In ECG we have a lot of concern with interval lengths
Equipment commonly samples at 100Hz (mobile devices) to 1000Hz (high resolution)
At 100Hz, due to the Nyquist rate, you miss any high-frequency features with a period of less than 0.02s (i.e., 20ms) (Period = 1 / frequency)
Moreover, at 100Hz, you can be up to 10ms late in seeing a rise or fall, and thus up to 20ms inaccurate in estimate of an interval