Background: Inappropriate sinus tachycardia (IST) is an uncommon disorder characterized by an exaggerated heart rate (HR). It is mostly treated with b-blockers or verapamil leaving the sinus node modulation for refractory cases. Ivabradine, a pure HR lowering agent, has proven anti-anginal efficiency linked to the If current inhibition. We conducted a small prospective experience investigating its efficacy in IST.
Methods: Four women exhibiting sinus rhythm with a resting HR ≥ 100 bpm and an average HR ≥ 90 bpm (Holter monitoring) were followed for three months. Structural heart disease and other causes of tachycardia were discarded. Electrocardiographic, Holter monitoring, exercise tolerance and quality of life determinations were performed. Ivabradine was initiated at 5 mg (bid) and increased to 7.5 mg (bid) after one week.
Results: All patients (mean age 33.7 years) presented a typical history of effort intolerance, palpitations and tachycardia. Resting HR (bpm) was decreased: 106.5 ± 3 to 88.5 ± 2 (week 1), to 77.0 ± 3 (week 2) and to 73.7 ± 13 (month 3). Reductions (Holter monitoring) of the maximum, average and minimum HR (beats) were: 152.0 ± 19 to 128.5 ± 18; 96.0 ± 1.4 to 73 ± 3.2 and 63.2 ± 6 to 48.2 ± 3. Total exercise time was amplified (555 ± 99 to 679 ± 90 s) and quality of life improved.
Conclusions: IST causes an elevated HR and its control is the treatment objective. If future data confirm our results, ivabradine could be used for this purpose. More information is necessary in order to define its role: initial option, second step (β-blockers non-responders or intolerants) or combined (refractory cases).
(Cardiol J 2010; 17, 2: 166-171)