Your symptoms etc sound like my husband, he was diagnosed at 43 and led an active life on a small dose of atenolol, in 2017 managed a gorilla trekking trip in Rwanda at 8000 ft. Last March had a complete heart block needed a pacemaker/ defibrillator and went down hill over the next few months although was still hiking etc walking 4 miles most days but started having symptoms which took him to Mayo where he had a septal myectomy in October 4. He made an amazing recovery and is back to normal 😊
Best wishes to you for your surgery and recovery. Mayo is the best, also a little biased cos our daughter is a nurse at Mayo in Jacksonville.