The most common ECG changes seen with thyrotoxicosis are:
- Sinus tachycardia
- Atrial fibrillation with rapid ventricular response
- High left-ventricular voltage — i.e “voltage criteria” for LVH without evidence of LV strain.
Other ECG abnormalities include:
- Supraventricular arrhythmias (premature atrial beats, paroxysmal supraventricular tachycardia, multifocal atrial tachycardia, atrial flutter)
- Non-specific ST and T wave changes
- Ventricular extrasystoles
Around 50% of patients with thyrotoxicosis will have a resting heart rate > 100 bpm. Atrial fibrillation is seen in up to 20% of patients. Severe thyrotoxicosis (thyroid storm) may present with atrial tachycardias at rates > 200 bpm.
- The ECG changes in thyrotoxicosis are principally related to increased activity of the sympathetic nervous system and the stimulatory effects of thyroid hormone on the myocardium.
- Atrial tissue is very sensitive to the effects of thyroid hormone, hence the preponderance of atrial tachydysrhythmias.
- Patients with unexplained sinus tachycardia or atrial fibrillation should have their TSH and T4 checked to look for evidence of thyrotoxicosis.
- Thyrotoxic atrial tachydysrhythmias are treated with intravenous beta-blockers (e.g. titrated IV boluses of propranolol or an esmolol infusion).
Example 1 – Sinus tachycardia
Example 2 – Rapid atrial fibrillation with high left ventricular voltage
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