One quick thing smitty....the reason the cardiologist put you on the levsin (hyoscyamine)is because it is an anti-cholinergic agent. You're right about what you read in the literature, but you have to remember that the same drug can be used for different purposes in the body because similar chemical processes can be occurring in different conditions.
The cardiologist, it looks like, has determined that your cause for syncope (fainting) is due to an exaggerated vasovagal response. This exaggerated response is part of the "parasympathetic nervous system", and this branch of the nervous system works through acetylcholine. The Levsin, as I said is an anticholinergic...i.e. it blocks acetylcholine and that is why you have been put on it.
Does that make sense?