Hyperthyroidism

ECG Abnormalities in Hyperthyroidism

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.

Mechanism

• 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.

Useful Tips

• 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).

ECG Examples

Example 1

Example 2

Related Topics

• Hypothyroidism
• Left ventricular hypertrophy

References

• Slovis C, Jenkins R. ABC of clinical electrocardiography: Conditions not primarily affecting the heart. BMJ. 2002 Jun 1;324(7349):1320-3

Advanced Reading

Online

• Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
• Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
• Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.

Textbooks

• Zimmerman FH. ECG Core Curriculum. 2023
• Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Hampton J, Adlam D. The ECG Made Practical 7e, 2019
• Kühn P, Lang C, Wiesbauer F. ECG Mastery: The Simplest Way to Learn the ECG. 2015
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest