Did You Know That: There are Two (2) Types of Mobitz I

Second degree AV Block Type I is also known as AV Wenckebach or Mobitz I. Did you know that there are two (2) types of AV Wenckebach? It could either be Typical or Atypical AV Wenckebach. This is how to recognize these ECG Patterns:

Second Degree AV Block Type I (Typical)

ECG Recognition:

• ·       The P wave is normal.
• ·       The PR interval progressively lengthens until a P wave is not followed by a QRS.
• ·       As the PRI lengthens, there is shortening of the RR interval.
• ·       The RR interval containing the dropped P wave is less than 2x of the shortest RR interval.
• ·       The PRI of the first conducted P wave (may be normal or prolonged) is shorter than the PRI of the       last conducted P wave.
• ·       The largest increment in the PRI is usually on the second conducted P wave.
• ·       There is "group-beating" on the ECG.

Figure 1 – Sinus rhythm, second degree AV block type I (Mobitz I/Wenckebach) with 3:2 AV conduction. There are regular sinus P waves at a rate of about 100 bpm. There is group-beating of the QRS with a P to QRS ratio of 3:2. The first conducted P waves are marked with green arrows with a PR interval (PRI) of 0.20 seconds. The next conducted P waves are marked with a blue arrow with a PRI of 0.28 seconds. The non-conducted P waves are marked with red arrows. As can be seen there is prolongation of the PRI interval until a non-conducted P wave.  This is typical AV Wenckebach.

“This strip is driving me nuts” - A simplistic approach

It never came up to me when I was reading 12L ECG before that we are just presented with a 10 seconds event of a lifelong cardiac activity. Then with those 10 seconds, you are expected to make a great diagnosis. My perspective of looking at cardiac activity changed when I got this task of watching them for 12 hours. That is 43,200 beats being watched for 12 hours (each) and if you are watching about 40 then it is about 1,728,000 beats. This is if they are beating at 60 per minute. Most of them are regular but some of them will “drive you nuts”.

After several years of being here, I have developed my way of looking at things. Take for example this 10 second strip.

Image 1

We have here an irregular narrow complex rhythm. Is this atrial fibrillation? Complete heart block or there is AV dissociation?

Move backwards and appreciate the “scenery”.

If you move backwards, you will see some “group-beating).

Image 2

From my previous post, these are telltale signs of a Wenckebach phenomenon.

Look for the P’s - Use all the available leads to look for the P wave

Classically ECG class would say to analyze a strip is to ask: IS THERE A P? I still follow it but I LOOK FOR THE P IN ALL AVAILABLE LEADS. The wonderful lead II is not at all wonderful and trusted. Other leads will reveal the elusive nib.

In this particular case, it is hard to find the rest of the P waves if viewed from lead II. So, I look at them in full disclosure (all 7 channels).

Image 3

My best candidate is to look at V1.

Image 4

But where are the rest of the P waves?

Going back to V1, One way of looking for the P waves is to look at normal-looking QRS. When I say normal looking QRs, I mean a QRS that is not deformed by anything (artifacts or extra nibs). The best candidate I can find here is QRS complex #3.

Image 5

QRS complex #3 (blue box) is the best normal-looking QRS. The other complexes are distorted (with green dots). This distortion is due to the presence of a P wave at the terminal (end) portion of the QRS.

Where are the rest of the P waves?

Bring out your calipers or if you have an electronic caliper then use it to march and look for the P waves.

Image 6

By the magic of the caliper, hidden P waves are marked (blue dots). Some of them are not so obvious and some are fully hidden from view. At a rate of less than 3 big boxes or about 14 small squares then the atrial rate is about 107 per minute (SINUS TACHYCARDIA). So, we solved the first part of the mystery.

Which sinus impulse is making the QRS (capturing the ventricles)? Ladder diagram

To answer this question, the ladder diagram is needed. Simply put, it is a line diagram representing the transit of an impulse from 3 levels (tiers) – A or atrial tier, AV or AVJ or AV node or AV junction and the V or ventricular tier.

Image 7

We have here groups of 4 P’s with 3 QRS (conducted) or 4:3 AV conduction and 3 P’s with 2 QRS (conducted) or 3:2 AV conduction and a long PRI at the beginning of the groupings.

So, the strip is sinus tachycardia with long PRI (aka first degree AV block) with 4:3 and 3:2 AV conduction. There is lengthening of the PRI. Thus is a Wenckebach.

For this case what we did are the ff:

     1. Move backwards and look at the rhythm (group-beating).

     2. Use full disclosure (7 channel/leads) in looking for the P’s.

     3. Use a normal-looking QRS as reference to look for the hidden P      waves in the QRS.

     4. Use a caliper to look for those P waves that are hidden from view.

     5. Made a ladder diagram.

#470

Group-Beating: The Footprints of Wenckebach

Vignette:

A 70 yo with history of diabetes mellitus (DM), hypertension (HTN), chronic kidney disease (CKD), heart failure with preserved ejection fraction. What is your interpretation? 

Image 1 - ECG case

Image 2 - Ladder Diagram

If you move backwards and look at the strip you will notice “group-beating”. R2R3, R7R8 and R9R10  is a group and there is progressive shortening of the RR interval in R4 to R6.  If you are an avid reader of ECG books, you will encounter the wisdom of the late Dr. Henry Marriott. According to Dr. Marriott, “”group-beating is a footprint of a Wenckebach”.

