Sx Reflex Tachy
Started by housepharmd
Pentaerythritol tetranitrate
Immunizations
huh? beta blockers don't cause reflex tachy - stopping them abruptly will - and what is a cardiac channel blocker?
Anything that causes vasodilation without concurrent beta blocking.
I usually think of reflex tachycardia as the bodies response to a stimulus (vasodilation) vs. direct effects on the pre/post-synaptic receptors (antimuscarcinics). In terms of board questions - for pharmacy/medicine ~ its the vasodilatory effects of drugs leading to tachycardia that is considered reflex tachycardia.
You may think that, but it's not true. It's a response to a change in vagal tone. It's not a direct effect as you would get with direct adrenergic stimulation. That makes it a reflexive response.....
The effects of antimuscarinics are mediated most predominantly at the level of the end-target. In this case, it would be the muscarinic receptors (post-synaptic receptors) on the cardiac cells. It very minimally involves the nerve itself.
--(pre-ganglionic)---< Ng (nicotinic) ----(post-ganglionic* vagus)---< M (muscarnic receptors found on cardiac myocytes stimulated via acetylcholine but blocked by anti-muscarinics)
--(pre-ganglionic)---< Ng (nicotinic) ----(post-ganglionic* vagus)---< M (muscarnic receptors found on cardiac myocytes stimulated via acetylcholine but blocked by anti-muscarinics)
But it meets the definition I gave you from a medical dictionary. Reflex tachycardia is note solely defined as response to vasodilatoin or volume depletion. Your definition is too narrow.
I think we have a misunderstanding here. The response your quoting isn't reflex tachycardia. It's the reasoning why antimuscarinics do not cause reflex tachycardia. They mediate their effects directly on the receptor found within the heart. No effect on blood vessels (hence will not activate the baroreceptors which is integral in the reflex response). Reflex tachycardia is the body's response to a stimulus (hence reflex). Your new explanation is more in-line with my first answer (which specifically was taking about medications - vasodilation).
