An Osborn wave on the electrocardiogram is most characteristic of which condition?

• A. Hypothermia
• B. Hyperkalemia
• C. Myocardial infarction
• D. Pericarditis

Answer: (A)

An Osborn wave, or J wave, is a distinct deflection that appears at the end of the QRS complex right at the junction with the ST segment. It is most characteristic of hypothermia because cold temperatures alter ventricular repolarization, enhancing a notch in the epicardial action potential via increased outward potassium current. As body temperature falls, the Osborn wave becomes more prominent and the risk of ventricular arrhythmias rises. Other conditions produce different ECG patterns—hyperkalemia gives tall, peaked T waves with QRS widening; myocardial infarction shows focal ST elevations and evolving Q waves; pericarditis shows diffuse ST elevations with PR depressions—making the Osborn wave a hallmark clue to hypothermia.