stella,
You need some compromise between controlling the a-fib and that low blood pressure. If the a-fib is extremely rare for you, then maybe you can do without the atenolol....NOBODY should medicate down to 90/48.
If it's a FREQUENT thing, then perhaps ANOTHER of the beta-blockers more specific for a-fib is a better choice (like sotalol perhaps.)
Probably people with normal blood pressure should think about avoiding beta-blockers entirely.
For the gall bladder, I STRONGLY recommend you try a gall bladder flush before considering surgery. Look in the LIVER forum in Healthboards for some recommendations. There are also references to liver/gall bladder flushes all over the internet. Surgery should be a last resort. Entirely TOO MANY gall bladders are removed unnecessarily.