Approach to Pediatric ECGs

Click for pdf: ECG basics

First thing’s first

  • Check the name on the top of the ECG – is this your patient?
  • Check the date – is this the one you ordered?
  • Check for old ECGs – just like a chest xray, it’s always a good idea to compare with an old one
  • Check for the age of the patient – the heart physiology and the normal values differ in different age groups in the pediatric population

Note: You may want to cover the top part of the ECG sheet now.  Do not rely on the computer calculated numbers; it may be wrong.  Trust yourself!

Technical Aspects

  • Is the ECG full standard?
  • Full standard means that the ECG was not reduced in size so that it can fit on the paper
  • Look at the left hand side of each line

If it is full standard, the rectangle’s height should be 2 big squares

If it is half standard, the rectangle’s height is only 1 big square.  You will need to double all the waves to normalize them

What is the paper speed?

  • The standard speed is 25mm/sec
  • That means each little box is 0.04 seconds, each big box is 0.2 seconds, the whole strip is 6 seconds
  • Now look at the top of the ECG, there should be a print out of what speed the ECG was ran at
  • For tachyarrhythmias, the speed of the ECG may have been increased to 50 mm/sec in order to visualize the p waves; in this case, the speed and duration of the ECG components will need to be doubled


  • Normal, Fast or Regular Rates
  • Find 2 adjacent R waves, count the number of big squares between the R’s
  • Divide 300 by the number of big squares : this is your rate
  • Or . . . .Find a QRS complex that starts on a thick line, then count the thick lines using these numbers “300-150-100-75-60-50” to the next QRS

Slow or Irregular Rates

  • The easiest way to calculate the rate is to count the total number of QRS complex along the length of the entire strip and multiply it by 10: this is your rate (bpm)
  • Note: The normal value for heart rate ranges dramatically depending on your patient’s age.  Please compare your patient’s age and heart rate with Table 1.



  • Is the rhythm sinus?

Sinus rhythm:

  • Is there a P wave before each QRS complex?
  • Is there a QRS complex after every P wave?
  • Are the P waves upright in leads I, II, III?
  • Do all P waves should look the same?
  • Are all P wave axis normal (0° to +90°)?
  • Are the PR intervals constant?
  • Is the rhythm fast or slow? (refer to Table 1 values)
  • Is the rhythm regular or irregular? Do the P waves and QRS follow a regular pattern?
  • If it is irregular, is it consistently irregular or consistently irregular?

Consistently irregular = some form to the pattern of irregular complex i.e. predictable
Inconsistently irregular = no pattern at all i.e. unpredictable

Abnormal Rhythms

Premature Atrial Contraction (PAC)
  • Length of two cycles (R-R) usually shorter
  • Preceded by P wave, followed by normal QRS
  • No hemodynamic significance
Premature Ventricular Contraction (PVC)
  • Premature, wide QRS, no P waves, T wave opposite to QRS
  • I.e. multifocal, bigeminy, trigeminy, couplets
  • Maybe normal if uniform and decrease with exercise
Atrial Flutter
  • Rapid atrial rate (~300 bpm) with varying ventricular rate
  • Sawtooth pattern
  • Suggests significant pathology
Atrial Fibrillation
  • Very fast atrial rate (350-600 bpm)
  • Irregularly irregular
  • No P waves, normal QRS
  • Suggests significant pathology
Ventricular Tachycardia
  • Wide, unusually shaped QRS
  • T waves opposite direction of QRS
  • HR 120-200 bpm
  • Suggests significant pathology
Ventricular Fibrillation
  • Very irregular QRS
  • Rate is rapid and irregular
  • “terminal arrhythmia”


  • Axis is the “conduction flow” of the heart
  • Normal axis varies with age – i.e. newborns have a right axis deviation because the left and right ventricles are the same size due to fetal circulation

  • Look at the QRS complex of Lead I and Lead aVF
  • Is the QRS complex of Lead I more negative (downgoing or conduction away from the lead) or positive (upgoing or conduction towards the lead)?
  • Is the QRS complex of Lead aVF more negative or positive?
Lead I Lead aVF Axis
+ + Normal
+ Left Axis Deviation
+ Right Axis Deviation
Extreme Right Axis Deviation

