A patient in the dental chair goes into cardiac arrest with a shockable rhythm. What single intervention most improves the chance of survival?

Correct answer: B. Early defibrillation with an AED, alongside high-quality chest compressions

• A. Oxygen delivered by mask is useless without circulation; there is no cardiac output to carry it.
• B. CORRECT. For ventricular fibrillation and pulseless VT — the rhythms responsible for most witnessed sudden cardiac arrests — DEFIBRILLATION is the only intervention that terminates the arrhythmia. Survival falls by roughly 7–10% for every minute defibrillation is delayed, which is why an AED is mandatory equipment in a dental office and why the chain of survival places early CPR and early defibrillation ahead of everything else.
• C. Ventilation alone does not address the underlying arrhythmia. Current guidance actually prioritises compressions over ventilation in the initial response.
• D. Activating EMS is an essential and immediate step, but calling for help does not itself restart the heart. In a witnessed arrest with an AED at hand, activate EMS AND defibrillate — the AED is what changes the outcome.

Note: ⚠️ The source keyed 'activate EMS.' Both actions happen essentially simultaneously, but the question asks what is most EFFECTIVE — and for a shockable rhythm that is defibrillation. Good item for group discussion.