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Complete AV Block With Junctional Escape Rhythm

Submitted by Dawn on Thu, 09/03/2015 - 23:02

This ECG was taken from a 90-year-old woman.  We have no other history, unfortunately.  It is a good example of a sinus rhythm with complete AV block, also called third-degree AV block.

The defining characteristics of this rhythm include:   1) an underlying rhythm that is regular and with a physiological rate.  In other words, the P waves are not so fast that they would not be expected to conduct one-to-one.  2)  a second rhythm of regular QRS complexes that is unrelated to the P waves.

Occasionally, a P wave may occur before a QRS and appear to have a PR interval.  This is just a chance meeting, as both rhythms (P waves and QRS complexes) are regular AT DIFFERENT RATES, so we would expect them to occur near each other from time to time.  NONE of the P waves are being conducted to the ventricles to produce QRS complexes. This is a good ECG to demonstrate "marching out" the P waves to see that they are very regular, even though some are hidden in the QRS, ST segment, or T waves.

In this case, the "escape rhythm" occurs from the AV junction.  The AV junctional pacemakers are "set" at a rate of about 40 - 60 beats per minute.  Normally, the sinus rhythm arrives in the AV junction faster than that, depolarizing the junctional pacemakers and preventing them from firing spontaneously.  In complete AV block, the atrial impulse never arrives, so the junctional pacemaker is free to "escape" and become the primary pacemaker of the heart.  We recognize this rhythm as junctional because the QRS complexes are narrow, and the rate is around 40 bpm.  Knowing that the escape rhythm is from the junction tells us that the AV block is in the AV node.  The AV junction is the first available pacemaker below the block.  Had the complete AV block been lower, in the bundle branches, the QRS would have come from the ventricles and would have been wide and slower.

In very general terms, this "supra-Hisian" type of AV block is preferable to a "sub-Hisian" block.  The rate is faster, and the QRS complexes narrow, both conditions causing a better cardiac output than wide QRS complexes and extremely slow rates.  However, the effect of the block on the patient has a lot to do with the cause of the block and the symptoms the slow rate cause.  Emergency treatment of the rate may be necessary if it causes a drop in blood pressure and perfusion.  Some patients with this type of block will need a permanent implanted pacemaker, but not all. 

 

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ECG Basics: Atrial Fibrillation With Complete AV Block

Submitted by Dawn on Tue, 05/19/2015 - 11:41

This patient has an underlying atrial fibrillation with complete heart block and an idioventricular escape rhythm.  She was treated successfully with a permanent implanted pacemaker.

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Complete AV Block

Submitted by Dawn on Tue, 09/16/2014 - 14:26

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.

 

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ECG Basics: Pacemaker Failure to Capture

Submitted by Dawn on Sun, 04/27/2014 - 17:29

This ECG is taken from a patient with an implanted pacemaker who was experiencing near-syncope.  She was taken to the hospital by EMS, where the pacemaker was adjusted to obtain ventricular capture.  This ECG did not have a Lead II rhythm strip, so the 12-lead ECG is being presented.  The P waves have been marked with a "P", pacemaker spikes marked with an arrow, and the QRS complexes marked with a "J" because they are junctional.  Because we can see 12 leads, or viewpoints, the morphology of the P waves and QRS complexes changes each time the machine switches to a new lead.

The underlying rhythm is sinus, with nearly regular P waves occuring at a rate of about 72 beats per minute.  The QRS complexes are also regular, but they are dissociated from the P waves.  Because the rate is near or just under 40 bpm, and the QRS complexes are narrow, this represents a slow junctional rhythm.  Because both atrial and ventricular rhythms are regular, but not associated with each other, an interpretation of complete heart block (third-degree AV block) can be made.  This explains why the patient had a pacemaker implanted.

The pacer spikes, for the most part, track the P waves, which is how this pacemaker is programmed.  They are not followed by a paced QRS complex, however.  This is failure to capture.  The second and fourth P waves did not stimulate a pacer spike because of their proximity to the T wave of the junctional beat.  The mA (energy setting) was adjusted in the Emergency Dept., and the pacemaker did not require repositioning.  The patient regained a reliable paced rhythm.

This section of the ECG Guru is meant to be for your basic students.  Pacemakers now have become very complex, with many options and variable settings.  So complex, that I would not feel comfortable getting into any more detail than I have here (although visitors to the site are welcome to).  It is important that, if you deal with patients in an emergency setting, you do not tell the patient that "something is wrong with their pacemaker" until it has been evaluated by a qualified person who can electronically interrogate the device.  It can be very difficult to determine from an ECG how a pacemaker is programmed, and how it should be reacting.  Since this patient had symptoms related to the bradycardia, and since pacemaker spikes occurred free of any refractory period and did not produce QRS complexes, it is safe to say there needs to be an adjustment.

In an emergency, with serious symptoms present, a transcutaneous or transvenous temporary pacemaker can be used.  Medications such as Atropine, epinephrine, and norepinephrine are also used, depending upon the type of AV block and the resources available.

 

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Inferior Wall M.I. With Junctional Rhythm

Submitted by Dawn on Fri, 01/10/2014 - 15:07

We do not have a patient history for this ECG, other than that it was an 81-year-old woman with chest pain.  The classic signs of acute ST-elevation inferior wall M.I. are there:  ST segment elevations in Leads II, III, and aVF.  There are the expected reciprocal ST depressions in Leads I and aVL.   The ST depression in V2 suggests posterior wall injury, and would normally be seen in V1 as well, unless something else is causing ST elevation in V1 at the same time.  That "something" would be right ventricular injury, and it can be confirmed by performing a V4Rt (or full set of right-sided V leads).  The slight elevation in V3 and V4 don't seem to "fit" with the IWMI - one might expect V5 and V6 to have ST elevation, reflecting injury in the low lateral wall.  We don't have the cath lab results, so we do not have an explanation for this (lead placement issues, perhaps?).

