HR of 40s - not pretty, but how is your patient? Does he look grey and dead, or NOT? Good peripheral pulses -- perfusing all tissues? then leave it alone. Good pressure - leave it alone. You mentioned pressures were fine, even high. This about what is happening. Think about hemodynamics: Heart is in sinus, and just reallllllly slow. So there is a LOT of time for the chambers to fill, you are getting a really good stroke volume and hence a good pressure. He isn't low on volume, so good preload --> good pressure. Contractility a problem? Doesn't sound like it. So, if you speed up a sick heart (and I say sick because most hearts don't beat 30 x minute -- so it is either sick or professional athlete healthy [doubt it is #2]).... speed up a sick heart, which is doing it's job just fine, just to make it "normal"... then you are going to screw yourself and your patient. Basically, don't fix what isn't broken -- and right now, it is working ok.
So what would happen to his BP if you gave some atropine --> probably go way higher.
You mentioned cushings and that you found out this triad after you looked it up. I am not bashing you, but I think this is basic knowledge for any ICU nurse and should have been covered in your training (or at least school - I cannot imagine you never covered this in school). Waiting 30 minutes for a CT read is also not acceptable. Your ICU docs should have looked at the CT... and then called radiology. If the pt was exhibiting signs of cushings, then he had a high risk for herniation and interventions would be warranted -- and sternal rubbing a pt with pending herniation is not a good idea. As you probably know.... high ICPs need HOB 30 degrees, MINIMAL stimulation (suction, turns, agitation, keep nice dark/quiet environment, ADEQUATE sedation, ICP monitoring and management) and maybe some mannitol or 3% NaCl. If the docs mentioned cushings... these COULD be life saving measures.
I would have put on pacer pads -- just to get ready :-))
So, these are my thoughts. I work in a medical ICU (not cards, not neuro). Others with more specialty might have more insight.
I think you are doing a good job by looking up more info ... you are responsible for you now (no professors encouraging you to study). Take all the free classes you can. GET ACLS (press your manager) and they say no, get the books from AHA and start studying on your own. Buy some CCRN study materials -- that will help you alot (not for the exam, but for everyday when you work). Read about ALLLLL the drugs you are giving. Pick your peers brains and absorb all you can from rounds with your docs. These are some of the things that will make you a good nurse.