A Tricky Strip

This is from 25 yo s/p AV valve and TV valve repair. This is a tricky strip.

Isorhythmic AV dissociation: SR + VT

A 70 yo patient admitted for shortness of breath. 

Is this ventricular tachycardia (VT) or aberrancy?

Image 1 - ECG case

Image 2 - Ladder diagram

The rhythm is sinus at a rate of about 100 bpm with a PRI of about 0.28 sec (first degree AV block). It is interrupted with episodes of wide QRS beats at a rate of about 94-107 bpm with predominant R wave in V1 with variable PRI. This would indicate that there is AV dissociation. If the sinus rate and the ventricular rate is almost the same then it is called isorhythmic AV dissociation. The presence of AV dissociation and the predominant R wave in V1 favors ventricular tachcycardia.Thus, this SR with first degree AVB with episodes of VT creating isorhythmic AV dissociation.

#686

Utilizing QRS Morphology in Deciphering Rhythms

 Aside from searching for the P waves to decipher rhythms, the QRS morphology can give us clues to the rhythm.

 

This strip is from a patient who was admitted due to abdominal pain. While on telemetry, I noticed this interesting teaching strip.

Figure 1

This is a regular narrow complex QRS rhythm. Starting from the left side of the screen, the P wave is seen to be merging with the QRs until it cannot be seen and reemerged before QRS #7.

Take a look at the QRS morphology/shapes in all leads. You will notice that there are 2 different QRS morphology. QRS #1-6 have the same shape and QRS #7-10 have the same morphology. This means that with a P wave at a conductible distance from the QRS, QRS #7-10 are sinus beats or the ventricles were depolarized by sinus beats.

QRS# 1-6 with some of the P waves fusing with the QRS are junctional beats or the ventricles were depolarized by junctional impulses.

You might also argue that QRS #1 should be a sinus beat because of the obvious P wave and a normal PRI. The argument against it is the similarity of morphology with the obvious junctional beats (QRS #2-6).

Figure - ladder diagram

This strip is best understood using a ladder diagram.

This is a nice teaching strip showing competition of 2 pacemakers - junction and sinoatrial node (SAN). The clue to the diagnosis which captured/depolarized the ventricles was revealed by the QRS morphology.

In this case, the atria was still depolarized by the SAN and it somewhat disappeared because the P waves were "buried" in the QRS. This is called isorhythmic AV dissociation - rhythms with atrial rates and ventricular rates that are almost the same and there is dissociation because the ventricles were controlled by competing pacemaker.

#530

Pseudo-first degree AV block

Figure 1 - 30 sec continuous strip

This looked like sinus bradycardia (~44 bpm) with a very long PR interval (800 ms or 0.80 sec) or first degree AV block.

Figure 2 - 30 sec continuous strip few minutes prior to the strip in Figure 1

In #1, a distinct P wave can be seen in R2 but you will note that it merged with the QRS. Because of the merging, the shape of the QRS is distorted. In #2 and #3, the P wvave can be seen after the QRS. On the last QRS complex, the P wave is seen farther awway from the QRS. The QRS are junctional complexes. So, there is AV dissociation. The rate of the sinus beat is almost the same with the junctional rate. This is called isorrhythmic AV dissociation.

The ECG strip in Figure 1 is not a true first degree AV block but a pseudo-first degree AV block. The strips are sinus bradycardia with junctional beats creating AV dissociation (isorhythmic AV dissociation)

After a few hours (of stopping a beta-blocker), the sinus rate increased to about 60 and captured the ventricles. 

#626

Isorhythmic AV dissociation

Figure 1 - Long lead II and V1

What is the rhythm?

This is regular narrow QRS complex rhythm (~88  bpm). Most would call this accelerated junctional rhythm.

Figure 2 - Full disclosure with P waves marked

P waves are marked in red arrows. They are upright in II and negative in aVR. This means that there still sinus rhythm. However, the ventricles is controlled by the junction. There is AV dissociation. When the atria and ventricles are dissociated and the rates are the same, this is called isorhythmic AV dissociation. 

Figure 3 - Follow-up strip 

Follow-up strip shows the separation and merging of the P and the QRS.

These are strips (static mode)  are difficult to interpret or often misled an interpreter. Longer strips like reviewing them on telemetry will make the interpretation easier. 

#278

A rhythm that is often read partly correct