Questions

1

What electrocardiographic abnormalities are seen in figure1?

2

What is the diagnosis ?

Answers

QUESTION 1

Junctional (J) waves, prolongation of the QT interval, bradycardia, atrial fibrillation, and shivering artefact.

QUESTION 2

Hypothermia.

Discussion

Junctional waves, hump-like deflections at the junction of the QRS complex and ST segment are seen best in the unipolar chest leads (V2-V6).1 These deflections (also known as Osborn waves) may appear in hypercalcaemia and in patients predisposed to early repolarisation.2 Possible mechanisms include altered myocardial repolarisation and depolarisation rates during cooling1 3 or altered epicardial action potential morphology resulting in a voltage gradient across the ventricular wall.2 The amplitude of J waves increases with the severity of hypothermia and they are consistently seen below 25°C. Their prognostic significance is uncertain.

Prolongation of the QT interval may persist beyond rewarming, as repolarisation recovers more slowly than depolarisation. Bradycardia is common below 33°C. Prior to reaching this temperature the patient is often tachycardic due to homeostatic mechanisms including shivering and sympathetic activation. At lower temperatures tremor may not be obvious but electrocardiographic shivering artefact is usual, as seen here. Other electrocardiographic abnormalities include QRS widening, ST segment depression, T wave abnormalities, atrioventricular block, and arrhythmias, of which atrial fibrillation is the commonest.3

These electrocardiographic abnormalities disappear with rewarming (figure 2). In this patient atrial fibrillation was longstanding and she was on no anti-arrhythmic medication. On rewarming her ventricular rate rose to 80–100 beats/min.

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Figure 2

Illustration of the J wave

Final diagnosis

Hypothermia.