I spoke with one of the Cards today. He "says" there isn't a lot of literature r/t obtaining chemically-induced bradycardia sufficient for the CTA. However, this is what he told me he does:
"I give a 5mg Metoprolol bolus (5mg and then chase it with NS) every 3-5 minutes, depending on the pt's response. By the time I give the 5mg, chase it, break open another 5mg vial and load it into the syringe and get a BP and HR, about 3 min have passed.
Ideally, HR in the 50's gives great images. I'm happy, though, if the HR ends up in the low 60's.
If the BP starts to drop, or hovers in the high 90's with the Metoprolol, I stop giving it and proceed with the scan at whatever the heart rate is at that time.
If I give 20mg and there is NO change whatsoever in the HR (say, baseline is 115 and after 20mg it's in the 90's), I don't give any more Metoprolol and we just scan the patient. (Cleveland Clinic's limit is 600 mg of Metoprolol, but I don't go that high)."
He doses out-patients and in-patients the same. He didn't indicate there was any recovery time (I looked up Metoprolol in Epocrates: half-life=3-7hr. I would touch base with Pharmacy, if your Cardiologists aren't really helpful, as to contraindications [absolute and relative] to Metoprolol administration in this manner); he has no nurse helping him; he screens the pts, arranges the CTA, goes down to CT to administer the dose and observe the scan, then re-formats the scan later.
Hope this helps. Perhaps you could find out from the CT vendor the names of some hospitals that have been using it for CTA, and then contact the involved depts (techs and nurses) for their protocols/suggestions.