Final answer:
The most crucial factor in cardiac arrest survival is the time to defibrillation, as it can stop life-threatening heart rhythms and allow the heart to beat effectively again.
Step-by-step explanation:
The single MOST important factor in determining survival from cardiac arrest is time to defibrillation. This is because when a person experiences cardiac arrest, their heart stops beating effectively, and defibrillation is the process of delivering a therapeutic dose of electrical energy to the affected heart with an automated external defibrillator (AED). This shock applied by the AED can stop the erratic, life-threatening rhythms of the heart and potentially allow it to resume its regular, effective heartbeat. Early defibrillation is critical because the chance of survival decreases significantly with each minute that passes without defibrillation, especially for cardiac arrhythmias like ventricular fibrillation. While CPR, including chest compressions and the availability of oxygen, plays a crucial role in maintaining blood circulation and providing oxygen to the brain, it is ultimately the restoration of the heart's own rhythm through defibrillation that most determines the patient's chances of survival.