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Inappropriate Sinus Tachycardia — EECC MCQ

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ModerateArrhythmia & ElectrophysiologyInappropriate Sinus TachycardiaEECC

A 42-year-old woman presents with recurrent palpitations and a resting heart rate of 115 bpm. ECG shows sinus tachycardia with normal P-wave morphology and axis. She has no structural heart disease, no anaemia, no thyrotoxicosis, and no anxiety disorder. Her heart rate remains elevated despite beta-blocker therapy. What is the most likely diagnosis?

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Correct answer: C — Inappropriate sinus tachycardia (IST)

Inappropriate sinus tachycardia (IST) is defined as a resting sinus rate >100 bpm (or mean 24-hour rate >90 bpm) with normal P-wave morphology and axis, in the absence of physiological causes (anaemia, hyperthyroidism, pain, fever, anxiety, deconditioning, medications). It predominantly affects young women. The mechanism involves enhanced automaticity of the sinus node and/or autonomic dysregulation. IST is distinct from POTS (which requires a HR increase of ≥30 bpm on standing, not persistent resting tachycardia). Treatment includes ivabradine (Class IIa), which selectively reduces sinus rate. Beta-blockers may be partially effective. Sinus node ablation or modification is reserved for highly symptomatic refractory cases (last resort due to risk of sinus node dysfunction).

Reference: ESC (2019): Guidelines on SVT Management