ECG Abnormalities associated with Hypothyroidism
Severe hypothyroidism (myxoedema) causes a triad of:
Other ECG changes that may be seen include:
ECG changes may be secondary to:
- Myxoedematous deposits of gelatinous connective tissue within the myocardium.
- Decreased activity of the sympathetic nervous system
- Effects on the myocardium of reduced levels of thyroxine (i.e. reduced inotropy/chronotropy)
- This is the admission ECG of a 79-year old man who was referred to ICU with coma, hypothermia, severe bradycardia and hypotension refractory to inotropes.
- TSH was markedly elevated with an undetectable T4.
- The ECG shows marked bradycardia (30 bpm) with low QRS voltages (esp. in the limb leads) and widespread T-wave inversions, typical of severe myxoedema.
Myxoedema coma (after treatment)
- An ECG of the same patient shortly after initiation of thyroid replacement with intravenous T3 and T4.
- The heart rate has normalised and the T-wave inversion has corrected.
- Low voltage in the limb leads persists and is likely due to myxoedematous infiltration of the myocardium.
- Example of low QRS voltage due to myxoedema.
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
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
- Wagner GS. Marriott’s Practical Electrocardiography 12e
- Chan TC. ECG in Emergency Medicine and Acute Care
- Rawshani A. Clinical ECG Interpretation
- Mattu A. ECG’s for the Emergency Physician
- Hampton JR. The ECG In Practice, 6e