Click here for answer Sinus Node Exit Block with likely junctional escape

This a very interesting telemetry strip. So lets start with the obvious, there is a large pause in between beat 2 and 3 and for beat three there is no preceding p wave. Also following the QRS complex in beat 3 there is some sort of artifact, or is it real activity? Click on the calipers link or use your own calipers and mark out the p-p interval between 1 and 2. Now march it out starting from the p wave in beat 2 and notice what lines up with in the p-p interval. You land just on top of the "distortion" after the 3rd beat. HUH?

So what does that mean. It means that the distortion is really Sinus node depolarization after the third beat. The size may not be the same but the direction and morphology in both leads is similar to the other p waves and may be smaller due to respiratory variation. So thinking about it, there is a "skipped" sinus node beat missing from this strip which should be in between beat 2 nd 3. That is because this is an example of Sinus Node Exit block. Sinus node exit block is similar to AV blocks. In this case the Sinus node depolarizes but does not capture the atrium instead of the impulse not being conducted to the ventricle in the case of av blocks. So how do we prove this?

This is proven by a P-P interval that makes you land (after the 2nd p) on the space where there should be a p but not, and than again marches out to the activity after the third qrs. SO what is really happening is that there is significant sinus node disease (which this man has because he is getting himself a pacemaker for symptomatic pauses and bradycardia) and the Sinus node is actually depolarizing but is not "capturing the atrium. That is why there is a long pause with a missing p wave in between. The pause also is long enough to allow the junction to escape and fire and be responsible for the third qrs.

So to summarize what is going on between beats 2 and 3. The Sinus Node depolarizes on time, you get qrs 2. Than the sinus node depolarizes again on time but does not capture the atrium to give you a p wave (hence the missing p), you get a pause and than you now get an escape beat from the junction because no impulse has gotten to it to suppress it from firing, and than after the third qrs you get the sinus node to depolarize on time and this time it captures the atrium but since the junction just fired, it is refractory so it does not conduct. Hence the diagnosis of Sinus Exit block proven on a telemetry strip.