You are on the telemetry floor and starting to round on your patients. The next patient you are about to see is a 65 year old male with CAD, DM, Gout admitted with the diagnosis of Sick Sinus Syndrome and awaiting a pacemaker. He has occasional brady arrhythmias and tachy arryhthmias. You are reviewing the vitals and before you walk into the room to see him you see the morning EKG. The EKG is below, what explains the tracings?

Click Here for Better Quality Image of EKG

This is a tough one. First, as always is to figure out the underlying rhythm. And looking at the rhythm strip will help us. The answer is there, but it is subtle.

Starting after the long pause after the first three complexes, the next three sets of three complexes all start with a similair looking QRS. There is no atrial activity in any of the leads (looking strait up on the EKG in the different leads to see if any signal was picked up) before these three similair complexes. From this we can infer that the underlying rhythm is a Junctional pacemaker. Also knowing that the patient has sick sinus syndrome helps.

So now we know it's junctional pacemaker, why all these different looking complexes in sets of three no less? Is this trigeminy? Are these all PVC's?

The first complex of each set is slightly delayed at .10 seconds and with the R' in V1 we can assume there is a incomplete Right Bundle when there is conduction with no interference. The rest is not so easy to see. What is happening after the first complex in all the sets is either a PVC or Abenrant conduction from the current pacemaker which is an example of Ashman's henomenon. Ashman's is based on the fact that the refractory period of myocardium is related to the previous R-R interval. So if there is a long R-R on the previous beat (a slow rhythm) the following refractory period will be long and if the following R-R interval is suddenly shortened by a Premature depolerazition that the impulse will find parts of the conduction system refractory and cause abberant conduction, hence ashmans phenomenon.

So lets look at the rhythm strip again. Th second to last set is the best example. So there is a long pause before the junctional pacemaker fires, and you get the incomplete RBBB conduction and than you get another depolerization from the same pacemaker, (we can say this because there is no p wave, and the initial deflection is the same) but now you get the ashman's because part of the conduction system is refractory because of the previous R-R interval and gets conducted abberantly in a LBBB pattern, than the next beat does the same thing except this one gets conducted in a complete RBBB and you get the long pause again and it starts all over.

IN the end the patient received his pacemaker and did well.