GABARITO: ALTERNATIVA B

Explanation:

Hypothermia is defined as a core body temperature <35°C (95°F). As body temperature falls, enzymatic and cellular activity slows. The sinoatrial (SA) node, responsible for initiating heartbeats, becomes progressively less active due to reduced phase 4 depolarization — the slow Na⁺/Ca²⁺ influx that generates spontaneous action potentials in pacemaker cells.

This results in bradycardia, which is not necessarily pathologic in hypothermia but is a direct physiologic effect of cold on cardiac pacemaker cells. Other ECG findings may include J (Osborn) waves, atrial fibrillation, and prolonged intervals.

Educational Objective:

In hypothermia, bradycardia results from direct suppression of spontaneous pacemaker activity in the sinoatrial node, specifically via reduced phase 4 depolarization. This is a hallmark of moderate to severe hypothermia and may be accompanied by J (Osborn) waves on ECG.

Answer Choice Explanations: