The Effect of Cardiac Mass and Venous Return in Children with Postural Orthostatic Tachycardia Syndrome: A Prospective, Observational Study

Low left ventricular mass index (LVMI) is thought to limit exercise tolerance in adult patients with postural orthostatic tachycardia syndrome (POTS). This finding has not been studied in children. We evaluated the effect of LVMI and hemodynamics at baseline and during exercise in POTS versus controls. POTS and control subjects aged 12-18 years were prospectively enrolled. POTS patients underwent autonomic studies. An echocardiogram was performed on all patients at baseline and during exercise. LVMI, venous return from inferior vena cava (IVC-VTI), left ventricular dimension, and cardiac output were assessed at baseline and during exercise. Generalized linear modeling with mixed effects was used to perform repeated measures testing between POTS and controls. Eighteen POTS patients (14 female, aged 15.4 +/- 1.4 years) and nine control subjects (six female, aged 15.0 +/- 1.3 years; p = 0.44) were enrolled. At baseline, LVMI was similar in both groups. During exercise, IVC-VTI, left ventricular end-diastolic dimension and volume, and stroke volume were lower in POTS patients. Peak heart rate was higher in POTS patients, but cardiac output was similar in both groups. Exercise time was higher in the control group (11.4 +/- 2.7 min vs 9.2 +/- 2.1, p = 0.024). Lower venous return resulted in smaller cardiac dimension and stroke volume during exercise. Higher heart rate in POTS may compensate to achieve similar cardiac output compared with control subjects. Lower ventricular filling and earlier time to peak heart rate may explain lower exercise capacity in pediatric POTS.