Orthostatic tachycardia with different onset time in patients with orthostatic intolerance

To investigate whether there is a difference in the neuro-autonomic and hemodynamic parameters in patients with postural tachycardia syndrome (POTS) according to onset time of orthostatic tachycardia during the Head-up tilt (HUT) test.

We retrospectively reviewed neuro-autonomic and hemodynamic data from patients with orthostatic intolerance. A standardized battery of neuro-autonomic tests, including the HUT, Valsalva maneuver, heart rate deep breathing and quantitative sudomotor axon reflex test, was performed. The beat-to-beat derived hemodynamic parameters, including systolic blood pressure (BP) (SBP), mean BP (MBP), diastolic BP, heart rate (HR), total peripheral resistance, stroke volume, and cardiac output, were also extracted from HUT test. According to onset time of orthostatic tachycardia (OT), we divided patients into two groups; HR increase "within 10 minutes" (i.e., early OT) and HR increase "after 10 minutes" (i.e., late OT).

We identified 210 patients with OT during HUT test. Forty-three percent of patients were included in early OT group and 57% were late OT group. Patients in late OT group were older than early OT group. Late OT group tended to have baseline hypertension more frequently compared to early OT group. After adjusting for age, late OT group showed higher baseline SBP and MBP, and lower increase of HR during HUT test than early OT group. However, other neuro-autonomic and hemodynamic parameters did not show significant differences between two groups.

Orthostatic tachycardia might be developed in the late period during the HUT test. There were no remarkable differences in neuro-autonomic and hemodynamic parameters between early and late OT groups. It seems reasonable to extend the duration of HUT test to at least 20 min, to increase the diagnostic yield in patients with a history of orthostatic intolerance suspected as having POTS.