The P waves are best seen in the V lead and do not rely on lead II because you might interpret it as atrial fibrillation. Distinct P waves can be identified (P1,P2,P4,P5,P8P9,P11,P12 and 14). P3 can be identified by comparing the R3 to the rest of the QRS complexes. The terminal QRS is pointed and it means a P wave is there. P6 is seen distorting the descent of the T wave after R5. P7 and P10 and P13 are P waves that are “buried” in the QRS. If there were more leads, then most likely these P waves can be seen on the other leads.

Having established and marched the P waves in the A tier, we can then connect the R waves in the V tier. So, we can see the 3:2 and 4:3 AV Wenckebach pattern.

Interpretation: Sinus rhythm, first degree AVB, 3:2 and 4:3 AV Wenckebach

#682

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

Is this Complete Heart Block?

Is this complete heart block?

Image 1 - ECG case

SR, Second Degree AV Block Type I, Junctional Escape Beats

No clinical hx. What is the ECG interpretation?

Image 1 - 2 Leads

Mobitz I with wrong lead placement

Vignette:

A 70 y.o complaining of chest pain. What is the ECG interpretation?

Image 1 - ECG case

 

Mobitz I interrupted by a PVC

 What is the interpretation?

Figure 1 - Lead II

The group-beating

What is the rhythm?

Figure 1

Group-beating: footprints of a Wenckebach

What is your ECG interpretation?

Figure 1-  ECG case

A 2:1 is not Mobitz II

Vignette: A 70 yo is admitted due to dizziness. What is your ECG interpretation?

Figure 1 - ECG case

The rhythm is sinus with an atrial rate of about 65 bpm and the ventricular rate of about 34 bpm. The PRI is 0.28 s and the QRS is 0.12 sec. There are 2 P wave for every 1 QRS (Figure 2).

Figure 2 - P waves marked with red arrows

Use all available leads in rhythm interpretation

Figure 1

A adult patient is admitted due to GI bleed.

What is the interpretation?

Figure 2

The rhythm is SR with long PR interval (first degree AV block), right bundle branch block (RBBB) and showing Wenckebach periodicity (aka Mobitz I) with 4:3 AV conduction.  If you rely only lead II, which is usually the monitoring lead. You will probably scratch your head. You have to utilize all available leads. Distinct P waves are marked with red arrow. The non-conducted beats are marked with black arrows.

The patient was asymptomatic and none was done for regarding the rhythm.

#274

Second degree AV block type I interrupted by nonconducted PAC's in bigeminy

An elderly was being worked-up for GI bleed and routine monitoring captured this (rates dropping to 40's). 

Figure 1

What is the rhythm diagnosis? 

*****

Figure 2

The baseline rhythm is sinus rhythm at  a rate (initially) about 75 bpm. The first 4 QRS beats had a prolonged PRI (~ 360 ms) . The next subsequent beats (~ 40 bpm) with a PRI of ~ 280 ms. This behavior is seen in Wenckebach type of block.

What is the probable cause of the sudden onset of bradycardia? (red arrows - P waves)

There is a small nib at the terminal portion of the 4th QRS complex.The nibs are distorting the shape of the 4th QRS complex  compared to the first 3 QRS complexes (best seen in I, III, aVF, aVL). In the subsequent bradycardic QRS complexes, nibs can all be seen (best seen in V1 in the  ST segment). These are P waves. The differential here can be non-conducted PAC's or atrial echos (reentry). The RP interval of those P waves  vary (shorter in the 4th QRS complex than the rest). Thus this is more of a PAC than a reentry.

Interpretation: 

SR with a prolonged PRI with a Wenckebach periodicity interrupted with non-conducted PAC's, RBBB.

Patient was asymptomatic during these events.

#255

What is this wide rhythm?

A 75 yo h/o HTN, DM, dyslipidemia and non-ischemic caridomyopathy. What is your interpretation?

Figure 1

This is sinus tachycardia (~125 bpm), second degree AV block type 1 (Mobitz I/Wenckebach), left bubndle branch block (LBBB), left axis deviation, poor R wave progression.

Distinct P waves are marked in red arrows. Blue arrows marked the non-conducted P waves of the Wenckebach cycle. After the conducted beats, most of the P waves are hidden from view or are buried in the T waves or distorting the T wave morphology. The 5th to the last R wave could be a premature junctional beat. The nondconducted P wave is hidden or buried on that wave.

Figure 2

#622

The "skipping" P waves

ECG case

Vignette: 70yo with h/o HTN, s/p valve replacement c/o one-sided facial numbness and dizziness. Work-up for stroke was negative. CBC - N, chemistry and troponin - N, CXR negative for acute disease.

What is the rhythm?

Image 1 - Long lead II

Long lead II can be interpreted as atrial fibrillation (AF). However, it is very odd for AF to be regular unless there is a complete heart block, AF with a pacemaker and AF with entrance block and junctional rhythm with an exit block. The machine read this rhythm as AF.

Image 2 - Long lead II and V1

Adding long lead V1 revealed a different story. Organized atrial activity can be seen in V1. The PP rate is about 88 bpm. Some of the P waves are distorting the initial and terminal portion of the QRS. 

Image 3 - Ladder diagram 

Image 3 marked in red arrows some hidden P waves. The complexes with red arrows highlight the typical morphology of a QRS with no P wave distortion.

The laddergram also illustrates an interesting pattern. The P waves depolarizing the the QRS is "skipping" the nearest QRS. The initial QRS complexes are conducted with 1:1 pattern and the latter part is conducted with a 2:1 pattern (rate ~ 40 bpm). There is a very long PRI of about 0.56 sec and a left bundle branch block.

Interpretation: Sinus rhythm, first degree AV block, second degree AV block type I (Wenckebach/Mobitz I), LBBB.

This patient eventually got a pacemaker.

#617