Hypothermia

Hypothermia commonly causes EKG changes that worsen as temperature decreases. Common findings include an increase in the intervals and decreased heart rate. As temperature decreases, patients become more prone to bradyarrhythmias, ventricular arrhythmias, and asystole. The bradyarrhythmias may include sinus bradycardia, atrial fibrillation with slow ventricular response (one of the few causes of this and the most common EKG manifestation of hypothermia), slow junctional rhythms, and high-degree AV block with escape rhythms. As temperature decreases to <30*C, the heart also becomes incredibly irritable; patients can be put into ventricular fibrillation simply by moving them (it is vital to very carefully move severely hypothermic patients because of the risk of putting them into ventricular arrhythmias). Furthermore, hypothermia can cause ST-T changes (even ST elevation). These all resolve with rewarming, though commonly do not respond to standard ACLS measures until the temperature is at least 30*C.

Osborn waves are a classic hypothermia finding on an EKG. Osborn waves are J waves (occur at the J point) and their size tends to correlate with the degree of hypothermia. In other words, as the patient becomes more hypothermia, the Osborn waves tend to increase in size. Subtle Osborn waves may be visible >30*C (ie 32*C), though they tend to become more apparent at <30*C. However, Osborn waves can occur from other conditions: hypercalcemia (most common other cause), SAH, Brugada syndrome, and severe ischemia. Although the J waves of early repolarization are not usually called Osborn waves, there is no sure way to differentiate these based on the waves themselves; however, Osborn waves of hypothermia tend to be larger.

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