What happens if a person can't die of a heart attack?
Mayo clinic defines heart attack as an obstruction of blood flow to the heart muscle, causing the body's natural blood pump to fail and/or die.

So a pacemaker won't save one from a heart failure once it happens, the device avoids them from happening (the real function is more complex, gugure kokkuri-san!).

Since a heart attack is a failure of the blood pump, it is safe to assume that a DN could make an artificial heart to fail as well.