P Wave and PR Interval

  • PR = beginning of P to beginning of QRS
  • P wave normal is 2-3 little squares (0.08-0.12); if wide P wave = left atrial enlargement
  • If P wave is taller than 2-3 little squares = right atrial enlargement
  • PR interval is dependent on age (Table 1); if PR is wide = first degree AV block

QRS Complex

  • If beginning of Q to end of S is longer than 2-3 small squares: bundle branch block
  • Look for the “M” sign in either V1 or V6
  • If the “M” is on V1:  Right bundle branch block (RBBB)

  • If the “M” is on V6 : Left bundle branch block (LBBB)

QTc Interval

  • Beginning of Q to end of T
  • QT corrected interval for heart rate because as HR decrease, QT lengthens and vice versa
  • Normal: <0.45 (<6 months), <0.44 (>6 months)
  • QTc = QT / square root of RR interval
  • DDx prolonged QT: long QT syndrome, hypokalemia, hypomagnesemia, hypocalcemia, neurologic injury
  • Prolonged QT predisposes to ventricular tachycardia and associated with sudden death

T wave

  • DDx of peaked, pointed T = hyperkalemia, LVH
  • DDx of flattened T waves = hypokalemia, hypothyroidism

Ventricular Hypertrophy

Right ventricular hypertrophy

If any of the following:

  • R wave >98% in V1 or S wave >98% in I or V6
  • Increased R/S ratio in V1 or decreased R/S in V6
  • RSR’ in V1 or V3R in the absence of complete RBBB
  • Upright T wave in V1 (>3 days)
  • Presence of Q wave in V1, V3R, V4R
  • DDx of RVH: ASD, TAPVR, pulmonary stenosis, TOF, large VSD with pulmonary HTN

Left ventricular hypertrophy

If any of the following:

  • R >98% in V6, S >98% in V1
  • Increased R/S ratio in V6 or decreased R/S in V1
  • Q >5mm in V6 with peaked T
  • DDx: VSD, PDA, anemia, complete AV block, aortic stenosis, systemic HTN


a) Table 1:  Normal Values

Age HR
in V1mm
in V1mm
in V6mm
in V6mm
1st week 90-160 60-180 0.08-0.15 0.03-0.08 5-26 0-23 0-12 0-10
1-3wks 100-180 45-160 0.08-0.15 0.03-0.08 3-21 0-16 2-16 0-10
1-2 mo 120-180 30-135 0.08-0.15 0.03-0.08 3-18 0-15 5-21 0-10
3-5 mo 105-185 0-135 0.08-0.15 0.03-0.08 3-20 0-15 6-22 0-10
6-11 mo 110-170 0-135 0.07-0.16 0.03-0.08 2-20 0.5-20 6-23 0-7
1-2 yr 90-165 0-110 0.08-0.16 0.03-0.08 2-18 0.5-21 6-23 0-7
3-4 yr 70-140 0-110 0.09-0.17 0.04-0.08 1-18 0.5-21 4-24 0-5
5-7 yr 65-140 0-110 0.09-0.17 0.04-0.08 0.5-14 0.5-24 4-26 0-4
8-11 yr 60-130 -15-110 0.09-0.17 0.04-0.09 0-14 0.5-25 4-25 0-4
12-15 yr 65-130 -15-110 0.09-0.18 0.04-0.09 0-14 0.5-21 4-25 0-4
> 16 yr 50-120 -15-110 0.12-0.20 0.05-0.10 0-14 0.5-23 4-21 0-4


Garcia, Tomas and Neil Holtz. 12-Lead ECG: The Art of Interpretation. Jones and Bartlett Publishers Canada. 2001

Interpreting Pediatric ECG. Pediatric Cardiology at the University of Chicago.


Written by: Jasmine Lam

Edited by: Jeff Bishop

2 responses to “Approach to Pediatric ECGs”

  1. dr fayyaz

    an excellent presentation,learning and a tremendous website.

  2. dr fayyaz


Post Comment

You must be logged in to post a comment.

a place of mind, The University of British Columbia

Learn Pediatrics
Vancouver, BC, Canada

Emergency Procedures | Accessibility | Contact UBC  | © Copyright The University of British Columbia