Disclosed is apparatus including a power source, an ECG front end, a processor, and a computer-readable medium. The ECG front end is configured to receive a signal corresponding to a cardiac waveform, and the computer-readable medium is encoded with instructions which, when executed by the processor, cause the apparatus to (a) determine a first temporal window during which a first instance of a first portion of a cardiac cycle is expected to appear in the cardiac waveform (b) at a start of the first temporal window, apply a first amount of power from the power source to the ECG front end, and (c) at an end of the first temporal window, at least partially reduce an amount of power applied from the power source to the ECG front end.
