December 23, 2016

A Simple Arrhythmia Complicated by a Common Phenomenon

What is your interpretation?

Image 1 - ECG case

Image 2 - Ladder diagram

A rhythm like this is better deciphered using a ladder diagram. A ladder diagram traces an impulse from the A (atria) tier, AV (junction) tier to the V (ventricle) tier. Marking the P waves in the A tier and the R wave in the V tier are the easy part. The challenging part is connecting the A to the V tier because the AV tier is an electrically silent suface ECG phenomenon. This means that it does not create a positive deflection on the surface ECG.

Cherchez le P

Image 3 - The P wave in A tier

Cherchez le P means search for the P in French. Electrocardioraphers would like to use this term because it sounds sexy in French. Looking for P is the first thing we look for. In image 2, P waves are numbered in red. 

The P waves looked regular with a rate that starts at about 60 bpm and increased to about 68 bpm. P4 and P7 appeared early and the morphology is different from the rest of the P waves. So, P4 and P7 are premature atrial complexes (PAC). We put the dot lower (A tier) in the ladder diagram and the rest in the upper part of the A tier.

Image 4 - The QRS in the V tier

Marking the the V tier is straightforward. Just trace the R waves and make a vertical line in the V tier

Image 5 - Connecting the AV junction

There are 2 QRS morphologies (shapes) in lead II. Most have a Rsr moprhology except R3 and R5 which is predominantly R (red arrows). The RR interval in R2R3 and R4R5 is about 1700 ms or a rate of about 30 bpm. We can conclude that from this R3 and R5 are non-sinus beats but are junctional beats. So, we put the dots in the AV junction. It is also possible that this junctional impulse will conduct retrograde. This will make the junction refractory to an incoming supraventricular impulse. Thus, P4, P5 and P8 are not conducted.  

P7 (PAC) is blocked because the AV node is still refractory from P6 capture. 

The Controversial R5

There is a P (P8) wave near R5. We can measure the PRI at about 0.20 seconds. However, sometimes surface ECG will give you a clue as to the origin or source of the impulse. In the case of R5, it has the same morphology (shape)with R3. Thus, R5 is a junctional beat.

So, what we have here is sinus rhythm with AV Wenckebach interrupted by non-conducted PACs with junctional escape with concealed retrograde conduction.

Take Home Message

1. For complex rhythm, use the ladder diagram.

2. Cherchez le P (Search for the P).

3. Examine the shape of P and QRS morphologies.

4. Examine RR intervals.

5. Some ECG's do not read books.

* I would like to thank Dr. K Wang for checking the ladder diagram and agreeing with it.

# 658

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