Artificial heart with no rythm...

So could a good sign of cyber-organ replacement be a lack of a pulse? And what happens when someone with one of these passes out or goes into a coma?

it also would make CPR much more difficult in case of bionic failure.

And that's why Dick Cheney no has no heartbeat.

I think that has a lot less to do with technology than it does to him being in league with the Chaos Gods...

Explains why he shot the lawyer in the face.

Well The Ventracore Australian artificial heart didn't have a pulse so it's not surprising that later devices operate similarly.

Given that the most reliable pumps and compressors are continuous feed systems like centrifugal pumps and screw compressors and not displacement pumps and reciprocal compressors, it's no shock that artificial hearts would move in the same direction.

It's a no-brainer from a Fluid Mechanics perspective.

These are the same kinds of pumps used in cardiopulmonary bypass and ECMO. Wonder how they plan to prevent SIRS...

And to answer the OPs question: if a person with such a pump fell into a comma and someone thought they were dead, there isn't a lot anybody could do that would hurt the person, except may chest compressions cracking a few ribs. Electrical cadioversion or ACLS drugs wouldn't really do anything (might be unpleasant but the person isnt awake anyway). An emergent thoracotomy would suck, but the trauma surgeon would very quickly realize what was going on.