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Case #24

You are on the Inpatient wards taking care of your patients. Your colleague on the other medical service waves you down. He says he has a puzzling EKG which he cant figure out. He wants your opinion on what is going on. The EKG is below, what do you tell him is the interpretation?

 

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The real puzzle for this EKG is what is the underlying rhythm? First off the rhythm is irregular, but it is regularly irregular. It also looks as if there is grouped beating in pairs. If you take your calipers (click on the caliper link) and compare the RR intervals for each of the pairs, they are exactly the same. And if you compare the distance between the pairs, they are also the same. This means that we have a regular source for this rhythm. Now to figure out where it is coming from.

There is no atrial activity preceding the QRS complex in any leads and especially in the Atrial leads (II and v1). So this cant be sinus, and it cant be atrial in origin. The QRS width is normal, so this must be a rhythm from the junction, a.k.a the AV node. So now that we know the rhythm is originating in the junction, why the grouped beating? Looking closer at the QRS complexes will reveal the answer.

In each "grouped" pair the QRS is slightly different. There is a difference in the terminal deflection. Take a closer look. Looking at lead II, the rhythm strip, the first QRS of each pair ends barely below the baseline, and all the first of each pair look the same to each other. The second qrs of each pair has a more negative deflection and they also look the same to each other in all the pairs. v1 also reveals a difference in the terminal ending of the QRS with a "notch" at the end of the second one. In this subtlety lies the answer. These are retrograde p waves distorting the qrs complex in the second qrs of each pair. This can only mean that this rhythm is actually a Junctional Pacemaker with Junctional premature beats, or Junctional bigeminy.

You do not see distortion of the qrs in the first of each pair because it is berried with in the qrs because it is originating probably from the Middle of the junction. Than you get a premature depolarization from a location slightly lower in the junction than the driving source, which causes a longer time to get to the atrium, and hence shows the retrograde p waves late enough to distort the qrs.

The other clue is the consistency of the intervals between the mid pacemaker to the lower premature ectopic focus. THis is classic for bigeminy because, bigeminy usually perpetuates itself. Hence, the fixed intervals making it regularly irregular.

So with these clue, the diagnosis of Junctional Pacemaker with Junctional Bigeminy is found.