I hike with a guy who has "been there, done that". So all I have are second hand observations. He maxed at 280 on a Holter, so it was the real deal.
It took two procedures, no pacemaker, and now, for the past year, he is strong and hearty. Hiking, skiing, riding, treking. All at altitude. I will also add that he has a incredibly positive outlook on life. Having watched others with serious issues, I have to say that PMA goes a long way toward a good outcome.
Best of luck.