Palpitations on and off for three weeks, now persistent for two hours with mild breathlessness

2026-09-13

The case

55-year-old woman. Palpitations on and off for three weeks, now persistent for two hours with mild breathlessness

Non-smoker, no cardiac history. Takes no regular medication. She has lost three kilograms over six weeks without trying and reports feeling hot and restless. No syncope, no chest pain.

On arrival

HR: 72
SpO₂ (%): 98
Respiratory rate: 18
Temperature (°C): 36.8
Systolic BP (mmHg): 128
Diastolic BP (mmHg): 78

Stage 1 of 2

She looks well. There is a fine tremor of the outstretched hands but no goitre. Heart sounds are normal apart from the irregular rate. No murmur, no signs of heart failure. This twelve-lead is recorded in the department.

The tracing for the quiz “Palpitations on and off for three weeks, now persistent for two hours with mild breathlessness”. — Twelve-lead on arrival, 25 mm/s, 10 mm/mV. Open this tracing in the studio

What is the atrial rhythm?

AMultifocal atrial tachycardia Your answer
BEctopic atrial tachycardia with variable AV conduction Correct answer Your answer
CAtrial flutter with variable block Your answer
DSinus tachycardia with dropped beats Your answer

The P waves are regular at about 145 per minute with a non-sinus axis, and the ventricular rate is approximately half that, indicating 2:1 AV conduction with occasional variation. This is ectopic atrial tachycardia with variable block, not sinus tachycardia, because the P-wave morphology and rate are inconsistent with a sinus origin. Atrial flutter typically runs at 300 per minute with a sawtooth baseline, and multifocal atrial tachycardia requires at least three distinct P-wave morphologies with an irregular atrial rate.

Stage 2 of 2

TSH comes back suppressed at 0.02 mU/L with a free T4 of 38 pmol/L. Potassium 4.1, magnesium 0.92, troponin T below the reporting threshold. She is haemodynamically stable and comfortable.

Bloods

TSH (m U/L): 0.02
Free T4 (pmol/L): 38
Troponin T (ng/L): <5
Magnesium (mmol/L): 0.92
Potassium (mmol/L): 4.1

Notes

Overt hyperthyroidism confirmed.

What is the most appropriate next step?

AUrgent referral for catheter ablation Your answer
BSynchronised DC cardioversion Your answer
CRate control with a beta-blocker and treat the thyrotoxicosis Correct answer Your answer
DIV flecainide to restore sinus rhythm Your answer

Thyrotoxicosis is the driver of this arrhythmia, and treatment should address both the rate and the underlying cause. A beta-blocker controls the ventricular rate and relieves the adrenergic symptoms while the thyroid disease is treated. DC cardioversion in a stable patient with an ongoing metabolic trigger is unlikely to hold, and flecainide is contraindicated without excluding structural heart disease and would not address the cause. Catheter ablation may have a role later if the tachycardia persists after the thyroid is controlled, but is not the acute step.

Diagnosis

Ectopic atrial tachycardia with variable AV conduction, driven by thyrotoxicosis

P wave morphology is often overlooked. Here it is clear that a sinus origin is highly unlikely. Closely scrutinizing lead III, there is regular atrial activity at 145/min with 2:1 AV conduction. Only in one beat there is brief 1:1 conduction.

References

Ross DS, Burch HB, Cooper DS, et al. 2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis. Thyroid. 2016;26(10):1343-1421.
Brugada J, Katritsis DG, Arbelo E, et al. 2019 ESC Guidelines for the management of patients with supraventricular tachycardia. Eur Heart J. 2020;41(5):655-720.

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This tracing was generated, not recorded. It opens in the studio with every dial live.

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