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Inappropriate sinus tachycardia (IST) refractory to standard medical therapy and sinus nodal modification can be treated successfully with ivabradine.
A 43-year-old female presented with complaint of palpitations and fatigue for 4 months. Her symptoms occurred with household chores. Her medical history included asthma and hypothyroidism. She denied smoking, alcohol intake, drug abuse, energy beverages and caffeine intake. Serum thyroid hormones were normal. Levothyroxine was discontinued. A 30-day event monitor showed episodes of sinus tachycardia with rates of 128 to 158 beats per minute (bpm). Tilt table testing was negative for orthostatic hypotension with reactive tachycardia. She developed hypotension on trials of nebivolol and metoprolol. While on nadolol she had syncope. She declined trying digoxin and non-dihydropyridine calcium channel blockers. Electrophysiology study (EPS) was done to elucidate mechanism of tachycardia. EPS showed normal sinus node function, with no evidence of dual atrioventricular node (AVN) physiology, AVN reentrant tachycardia and AV reciprocating tachycardia despite aggressive EPS protocol. At this point, she tried diltiazem and digoxin. Tachycardia persisted. Per her request, we repeated EPS. An activation map was created prior to and after isoproterenol. It appeared the earliest site of activation was in the mid high crista terminalis region. With establishment of diagnosis of IST, sinus modification in the inferior crista was done. We ceased further ablation. Subsequent 3- week event monitor showed pulse rates up to 128 bpm. With initiation of ivabradine, palpitations ceased and her quality of life improved.
IST is a diagnosis of exclusion and occurs mostly in young women with normal cardiac structure and function. Ivabradine is a direct antagonist of hyperpolarization-activated cyclic nucleotide-gated ion channels (HCN 1 to 4) which carry the pacemaker current and hence determine function of sinoatrial node.
Ivabradine has an outstanding effect on IST, and thus should be considered as a first line option in IST management.
Poster Hall, Hall A/B
Monday, March 12, 2018, 9:45 a.m.-10:30 a.m.
Session Title: FIT Clinical Decision Making: Arrhythmia and Electrophysiology
Abstract Category: Arrhythmias and Clinical EP
Presentation Number: 1282-193
- 2018 American College of Cardiology Foundation