A defibrillator (20) employs a ECG monitor (23), a shock source (24) and a controller (25). In operation, the controller synchronizes a ECG analysis window (EAW) to a shock activation of the defibrillator, and analyzes a ECG waveform (30) of a heart (11) of a patient (10) as monitored by the ECG monitor within the ECG analysis window for detecting the patient experiencing an organized heartbeat condition or an unorganized heartbeat condition. The controller further controls a delivery by the shock source of a synchronized defibrillation shock to the heart of the patient in response to a detection within the ECG analysis window by the controller of the patient experiencing the organized heartbeat condition, or controls a delivery by the shock source of an unsynchronized defibrillation shock to the heart of the patient in response to a detection by the controller within the ECG analysis window of the patient experiencing one of the unorganized heartbeat condition or an undetected organized heartbeat condition.
