Ivabradine in patients with inappropriate sinus tachycardia

Inappropriate sinus tachycardia (IST) is characterized by paroxysmal tachycardia originating in the sinus nodal area. IST predominately affects young, female patients. Current antiarrhythmic drug treatment (ß-blockers, calcium antagonists), frequently complicated by side effects, is often not successful. Ivabradine, approved for angina pectoris, selectively reduces heart rate by blocking the "funny current" in the sinus node. We therefore evaluated the effect of ivabradine in patients with symptomatic IST. Ten female patients (median age 32.5 years, range 12-57) suffering from symptomatic IST who had either failed (n = 8) or refused (n = 2) conventional therapy were analyzed. Symptoms included palpitations, pre-syncope, syncope, dyspnea, and exercise intolerance. After obtaining informed consent for individual off-label therapy, patients were treated with ivabradine (5-7.5 mg bid) in addition to beta-blocker therapy (n = 3) or as mono- therapy (n = 7). Therapy was monitored by 72-h Holter ECG and a symptoms questionnaire. Ivabradine significantly reduced maximum and mean heart rate (baseline, maximal heart rate 176 ± 45/min, mean heart rate 84 ± 11/min; ivabradine, maximal heart rate 137 ± 36/min, mean HR 74 ± 8/min, both p < 0.05, all values as mean ± SD). Minimum heart rate was not significantly changed. Three patients reported transient phosphene-like phenomena without discontinuation of ivabradine while on therapy. IST-associated symptoms were ameliorated (3 pts) or suppressed (5 pts) in all eight patients who could be contacted after a mean follow-up of 16 ± 9 months. Ivabradine appears effective and safe in patients with symptomatic inappropriate sinus tachycardia.