In practice what you do is design it to crash easily and recover quickly. Computers are fast, hearts are slow. Your microcontroller can go "huh, that set of rea

In practice what you do is design it to crash easily and recover quickly. Computers are fast, hearts are slow. Your microcontroller can go "huh, that set of readings is bollocks, let's restart and try again" several times between beats. Even better, a pacemaker is not literally constantly driving a patient's heart, continuously. It's giving it a nudge every now and again if it's drifting out of whack. Think PLL rather than master clock ;-)