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Mobitz II vs. Third Degree Heart block?

CCU   (1,366 Views 4 Comments)
by nursiebean nursiebean (Member)

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I'm about to start working on a progressive care unit/tele floor in a couple months, and I'm just polishing up on my cardiac knowledge and I have been reviewing EKG's. I could always understand your basic rhythms being a surgical nurse that would have patients on tele, but I will say, I always had a harder time understanding heart blocks.

However, since reviewing, its making A LOT more sense to me and I feel more confident in my tele knowledge. But I've come across a bit of a stumbling block (block, haha, no pun intended) in trying to figure out how to determine a second degree type II and a third degree heart block?

I understand that the QRS is occasionally missing from a Mobitz II, and a third degree is where the P waves have no relationship with a QRS, right? But looking at practice EKG's, I can't tell the difference! Anyone with a bit more tele experience have any tips for how to discern between the two?

Thanks so much!

Sincerely, an excited PCU RN-to-be

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1 Follower; 47,366 Visitors; 2,145 Posts

These two can be difficult to differentiate, especially if you are looking at a short strip. However, if you run a 12 - 15 second strip, this makes it much easier. In the

2nd degree type 2 heart block (Mobitz II) you will find a consistent PR interval for the P waves that conduct, although the ratio of conducted-to-blocked impulses can vary. In the 3rd degree heart block, none of the P waves are conducted, and while there really isn't a true PR interval, the pseudo PR interval will vary from beat to beat.

Learning ECG interpretation is like learning heart or lung sounds. This isn't something you can learn by trying to memorize what a particular rhythm looks like. You need to learn the criteria for each of the rhythms you will be responsible to identify, and then apply those criteria, using a consistent, systematic approach, to each strip you are evaluating.

When I analyze an ECG rhythm strip I use the following mnemonic: RRPPQQS.

Rate: What is the rate? Less than 60 or greater than 100? If an ectopic pacemaker site, is the rate less than or greater than the intrinsic rate for the pacemaker.

Regularity: Is the rhythm regular? If irregular, Is there a pattern to the irregularity?

P wave: Are P waves present? Is each P wave followed by a QRS complex?

PR interval: 0.12 - 0.2 seconds.

QRS complex: 0.06 - 0.1 seconds, although you will find some variation to these values.

QT/QTc interval: Some centers will have you measure, and correct for rate, the QT interval.

ST segment

If you aren't familiar with ECG interpretation, you find the Life in the Fastlane ECG Library helpful.

Best wishes in learning ECG interpretation.

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Pheebz777 has 18 years experience and works as a BSN-RN, CCRN-CMC-CSC, CEN.

4,168 Visitors; 217 Posts

Don't start by looking for a dropped QRS. Pay attention to the PR/QRS pairing which is key. On Mobitz II, technically you'll find a consistent PR/QRS interval pairing on every QRS that isn't blocked. On 3rd Degree you will not, PR interval will vary from QRS to QRS (technically there is no PR interval because there is atrioventricular disassociation). But don't think of that, just concentrate on the PR interval.

Just start with that. YouTube has a lot of videos and examples to practice on.

Edited by Pheebz777

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1,382 Visitors; 41 Posts

Thanks very much for the help. That makes more sense. I'll definitely be practicing and looking up some videos and practice strips online!

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