What do you guys think?

Specialties MICU

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Specializes in long-term-care, LTAC, PCU.

I was at clinical in the DEM and my nurse an I were analyzing a strip on a man who was about 80 years old. He was on metoprolol 50 mg bid. The rhythm was slightly bradycardic at 52-56 bpm with a very slight irregularity. The only other abnormality was that the PR interval was very short (.06). What do you guys call that? I said the rhythm was junctional due to the rate and the short PR interval. My nurse said it was it was sinus brady with an occasional irregularity and the short PR interval was due to being beta-blocked. If this is the case could someone explain why the PR interval is short with beta-blockers. I would think the PR interval would be normal to high normal. This nurse said that rhythms can only be considered junctional if the p wave is absent, inverted, or behing the qrs. I'm pretty sure that we learned the a short PR interval could indicate a junctional or accelerated junctional depending on the rate. Please set me straight.

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Specializes in Pulmonary, MICU.

She's right. On a lead with a positive R deflection (such as lead II) a junctional rhythm will exhibit a negative deflection that is either prior to, during, or after the QRS, and this is always. The reasoning is that in Sinus Rhythms the atria contract from top to bottom, creating a positive deflection in leads with positive R deflection. In Junctional rhythms the atria contract from bottom up (starting at the AV node and going up toward the sinus in reverse of normal). Since the signal is reversed, the wave deflection has to be reversed...and this is regardless of rate.

Now, to address the Bradycardia and irregularity. The bradycardia is probably related to the B-Blocker and or fitness. The irregularity is probably normal. Sinus Arrhythmias are considered normal. Increased negative pressure in the thoracic cavity during inhalation causes increased venous return causing a higher heart rate during inspiration, slower during expiration. This causes irregularity in the rhythm.

As for the PR interval, you are right that a B-Block will increase the PRI. It can even increase it to the point of induced 1st Degree Block. As for why it is rapid...it's probably the patients natural rhythm. Do you (did you?) have access to older EKG's to compare? If the patient has accessory pathways it could decrease the PRI. Remember that the job of the AV node is to create a pause between atrial and ventricular contraction (PRI) and then create a RAPID depolarization of the ventricles (QRS <.12s did the patient have wide qrs complexes>.12s)? If so, the answer is that the patient was in Sinus Brady Arrhythmia with an pathway that bypassed the AV node. This method causes a wide QRS because bypassing the AV node creates a very slow conduction through the ventricles.

This type rhythm is something that cardiologists love to correct with ablation of the extra pathway. Having this external pathway can lead to runs of SVT or Atrial Tachycardia...which can be fatal rhythms.

Hope this helped!

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Specializes in Pulmonary, MICU.

So, a little more research led me to a phenomena that might fit the bill of your patient. Lown-Ganong-Levine syndrome. It is similar to what I described above EXCEPT: In LGL you have an accessory pathway that links the SA node to the Bundles of His bypassing the AV node. So you will have a short PRI and a normal QRS. LGL is also capable of causing sudden death from SVT/Atrial Tach leading to V-Fib. Think A-flutter where your Atrial rate is 300...but without the AV node to block impulses, the Ventricular rate can become Ventricular Tach / Ventricular Flutter or V-Fib.

If this guy does have an external pathway, whether cardiologists would try to fix an 80 year old's arrhythmia when it has thus-far been asympotmatic...

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Specializes in long-term-care, LTAC, PCU.

Wow. Thanks a lot! I have so much to learn. They admitted my patient to a cardiac floor to evaluate him for a pacer. I don't know what the final outcome was since i was in the DEM and we don't really get to follow the patients we have there. Thanks again!

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Specializes in Critical care, neuroscience, telemetry,.

I'd have to know a lot more about this guy to even hazard a guess as to why he's bradycardic with a short pr interval. Given his age and hx of beta blockers, however, could the pr be due to hypertension? Hypokalemia and hypocalcemia can also cause short pr intervals, I think. Not uncommon for an 80 yr old.....

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