Background: Inappropriate sinus tachycardia (IST) is characterized by an elevated heart rate (HR) at rest and an exaggerated HR response to physical activity or emotional stress. Beta-blockers and calcium channel blockers are the first-line therapy but sometimes are poorly tolerated due to side effects.
Objective: The purpose of this study was to evaluate the efficacy and safety of ivabradine, a selective inhibitor of the I(f) current of the sinoatrial node, in patients affected by IST.
Methods: Eighteen consecutive symptomatic patients (2 men and 16 women; mean age 45 +/- 15 years) affected by IST were enrolled in the study. Every patient underwent resting ECG, 24-hour Holter ECG, and exercise ECG at baseline and at 3-month and 6-month follow-up.
Results: Sixteen patients (14 women; mean age 41 +/- 14 years) completed the study. Holter ECG assessment showed a significant reduction of medium HR (P <.001) and maximal HR (P <.001, basal vs 3-6 months; P = .02, 3 vs 6 months). Minimal HR slightly decreased at 3 months and then stabilized (P = .49, 3 vs 6 months) despite an increased drug dose. Stress test showed a significant decrease at rest (P <.001) and maximal HR (P <.05), suggesting an increased tolerance to physical stress, which was confirmed by a progressive increase of maximal load reached (>100 W) during stress test at 3 months (75%) and 6 months (85%). One patient was excluded because of phosphenes despite dose lowering, and another patient did not complete the protocol.
Conclusion: Ivabradine could represent an effective and safe alternative to calcium channel blockers and beta-blockers for treatment of IST.
Copyright 2010 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.