 45 minutes in an upward position. Results: Eight of the 16 patients had a positive HUT, while all control subjects had a negative HUT. Decreased stroke volume and cardiac index were observed in all subjects and subgroups in the upward position, compared to the rest position (P < 0.01). Systemic vascular resistance rose in patients with a negative HUT and all controls (P < 0.03), but did not change in the HUT-positive patients (P = 0.25), during the HUT. Systemic vascular resistance was significantly lower in the upward position in the positive HUT than in the other groups (P < 0.04), but there were no differences in the cardiac index. Conclusions: Failure to achieve an appropriate increase in systemic vascular resistance may be an important mechanism in some cases of NCS and should be taken in account when considering therapeutic options. Impedance cardiography is a noninvasive technique for the detection of this abnormal response and can be used to assess the effect of drug therapy on systemic vascular resistance.

Original languageEnglish
Pages (from-to)121-129
Number of pages9
JournalAnnals of Noninvasive Electrocardiology
Issue number2
StatePublished - 13 Jul 1999
Externally publishedYes


  • Cardiac output
  • Cardiographic impedance
  • Neurocardiogenic syncope
  • Systemic vascular resistance
  • Tilt test

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)


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