Impaired Left Ventricular Diastolic Function in the Postural Orthostatic Tachycardia Syndrome

Postural Orthostatic Tachycardia Syndrome (POTS) is characterized by inability to remain upright for prolonged periods of time due to excessive tachycardia. We have recently shown that a small heart coupled with reduced blood volume contributes to POTS, while endurance exercise training is effective therapy. However, cardiac function in this syndrome has not been investigated. PURPOSES: Thus, the purpose of this study was to evaluate left ventricular (LV) diastolic function in POTS. METHODS: We studied 28 POTS patients (27 females and 1 male). LV diastolic function was evaluated by 4 indices with Doppler echocardiography in the supine position; 1) early and late mitral inflow velocity ratio (E/A), 2) isovolumetric relaxation time (IVRT), 3) tissue Doppler velocities of the mitral annulus (TDI-E), and 4) propagation velocity of mitral inflow (Vp). Nineteen out of 28 patients completed a 3-month exercise training program, which increased (but did not normalize) the blood volume and heart size, and was effective at improving POTS symptoms. Diastolic function was evaluated again after exercise training. Results were compared with those of age and sex-matched controls (N=9). RESULTS: There was no difference in E/A, IVRT, and TDI-E between POTS and controls, while Vp was significantly lower in POTS than in controls (POTS: 60±14, Control: 73±16 cm/sec, P=0.031). Neither E/A, IVRT, TDI E, nor Vp changed after 3 months of exercise training. Consequently, Vp remained significantly lower in POTS even after exercise training compared with controls (59±13 cm/sec, P=0.024 vs. Control, P=0.767 vs. Pre-training). CONCLUSIONS: The lower Vp suggests that POTS patients have impaired LV function early in diastole, which may be associated with impaired LV diastolic suction similar to that after bed rest deconditioning. This reduced suction may be especially important in the upright position and could contribute to the very low upright stroke volume and postural tachycardia. Three months of endurance training was not enough to normalize diastolic suction, suggesting that either this represents an intrinsic defect in these patients, or that more training is required to fully normalize cardiac diastolic suction in this syndrome. Supported by the NIH K23 grant HL075283 and the NSBRI Career Development Award EO00007