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High-grade AV Block

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Dawn's picture

High-grade AV Block With Profound Bradycardia

Thu, 06/04/2020 - 14:24 -- Dawn

If you are an ECG instructor, you probably carefully choose ECGs to illustrate the topic you are teaching. One of the reasons for the existence of the ECG Guru website is our desire to provide lots of such illustrations for you to choose from.

Sometimes, though, an ECG does not clearly illustrate one specific dysrhythmia well, because the interpretation of the ECG depends on so many other factors.  In order to get it “right”, we would need to know information about the patient’s history, presentation, lab results, or previous ECGs. We might need to see the ECG done immediately before or after the one we are looking at.  Some ECG findings must ultimately be confirmed by an electrophysiology study before we can know for sure what is going on.

For those of us who are “ECG nerds”, it can be fun to debate our opinions and even more fun to hear from wiser, more advanced practitioners about their interpretations.

My belief, as a clinical instructor, is that we must teach strategies for treating the patient who has a “controversial” ECG that take into account the level of the practitioner, the care setting, and the patient’s hemodynamic status.  In some settings, it might be absolutely forbidden for a first-responder to cardiovert atrial fibrillation, for example.  But atrial fib is routinely cardioverted under controlled conditions in hospitals.  The general rule followed by emergency providers that “all wide-complex tachycardias are v tach until proven otherwise” has no doubt prevented deaths in situations where care providers did not agree on the origin of the tachycardia.

The ECG:    We do not have much patient information to go with this ECG, just that it is from a 71-year-old woman who developed severe hypotension and lost consciousness, but was revived with transcutaneous pacing.   Here is what we do know about this ECG:

·        There are regular P waves, at a rate of about 39 bpm (sinus bradycardia).

Dawn's picture

Complete Heart Block

Tue, 12/17/2019 - 18:02 -- Dawn

 


The Patient         This ECG was obtained from a 76-year-old woman who had just lost responsiveness while under care of an EMS crew. This tracing was obtained before a trans-cutaneous pacemaker was applied.

The ECG              The most noticeable feature of this ECG is the extremely slow rate. In fact, there are only two QRS complexes visible. The P waves are regular at a rate of about 145 bpm, so the underlying rhythm is sinus tachycardia.  NONE of the P waves are conducted, as evidenced by the different “PR intervals” in the two QRS complexes seen.  This is complete heart block at it’s most extreme – the QRS complexes represent a very insufficient escape rhythm.  A pacemaker is the only immediate treatment for this rhythm. Unfortunately, we don’t know the outcome for this patient.

It is very difficult to make judgements about the QRS complexes with only two of them, visible in three leads each.  The first set show the criteria for left ventricular hypertrophy.  The QRS in aVL is 20 mm tall, and anything over 11 mm meets voltage criteria for LVH.  In addition, the ST segments have the “strain” pattern, another sign of LVH.  The second QRS complexes are not typical of a normal ECG or one with LVH.  We cannot vouch for the precordial lead placement.

There is some disagreement in the literature regarding the naming of the blocks. Some consider “high-grade” to be only second-degree AVB with two or more consecutive non-conducted P waves. Others include third-degree AVB in the “high-grade” category.  It can come down to just semantics – the RATE and how the patient responds to the rate is the primary consideration.  Classification as to the origin of the block is helpful when determining the best long-term treatment decisions.

This is a good ECG for teaching the concept of AV dissociation, and how dangerous third-degree AV blocks and high-grade second-degree AV blocks can be.  

 

Dawn's picture

AV Block of Undetermined Type

Wed, 11/22/2017 - 16:48 -- Dawn

This strip was obtained from a woman who presented to her doctor’s office with hypertension. While there is some artifact in the baseline, it is possible to determine the presence of P waves, thanks in part to having two leads to assess.  We have provided an unmarked version of the strip for you to use, and also a marked version for the sake of this discussion.

The underlying rhythm is sinus bradycardia, at about 60 bpm, but with some slight variation in the P to P intervals (about 920 ms to 1040 ms). Because of the artifact, it is difficult to determine the exact P to P intervals, and the exact morphology of the P waves. So, we can’t say for sure that the P waves are all alike.

The AV block occurs at a 3:1 ratio.  That is, for every three P waves, one is conducted and produces a QRS complex.  When the P waves are not conducted, an escape rhythm occurs.

The escape rhythm occurs at an escape interval of about 1720 ms.  In other words, when a QRS does not occur by that time, the escape beat is produced.  It appears to be from the AV junction, in spite of the slow rate, because the escape QRSs look like the sinus conducted QRSs.  Both sinus and junctional rhythms are conducted along the bundle branches and produce the same QRS morphology.  The QRS complexes are approximately .08-.10 seconds wide.  Note that QRS complexes numbered 3, 5, and 7 have a P wave fused to the beginning of the QRS, making the QRS look wide when it is not.   A junctional escape rhythm results from AV block in the AV node, as the junction is the first available pacemaker below the AVN. 

