QuestionSBA
QuestionChoice
Capture beats occur when the sinoatrial node "captures" current from the ventricles during atrioventricular dissociation. This produces a normal QRS complex during ventricular tachycardia. They can help differentiate between VT and supraventricular tachycardia (SVT) with aberrancy rhythms as they are more likely to occur in VT
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Capture beats
QuestionChoice
Pathological Q waves usually indicate ongoing or historic myocardial infarction. Q waves are considered pathological if they are wider or deeper than normal
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Pathological Q waves
QuestionChoice
Brugada syndrome is due to an abnormality in a cardiac sodium channel which can lead to sudden death. Brugada sign is potentially diagnostic but does not necessarily lead to Brugada syndrome. There is ST elevation in more than one lead, followed by a negative T wave
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Brugada sign
QuestionChoice
These occur when sinus and ventricular rhythms coincide. They can help differentiate between Ventricular Tachycardia (VT) and Supraventricular Tachycardia (SVT) with aberrancy rhythms as they are more likely to occur in VT
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Fusion beats
QuestionChoice
This patient has presented with signs and symptoms of hypothermia. J waves can be seen in hypothermic patients, often at a temperature of less than 30 degrees. The height of the J wave is thought to be approximate to the degree of hypothermia. They are positive deflections between the QRS and the ST segment
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J waves
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thought it was RBBB :(

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# Summary

Hypothermia refers to an abnormally low body temperature (usually defined as under 35°C). It can occur due to exposure to cold surroundings or because of another illness or event such as infection or trauma. Symptoms and signs include shivering, reduced level of consciousness, tachycardia and tachypnoea and arrhythmias. Investigations should include an ECG (with J waves being a key finding), blood tests and a chest X-ray looking for complications of aspiration pneumonia and pulmonary oedema. Management involves rewarming via a number of strategies, monitoring for and treating both causative factors and complications, and fluid resuscitation. Cardiac arrest may occur in severe hypothermia and in this case resuscitation should not be stopped until the patient has been rewarmed. 

# Definition

Hypothermia refers to a core body temperature below 35°C - it is a pathological state which has significant adverse effects on many body systems and can lead to death.

# Classification

Hypothermia may be classified as **primary** or **secondary**:

- **Primary hypothermia** is environmental, occurring for example after immersion in cold water or prolonged exposure to cold weather conditions
- **Secondary hypothermia** occurs secondary to an insult or illness such as infection, alcohol excess, hypothyroidism or major trauma

It can also be classified by core body temperature as follows:

- Mild - 32 to 35°C
- Moderate - 28 to 32°C
- Severe - 20 to 28°C
- Profound - < 20°C

# Signs and Symptoms 

Symptoms include:

- Shivering
- Hunger 
- Dizziness
- Chills
- Slurred speech
- Paradoxical undressing

Signs include:

- Tachycardia initially; bradycardias may occur if severe with arrhythmias
- Tachypnoea; respiratory depression followed by apnoeas if severe
- Cool peripheries secondary to vasoconstriction
- Hypotension
- Ataxia
- Reduced level of consciousness
- Pupils may be fixed and dilated if severe

# Investigations

**Bedside tests:**

- **Urine toxicology screen** if drug intoxication is suspected (e.g. patient found unconscious outside 
- **Arterial blood gas** may show an initial respiratory alkalosis, followed by respiratory acidosis as hypothermia worsens
- **ECG** may show:
    - Prolonged PR, QRS and QT intervals
    - Osborn (or J) waves - positive deflections where the QRS complex joins the ST segment
    - Bradyarrhythmias e.g. sinus bradycardia, atrial fibrillation with a slow ventricular response, slow junctional rhythms and AV block
 - Shivering artefact
 - Ventricular ectopics
 - Cardiac arrest (ventricular tachycardia, ventricular fibrillation or asystole)
 

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**Blood tests:**

- **FBC** and **CRP** for inflammatory markers
- **U&Es** looking for renal complications of hypothermia and electrolyte derangement
- **Coagulation screen** as hypothermia can cause a coagulopathy
- **Creatinine kinase** as hypothermia can cause muscle damage and rhabdomyolysis
- **Amylase** as pancreatitis can result from hypothermia
- **Bone profile** and **magnesium** so that any electrolyte disturbance can be corrected
- **Blood cultures** if sepsis is suspected as a driver of hypothermia

**Imaging:**

- **Chest X-ray** as aspiration pneumonia and pulmonary oedema may complicate hypothermia
- **CT head** may be indicated e.g. elderly patients who become hypothermic after a fall and long lie

# Management

**Conservative management involves:**

- Take an A to E approach; patients may require escalation to intensive care for intubation and ventilation e.g. if reduced levels of consciousness
- Rewarming, which may be:
    - Passive rewarming - e.g. removing cold or wet clothes, cover with a blanket and cover head to reduce heat loss (useful in mild hypothermia)
    - Active external rewarming - usually using forced air systems such as a Bair Hugger
    - Active core rewarming - e.g. warmed intravenous fluids and warmed humidified oxygen
- Core temperature monitoring may be required in more severe cases, with either a rectal or (if intubated) an oesophageal probe
- Cardiac monitoring


**Medical management involves:**

- Fluid resuscitation as patients are usually dehydrated - careful fluid balance monitoring is needed due to the risk of fluid overload
- Monitoring for and treating complications of hypothermia (see below) 
- Antiarrhythmic medication is rarely required for cardiac complications, with rewarming being the mainstay of treatment
- Consider thiamine for malnourished or critically unwell patients, or those with suspected alcohol excess
- Investigating for and treating causes of hypothermia (e.g. infection)
- In the case of a cardiac arrest secondary to severe hypothermia, Resuscitation Council guidelines should be followed (e.g. defibrillation for VF arrests) and resuscitation should be continued at least until the patient has been rewarmed

**Invasive management:**

- In severely hypothermic patients with life-threatening complications who are not responding to other treatments, options include cavity lavage using warm fluids and extracorporeal blood rewarming (e.g. cardiopulmonary bypass)

# Complications

- Frostbite, which in severe cases may warrant amputation of non-viable tissues
- Arrhythmias
- Hypotension (especially on rewarming due to vasodilation)
- Aspiration pneumonia
- Pulmonary oedema
- Pancreatitis
- Acute tubular necrosis
- Cardiac arrest and death

# References

[RCEM Learning - Hypothermia](https://www.rcemlearning.co.uk/reference/hypothermia/)
 
[RCEM Learning - Severe Hypothermia](https://www.rcemlearning.co.uk/reference/severe-hypothermia/)

[Patient UK - Hypothermia](https://patient.info/doctor/hypothermia-pro)
 
[Life In The Fast Lane: ECG Changes in Hypothermia](https://litfl.com/hypothermia-ecg-library/)
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J waves seen on the ECG of someone with hypothermia.
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Hypothermia
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Emergency Medicine
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J waves on ECG are indicative of hypothermia, typically appearing when body temperature falls below 30 degrees Celsius.
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Emergency Medicine
An 86-year-old woman attends A&E after her carers found her with slurred speech and pale skin. This is her ECG:

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Atrial fibrillation is noted. What other abnormality can be seen on the ECG?
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