Puppy Pacemaker?

Over the past few weeks, Oliver has been occasionally panting very hard at what seems to be completely random times. Last week he had his yearly check-up and the vet discovered both an arrhythmia and a murmur in his heart. A dog's heart is supposed to beat at about 80 beats per second, and Oliver's was running on about 50. Thus the panting. I have also noticed that Oliver is getting bonier. His spine sticks out quite a bit as does his hips. Poor thing. His vision continued to go but he is certainly functional. It might take him a moment to find you in a room, but once he does, there's no running into anything to get to you. His hearing is also going.

Yesterday Oliver went back to the vet for an echocardiagram. They discovered that yes, his heart has some damage to it and his internal pacemaker is not working right. Further tests and possibly a visit to Angell Memorial Hospital will determine what's next.  Hopefully he will only need medication, because the alternative is to leave him be, which will result in his heart continuing to deteriorate and he will start passing out (which to me sounds like he will simply start having heart attacks until one of them does him in).
The other option, should it come to that, is to have a pacemaker installed. I did some research; a new pacemaker? Very expensive. A used one? Far less but still expensive.

How far to we go for our animals?  Will it buy him a year? Two years?  We call him "puppy" and most of the time he acts like one, but he is getting up there in years. Could the pacemaker be put in only for him to go completely blind and deaf within six months, and thus giving him a healthier heart situation but him having less quality of life because he's running in to things?

Right now, it's hard to imagine putting him down. He has a great zest for life. Granted, he is sleeping more these days than usual, but again, that's the heart thing. In nature, he would have been eaten by now, I get it. But, we're not in nature. We're in my house, where he has a bed that looks like a couch and a doggy playmate who thinks he's the coolest old man she knows (Dad said Bootsie was thrilled to see him when he returned from his day at the vet), and more people who want to pet him and hold him than there are hours in the day.

I know he is simply a dog. I know that. I am not unaware of the absurd idea of putting a pacemaker in my dog and I certainly hope it doesn't come to that. My Mom says that all our past dogs have told her when they were ready to go. They were always big animals and got to a point where there joints wouldn't hold them any more. And they would tell us "I'm done".  They were not small like Oliver and with heart conditions. So, how do you know?