This patient was scheduled for a treadmill stress test in her doctor’s office, which was cancelled. She had no cardiac symptoms at the time of the ECG, except the above-noted hypertension.  Unexplained bradycardia, especially when accompanied by AV node blocks, should trigger an assessment for inferior wall M.I., since the inferior wall of the LV shares a blood supply with the SA and AV nodes in the majority of people.

Dawn's picture

Inferior Wall M.I. With Right Ventricular M.I.

Sat, 10/28/2017 - 18:36 -- Dawn

This ECG was recorded from a 75-year-old man with substernal chest pain and diaphoresis.  It shows a pretty classic picture of acute inferior wall M.I. The second ECG is a repeat tracing with the V4 wire moved to the V4 Right position, and it is positive for right ventricular M.I.  The patient was found to have a 100% occlusion of the right coronary artery, which was opened and stented in the cath lab.

There are several other examples of IWMI with RVMI in our archives, so we will confine this commentary to the ECG signs that make these tracings so typical of right coronary artery occlusion. Once you are familiar with the typical pattern of IWMI / RVMI, it is easy to see, even when the ST elevation is subtle (as this one certainly is NOT).

Signs of IWMI in these ECGs are

·         ST elevation in inferior leads II, III and aVF.

·         Reciprocal ST depression in leads I and aVL. 

Signs of RVMI in these ECGs are:

·         ST elevation in V4 right.

·         ST elevation in V1 without ST elevation in V2.

Dawn's picture

Second-degree AV Block, Type II?

Wed, 02/01/2017 - 23:09 -- Dawn

This ECG is taken from an elderly woman who complains of feeling weak and tired. We have no other clinical information, unfortunately.

There is an obvious bradycardia, with more P waves than QRS complexes.  Here is what we see:

*  Atrial rate is around 115/min. and P waves are regular and all alike.

*  Ventricular rate is around 35/min. and QRS complexes are regular and all alike.

*  PR intervals, when they occur, are all the same at 162 ms.

*  QRS duration is wide at 122 ms.

*  QTc interval is prolonged at 549 ms.

What does this mean?  There is sinus tachycardia with second-degree AV block because the atrial rate is over 100/min, but not all P waves are conducted.  The AV block looks like a Type II (Mobitz II) block because the PR intervals are all the same.  This is a reliable indicator of conduction. (Not third-degree AVB).  The wide QRS complexes are due to right bundle branch block.  The ECG signs of RBBB are: 1) wide QRS; 2) supraventricular rhythm; and 3) rSR’ pattern in V1 and Rs, with a wide little s wave, in Leads I and V6.

Dawn's picture

High-Grade AV Block, Second-degree AVB Type II

Wed, 06/03/2015 - 21:25 -- Dawn

This ECG shows a second-degree AV block, Mobitz Type II.  It is also called “high grade AV block” because there is a 3:1 ratio of P waves to QRS complexes and a resulting slow rate.

Right bundle branch block and left anterior fascicular block are also present, as is common with Type II blocks.  The underlying rhythm is sinus.  Second-degree AVB, Type II, usually represents an intermittent tri-fascicular block:  often right bundle branch block and left anterior fascicular block (hemiblock) are present, and the left posterior fascicle develops an intermittent block.  During times of tri-fascicular block, the P waves are not conducted.  When the posterior fascicle is conducting, a QRS occurs.

A differential diagnosis for this ECG is complete heart block with ventricular escape rhythm.  A longer strip would be needed to see the P waves eventually dissociate from the QRSs, if they are going to do so.  Clinically, there is really little difference in the treatment of a high-grade "second degree" block and a "third degree" block. Both are treated with emergency support of the slow rate, as needed, and then a permanent implanted pacemaker.

It is notable that, in this case, the interpretation given by the machine is completely incorrect, even including the intervals.  This is not common, but does occur.  The machine's interpretation should be considered, but not followed blindly.

Dawn's picture

Complete AV Block

Tue, 09/16/2014 - 14:26 -- Dawn

This ECG is from an 84-year-old man who experienced dizziness and a fall.  He was not injured in the fall.  In this ECG, we can clearly see regular P waves at about 110 per minute.  We also see wide QRS complexes at about 52 per minute.  There is AV  dissociation - there are no regular PR intervals, or even progressively-prolonging PR intervals.  The atrial and the ventricles are beating to separate rhythms.  What is interesting about this rhythm is the origin of the escape rhythm.  The wide complex suggests a ventricular focus and the rate suggests supraventricular origin.  Near the end of the ECG, the escape rhythm either fails or slows significantly.  To see the next 12-lead ECG for this patient, go to this LINK.

