Orthostatic Tachycardia-Hypotensive Syndrome: A Novel Form of Orthostatic Intolerance in the Young.

Postural orthostatic tachycardia syndrome (POTS) and neurocardiogenic syncope (NCS) are frequently observed causes of orthostatic intolerance (OI). Clinical experience reveals patients with overlapping symptoms of both. This observation led to the hypothesis of orthostatic tachycardia hypotensive syndrome (OTHS), a distinct OI variant, combines POTS and NCS features. This study aims to define and characterize it. A retrospective chart review of patients presenting with OI and underwent head up tilt (HUT) between 2014 and 2020. We extracted demographic data, findings during HUT including heart rate (HR), systolic blood pressure (SBP), stroke volume (SV), near infrared spectroscopy (NIRS), syncope, cardiac asystole, and convulsions. We divided the subjects into three groups: POTS, NCS, and OTHS. We included patients with POTS (n = 90), NCS (n = 86), and OTHS (n = 101). POTS patients showed higher HR (baseline, recovery, minimum) vs. OTHS (p = 0.047, < 0.001, < 0.001), while OTHS patients had higher HR (5 min, 10 min, minimum, maximum) vs. NCS (p = 0.047, < 0.001, < 0.001, < 0.001). Minimum SBP was higher in POTS vs. OTHS (p < 0.001), and OTHS patients had higher SV (baseline, recovery, minimum, maximum) vs. POTS (p = 0.006, < 0.001, 0.002, 0.005). Patients with POTS have lower baseline NIRS compared to NCS and OTHS (p =  < 0.032, < 0.011). Asystole was significantly more frequent in the NCS group (n = 24, 27.9%) than in the OTHS group (n = 9, 8.9%), with p < 0.001. OTHS is a form of OI characterized by initial orthostatic tachycardia with increased HR > 30-40 bpm followed by hypotension leading to syncope.