CHF, HBP, A-Fib & Altitude

My husband is a retired 53 year old non smoker, non over weight 6'1 with afib history for 25 years, 16 months ago he also added to his list CHF & HBP. After spending 4 days in the hosptial,Diagnosed with an EF of 30% & CHF & a leaky Mitrial valve, he was released and went back later for a cardioversion which worked for about a year.
About 7 months ago we moved to a higher elevation near Lake Arrowhead, Ca elevation around 6500 ft.
Shortly after our move he began to feel worse and it wasn't long maybe a month & his BP shot up and he was back in afib, that has been going on since April. His BP is an average 165/105 pulse varies from 90-116, he NOW, he has trouble breathing, cannot sleep, he wakes up gasping for air, he is fatigued all the time. When he leaves this mountain he feels somewhat better.
Since he retired we no longer have health insurance, he at this point is only taking 1- 20mg Lisinopril per day, all the other meds did nothing to help him, and obviosly the lisinopril doesn't "seem" to be doing much either.
Could the ALTITUDE be aggravating his condition? I would rather move if it would help him live a better life.
Thanks,,,,,,Jennifer