Cardiac Origins of the Postural Orthostatic Tachycardia Syndrome

Abstract

Objectives To test the hypothesis that a small heart coupled with reduced blood volume contributes to the Postural Tachycardia Syndrome (POTS), while exercise training improves this syndrome. Background Patients with POTS have marked increases in heart rate during orthostasis. However, the underlying mechanisms are unknown and the effective therapy is uncertain. Methods Twenty-seven POTS patients underwent autonomic function tests, cardiac MRI, and blood volume measurements. Twenty-five of them participated in a 3-mo specially designed exercise training program with 19 completing the program; these patients were reevaluated after training. Results were compared with those of 16 healthy controls. Results Upright heart rate and total peripheral resistance were greater, while stroke volume and cardiac output were smaller in patients than controls. Baroreflex function was similar between groups. Left ventricular mass (median [25%, 75%], 1.26 [1.12, 1.37] vs 1.45 [1.34, 1.57] g/kg; P<0.01) and blood volume (60 [54, 64] vs 71 [65, 78] ml/kg; P<0.01) were smaller in patients than controls. Exercise training increased left ventricular mass and blood volume by ~12% and ~7%, and decreased upright heart rate by 9 [1, 17] bpm. Ten out of 19 patients no longer met POTS criteria after training, while patients’ Quality of Life assessed by Short-Form 36 was improved in all patients after training. Conclusions Autonomic function was intact in POTS patients. The marked tachycardia during orthostasis was attributable to a small heart coupled with reduced blood volume. Exercise training improved or even cured this syndrome in the majority of patients. It seems reasonable to offer POTS a new name based on its underlying pathophysiology – “The Grinch Syndrome”, because in this famous children’s book by Dr. Seuss, the main character had a heart that was “two sizes too small.”

Postural Hyperventilation as a Cause of Postural Tachycardia Syndrome: Increased Systemic Vascular Resistance and Decreased Cardiac Output When Upright in All Postural Tachycardia Syndrome Variants

“…Decreased upright CO in POTS has been reported by our group and by others,27, 30, 31 and is associated with increased SVR,27, 31 consistent with sustained BP and marked reduction in upright stroke volume 32. However, a subset of POTS may have increased CO during exercise 33.…”

“…Supine CBV is reduced in some patients with POTS 31, 34, 35, 36. This is striking in those patients with evidence for increased supine sympathoexcitation 37.…”

Small Heart With Low Cardiac Output for Orthostatic Intolerance in Patients With Chronic Fatigue Syndrome

“…4,5,25 In addition, reduced cerebral perfusion induced by excessive lowerbody venous pooling with delayed orthostatic hypotension has been suggested to be involved in the orthostatic component of fatigue in CFS patients. 26 Recently, by using a cardiac magnetic resonance imaging technique, Fu et al 13 assessed precisely the heart size and mass in patients with POTS and found that cardiac size and mass and blood volume were much smaller in the patients than in healthy sedentary controls. The marked orthostatic tachycardia in these patients seemed to be a physiologic compensatory response to a smaller stroke volume, and exercise training improved this syndrome in most patients.…”

“…The marked orthostatic tachycardia in these patients seemed to be a physiologic compensatory response to a smaller stroke volume, and exercise training improved this syndrome in most patients. 13 In their assessment of both sympathetic baroreflex sensitivity and cardiovagal baroreflex sensitivity, the function of the autonomic nervous system was intact in the patients, 13 although other researchers have postulated autonomic nervous dysfunction with exaggerated sympathetic nervous activation over compensatory levels while standing as a major mechanism behind the symptoms. 4,5,20,24,27 Elucidation of the pathophysiology of CFS and OI may lead to better therapeutic strategies.…”

“…10 -12 Furthermore, Fu et al 13 have recently reported that patients with postural orthostatic tachycardia, which is often noted in patients with chronic OI, have small hearts coupled with reduced blood volume compared with healthy controls, as determined by magnetic resonance imaging and blood volume measurements.…”