Created on 8/4/2016 by Hiral Mehta, MD
Griffin is a 5 y/o boy who comes into the ER. Parents state that earlier today he began complaining of his “heart running fast” and his chest hurting. His cardiac exam is unremarkable. You decide to get an EKG as part of your work up.
What should I know when interpreting a pediatric EKG?
EKGs are simple, relatively straightforward to obtain, and provide a great deal of important information- if you are able to interpret them!
First: Lead placement
There are several different types of lead set ups. Intuitively, more leads generally provide more information. Remember, EKGs are vector representations of electrical depolarization. The more “viewpoints” you have, the more information you can gather.
5 Lead-ECG: This is what we generally have on our hospitalized kids who are on CRM (cardio-respiratory monitoring).
Think “smoke (black) over fire (red), snow (white) over grass (green)” and “white on right”.
12-lead EKG: This is the standard 12 lead EKG that we order. In pediatrics, we use the “V4R lead” to better assess the right ventricular potentials because the RV extends to the right of the sternum in children. This gets confusing- you should still use the leads that the machine labels “V1”-”V6” in that order (R->L anatomically), but start V1 further to the right (and relabel the EKG when it prints out).
How do I interpret this EKG?
Good general guidelines: have a systematic approach. Look at as many EKGs as possible to start getting a sense of what is “normal”, especially at various ages. One standard approach is to think through EKGs as an approach of “rate, rhythm, and axis” but really, everyone tends to develop their own methodology.
It is helpful to think of the EKG as a “graph” of electrical activity on the “Y-axis” and time on the “X-axis.” (For more in depth explanation, please see videos at end of the post).
- The standard speed of paper is 25mm/sec, but it is always helpful to make sure EKG strips you are looking at are run at the standard speed
- A “small box” is 0.04 seconds on the time axis and 0.1mV on the electrical axis
- A “big box” is 0.2 seconds on the time axis and 0.5mV on the electrical axis
Basic components of Interpretation:
- For regular rhythms (more below on how to determine this), Rate = 300/ #of big boxes between 2 consecutive R waves
- For faster rhythms (infants), Rate = 1500/ #small boxes between 2 consecutive R waves
- For irregular rhythms, Rate = number of complexes on rhythm strip (usually lead II), multiplied by 6
- P waves: absent or present?
- Relationship between p- waves and QRS
- For sinus rhythm, there is a 1-1 relationship between p waves and QRS
- Regular vs Irregular (are intervals consistent across the rhythm strip)?
- If Irregular, is it regularly irregular (classically A-flutter) or irregularly irregular (classical atrial fibrillation)
- QRS morphology
- Narrow (sinus or junctional origin)
- Wide (ventricular origin)
Axis: There are multiple ways of determining the “axis.” Below highlights 1 of these methods. “Normal” axis changes with age, with infants having a “rightward” axis. As children grow older, the axis becomes more leftward.
Waves and Intervals:
- P wave- represents atrial depolarization
- QRS complex- represents ventricular depolarization
- T wave- represents ventricular repolarization
(Note: In case you were wondering, there is an atrial repolarization wave, but it is “hidden” in the QRS complex).
Note: Remember, standard speed of paper is 25mm/sec, therefore, a “small box” is 0.04 seconds on the time axis and 0.1mV on the electrical axis and a “big box” is 0.2 seconds on the time axis and 0.5mV on the electrical axis
PR interval: This reflects conduction from the SA node → AV node.
- Normally thought of as 0.12- 0.2 sec (one “big box”) for adults; however in children it varies with age and HR.
QRS interval: Represents ventricular depolarization. The Q wave reflects depolarization from L -> R across the interventricular septum, the R wave reflects depolarization through the thick ventricular walls, and the S wave reflects depolarization of the Purkinje fibers. Again, normal intervals vary by age.
QT interval: Represents the time it takes for ventricular depolarization and repolarization. This is one of the intervals that can’t really be obtained just by reading off what the EKG machine calculates, since QT varies with the HR and the individual RR intervals. This will be expanded upon in a future topic, but for now:
- The calculated “corrected QT” interval (QTc) is most commonly derived with Bazett’s Formula:
- Use the RR interval preceding the QT interval that you’re looking at. This formula is most accurate for HRs 60-100!
- Infants normally have a longer QTc (under 6 months, QTc of <490 msec is considered normal). Children older than 6 months should have a QTc <440msec.
- MD Calc
For reference, here is a table with some normal EKG values for children (adapted from Sharieff et al, 2006):
Videos From around the web:
Basics of EKG leads
The Limb Leads
The Precordial Leads
Faculty Reviewer: Sara Ford, MD
Resident Reviewer: Brian Lee, MD
“ECG Basics.” http://lifeinthefastlane.com/ecg-library/basics/
“Paediatric ECG Interpretation.” http://lifeinthefastlane.com/ecg-library/paediatric-ecg-interpretation/
Sharieff GQ, Rao SO. The pediatric ECG. Emerg Med Clin North Am 2006;24:196.