Which emergency situation requires immediate defibrillation?

Defibrillation is a critical intervention for restoring a normal heart rhythm in patients experiencing certain types of cardiac arrest. Ventricular fibrillation is characterized by chaotic electrical activity in the heart, which leads to ineffective pumping and lack of blood flow to vital organs. Immediate defibrillation is essential in this scenario because it can deliver a controlled electrical shock to the heart, allowing it to resume a functional rhythm. The sooner defibrillation is applied in cases of ventricular fibrillation, the better the chances of survival and recovery.

In contrast, asystole represents a complete absence of electrical activity in the heart, making defibrillation ineffective. Ventricular tachycardia may or may not require defibrillation depending on the stability of the patient; if it is not pulseless or causing impaired circulation, other interventions may be more appropriate. Bradycardia, a slower than normal heart rate, often requires medication or pacing rather than defibrillation. Thus, in the context of this emergency question, the correct answer highlights the critical need for immediate defibrillation in cases of ventricular fibrillation.