Excessive heart rate response to orthostatic stress in postural tachycardia syndrome is not caused by anxiety, 2007, Masuki et al

(An old study, but one that deserves to be remembered as it addresses the question of whether the increased heart rate of POTS could be caused by a fear of standing. Yes, that idea sounds ridiculous but a recent paper proposed it. Thanks to Sid for bringing this 2007 paper to our attention.)

Excessive heart rate response to orthostatic stress in postural tachycardia syndrome is not caused by anxiety
Shizue Masuki, John H. Eisenach, Christopher P. Johnson, Niki M. Dietz, Lisa M. Benrud-Larson, William G. Schrage, Timothy B. Curry, Paola Sandroni, Phillip A. Low, and Michael J. Joyner

Postural tachycardia syndrome (POTS) is characterized by excessive increases in heart rate (HR) without hypotension during orthostasis. The relationship between the tachycardia and anxiety is uncertain. Therefore, we tested whether the HR response to orthostatic stress in POTS is primarily related to psychological factors. POTS patients (n= 14) and healthy controls (n = 10) underwent graded venous pooling with lower body negative pressure (LBNP) to −40 mmHg while wearing deflated antishock trousers. “Sham” venous pooling was performed by 1) trouser inflation to 5 mmHg during LBNP and 2) vacuum pump activation without LBNP. HR responses to mental stress were also measured in both groups, and a questionnaire was used to measure psychological parameters. During LBNP, HR in POTS patients increased 39 ± 5 beats/min vs. 19 ± 3 beats/min in control subjects at −40 mmHg (P < 0.01). LBNP with trouser inflation markedly blunted the HR responses in the patients (9 ± 2 beats/min) and controls (2 ± 1 beats/min), and there was no HR increase during vacuum application without LBNP in either group. HR responses during mental stress were not different in the patients and controls (18 ± 2 vs. 19 ± 1 beats/min; P > 0.6). Anxiety, somatic vigilance, and catastrophic cognitions were significantly higher in the patients (P < 0.05), but they were not related to the HR responses during LBNP or mental stress (P > 0.1). These results suggest that the HR response to orthostatic stress in POTS patients is not caused by anxiety but that it is a physiological response that maintains arterial pressure during venous pooling.

Postural tachycardia syndrome (POTS) is a clinical syndrome of orthostatic intolerance characterized by excessive increases in heart rate (HR) during orthostatic stress in the absence of orthostatic hypotension. It generally affects young and middle-aged women (20, 33). Symptoms include fatigue, light-headedness, and nausea, and POTS can be quite debilitating with significant limitations to activities of daily living (1, 18, 30). Although POTS is now better recognized, the mechanisms underlying this condition remain unclear.

Clinical observations suggest that these patients often experience marked anxiety and other psychological symptoms (19, 20, 30), and many POTS patients report being told by at least one physician that the cause of their tachycardia is psychogenic (1). On the other hand, several studies have consistently demonstrated that the excessive tachycardia may be a compensatory response to other cardiovascular impairments during orthostasis (14, 34–37). However, there have been no attempts to assess the direct psychogenic component of the tachycardia in POTS. Therefore, we tested the hypothesis that the HR response to orthostatic stress in POTS patients is not due to anxiety. Utilizing several experimental approaches, our findings indicate that anxiety is not the primary cause for the excessive orthostatic tachycardia seen in POTS. In a larger context, our findings suggest that although psychological symptoms are common in POTS, they may not be causal.

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