Postural tachycardia syndrome - Diagnosis, physiology, and prognosis

Abstract

Postural tachycardia syndrome (POTS) is a heterogeneous clinical syndrome that has gained increasing interest over the past few decades due to its increasing prevalence and clinical impact on health-related quality of life. POTS is clinically characterized by sustained excessive tachycardia upon standing that occurs in the absence of significant orthostatic hypotension and other medical conditions and or medications, and with chronic symptoms of orthostatic intolerance. POTS represents one of the most common presentations of syncope and presyncope secondary to autonomic dysfunction in emergency rooms and in cardiology, neurology, and primary care clinics. The most sensitive method to detect POTS is a detailed medical history, physical examination with orthostatic vital signs or brief tilt table test, and a resting 12-lead electrocardiogram. Additional diagnostic testing may be warranted in selected patients based on clinical signs. While the precise etiology remains unknown, the orthostatic tachycardia in POTS is thought to reflect convergence of multiple pathophysiological processes, as a final common pathway. Based on this, POTS is often described as a clinical syndrome consisting of multiple heterogeneous disorders, with several underlying pathophysiological processes proposed in the literature including partial sympathetic neuropathy, hyperadrenergic state, hypovolemia, mast cell activation, deconditioning, and immune-mediated. These clinical features often overlap, however, making it difficult to categorize individual patients. Importantly, POTS is not associated with mortality, with many patients improving to some degree over time after diagnosis and proper treatment. This review will outline the current understanding of diagnosis, pathophysiology, and prognosis in POTS.

Keywords: Diagnosis; Etiology; Orthostatic intolerance; Postural tachycardia syndrome.

Figure 1. Hemodynamic Pattern during Head-Up Tilt Table Testing (HUTT) in POTS

Panel A: In a healthy subject, heart rate increases only modestly with HUTT, with no significant change in blood pressure. Panel B: In Postural Tachycardia Syndrome (POTS), there is an excessive rise in HR during HUTT, with stable blood pressure.

Figure 2. Orthostatic Heart Rate Increase with Head-Up Tilt Table Testing (HUTT) versus Active Standing

The mean orthostatic change in heart rate (HR) is shown over a 10-minute period during HUTT and active standing in healthy subjects (blue symbols) and patients with Postural Tachycardia Syndrome (POTS; red symbols). Orthostatic tachycardia is exaggerated with HUTT, with the mean HR value over 30 bpm in both groups, suggesting less sensitivity of this method for diagnosis compared with active standing.

Figure 3. Schematic Diagram of Multiple Potential Pathophysiologic Processes in POTS

NE, norepinephrine; NET, norepinephrine transporter; NETi, norepinephrine transporter inhibitor; SNRI, selective norepinephrine reuptake inhibitor; SNS, sympathetic nervous system.

Figure 4. The Problem with POTS “Subtype” Labels

Panel A: This shows a representation of how many people think about the various POTS “subtype” labels – as clearly distinct entities from each other; Panel B: In reality, these “subtypes” are not mutually exclusive of each other, and many patients may have features consistent with more than one subtype, leading to overlapping subsets.