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Comparative Study
. 2010 Jun 22;55(25):2858-68.
doi: 10.1016/j.jacc.2010.02.043.

Cardiac origins of the postural orthostatic tachycardia syndrome

Qi Fu  1 , Tiffany B Vangundy, M Melyn Galbreath, Shigeki Shibata, Manish Jain, Jeffrey L Hastings, Paul S Bhella, Benjamin D Levine
Affiliations
Comparative Study

Cardiac origins of the postural orthostatic tachycardia syndrome

Qi Fu et al. J Am Coll Cardiol. .

Abstract

Objectives: The purpose of this study was to test the hypothesis that a small heart coupled with reduced blood volume contributes to the postural orthostatic tachycardia syndrome (POTS) and that 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 magnetic resonance imaging, and blood volume measurements. Twenty-five of them participated in a 3-month specially designed exercise training program with 19 completing the program; these patients were re-evaluated after training. Results were compared with those of 16 healthy controls.

Results: Upright heart rate and total peripheral resistance were greater, whereas stroke volume and cardiac output were smaller in patients than in controls. Baroreflex function was similar between groups. Left ventricular mass (median [25th, 75th percentiles], 1.26 g/kg [1.12, 1.37 g/kg] vs. 1.45 g/kg [1.34, 1.57 g/kg]; p < 0.01) and blood volume (60 ml/kg [54, 64 ml/kg] vs. 71 ml/kg [65, 78 ml/kg]; p < 0.01) were smaller in patients than in controls. Exercise training increased left ventricular mass and blood volume by approximately 12% and approximately 7% and decreased upright heart rate by 9 beats/min [1, 17 beats/min]. Ten of 19 patients no longer met POTS criteria after training, whereas patient quality of life assessed by the 36-item Short-Form Health Survey 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 most 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."

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Figures

Figure 1
Figure 1. Muscle sympathetic nerve activity (MSNA) responses during graded upright tilt
Values are expressed as median [25%, 75%]. §P < 0.10 and †P < 0.05 compared to controls after 5 and 10 min of 60° upright tilt.
Figure 2
Figure 2. Blood volume and left ventricular mass in POTS patients before and after 3 mo of exercise training as well as in controls
Values are expressed as individuals and median [25%, 75%]. **P < 0.01 compared to before training in POTS. ††P < 0.01 compared to controls.
Figure 3
Figure 3. Heart rate responses during 10-min stand in POTS patients before and after exercise training as well as in controls
Values are expressed as individuals and median [25%, 75%]. **P < 0.01 compared to before training in POTS in the same posture. ††P < 0.01 compared to controls in the same posture.
Figure 4
Figure 4. Effects of training on patients’ Quality of Life assessed by the SF-36
Values are expressed as individuals and median [25%, 75%]. **P < 0.01 compared to before training in POTS.
See this image and copyright information in PMC

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