Junctional Rhythms

A junctional escape rhythm is technically supraventricular. the p wave can be inverted if there is retrograde depolarization of the atria because the focus of the heartbeat occurred in the AV node. If the p wave is absent then it probably is occurring just the way you stated, the atrial depolarization is "lost" due to the ventricular depolarization being so much "bigger" in terms of electrical energy. If an inverted p wave appears following a qrs complex, then the origin or focus of the beat probably occurred low in the AV node, depolarizing the ventricles first and then the atria (again, retrograde....antegrade causes an upright p wave because of the electrical flow through the heart).

Hope this helps understand what's occurring in a junctional rhythm. Also remember, the vagus innervates the AV node but doesn't affect a rhythm below it. In ACLS you hear people say "atropine doesn't work in 3rd degree blocks"...not necessarily true. There can be a junctional escape in a complete heart block, it would appear with a narrow qrs complex. The only patient who would never benefit from atropine would be a recipient of a heart transplant.

Getoverit, just a question, why wouldnt atropine benefit a heart transplant recipient? Just curious, thanks!

Getoverit, just a question, why wouldnt atropine benefit a heart transplant recipient? Just curious, thanks!

Hey. Good question.

Atropine is a vagolytic, meaning it suppresses vagal tone throughout the body. In a heart transplant, the vagus nerve doesn't innervate the transplanted heart. There's no way a surgeon could attach the nerve in a way to make it work. That's the great thing about automaticity of the cardiac cells....without that, a heart transplant would be impossible.

I hope when I have 18 yrs expercience that I will be as smart as you I can only hope!

so if the p wave is inverted are you saying possibly that the av node conducts then tries to reach the sa node.. is that why it would be inverted?

The reason any wave of the ECG looks the way it does is because of the way that the impulse travels. In a sinus rhythm the impulse travels through the atria and as the impulse travels toward the positve lead of the ecg, the monitor interprets this as a positive deflection, ie - an upright p wave. With this in mind, an impulse that orriginates in the av node and travels retrograde through the conduction fibers of the atria would be traveling away from the positive lead and would be interpreted as a negative deflection or inverted p wave. That also explains why different leads have a different appearance to the p, qrs, and t waves.

I hope when I have 18 yrs expercience that I will be as smart as you I can only hope!

thanks, most would probably say I'm filled with useless trivia!!.....at least that's what I hear at home a lot!!!

In answer to your question, like CRNAhopeful said, deflections on ekg tracings are made by the way they travel toward the leads.

You're exactly right about the P wave inversion. Think of each heartbeat beginning with an electrical impulse, the electricity is going to spread throughout the heart muscle by the fastest path possible. If the beat starts in the AV junction (intrinsic rate 40-60) then it will travel through the ventricles downwardly, but also has a retrograde (basically, backwards) path through the atria. This is opposite from the normal conduction, which is why the ekg tracings are opposite too, inverted instead of upright. The impulse isn't trying to reach the SA node though, it's just depolarizing the atria. when the SA node isn't the primary pacemaker (for whatever reason), it's just another bunch of cells in the myocardium...hoping to take the beat back!

Hope this helps some, sounds like you already know a good deal about cardiology!!

thanks for all the info... i aways doubt myself and need to hear what others think! thanks!!