Hypothyroidism

ECG abnormalities associated with Hypothyroidism

Severe hypothyroidism (myxoedema) causes a triad of:

Other ECG changes that may be seen include:


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 1a
ECG hypothyroid myxoedema coma 1

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 1b
ECG hypothyroid myxoedema coma 2

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 2
ECG low QRS voltage

Myxoedema

  • Example of low QRS voltage due to myxoedema.


Advanced Reading

Online

Textbooks


LITFL Further Reading

ECG LIBRARY

Electrocardiogram

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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