WPW Lido vs Procanamide

[Hunter]

So we were going over ACLS in class and we where discussing that Lidocaine cannot be used for patients with WPW (Wolf Parkinson White Syndrome). Because it would just knockout the AV node and because of the accesory pathways from WPW the atrium and ventricals would contract at basically the same time. It was stated that procanamide however could be used as a substitute for Lidocaine. I thought that both of these medications were Sodium Channel blockers. My question is; Why is it that Procanamide CAN be used as an Antiarrythmic if both drugs work on sodium channels?

 

[Aidey]

Are you sure you're not thinking of adenosine instead of lidocaine? Lidocaine won't make WPW worse, it just usually doesn't work. Procainamide is a class 1a antiarrhythmic, lido is a class 1b which is probably why one works on WPW and the other doesn't. Class 1a meds lengthen the action potential while class 1b meds shorten it.

 

[TomB]

I'm assuming you're referring to rate control in the setting of AF/WPW. From what I've seen 99.9% of paramedics will not recognize this phenomenon in the field making it a moot point. Procainamide is a great drug but it's difficult to administer. It seems much more sensible to me to shock it if it's hemodynamically unstable and otherwise leave it alone! If it's orthodromic or even antidromic AVRT (regular rhythm) you're probably okay giving adenosine. As for exact pharmacology I think it boils down to the difference in histology between the cells of the accessory pathway versus the AV node. This is a difficult topic to understand but the best explanation I've heard is that procainamide prolongs (or impairs) the accessory pathway in the anterograde direction (meaning atria to ventricles) whereas others exert their affect on the AV node and may even paradoxically accelerate conduction through the accessory pathway. Cellular physiology is complex and even drugs within the same SVW class do not function exactly the same.

 

[Hunter]

Are you sure you're not thinking of adenosine instead of lidocaine? Lidocaine won't make WPW worse, it just usually doesn't work. Procainamide is a class 1a antiarrhythmic, lido is a class 1b which is probably why one works on WPW and the other doesn't. Class 1a meds lengthen the action potential while class 1b meds shorten it.

No I'm reffering to Lidocaine, sorry I didn't speficy, this would be when dealing with Pulseless V Tach and VFib.

I'm assuming you're referring to rate control in the setting of AF/WPW. From what I've seen 99.9% of paramedics will not recognize this phenomenon in the field making it a moot point. Procainamide is a great drug but it's difficult to administer. It seems much more sensible to me to shock it if it's hemodynamically unstable and otherwise leave it alone! If it's orthodromic or even antidromic AVRT (regular rhythm) you're probably okay giving adenosine. As for exact pharmacology I think it boils down to the difference in histology between the cells of the accessory pathway versus the AV node. This is a difficult topic to understand but the best explanation I've heard is that procainamide prolongs (or impairs) the accessory pathway in the anterograde direction (meaning atria to ventricles) whereas others exert their affect on the AV node and may even paradoxically accelerate conduction through the accessory pathway. Cellular physiology is complex and even drugs within the same SVW class do not function exactly the same.

Sorry again I was reffering as to VFib and Pulseless Vtach I didn't speficy, probably the only way most people would recognize the patient as a WPW patient would be from family telling you about it. Ofcourse shocking for these patients is indicated but as I was going through the ACLS algorithms for cardiac arrests, ect. and after the 3rd shock it says to consider giving antiarrhythmics.

 

[Aidey]

So your question is "Should lidocaine be used patient's with WPW who are in VT/VF"?

As to that I'm not sure, but either way lidocaine does not "knock out" the AV node. What you are describing doesn't make a lot of sense.

 

[18G]

Im confused by the questions being asked as well.