Final answer:
Rapid rewarming of a hypothermic patient can cause ventricular fibrillation, which is a serious, often fatal, medical condition due to irregular heartbeat and lack of blood circulation.
Step-by-step explanation:
Rewarming a hypothermic patient too rapidly can lead to serious complications, including ventricular fibrillation. When hypothermic, the body's metabolism slows down and the rate and strength of heart contractions decrease. Rapid rewarming can disrupt the heart's electrical patterns, causing it to beat irregularly and ineffectively, a condition known as ventricular fibrillation. This condition is often fatal due to a lack of blood circulation. Controlled hypothermia, on the other hand, is used in medical settings to reduce damage after a cardiac arrest by slowing the patient's metabolic rate and reducing the heart’s workload.