Hypothermia and Its Effect on the ECG

Introduction

Hypothermia is a medical condition where the body's core temperature drops below 35°C (95°F). This can have significant effects on the cardiovascular system, particularly on the electrocardiogram (ECG). Understanding these changes can be crucial for diagnosing and managing hypothermia in an emergency setting.

ECG Changes in Hypothermia

Several hallmark ECG findings are associated with hypothermia:

1. Osborn Waves (J Waves)

  • These are upward deflections at the junction of the QRS complex and the ST segment.
  • More pronounced in leads V2–V5.
  • Their presence is strongly associated with hypothermia but can also be seen in other conditions.

2. Bradycardia (Slow Heart Rate)

  • Hypothermia reduces the metabolic rate, leading to a slower heart rate.
  • Sinus bradycardia is common, and in severe cases, junctional or ventricular rhythms may appear.

3. Prolongation of Intervals

  • PR Interval: May be prolonged due to delayed atrioventricular conduction.
  • QT Interval: Can be prolonged, increasing the risk of arrhythmias.
  • QRS Complex: Can become wider with severe hypothermia.

4. Atrial and Ventricular Arrhythmias

  • Atrial Fibrillation: A common arrhythmia in severe hypothermia.
  • Ventricular Arrhythmias: Including ventricular fibrillation (VF), which can be fatal.

Clinical Implications

  • Diagnosis: ECG findings, along with core body temperature measurement, help confirm hypothermia.
  • Treatment:
    • Rewarming strategies (passive, active external, or internal warming).
    • Correction of electrolyte imbalances.
    • Avoiding unnecessary rough handling, as it may precipitate arrhythmias like VF.

Conclusion

Recognizing ECG changes in hypothermia is crucial for timely intervention. The presence of Osborn waves, bradycardia, and prolonged intervals should raise suspicion of hypothermia, especially in emergency settings.

Source recommendations

1. American Heart Association Guidelines on Hypothermia

  1. https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.105.166566
  2. https://www.heart.org/-/media/Files/Affiliates/FDA/Shock-Symposium-Speakers-and-Presentations/Shock-Symposium-Presentation_Targeted-Temperature.pdf?sc_lang=en
  3. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001164
  4. https://www.heart.org/en/health-topics/consumer-healthcare/what-is-cardiovascular-disease/cold-weather-and-cardiovascular-disease
  5. https://cpr.heart.org/-/media/cpr-files/cpr-guidelines-files/highlights/hghlghts_2020_ecc_guidelines_english.pdf

2. European Resuscitation Council Guidelines on Accidental Hypothermia

  1. https://www.resuscitationjournal.com/article/S0300-9572(21)00064-2/fulltext
  2. https://cprguidelines.eu/assets/guidelines/European-Resuscitation-Council-Guidelines-2021-Ca.pdf
  3. https://pubmed.ncbi.nlm.nih.gov/20956045/
  4. https://www.sciencedirect.com/science/article/abs/pii/S0300957221000642
  5. https://pmc.ncbi.nlm.nih.gov/articles/PMC5623293/

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