ECG basics in kids

Question 1

Normal electrical axis

Answer 1

Positive in Lead I, II and AvF

Question 2

Differences in paediatric ECGs vs adults

Answer 2

Faster heart rates
Shorter PR and QRS intervals
RV dominance (apparent RV strain pattern)
i. R axis deviation (> +90°)
ii. T wave inversions in V1-V3
1. Starts in first weeks of life, disappears by school / teenage
iii. Dominant R wave in V1

Q waves in inferior and lateral leads
i. 0-1 month in III up to 4 small squares expected
ii. Abnormal after school age

Question 3

Potential site of blocks

Answer 3

SAN – internodal tracts – AV node – His – AP fascicles – Purkinje

Question 4

Sinus p wave characteristics

Answer 4

P wave axis [0° and +75°]
Best seen in leads Il and V1
Upright in leads I and II
Usually biphasic in lead V1 inverted in aVR
Amplitude: < 2.5 small squares (<0.25mV)
Duration: < 3 small squares (< 120ms)

Question 5

Abnormal p-wave characteristics

Answer 5

• Lack of p-wave
• Retrograde p-wave

Question 6

Sinoatrial block definition

Answer 6

Delay from SAN to atrial activation - before p wave

Question 7

First degree SAN block characteristics

Answer 7

can not dx on ECG as this is delay from SAN and P wave

Question 8

Second degree type I SAN block

Answer 8

with each other beat reduced conduction from SAN to atria, then dropped p-wave, PP interval prolongs across beats

Question 9

Second degree type II SAN block

Answer 9

regular p-wave, regular QRS, then missed p-wave regularly missed, PP interval regular

Question 10

Third degree SAN block

Answer 10

full loss of p-waves irregularly

Question 11

AV block - I degree

Answer 11

PR prolonged

Question 12

AV block - II degree type I

Answer 12

PR prolongs then drops
Block at the level of the AV node

Question 13

AV block II degree type II

Answer 13

regular drop
* Block at His – narrow QRS
* Block at Tawara branches – wide QRS
* Block at right and left bundle fascicles – wide QRS

Question 14

AV block III degree

Answer 14

Complete AV dyssynchrony, ventricular or junctional escape

Question 15

RBBB characteristics

Answer 15

98th centile or 0.12s
Rightward - anterior terminal vector
V1, V2: rSR’ [R’ > r], downsloping ST segments
V5, V6, I, aVL: broad S waves [duration of S > R]
T wave discordance
ORS axis not be affected
Left axis deviation: concomitant left anterior hemiblock [LAH] or other causes
Right axis deviation: concomitant left posterior hemiblock [LPH] or other causes

Question 16

LBBB charcteristics

Answer 16

Duration ‚98th centile or 0.12s
Leftward-posterior terminal vector
V1, V2: - broad, deep S [r wave may be absent = QS]
ST elevation, positive T waves
V5, V6, I, aVL: broad (notched) R waves
ST depression, inverted T waves

Question 17

Left anterior hemiblock [LAH]

Answer 17

QRS prolonged (<98th centile or <0.125]
Terminal vector left-posterior + upward orientation
Left axis deviation (-45° to -90° adults]
II, III, aVF - rS
I, aVL-qR

Question 18

Left posterior hemiblock [LPH]

Answer 18

QRS prolonged (<9th centile or <0.125]
Terminal vector right-downward orientation
Right axis deviation (+90° to + 180° adults]
II, III, aVF - qR
I, aVL – rS
Always occurs in AVSD

Question 19

Mechanisms of SVT

Answer 19

Abnormal automaticity
Triggered activity (early and delayed after depolarization)
Re-entry mechanism (abnormal impulse conduction)

Question 20

Dual AV node pathway (AVNRT) characteristics

Answer 20

Fast (normal) and slow (abnormal) pathway in dual AV node physiology
On usual rhythm, re-entry will compete with forward conduction in slow pathway therefore does not lead to tachycardia
When atrial ectopic happens, this can happen while fest pathway is still refractory, therefore goes down the slow pathway, and then conducts retrograde via fast where it is now no longer refractory (slow-fast)
On ECG key feature will be a retrograde p-wave and short RP interval
When ventricular ectopy, this will lead to an anti-clockwise direction of conduction (up the slow pathway, down the fast pathway) (fast-slow)
On ECG the key feature will be retrograde P but long RP interval

