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Pediatric ECG With Junctional Rhythm

Tue, 10/07/2014 - 00:07 -- Dawn

This ECG, taken from a nine-year-old girl, shows a regular rhythm with a narrow QRS and an unusual P wave axis. Unfortunately, we do not have any clinical information. 

Normally, P waves are positive in Leads I, II, and aVF and negative in aVR.  They can be biphasic in V1, but are usually positive in the rest of the precordial leads. . The P waves in this ECG are NEGATIVE in Leads I,II, III, aVF, and V3 through V6.  This indicates RETROGRADE conduction through the atria - the impulse starts low and continues in a backward fashion through the atria. This tells us that the rhythm originated in the AV junction or low atria.  The "junction" is usually defined as all of the complex AV node and the Bundle of His. 

The literature over the years has been very confusing about the exact location of the "junctional" pacemakers.  One commonly-accepted guideline was that a rhythm is "junctional" if there are retrograde P waves with a short PR interval, or a P wave that occurs within or after the QRS.  A rhythm with a retrograde P wave and a NORMAL PR interval is said to be "low atrial", indicating that the ectopic pacemaker involved was located in the low atrium, producing retrograde conduction through the atria and normal delay through the AV node.

While both of these scenarios are plausible, it probably is not possible to say with certainty where the actual pacemaker is just by looking at the surface ECG.  The AV node has been found to have pacemaking capability in all three of it's regions, and the Bundle of His is also able to produce ectopic impulses.  PR intervals vary greatly, especially in pediatric patients, and can be influenced by heart size and heart rate.  The retrograde conduction through the AV node toward the atria can occur over the fast or slow pathways. The "major" junctional pacemaker is thought to be in the proximal Bundle of His.  Junctional or low atrial ectopic rhythms can occur because they override the rate of the sinus rhythm, following the rule that "The fastest pacemaker controls the heart".  junctional rhythms can also occur as "escape" rhythms, only occurring because the sinus impulse has failed or been vlocked - often due to AV block.

Since the exact location of the ectopic pacemaker in this case cannot be determined without electrophysiology studies, it is important to evaluate the effect, if any, the rhythm is having on the patient. Since there is a P wave before every QRS, and the QRS complexes are narrow, it can be assumed that there will be no clinical effect on this patient.  In addition, the rate is within normal range, and that is also unlikely to produce any clinical effect.

The causes of ectopic rhythms are many, and range from completely benign to serious.  So, this child should be evaluated in light of her symptoms, history, and physical assessment.

The ECG remains a good teaching example of retrograde P waves that are NOT dissociated from the QRS complexes.

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Comments's picture

     As per Dawn - this tracing obtained from a 9-year old child shows what appears to be an AV Nodal rhythm - with 1:1 AV conduction from negative P waves preceding each of the inferior leads with a constant PR interval. I'd add the following points to Dawn's discussion. 

  • For practical purposes - I have always referred to "AV Nodal rhythms" and "Junctional rhythms" are synonyms. Technically - this may not be correct ... - as some view the AV Junction as being a composite structure that includes the AV Node as well as entering regions to the structure and departing regions (which is comprised of the upper portion of the Bundle of His). In theory - the upper portion of this AV nodal composite manifests a slightly faster escape rate (45-60/minute in adults) and is more likely to be subject to autonomic tone than the lower portion (the His) which manifests a slower escape rate (40-45/minute) and is less subject to autonomic influence. That said - my impression is less than total consensus on the makeup of the AV junction. Due to popular usage - I've continued synonymous use of the terms "AV Node" and "AV Junction", while realizing that technically this usage may be questioned ...
  • The above "escape rates" are different in children! Whereas we typically think of AV Nodal "escape" at a rate range between 40-60/minute in adults - this rate range is closer to 50-80/minute in children. Those limits may further vary depending on the age of the child. 
  • The ventricular rate appears to vary by a slight-but-definite amount in this tracing. The R-R interval is most often slightly less than 3 large boxes in duration - but sometimes more than 3 large boxes (ie, rate variance between ~ 95-to-110/minute). It would seem that an AV nodal escape rate of between 95-110/minute as seen here is a bit faster than is normally anticipated. Slight-but-real variation in the R-R interval throughout the tracing though suggests autonomic influence is operative.
  • Duration of the negative PR interval preceding each QRS in the inferior leads can not be used to accurately predict site of origin of the escape impulse from the surface ECG. Rather than distance - the relatively longer negative PR interval seen here more accurately reflects relative speed of the impulse retrograde compared to forward conduction down to the ventricles. Faster downward conduction may produce a longer negative PR interval. In contrast - comparable retrograde and downward conduction typically results in no P wave at all on the surface ECG (because the negative P wave in such cases is hidden within the QRS). While unable to absolutely rule out the possibility of a low atrial rhythm - the autonomic influence and relatively large amplitude of atrial activity seen here lead me to favor an AV Nodal site of origin.
  • Beyond-the-Core: Two other possibilities might initially be considered for the atrial activity seen here: i) Lead V2 almost suggests 2:1 conduction; and ii) Could this be reentry via fast-slow conduction through the AV node? That said - Neither of these possibilities is operative here. Lead V2 is the only lead suggesting the possibility of an extra P wave - and the fact that the interval between the 1st-to-the-2nd P-P vs the interval from the 2nd-to-the-1st P-P is not equal - therefore 2 P waves are not present. This also can't be a reentry tachycardia at slow ventricular rate with retrograde conduction over the slow pathway because the RP' interval (distance from the QRS to the negative P wave that occurs after it) is changing! With fast-slow reentry - the RP' distance is constant. I would also expect a more common escape rate if site of origin was from a low atrial focus.
BOTTOM LINE: I would interpret this tracing as a relatively fast and slightly variable AV Nodal Rhythm in a 9-year old child. Clinical correlation (which unfortunately we don't have) would be needed to determine if this was a normal phenomenon in this child vs an indicator of underlying structural disease or some other disorder. If the child was otherwise healthy and asymptomatic - I'd favor the former.

Ken Grauer, MD 

Submitted by drk on

I'm not an expert.

It looks like a slightly variable supranodal or junctional paroxistic rythm or inferior posterior left atrial rythm. Maybe para and supranodal.

The variability may be to the respiration, it has 5 cicles repetion( in D II bellow ). 

What about ST in D I, aVR and V 3 leads?

What about the variations in aVL and V 2?

Underlyng structural disease, intoxication?'s picture

@ drk - I think we essentially agree about the rhythm - namely that it is difficult to be certain of etiology but that it may indeed by a slightly variable junctional rhythm in this 9-year old child (but that we can't rule out a low atrial source). There may be respiratory variation. I do see slight ST-T wave deviations. Some of this may reflect T of the abnormal P wave ... Overall - given that the patient is a 9-year old child, I don't think ST-T wave deviations are of clinical significance - but then again we unfortunately have no clinical correlation ...

Ken Grauer, MD 

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