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Case #21

You are the resident on the wards and about to start morning rounds with your interns. Before you start your intern pulls you over and says, "This mornings EKG on Mrs. X has got me really puzzled, what the heck is the Rhythm?". You grab the EKG with a confident look and tell him.....?

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At first glance it looks a little confusing, but with the use of some calipers and patients the answer will become clear.

Starting off as always with our method of interpretation is to figure out the rhythm. It is irregular. Starting at the rhythm strip, it begins with two Sinus Node Driven beats (P II, III, upright. Cant use AvF because it is not in the same time frame). Than a different morphology p wave with a different PR (use a caliper) representing a PAC and earlier than the regular p-p interval.

Than a pause that is greater than compensatory,(Greater than two P-P intervals from the last Sinus beat) due to retrograde depolarization of the Sinus Node. Than the next beat is started with a complex with a different P-R than the first two sinus beats, so this is a non Sinus Node but an ectopic atrial focus and it is also conducted abberantly as you can see from the different morphology of the QRS complex. The next is the same P-R as the first two beats, so this is from the sinus node. Than the following is another PAC as the morphology of the p wave is different. Than a pause, than another two Sinus Node beats, than two consecutive depolarizations from the same ectopic focus in the atrium somewhere (same focus because they have different morphology and different P-R from sinus beats but both same morphology and P-R to each other, check in v3 with caliper). Than another ectopic atrial focus beat because the P morphology and P-R interval are different again. The last complex is difficult to interpret as you can see the baseline get distorted so we just ignore it.

Therefore, we have the criteria for a Wandering Atrial Pacemaker (Irregular Rhythm with three different P wave morphologies with different P-R intervals) and a couple of PAC's.

A simpler way to picture the rhythm and where each focus came from is to draw a Ladder Diagram. This is an old method which is very handy. Below is the image of the Ladder diagram for the Rhythm strip. The top line represents the SA node in top R of the Atrium, The middle line represents the AV node and the third line represents the end of ventricular depolarization. The X represents where the Impulse originated from and the lines represent direction of depolarization. Try and line up the image with the EKG to picture it better.

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