The rhythm here is interesting, but not unexpected with IWMI.  The rhythm is junctional, as reflected by the regular, narrow QRS complexes at a rate of about 54/min.  IWMI often causes blocks of the AV node, which has the same blood supply as the inferior wall in most people.  Even though there appear to be some "PR intervals", they are not consistent, and also do not meet the criteria for second-degree AVB Type I, so we are left with an interpretation of complete heart block.  The P waves here are also inconsistent.  They are regular at times, then disappear.  The SA node can be affected in IWMI also, and develop rate irregularities and exit blocks.  The IMPORTANT thing to consider is how the patient is handling the rate.  If this rate is not causing perfusion problems, that is - the patient has enough rate to maintain her blood pressure and level of consciousness, the rate is not harmful, and the junctional rhythm is not harmful.  In fact, one could argue that this junctional rhythm is more beneficial to the injured heart than a faster sinus rate would be.

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ECG Basics: Sinus Rhythm With Complete AV Block and Ventricular Escape Rhythm

Submitted by Dawn on Sun, 07/28/2013 - 13:36

This rhythm strip shows a good example of complete (third-degree) AV block with ventricular escape rhythm.  It will be easy for your basic students to "march out" the P waves.  They are regular at a rate of about 88/min., and they are either visible, or are "hiding" in the QRS complex.  The ventricular rhythm is wide and very slow, and completely dissociated from the sinus rhythm.

For your more advanced students, you may want to discuss the likely origin or "level" of the block.  Blocks above the Bundle of His can have JUNCTIONAL escape rhythms, while blocks that occur below the Bundle of His generally have ventricular escape rhythms.  Ask your students which type of CHB they would prefer to have:  suprahisian or subhisian - and why?

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High-grade AV Block vs. Complete Heart Block

Submitted by Dawn on Sat, 04/27/2013 - 21:38

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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Third-degree AV Block and Junctional Escape Rhythm With Right Bundle Branch Block and Prolonged QTc Interval

Submitted by Dawn on Sat, 01/26/2013 - 13:48

This ECG is from a 70 year old woman for which we have, unfortunately, no clinical information.  It shows a sinus rhythm with a rate of about 72 bpm (NSR) with AV dissociation caused by third-degree heart block.  The escape rhythm is junctional at a rate of 38 bpm.  There appears to be a right bundle branch block, based on the QRS duration of 132 ms, and a wide S wave in Leads I and V6.  The precordial leads do not show the usual RBBB pattern of rSR' in V1 and V2, and the r wave progression is poor (non-existent).  This is felt to be due to poor lead placement (a good teaching point).  Of interest, the ECG machine has reported a "severe right axis deviation" based on the tall upright R wave in aVR and the deep S in avF.  In RBBB, the first part of the QRS represents left ventricular depolarization, and the terminal wave represents the delayed right ventricle.  In effect, the two ventricles have their own electrical axes, which we can see because the ventricles are not depolarizing simultaneously.  The axis of the LV appears to be normal in this tracing.

In addition to the above, this patient has a very prolonged QT interval.  The QT is longer in bradycardic rhythms, but when corrected to a standard of 60 bpm (QTc), this patient's QT interval is still prolonged at QTc: 552 ms.  Without clinical data, we cannot speculate  as to why this patient's QTc is prolonged, but it can be a very dangerous situation.  Follow the links for more information on QT prolongation and Torsades de Pointes and Long QT Syndrome.

As always, we welcome comments from our members adding insight to this interesting ECG, and also questions you would like to ask our Guru members.

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Inferior Wall M.I. With Third-degree AV Block

Submitted by Dawn on Thu, 11/15/2012 - 23:15

This ECG was obtained from an elderly woman who suffered a complete right coronary artery occlusion and inferior wall M.I.  In her case, the AV node was also affected, and she developed a third-degree AV block with a junctional escape rhythm.  A good ECG for ACLS classes as well as for ECG classes.  A lively discussion can be had regarding "types" of complete heart block and the nature of the escape rhythm - when to treat and when to leave the rhythm alone.  In this case the rate of the junctional escape rhythm was adequate for perfusion, and the patient's blood pressure was stable. Priority for treatment in this situation is restore blood flow through the coronary artery, if the patient is a candidate for PCI.  You might want to review Christopher Watford's contribution to the Ask the Expert page on AVB vs. AV Dissociation.

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Third-degree AV Block (Complete Heart Block)

Submitted by Dawn on Wed, 08/22/2012 - 16:37

This 84-year-old man called 911 because he felt dizzy and fell.  He was not injured in the fall, but the paramedics noted a slow pulse. He denied significant medical history. The initial ECG showed sinus rhythm at about 80 bpm and AV dissociation with an apparent acellerated idioventricular rhythm at about 40 bpm.  Less than one minute later, he has developed a complete heart block with an idioventricular escape rhythm less than 30 bpm.  The escape rhythm speeds slightly toward the end of the strip.  He retained stable vital signs and adequate perfusion during transport.  It is presumed that he was scheduled for an implanted pacemaker.  It is interesting to note the machine's interpretation, and it reminds us to always interpret the ECG ourselves.   Thanks to ECG Guru member, Sebmedic, for his contribution of this ECG. 

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