ECG Guru - Instructor Resources

A gathering place for instructors of ECG and cardiac topics.

       

Subscribe to me on YouTube

CHB

Complete AV Block With Junctional Escape Rhythm

Thu, 09/03/2015 - 23:02 -- Dawn

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. 

 

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.

 

Inferior Wall M.I. With Junctional Rhythm

Fri, 01/10/2014 - 15:07 -- Dawn

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.

ECG Basics: Idioventricular Escape Rhythm

Tue, 11/12/2013 - 14:38 -- Dawn

This six-second monitor strip was from a patient who was designated "Do Not Resuscitate", and whose heart rhythm was slowing dramatically.  It shows an idioventricular escape rhythm, with very wide QRS complexes and only two complexes in six seconds. (The top arrows mark three-second segments.)  If you look closely at the points marked by the lower arrows, you will see small, uniform, regular P waves.  The mechanism leading to this agonal rhythm was complete heart block.  A longer strip would show the P waves as all alike, and fairly regular, but slowing.  

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.

 

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

Thu, 11/15/2012 - 23:15 -- Dawn

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.

Third-degree AV Block (Complete Heart Block)

Wed, 08/22/2012 - 16:37 -- Dawn

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. 

All our content is FREE & COPYRIGHT FREE for non-commercial use

Please be courteous and leave any watermark or author attribution on content you reproduce.

Subscribe to RSS - CHB