Inherited and environmental
Hypothermia and the Osborn wave
A positive deflection at the J point, with bradycardia, tremor artefact and long intervals.
42 bpmSinus bradycardia
What you see
- Osborn (J) waves — a positive deflection at the QRS–ST junction, size increasing as temperature falls.
- Bradycardia, often with slow atrial fibrillation.
- Prolongation of every interval: PR, QRS and QT.
- Muscle tremor artefact from shivering, which disappears as the patient cools further.
Why it looks like that
Cooling delays epicardial repolarisation more than endocardial, producing a transmural voltage gradient at the end of depolarisation — the same mechanism that generates the Brugada pattern. Conduction slows throughout, lengthening all intervals.
What to do
- Rewarm, and handle the patient gently — a cold myocardium fibrillates with remarkably little provocation.
- In cardiac arrest, withhold drugs below 30 °C and limit defibrillation to three attempts until rewarmed.
- Continue resuscitation until the core temperature is near normal: 'not dead until warm and dead'.
- Consider extracorporeal rewarming for severe hypothermia with cardiac instability.
The trap
Osborn waves are not specific to hypothermia — hypercalcaemia, subarachnoid haemorrhage, and normal variants all produce them. And the flip side matters more: a hypothermic patient with no output may still be salvageable, so the arrest algorithm changes rather than stops.
J waverewarmingwarm and deadbradycardia