Inappropriate Sinus Tachycardia

Inappropriate sinus tachycardia is a persistent resting sinus rate above 100 beats per minute (mean 24-hour rate above 90 beats per minute) that is out of proportion to physiological, emotional or pathological stress and that is not explained by another cause. It is a diagnosis of exclusion, most often seen in young women and healthcare workers, and may be due to enhanced sinus node automaticity or autonomic dysregulation.

• Resting heart rate above 100 beats per minute, with an excessive rise on minimal exertion; sinus rate may fall to normal during sleep.
• It has a benign prognosis and does not cause mortality, but symptoms can be disabling.
• Overlaps with postural orthostatic tachycardia syndrome; in inappropriate sinus tachycardia the rate is high both supine and on standing, with no or little blood pressure change.

• Persistent palpitations, fatigue, light headedness, exercise intolerance, chest discomfort, dyspnoea, anxiety, near syncope.
• Symptoms present at rest and on trivial effort; may be disabling.
• Examination: resting regular tachycardia at 100 to 130 or more, normal blood pressure, no cause on examination.
• Red flags prompting alternative diagnosis: fever, weight loss, anaemia, goitre, tremor, hypotension, syncope, murmur, heart failure.

• 12-lead ECG: sinus rhythm with P wave axis and morphology identical to normal sinus rhythm, rate above 100.
• 24-hour Holter: mean heart rate above 90 beats per minute with resting rate above 100 while awake and a normal nocturnal fall.
• Exclude secondary causes with full blood count, ferritin, urea and electrolytes, glucose, thyroid function, C-reactive protein, pregnancy test, drug and caffeine review, and plasma or urinary metanephrines if suspicion.
• Echocardiography to exclude cardiomyopathy and structural disease.
• Active stand or tilt test to exclude postural orthostatic tachycardia syndrome.
• Electrophysiology study via specialist if sinus tachycardia cannot be distinguished from atrial tachycardia (P wave morphology or abrupt onset).
• Differentials: physiological tachycardia, atrial tachycardia, atrioventricular nodal re-entry tachycardia, thyrotoxicosis, anaemia, anxiety, withdrawal, postural orthostatic tachycardia syndrome, phaeochromocytoma, pulmonary embolism.

General

• Explain benign nature and chronic course. Stop caffeine, energy drinks, nicotine, decongestants, stimulants and alcohol.
• Regular graded aerobic exercise, adequate hydration, sleep regularisation and stress management; cognitive behavioural therapy for anxiety.

Pharmacological (symptomatic)

• Beta blocker first line: metoprolol 25 to 100 mg orally twice daily (or modified release 50 to 200 mg once daily) or bisoprolol 2.5 to 10 mg once daily, or propranolol 10 to 40 mg two to three times daily. Contraindications: asthma, severe bradycardia, heart block, decompensated heart failure.
• Ivabradine 5 mg orally twice daily, increased to 7.5 mg twice daily after 2 weeks if tolerated and heart rate above 60; most effective drug in this condition. Avoid in pregnancy, severe hepatic impairment, with strong CYP3A4 inhibitors (clarithromycin, ketoconazole), and in sick sinus syndrome. Monitor for visual phosphenes, bradycardia and atrial fibrillation.
• Ivabradine may be combined with a beta blocker by cardiology for resistant disease.
• Non-dihydropyridine calcium channel blockers (verapamil modified release 120 to 240 mg daily) if beta blockers are not tolerated and ejection fraction is normal.

Procedural (specialist; refractory disabling cases)

• Catheter modification of the sinus node has high relapse and complication rates and is not routinely advised.

Special groups

• Pregnancy: avoid ivabradine; beta blockers with specialist advice (metoprolol preferred).
• Young women of childbearing potential on ivabradine: effective contraception.
• Older adults: monitor for bradycardia and heart block on treatment.

Follow up and referral

• Review at 4 to 6 weeks, then 6 monthly; check heart rate, blood pressure and tolerance.
• Refer to cardiology for diagnostic confirmation, treatment failure, or disabling symptoms.