One of my former staff, a cardiovascular surgeon, (yes he was that old) also invented the cardiac pacemaker. Only problem was he couldn't figure out how to implant it. The solution was to push the electrode down to the bottom of the ventricle and trigger the ventricle from the reverse direction. As he said (he's long deceased) the problem was that he "was only about 4" too short".Two fun facts, oilBabe got a pacemaker about a decade ago as she has AV node block.
Second, the first pacemaker recipient outlived the inventor of the pacemaker and the doctor who implanted it.
https://www.hmpgloballearningnetwork.com/site/eplab/articles/look-back-85-years-cardiac-pacing#:~:text=The surgery was successful and,more than one billion times.
Nowadays they implant an electrode at the SA node and another at the top of the ventricle. The pacemaker observes a beat from the SA node and watches for it to arrive at the top of the ventricle (meaning the beat has made it through the AV node block). If it doesn't arrive the pacemaker sends out an impulse which causes the ventricle to beat. It also checks to make sure the SA node is beating often enough. If it doesn't it just takes over. So you have a pacemaker that ensures the heart is paced just as the SA node prefers (responding to activity, excitement, etc) but takes over entirely if the SA node ever goes for a dump. The result is a pacemaker that only uses as much energy as is absolutely necessary so the battery will last for a very long time.
Ask me how I know.