Related Experiment Video
Updated: Jun 10, 2026

Tilt Testing with Combined Lower Body Negative Pressure: a "Gold Standard" for Measuring Orthostatic Tolerance
Published on: March 21, 2013
Cardiac repolarization variability in patients with postural tachycardia syndrome during graded head-up tilt
Mathias Baumert1, Elisabeth Lambert, Gautam Vaddadi
1Cardiovascular Research Centre, School of Medicine, School of Paediatrics and Reproductive Health, University of Adelaide, Australia. mathias.baumert@adelaide.edu.au
Objective:
The aim of this study was to assess cardiac ventricular repolarization in patients with postural tachycardia syndrome (POTS) and further the possible link between ventricular repolarization and sympathetic nervous system activity.
Methods:
We recorded body surface ECGs together with plasma noradrenaline (NE) spillover, and muscle sympathetic nerve activity (MSNA) in twelve healthy control subjects (CON; 5 males; age: 23±2 yrs) and 13 subjects with postural tachycardia syndrome (POTS; 4 males; 32±13 yrs) during graded head-up tilt (0°-20°-30°-40°). Ventricular repolarization was assessed by computing various measures of beat-to-beat QT interval variability and T wave amplitude.
Results:
In patients with POTS, baseline heart rates were higher and MSNA increases during tilt were more pronounced than in CON. None of the QT variability measures was significantly affected by tilt or different between CON and POTS when corrected for heart rate. Contrary, the T wave amplitude flattened due to tilt (p<0.001) and this effect was significantly more pronounced in POTS (32% at 40°) than in CON (21% at 40°; p=0.03).
Conclusions:
Beat-to-beat variability of the QT interval is normal in patients with POTS. However, significantly more attenuated T waves during head-up tilt together with elevated MSNA levels suggest increased sympathetic outflow to the ventricular myocardium in patients with POTS.
Significance:
Monitoring of the T wave during tilt test may provide a non-invasive tool for assessing excessive sympathetic outflow to the ventricular myocardium.
Related Concept Videos
Dysrhythmias II: Classification of Tachyarrhythmias
Dysrhythmias III: Characteristics of Dysrhythmias
Imbalances in Cardiac Output
CHF can occur due to the failure of either side of the heart. Left-side failure leads to pulmonary congestion—the right side continues to send blood...
Cardiac Action Potential
The cardiac action potential process involves a series of phases characterized by the movement of ions across the cardiac cell membranes, leading to the depolarization and repolarization of the cardiac myocytes.
Ionic Basis of Cardiac Action Potentials
Dysrhythmias V: Evaluating Dysrhythmias
Dysrhythmias IV: Characteristics of Bradyarrhythmias

