Table 1.
Demographic data and clinical measurements in patients with orthostatic intolerance.
Figure 1.
Findings of the corrected QT interval.
Patients with orthostatic hypotension (OH) had a more prolonged corrected QT (QTc) interval (448.8±33.6 msec) than patients with neurocardiogenic syncope (NCS) (429.1±24.6 msec, p = 0.001) and postural orthostatic tachycardia syndrome (POTS) (421.7±28.6 msec, p<0.001). No difference in QTc interval was observed between NCS and POTS patients (p = 0.766).
Figure 2.
Comparisons of the QTc dispersion showed significant differences between groups (p = 0.021). Post-hoc analysis revealed that patients with orthostatic hypotension (OH) had more increased QTc dispersion than patients with neurocardiogenic syncope (NCS) (uncorrected p = 0.037, age and gender-corrected p = 0.013). The top and bottom borders of the boxes represent the upper and lower limits of the 95% CI range, respectively. The horizontal lines in the middle represent the mean value. Asterisk (*) indicates significant results after correction for post-hoc comparisons.
Figure 3.
Results of heart rate response to deep breathing and Valsalva ratio.
Orthostatic hypotension (OH) patients showed the smallest values in both heart rate response to deep breathing (HRDB; 10.3±6.0 beats/min) and Valsalva ratio (1.34±0.20) and postural orthostatic tachycardia syndrome (POTS) patients showed the largest values in both HRDB (24.5±9.2 beats/min) and Valsalva ratio (1.78±0.30). Neurocardiogenic syncope (NCS) patients showed intermediate levels of HRDB (15.4±9.1 beats/min) and Valsalva ratio (1.54±0.20) compared with OH and POTS patients.
Figure 4.
The quantitative sudomotor axon reflex test results according to body site.
Postural orthostatic tachycardia syndrome (POTS) patients had greater proximal leg sweat volume (1.21±0.97 µL) than OH (p = 0.001) and NCS (p = 0.006) patients. In addition, patients with POTS had greater distal leg sweat volume (1.19±0.85 µL) than OH patients (p<0.001). No difference in proximal and distal leg sweat volume between OH and NCS patients was observed. No difference in proximal and distal forearm sweat volume was found between groups. The top and bottom borders of the boxes represent the upper and lower limits of the 95% CI range, respectively. The horizontal lines in the middle represent the mean value.
Figure 5.
Correlation of corrected QT interval with heart rate response to deep breathing and Valsalva ratio.
The corrected QT (QTc) interval showed negative correlations with HRDB (r = −0.443, p<0.001, left panel) and Valsalva ratio (r = −0.425, p<0.001, right panel). In the partial correlation analysis controlling for age, associations between QTc interval and HRDB (r = −0.364, p<0.001), and QTc interval and Valsalva ratio (r = −0.336, p<0.001) remained statistically significant.