**Core Concept**
Hypothermia is a critical condition that can occur in individuals exposed to cold environments, such as the Siachen glacier. It leads to a range of physiological changes, including alterations in cardiovascular function, neurological responses, and electrocardiographic patterns.

**Why the Correct Answer is Right**
The ECG changes in hypothermia are well-documented. Osborn waves, also known as J waves, are a characteristic feature of hypothermia, representing an unusual deflection at the junction between the QRS complex and the ST segment. ST segment elevation and bradycardia are also common in hypothermia due to the cold-induced depression of myocardial contractility and conduction. However, atrial bigeminy, which refers to an irregular heartbeat characterized by a premature atrial contraction (PAC) followed by a normal sinus beat, is not typically associated with hypothermia.

**Why Each Wrong Option is Incorrect**
**Option A:** Bradycardia, or a slow heart rate, is indeed a common finding in hypothermia, as cold stress can lead to a decrease in sympathetic nervous system activity, resulting in a decrease in heart rate.
**Option B:** Osborn waves, or J waves, are a hallmark of hypothermia and are caused by the cold-induced disruption of normal myocardial electrical activity.
**Option C:** ST segment elevation can occur in hypothermia, likely due to the cold-induced ischemia of the myocardium.

**Clinical Pearl / High-Yield Fact**
In hypothermia, the ECG changes can be mistaken for those seen in myocardial infarction or other cardiac conditions. Therefore, it is essential to consider the patient's clinical context and exposure history when interpreting ECG findings.

**✓ Correct Answer: D. Atrial bigeminy**