My husband was on lopressor, does this affect potassium, as he is also on klor-con, he has had 4 heart attack, one in 1988, one in 1992, and 2 in 2010, after which he had open heart surgery, 4 block arteries, and could only by pass 2 as the other 2 arteries were 100% block off. He was switched frome lopressor to Bystolic, which is better of the 2 and do either one affect potassium levels?