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Case #23

You are on call in the CCU. You are about to go to sleep as all the work is finally done when your pager goes off. It's a 77 year old male and he is vomiting and his heart rate is now in the 30's. He was recently admitted with a Right Coronary Artery Distribution MI. He had a stent placed but according to the notes, it took a long time for him to come to the hospital and he had significant myocardium lost. You quickly assess the situation and decide to put in a temporary pacer because of his symptoms and his rate. Before you do, you get a 12 lead EKG and this is what you see. What is going on and why?

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This is a result of significant infarction of the conduction system. The Right Coronary typically supplies the SA node, the AV node and much of the conduction tissue. With significant damage to these areas, bradycardias are very typical. So how do we determine where the rhythm is coming from?

First, the rhythm is regular and all the complexes look the same on the rhythm strip. So this tells us that is it coming from the same place where ever it is. Now location is the next issue. This is relatively easy if you think from top to bottom, ie SA node to the epicardium of the ventricles where depolarization happens last. So there is no p waves or any atrial activity seen anywhere in any lead. This eliminates the SA node for the source or any ectopic atrial pacemaker. The next area to consider is the AV node. However, the qrs complex is wide at .16. If the AV node was the driving source for this rhythm it would need to be narrow. So now with the SA, atrium and av node eliminated, we can safely assume that the rhythm is ventricular in origin and coming from the same focus because it is regular. Another interesting fact is that the rhythm is probably originating with in the left ventricle's conduction fibers as the complex is not grossly wide as one would expect and noticing the RsR' pattern in v1 making it seem like a RBBB pointing towards a left sided source as well.