Notes on the basics of pediatric ECG interpretation.

1. ECG Notes

2. Learning objectives
• Basics of ECG
• Establish consistent approach to interpreting ECGs
• Rate, rhythm, axis and identifying ischemia
• Review essential life- threatening cases
• Provide additional resources for future learning
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3. Normal impulse conduction
• Sinoatrial node
• AV node
• Bundle of His
• Bundle branches
• Purkinje fibers
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4. PQRST
• P wave = atrial depolarization = SA node
function
• PR interval = atrial depolarization + delay
in AV junction (AV node & bundle of His) =
delay allows time for the atria to contract
before the ventricles do
• QRS wave = ventricular depolarization
(muscle contraction)
• T wave = ventricular repolarization
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5. Pacemakers of heart
• SA node: dominant pacemaker with an intrinsic rate of 60- 100 beats/ min
• AV node: back- up pacemaker with an intrinsic rate of 40- 60 beats/ min (= nodal rhythm = seen in
heart blocks)
• Ventricular cells: back- up pacemaker with an intrinsic rate of 20- 45 beats/ min (= last resort)
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6. The ECG paper
• It is a thermal paper that records
electrical activity of the heart
• Horizontally we measure in seconds
(time)
• Vertically we measure in mm (amplitude)
• 1 small box = 0.04 seconds & 1 mm
• 1 big box = 0.2 seconds & 5 mm
• 1 big box has 5 small boxes up & down
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7. Heart rate
• Every six seconds = 30 large boxes
• This helps when calculating the heart rate
• Heart rate = # of R waves x 10
• Normal resting HR:
• Newborn: 110- 150 bpm
• 2 years: 85- 125 bpm
• 4 years: 75- 115 bpm
• > 6 years (like an adult): 60- 100 bpm
• Adult: 50- 100 bpm
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9. Steps of any rhythm analysis
1. Calculate rate: # R waves in 6 seconds x 10
2. Determine regularity: look at the distance between the R waves - use a caliper or marking on
pen/ paper. Are they equidistant apart, occasionally irregular, regularly irregular or irregularly
irregular?
3. Assess P waves
4. Determine PR interval
5. Determine QRS interval
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10. Step 3: assess the P waves
• Are there P waves?
• Do all the P waves look alike?
• Do the P waves occur at a regular rate?
• Is there one P wave before each QRS?
• Normal = Normally shaped P waves with 1 P wave before each QRS
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11. P mitrale = left atrial enlargement
• P mitrale indicates left atrial enlargement
• The wave is widened and has 2 peaks
• Indicates pulmonary hypertension and mitral stenosis
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12. P pulmonale = right atrial enlargement
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• May also occur in mitral stenosis or
pulmonary hypertension
• Note than in pulmonary HTN there
will also be inversion of T waves in V1

13. Step 4: determine PR interval
• Normal is 0.12- 0.20 seconds (3- 5
small boxes)
• PR should not be more than 5 small
squares
• Measure from start of P to start of R
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14. Long PR interval
• First degree AV block
1. Drugs (all increase vagal tone or antagonize sympathetic system  can lead to sudden
death)
a. Calcium channel blockers
b. Beta blockers
c. Digoxin toxicity (can cause any arrhythmia, but mainly tachyarrhythmias in children &
bradyarrhythmias in adults)
d. Opioids
e. Clonidine
f. Sedative- hypnotics
2. Atrial surgery (scar tissue)
3. Acute rheumatic fever (minor Jones criteria)
4. Kawasaki disease
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15. Short PR interval
1. Wolff- Parkinson- White syndrome
2. Pompe’s disease (glycogen storage disease IIa)
3. Fabry’s disease (heart + kidney)
4. GM- 1 gangliosides
5. Friedreich’s ataxia
6. Duchenne muscular dystrophy
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16. WPW syndrome
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17. Step 5: QRS wave
• Normal: 0.04- 0.12 seconds (1- 3 small boxes)
• QT interval will be short in digoxin toxicity and hypercalcemia
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18. Long QT interval
• Congenital
1. Jervell- Lange- Nielsen syndrome: AR + deafness
2. Romano- Ward syndrome: AD + each generation will have a sudden death + normal hearing
• Acquired:
1. Metabolic:
a. Hypocalcemia
b. Hyperkalemia
c. Hypomagnesemia
d. Malnutrition
2. Drugs:
a. Type Ia and III anti- arrhythmics
b. Phenothiazines
c. TCAs
3. CNS trauma (brain edema  long QT  sudden death)
4. Myocardial ischemia or myocarditis
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20. QTc calculation
• Normal must be < 0.40- 0.45 seconds
• Formula = Bazett formula
• < 0.45 s = normal
• 0.45- 0.48 s = doubtful
• 0.48- 0.50 s = highly suspicious of prolonged QT
• > 0.50 s = confirmed prolonged QT
• So just remember 1 small square = 0.04 s
• Your QT & RR in the formula will be the # of small
squares times 0.04   
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23. Arrhythmia formation
• Arrhythmias can arise from problems in the:
• Sinus node
• Atrial cells
• AV junction
• Ventricular cells
• SA node may fire too slow or fast  sinus bradycardia or sinus tachycardia
• Atrial cell problems:
• Fire occasionally from a focus = premature atrial contractions (PACs)
• Fire continuously due to a looing re- entrant circuit = atrial flutter or paroxysmal SVT
• Block impulses coming from SA node = AV junctional blocks
• Ventricular cell problems:
• Fire occasionally from 1 or more foci = premature ventricular contractions (PVCs)
• Fire continuously from multiple foci = ventricular fibrillation
• Fire continuously due to a looping re- entrant circuit = ventricular tachycardia
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24. Sinus tachycardia
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25. Sinus bradycardia
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26. Atrial flutter (always regular rhythm)
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• Mechanism: Re- entrant pathway in the right atrium with every 2nd, 3rd or 4th impulse generating a
QRS (others are blocked in the AV node as the node re- polarizes)

27. Atrial fibrillation (always irregular rhythm)
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28. Premature atrial, junctional and ventricular contractions
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29. First degree heart block (fixed prolonged PR with NO drop beat)
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30. Second degree Mobitz Type I heart block (progressive longer PR + drop)
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31. Second degree Mobitz type II heart block (normal PR + drops)
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32. Third degree heart block (complete dissociation between P and QRS, but
their inter- distances are fixed)
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33. Paroxysmal SVT (fast HR + P wave absent + narrow QRS + ST changes)
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34. More PSVT examples 
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35. Ventricular tachycardia
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36. Ventricular fibrillation
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37. Torsade's de pointes
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38. Ventricular Hypertrophy 
• Left ventricular hypertrophy
looks like:
• Deep R in V1
• High S in V 6
• Right ventricular
hypertrophy looks like:
• Deep R in V1
• Deep S in V6
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41. Right bundle branch block 
• Basically V1 and V2 have rabbit ear kind of QRS
• Can be seen in ASD as right atrial enlargement will cause delay of signal conduction from there
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43. Left bundle branch block (LBBB) 
• V1 and V2 have the same kind of wide predominantly negative QRS
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44. LBBB 
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