Morphines effect on AV node conduction?

[OzMedic]

This often quoted side effect of morphine administration is starting to tick me off as I have never been able to find a decent piece of literature that will explain the mechanism of this alleged side effect of morphine. My understanding of the effect of morphine on AV conduction is via secondary mechanisms such as a decrease in sympathetic tone resulting in a decreased stimulus via the SA node or that morphine in large doses can cause bradycardia due to a direct effect on vagal neurones. However, I still hear people mentioning morphine decreasing AV conduction via a direct effect on the AV node but when pressed no-one can explain the mechanism. Am I missing something or is this just another medical old wives tale? I'm pretty sure that if there is any substance to it there will be someone on this site that knows how it works!

[AZCEP]

That is a new one on me. Never heard of it before, not that that means anything.

Here's an abstract about fentanyl's effects. Not the same, but similar perhaps.

http://eurheartj.oxfordjournals.org/cgi/co...tract/13/9/1277

[OzMedic]

That is a new one on me. Never heard of it before, not that that means anything.

Here's an abstract about fentanyl's effects. Not the same, but similar perhaps.

http://eurheartj.oxfordjournals.org/cgi/co...tract/13/9/1277

Thanks for that, I have seen this and other similar canine studies however they do not seem to demonstrate the stated effect of morphine slowing AV conduction. Like I said it may be an old wives tale but it is mentioned in our morphine protocol as well as some other readings I have seen but I am yet to hear a plausible cause. :?

[BushyFromOz]

Well Oz, you got me into the books for this, but its completely out of my level of education.

The best my brain (for what its worth) can come up with is the sedation effects cause by kappa receptor stimulation in the hypothalamus and the sedatory effect kappa stimulation has on the ANS, including the vagal neurones., This could be wrong, the text was a bit average concerning this (damn tortora)

No direct action on the SA node that i can find, but that don't mean much

I find in class a lot of the time people over simplify some things, and the SA node stimulation/suppression is often implied to as a direct action on the node, rather than a vagal/CNS effect which i find amusing considering they can still cite atropines effect for systolic arrest, bradycardia and organo phosphat OD

Maybe its just a wives tail? I dunno, thanks for the headache Oz

[OzMedic]

Well Oz, you got me into the books for this, but its completely out of my level of education.

The best my brain (for what its worth) can come up with is the sedation effects cause by kappa receptor stimulation in the hypothalamus and the sedatory effect kappa stimulation has on the ANS, including the vagal neurones., This could be wrong, the text was a bit average concerning this (damn tortora)

No direct action on the SA node that i can find, but that don't mean much

I find in class a lot of the time people over simplify some things, and the SA node stimulation/suppression is often implied to as a direct action on the node, rather than a vagal/CNS effect which i find amusing considering they can still cite atropines effect for systolic arrest, bradycardia and organo phosphat OD

Maybe its just a wives tail? I dunno, thanks for the headache Oz

Thanks for looking anyway dude! I'm pretty much ready to put this one down to BS as I tend to believe basically what you said, that is is simply a flow-on from decreased sympathetic activity. Oh by the way, did you read about morphines effects on the sphincter of oddi? heh heh heh, happy reading :twisted: