Which hemodynamic parameter predicts nitroglycerin-potentiated head-up tilt test response?

Abstract

Background: The aim of our study was to identify the early hemodynamic predictors of head-up tilt test (HUTT) outcome in healthy patients with recurrent unexplained syncope.

Methods and results: The study involved 95 patients (mean age 38 ± 15; 42 male) who were referred for the evaluation of the syncopal episodes from October 2012 to May 2013. According to the nitroglycerin-potentiated diagnostic tilt test response, the study population was divided into two groups: HUTT+ Group (61 patients, mean age 37 ± 10; 27 male) and HUTT- Group (34 patients, mean age 38 ± 11; 15 male) with no tilt-induced syncope. Finger arterial blood pressure (BP) was recorded during tilt testing. Left ventricular stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR) were computed from the pressure pulsations. After nitroglycerin administration, the HUTT+ Group showed a significant increase in heart rate (92.0 ± 7.3 beats/min vs 68.9 ± 8.7 beats/min, P < 0.0001), with well-maintained systolic BP (111.6 ± 14.1 mm Hg vs 108.8 ± 11.5 mm Hg; P = 0.332) and diastolic BP (66.1 ± 8.5 mm Hg vs 63.1 ± 6.9 mm Hg; P = 0.0913); a significant decrease in SV (53.9 ± 8.0 mL vs 78.6 ± 8.2 mL; P < 0.0001) and CO (4.0 ± 0.5 L/min vs 5.8 ± 1.0 L/min; P < 0.001), and a significant increase in TPR (1.3 ± 0.3 U vs 0.9 ± 0.2 U, P < 0.0011). We tested three hemodynamic parameters (SV, CO, and TPR) as predictors of positive tilt test response with receiver-operating characteristic curve analysis.

Conclusions: Our results show that, 2 minutes after nitroglycerin administration, a statistically significant decrease of SV values (<67 mL) strongly predicts (area under the curve, 0.985; P < 0.0001) the HUTT-positive response in healthy patients with recurrent unexplained syncope.

Keywords: cardiac output; head-up tilt test; hemodynamic variables; stroke volume; total peripheral resistance; vasovagal syncope.