Sunday, January 22, 2017

A very fast narrow complex tachycardia in an Infant

Case 1

A 4 month old infant with known co-arctation of the aorta and reflux presented with respiratory distress.

Here is the ECG:
A Narrow Complex Tachycardia with a rate of 218.
What is the rhythm?

Answer: there are clear P-waves in nearly every lead.  Notice the intervals are very short, which is typical of infants.  Infants can have very fast sinus tachycardia, easily reaching a rate of 220.  Most SVT in infants is faster than 220.

Throughout this case, the patient was on a cardiac monitor and the rate drifted up as high as 246, still in sinus (not recorded)!

The tachycardia turned out to be a result of disease (pneumonia), not a cause of it.

Case 2

This newborn presented to the ED for some exudate on the umbilical stump. There was no fever.  The infant was very well appearing.  The palpated heart rate at triage was 140.  There were no respiratory symptoms.

The ECG was performed because, on auscultation, the heart rate was far higher than palpated by pulse.
Narrow complex tachycardia at a rate of 300.

This shows how fast SVT can go in an infant and how well tolerated it might be.  This infant was completely without any signs of illness.

There is also electrical alternans, which is a normal finding in PSVT.

If you see this in sinus tachycardia, it indicates tamponade.

It was converted to sinus with adenosine.

Learning points

This shows how well a newborn/young infant tolerates a very fast heart rate, and that sinus tachycardia of 218 is not unusual, and may even go as high as 240!

If in doubt, use Lewis leads to find otherwise hidden P-waves

I don't have a case of use of Lewis leads in pediatrics, but here is a nice one in an adult:

Wide Complex Tachycardia. What is the Diagnosis? Use of the Lewis Lead.


  1. Most of us (assuming no pediatric cardiologists are listening) do not see a large number of pediatric arrhythmias (certainly far less than we’ve all seen in adults). As a result — level of comfort in both diagnosis and management tends to be less than that attained with adult arrhythmias. As wonderfully emphasized by Dr. Smith by the 2 pediatric arrhythmia examples shown here — accurate determination of rate is CRITICAL in the assessment of pediatric arrhythmias. For this determination — I have found use of the “Every-other-Beat” (or sometimes, “Every-third-Beat”) method a user-friendly way to rapidly and accurate determine heart rate for any regular fast rhythm. While most of us recall, “300- 150 - 100 - 75 - 60 - 50” as the answers for rate calculation when the R-R interval of a regular tachycardia is 1, 2, 3, 4, 5 or 6 large boxes, respectively — this becomes problematic with very fast rates. That’s because small differences in measurements may translate into significant under- or over-estimates of rate when rounding off dimensions of the R-R interval. But IF you instead only look at every-OTHER beat — you’ll find it a MUCH more accurate way for determining HALF the rate — which you then just double to accurately determine the actual rate.

    START by selecting a part of the QRS complex that begins or ends on a heavy line. For example — the 3rd S wave in lead 1 of the 1st ECG here begins right on a heavy line (it begins on the 4th heavy line that we see). Now count over 2 beats. You should see that 2 beats over (ie, the 5th beat in lead I) shows the S wave point to be just in front of the 7th heavy line). This means that 2 beats have occurred in just UNDER 3 large boxes. This means that HALF the rate is just a little bit faster than 100/minute, or~110/minute. Since HALF the rate ~110/minute — if we double this, we get 220/minute as an accurate estimate of the rate.

    Knowing that infants and young children may have sinus tachycardia rates of 200-220/minute then tells us NOT to worry about the rate of 220/minute seen here in which there are clear sinus P waves. The slight right axis and incomplete RBBB pattern we see here are also not of concern.

    The rate in the 2nd example here is easier to determine — because the R-R interval is approximately 1 large box in duration — which we know corresponds to a heart rate of ~300/minute. One might also think of AFlutter with 1:1 conduction in the differential — though prompt resolution with adenosine confirmed reentry SVT in this case. (Of note — AFlutter is a highly unusual rhythm in otherwise healthy children — but when it occurs, the rate of the atria with pediatric flutter may actually be much faster than the 250-350/minute range typically seen for flutter in adults). THANKS for presenting these insightful examples Steve!


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