A defibrillator or other patient monitoring device (20) employing an ECG monitor (23) and a controller (25). The ECG monitor (23) monitors an ECG waveform of a heart of a patient. The controller (25) segments the ECG waveform, and for each ECG waveform segment of a series of ECG waveform segments, generates an ECG shock advisory between a shock decision, a no-shock decision and an optional shock indecision. The controller (25) further monitors a consistency of the ECG shock advisories between consistent shock decisions, consistent no-shock decisions, and optional inconsistent shock decisions.