EKG of the Week 2016 7-24

A 65 y/o male with a history of CAD presents to the ED for an unrelated complaint and he is found to have this rhythm on EKG.

1.       What is the rhythm?

2.       How would you manage this rhythm?

The rhythm is sinus with bigeminal PAC’s (and a right bundle branch block). No specific treatment is needed.

The EKG demonstrates an irregular rhythm which may be mistakenly interpreted as atrial fibrillation. In fact, the computer read this EKG as a-fib. However, there are clear P waves preceding beats #1, 3, 5, 7, 9 and 11. Beats #2, 4, 6, 8 and 10 come earlier than expected, likely have a preceding P wave buried in the T wave (seen best in beats #6 and 8), and the QRS morphology is the same as the sinus beats. This is consistent with PAC’s. Since the PAC’s are every second beat, they are called bigeminal PAC’s (or atrial bigeminy). In atrial fibrillation, there will be no P waves, possibly an undulating baseline, and complete irregularity to the rhythm. On this EKG, although it is irregular, there is some pattern to it. There are two beats followed by a pause, then another two beats followed by a pause, etc.

This rhythm can also be confused with second degree type I AV Block. However, on this EKG, there are no dropped P waves. Every P wave is followed by a QRS. So there is no AV block.

Premature beats can originate from the atria (PAC’s), the junction (i.e. the AV node – called PJC’s) or from the ventricles (PVC’s). PAC’s appear as a P wave which comes earlier than expected followed by a QRS complex that looks the same as all the other QRS complexes in that lead. Following the PAC, there is a non-compensatory pause. This means that the length from the P wave preceding the PAC to the P wave of the next normal beat is random. It is not related at all to the distance between the normal P waves in the normal beats. This happens because the PAC “re-sets” the SA node. This means, the PAC depolarizes the SA node, so it has to recover before it can generate the next normal beat.

PJCs may have a P wave before or after the QRS complex. The P wave will look different than the sinus P waves and it will often be retrograde (i.e. inverted). PJC’s are uncommon in healthy hearts. They occur in CHF, digoxin toxicity, ischemic heart disease, and AMI (especially of the inferior wall).

PVC’s have no preceding P wave and the QRS complex is wide and bizarre. It looks distinctly different than the other QRS complexes in that lead. Following the PVC, there is a compensatory pause. This means, if you “march out” the R waves, the R waves will continue to arrive at the expected time after the PVC. This occurs because the PVC does NOT reset the SA node. As far as the SA node is concerned, the PVC never happened. So, the SA node continues to fire at its normal pattern.

This EKG also demonstrates a right bundle branch block pattern – wide QRS complex, RSR’ pattern in leads V1-V3, secondary ST-T changes in leads V1-V3 (on this EKG, ST elevations in V1-V2), and deep terminal S waves in leads V5, V6, I and aVL.