Heart Rate Lowering With Ivabradine and Burden of Symptoms in Patients With Postural Orthostatic Tachycardia Syndrome.

Postural orthostatic tachycardia syndrome (POTS) is a clinical syndrome of tachycardia on standing leading to palpitations, dizziness, chest pain, and/or fatigue. An exaggerated norepinephrine response with standing is often present in POTS, but it remains unclear whether the tachycardia is compensatory for a reduced stroke volume or whether the tachycardia is itself causing the symptoms of POTS. We herein report the effects of heart rate (HR) lowering with ivabradine, a selective I f channel blocker, on symptom burden in patients with POTS. After ivabradine treatment, there was a significant reduction in the change in HR with standing in all patients from 40 (30-70) to 15 (8-19) bpm ( P = 0.011), without significant changes in blood pressure. The Malmö score was significantly reduced in all patients from 86 (74-92) to 39 (32-66) ( P = 0.005). A correlation between change in HR with standing and the change in Malmö score (R = +0.828; R 2 quadratic = 0.635; P < 0.001) was present. The parallel improvement in HR response and symptoms with ivabradine suggests that the tachycardia response in POTS may not be considered compensatory but rather central to the pathophysiology of POTS symptoms.