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Home | ECG Library | ECG Basics | Hypothyroidism

Hypothyroidism

by Edward Burns, Last updated April 4, 2017

ECG Abnormalities associated with Hypothyroidism

Severe hypothyroidism (myxoedema) causes a triad of:

  • Bradycardia
  • Low QRS voltage
  • Widespread T-wave inversions (usually without ST deviation)

Other ECG changes that may be seen include:

  • QT prolongation
  • First degree AV block
  • Interventricular conduction delay

Mechanism

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)

ECG Examples

Example 1

Myxoedema coma
Myxoedema coma

  • 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.

Example 2 –

Myxoedema coma (after treatment)
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 3

ECG myxoedema low voltage

Myxoedema

  • Another example of low QRS voltage due to myxoedema.

Related Topics

  • Hyperthyroidism
  • Low QRS voltage

Advanced Reading

  • Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
  • Hampton, JR. The ECG In Practice, 6e
  • Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric, 6e
  • Wagner, GS. Marriott’s Practical Electrocardiography 12e
  • Chan, TC. ECG in Emergency Medicine and Acute Care
  • Mattu, A. ECG’s for the Emergency Physician

LITFL Further Reading

  • ECG BASICS — Waves, Intervals, Segments and Clinical Interpretation
  • ECG A to Z by diagnosis –alphabetical diagnostic approach to the ECG
  • ECG CLINICAL CASES — ECG’s placed in clinical context with a challenging Q&A approach
  • 100 ECG Quiz — Self-assessment tool for examination practice
  • ECG Reference SITES and BOOKS — the best of the rest
  • LITFL ECG IMAGE Database — Searchable database of LITFL ECG’s
  • ECG and Cardiology Eponymous Syndromes — Cheats guide to eponymous emancipation
  • ECG Exam Template — a framework for answering ECG exam questions.

Last update: [last-modified]

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About Edward Burns

Ed Burns is an Emergency Physician working in Prehospital & Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education. Ed is the force behind the LITFL ECG library | + Edward Burns | @edjamesburns

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