Background: Postural orthostatic tachycardia syndrome (POTS) is a disorder of orthostatic intolerance characterized by excessive tachycardia of unknown etiology. Whether this condition involves abnormal cardiac sympathetic innervation or function remains elusive. Metaiodobenzylguanidine (MIBG) resembles guanethidine and is a pharmacologically inactive analogue of norepinephrine, which is similarly metabolized in noradrenergic neurons. MIBG myocardial scintigraphy is clinically used to estimate local myocardial sympathetic nerve damage in some forms of heart disease and autonomic neuropathy. Our objective was to evaluate cardiac sympathetic innervation in POTS-patients.
Methods: We studied twenty patients with POTS using 123I- MIBG-SPECT, standardized autonomic testing, assessment of catecholamine plasma levels and sympathetic skin response.
Results: In four POTS-patients (20.0 %) myocardial MIBG uptake was markedly decreased. The mean heart-to-mediastinum ratio was reduced to 1.22 ± 0.08 compared to the normal range of >1.7. We found no correlation between myocardial MIBG uptake and degree of postural tachycardia, baroreflex sensitivity, catecholamine plasma levels or other autonomic parameters. Sympathetic skin responses were normal in all patients.
Conclusions: These findings suggest that POTS may be, in part, a manifestation of autonomic cardiac neuropathy. MIBG myocardial scintigraphy may be helpful to distinguish patients with neuropathic POTS from patients with orthostatic intolerance of other origin.