Bradycardia

I have had bradycardia for a while now. I never realized that it could be a problem. My doctor wants to put me on a beta blocker because I had a prolonged QT on my last ECG but is scared it will cause too much problems with my bradycardia and low blood pressure. My blood pressure is usually around 85/50 and sometimes even lower and my resting heart rate is 50 or lower. I do have alot of dizziness and near blackouts. The doctors are not sure if it is from the blood pressure or from the prolonged QT. Other members in my family have borderline qts so we are not sure why I have it for sure yet. What could be causing my bradycardia and is it dangerous to take beta blockers or is he being too cautious. I am going to a heart specialist next month and am just a bit anxious about it.
Thanks

[heart_of_mine]

I guess I should have mentioned that I am a 40 year old woman. Not over weight but not overly active either.
Thanks

[SwanSong]

Have you been tested for thyroid disease? Hypothyroidism can cause bradycardia, 10 or more bpm under 60, and low blood pressure.

Does anyone in your family have a history of thyroid disease?

I had bradycardia and low blood pressure for years before being diagnosed with hypothyroidism and Hashi's. My resting heart rate was 42 and sometimes lower.