Question 21

How can P waves help differentiate narrow complex SVTs

Answer 21

Sinus p-waves with long RP interval = sinus tachycardia with atrial ectopy OR sinoatrial node reentrant tachycardia

Abnormal p-waves with one single morphology with long RP interval = ectopic atrial tachycardia

Abnormal p waves with >3 morphologies = multifocal atrial tachycardia

Retrograde p-waves with SHORT RP interval = Typical AVNRT, AVRT or JET

Retrograde p-waves with LONG RP interval = AVRT with slo accessory pathway, atypical AVNRT

Flutter waves = arial flutter

Fibrillatory waves = AF

Question 22

Retrograde p-waves with LONG RP interval ddx

Answer 22

= AVRT with slo accessory pathway, atypical AVNRT

Question 23

Retrograde p-waves with SHORT RP interval ddx

Answer 23

= Typical AVNRT, AVRT or JET

Question 24

Abnormal p waves with >3 morphologies dx

Answer 24

= multifocal atrial tachycardia

Question 25

SVT, post-adenosine or vagal manouvres NO p-waves seen ddx

Answer 25

JET, atypical AVNRT, AVRT

Question 26

Wide complex SVT ddx

Answer 26

o SVT with BBB
o Antidromic AVRT (orthodromic – down AV node, back via accessory; antodromic down accessory, back via AV node) NB here you would still see delta wave even within tachycardia
o Aberrant conduction

Question 27

Differentiating SVT with aberr conduction vs VT

Answer 27

AV dissociation – supports VT
Capture beats
Fusion beats – consistent with VT
Extreme axis deviation (“northwest axis”) - 90° to +180°
Positive or negative concordance in the precordial leads – suggests VT
Absence of RBBB or LBBB morphology – suggests VT
RSR’ in V1 with R>R’ / notched downslope to R wave
QRS complexes > 160ms (adults) suggests VT
Brugada sign – onset of R wave to nadir of S wave >100ms in precordial leads, suggests VT
Josephson sign – notching near the nadir of the S wave, typical of VT

Question 28

Brugada sign to differentiate SVT aberr cond vs VT

Answer 28

Brugada sign – onset of R wave to nadir of S wave >100ms in precordial leads, suggests VT

Question 29

Josephson sign to differentiate SVT aberr cond vs VT

Answer 29

Josephson sign – notching near the nadir of the S wave, typical of VT

Question 30

VT types

Answer 30

Defined as consecutive ventricular beats (100-250bpm), QRS > 98th centile (>0.12s) [if HR >250bpm - ventricular flutter]
Non-sustained (<30 seconds) vs sustained (>30 seconds)
Idiopathic vs secondary to heart disease
Monomorpic VT
(includes RVOT VT and fascicular VT) RVOT = LBBB pattern and inferior axis
Polymorphic VT
(includes torsades de pointe)

Question 31

Characteristics of RVOT VT

Answer 31

LBBB pattern and inferior axis

Question 32

Definition of RVH in children

Answer 32

o R/S ratio in V1 > 98th percentile for age
o R/S ratio in V6 < 1 (after one month of age)
o Upright T waves in V1 (first week - early school age when we expect TWI)
o RSR’ in V1 - R’ > R1) [or >15mm (<1year), >10mm (after 1 year)]

Question 33

Characteristics of non-pathological early repolarization in children

Answer 33

• Lack of clear definition
• J point elevation (> 0.1 mV - excluding
V1-V3) in > 2 leads (same territory)
• Onset of QRS slurring or notching above baseline
• Amplitude and slope of the ST-segment not defined (ST elevation modest compared to T wave amplitude, no reciprocal depressions)

Question 34

Characteristics of normal T waves

Answer 34

• Upslope less steep than downslope
• Concordant with QRS (positive net QRS, positive T-wave)
• Amplitude (adults): Limb leads <5mm, Precordial ieads <10mm men, <8mm women
• aVR- negative
• V1 may be flat or inverted
• !ll, aVL - isolated inversion possible (abnormal if in ≥2 leads from same area)
• aVF - may be flat
• I, I, V5-V6 – positive
• Remember normal TWI in children V1-3 until school/early adolescent

Question 35

Key points re measuring QTc

Answer 35

U waves should be excluded
Leads II, V5 or lead with longest measurement
Bazzett / Framingham