The second ECG makes it more clear that this is an idioventricular escape rhythm, but the morphology of the QRS complexes suggested that, even in the first ECG when the rate was faster.  There are several clues that this is probably ventricular, including a very "backward" axis with aVR being upright and II, III, and aVF all being negative.  Also, V6 is negative, and there is nearly precordial concordance:  all except V1 are negative.  The morphology of the QRS does not fit a diagnosis of either left bundle branch block OR right bundle branch block.  The evidence points to a ventricular origin for this escape rhythm, and the patient quickly goes on to slow down severely.  Ventricular escape rhythm strongly suggests a sub-Hisian location for the block, and they tend to be more life-threatening than supra-Hisian blocks.

The take-home clinical lesson here is to BE PREPARED for worsening of the rate whenever AV block is present, especially high-grade AV block or sub-Hisian block.  This ECG is a very good one for teaching students to "march out" P waves, and find "hidden" P waves.  We have included a marked copy of this ECG to indicate those P waves.

Thanks to Sebastian Garay for donating these ECGs.

 

Dawn's picture

High-grade AV Block

Thu, 03/13/2014 - 14:42 -- Dawn

To continue on a topic started by Jason Roediger in his February ECG Challenge -

This series of two ECGs was taken from a 71-year-old man who complained of dizziness and near-syncope the day before these ECGs were done.  He was seen in an Emergency Dept., and advised to follow up with a neurologist. On the day of these ECGs, still feeling dizzy and like he would pass out, he called EMS again.  He denied chest pain.  We do not know his past medical history.  The first ECG was taken at 10:22 am.  His BP was 177/76 and SpO2 99%.  It shows a regular sinus rhythm (p waves marked by small asterisks) at a rate of about 75 / min.  There is a high-grade AV block, meaning that some P waves are conducted (beats 2, 4, 7), but most are not.  In addition, he has an escape rhythm, probably ventricular, at a rate of just over 40 / min.  The overall effect of the escape rhythm is to keep the heart rate above 40 beats per minute.

Fifteen minutes later, at 10:37 am, another ECG is taken.  The patient's BP is 154/86.   This ECG shows the high-grade AV block quite well, but this time, most of the QRS complexes on the strip are conducted from P waves.  It is difficult to see all the P waves in every lead, but if you remember that all three channels are run simultaneously, you will find evidence of the P waves in at least one of the three leads represented at any given time.  (Example:  V1, V2, and V3 - V3 shows the P waves well).  The next-to-last QRS on the page is interesting, as it has a different PRI than the normally conducting beats.  Is this a fusion beat or an aberrantly-conducted one?   It probably does not matter to the outcome of the patient. 

The slowing of the rate in the second strip gives us a clue as to why the patient felt dizzy, but the blood pressures recorded did not catch hypotension.  Possibly if the patient had been standing instead of lying on a stretcher, we would have seen more hemodynamic changes.

Unfortunately, we do not know the outcome of this patient, but it seems he is a candidate for an implanted pacemaker.

Dawn's picture

High-grade AV Block vs. Complete Heart Block

Sat, 04/27/2013 - 21:38 -- Dawn

This week's ECG of the WEEK was donated to us by Sebastian Garay. These two ECGs were obtained less than 30 seconds apart from an 84 year-old man who called fire-rescue because he felt dizzy and fell.  He was not injured in the fall, and his vital signs remained stable, with an adequate BP.  These two ECGs were obtained prior to arrival in the Emergency Dept.

The first one shows a sinus rhythm at about 110/min.  There is a complete heart block (third-degree AV block), and the escape rhythm is a wide-complex rhythm at a rate of about 54/min and slowing severely toward the end.  The second ECG was taken less than 30 seconds after the first, and shows a significantly slower escape rhythm rate at 27/min., while the sinus rate increases to 120/min.  The change is sinus rate is likely an attempt by the nervous system to compensate for the lower cardiac output as the ventricular rate slows. The escape rhythm is not only slower, but there are some changes in the QRS morphology from the first ECG.

For your basic students, this ECG serves to demonstrate the AV dissociation seen in complete heart block.  It is easy to "march out" the P waves, and see that some of them are "hiding" in the QRS comlexes.  It also shows how quickly a rhythm can change rates.

For your more advanced students, you will want to have a discussion about escape rhythms.  This one initially has a fairly fast rate, suggesting junctional origin. The QRS morphology is of the right bundle branch type, with left anterior fascicular block.  However, ventricular rhythms originating from the posterior fascicle region can have the "RBBB / LAFB" morphology.  If this escape rhythm is fascicular (ventricular) in origin, it is an accelerated idioventricular rhythm.  The second escape rhythm appears very similar to the first, with the very noticeable exceptions of QRS morphology, especially in V1 and V2, and the rate.

This patient was given Atropine in the ED, with no change to the rhythm.  We do not know what transpired after that, but suspect a pacemaker was in his future. 

We look forward to comments from our members about these two very interesting ECGs.

 

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