Graphing $f$ from $f'$ (anti derivative) if $f'$ is an ECG curve

Question

I was interested in the anti derivative of an ECG curve. The idea was electromagnetic induction occurs when current changes, and that what ECG might be reading is the derivative, the rate of change, of electrical activity in the heart. The assumption (ECG is rate of change) might be wrong, but an antiderivative can still be drawn in that case, so if anyone wants to help me out with that regardless of if the "why" is sound, it is welcome. I thought I'd ask here since there might be many people who are good at anti-derivatives. This is actually a pretty interesting question, that has not been asked or explored that many times.

Attached image of a generic ECG curve

This was my own best attempt so far