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ECG - Normal & Abnormal ; ECG Interpretation in the Young


M. Zulfikar Ahamed MD, DM

Prof and HOD of Ped Cardiology

Govt Medical College, Thiruvananthapuram.

The ECG is an important tool for the diagnosis of childhood heart disease, especially congenital heart disease. It is very often specific for anatomical defects when combined with other clinical findings and diagnostic tests. It also gives us a road map in many CHD and the more sophisticated investigations are often helped by the ECG data.

In children we should take a 14 lead ECG including V3R and V4R; the other leads being standard limb leads (I, II, III), augmented limb leads (aVR, aVL, aVF) and precordial leads (V1-V6).

ECG can be recorded in single channel or multi channel. In the standard ECG, paper speed is 25 mm/sec i.e. I second is divided into 25 small divisions of 1 mm each. Time is measured horizontally, the distance between two thick lines being 0.2 seconds and distance between two thin lines representing 40 msecs. (0.04 sec). Paper speed is made 50 mm/Sec for a more accurate assessment of various intervals, detection of AF etc. Voltage is represented vertically, 1 mm being 0.1 mv.

Overall, pediatricians all over the world tend to be a bit overawed by ECG either adult or pediatric. This phenomenon is quite uncalled for and we can overcome it by systematic review of a given ECG. ECG interpretation in the young is so different from that of an adult because almost all ECG parameters - normal and abnormal are age dependent and is also related to changes in the circulation especially so in the newborn. The transitional circulation in the very young makes changes more difficult. Pediatric training generally is soft on ECG interpretation, particularly arrhythmias. These are compounded by the fact that many structural lesions, both congenital and acquired need not produce definite and well defined abnormalities in ECG. I will be dealing with normal and abnormal ECG s in children and their interpretation and go on to special issues, problems and solutions later.


Calculating Heart Rate

When reading an ECG we usually take note of the standardization. Then we calculate the heart rate. The best method is dividing 1500 by the number of small divisions between 2 R's (RR interval). RR intervals may vary slightly, but, by not more than 3 small divisions, if variation is more than 120 msec (3 divisions) it is called sinus arrhythmia. It can be respiratory or non respiratory. Respiratory sinus arrhythmia is more common.

Heart rate is age dependent and bradycardia is said to exist in an older child when HR is less than 60/mt.In the neonate heart rate < 90 is bradycardia. Tachycardia is considered when in a neonate, heart rate is >150/mt, in the child >120/mt and older child >100/mt.

P Wave

Next we look at the P wave to know whether rhythm is sinus or not. P wave is due to atrial depolarization. First half of the P Wave is inscribed by RA depolarization and second half by LA depolarization. In situs solitus (normal situation) P wave is always +ve in I, II, V4 & V6 and -ve in aVR and variable in other leads. It could be either positive or negative in aVL, V1-V3 and III. In a aVF it is almost always upright. In situs inversus P wave is positive in aVR and negative in I, II, V5-V6.

The Axis of P wave is normally between 30o-60o. If it is > 75o it is most likely abnormal. Axis of > 90o indicates situs inversus.

Widest P wave can be up to 100 msec . Abnormal width of P wave is > 120 msec (3m).

Maximum amplitude of P wave is 2.5 small divisions. So amplitude of >3mV (3mm) is abnormal. Morphology of P wave can vary. It can be monophasic, biphasic, notched, inverted etc.

Wandering pacemaker is a benign finding seen in ECG where there are continual changes in P wave morphology, amplitude and PR interval.

PR Interval

Physiologically it represents the interval between onset of atrial depolarization and ventricular depolarization. The distance between beginning of P wave to beginning of QRS complex is measured. Normal PR interval in a child is 110-160 msec and in a neonate it is < 140 msec. Adult value is 120-200 msec. The longest PR interval is taken for measuring.

Prolonged PR interval is commonly found in Rheumatic carditis, Rheumatic valvular disease etc. Short PR interval (<100 msec) is seen in very small infants, WPW syndrome, LGL syndrome and Pompe's disease.

PR segment is the interval between end of P wave and beginning of QRS complex.

QRS Complex

QRS indicates ventricular depolarization. The direction is from endocardium to epicardium. QRS duration is traditionally measured in limb leads or V1-V2. The average duration is between 50-100 msec. If it is >100 msec, it is abnormal - may indicate intraventricular conduction defect or bundle branch block.


Low voltage QRS complexes are defined as having <5mm height in limb leads and <10 mm height in precordial leads. High voltage QRS complexes are >20mm in limbs leads and >30mm in precordial leads. High voltage complexes need not be abnormal. Tallest R are found in V4, V5.

Q Wave

Small q is normally is seen in 1, aVL, V4, -V6 and aVF. Depth of such q is < 3 mm and width <1mm. A q wave of > 4mm depth is considered abnormal. Usually depth of Q is less than 25% of corresponding R height.

In adults and in older children R/S in V1 is always less than I and in V6 more than I.


This is the point at which dominant polarity changes in the precordial leads. It usually occurs in V3 or V4. If it occurs in V2 it is called early transition and if it occurs in V5 it is late transition.

QRS Axis

Axis determination is crucial in evaluation of CHD, especially in congenital cyanotic heart disease where axis may point to a definite diagnostic possibility like left axis deviation in Tricuspid Atresia.

According to NYHA

Normal axis - 0o to + 90o

Right Axis Deviation - +90o to + 180o

Left Axis Deviation - 0o to -90o

Right Upper Quadrant Axis - 90o to +80o

From birth to 1 year, normal axis is from +90o to + 150o. Between 1 - 8 yrs it varies between +45o and +105o. Above 8 years it is <90o.

To determine the axis, initially concentrate on QRS complexes in I and aVF.

A. If I and aVF.

Are +ve = Normal Axis

I. is -ve; aVF is +ve = RAD

I. is +ve; aVF is -ve = LAD

Both are -ve = RUQ Axis

Once this broad categorization is done, go on to calculate axis more specifically

B. If axis is normal, look at III and aVL. If III is equiphasic axis is +30o; If aVL is equiphasic axis is +60o.

It is RAD look at II and aVR. If aVR is equiphasic axis is +120o. If II is equiphasic axis is +150o.

If it is LAD look at II and aVR again. If II is equiphasic axis is -30o. If aVR is equiphasic axis is -60o.

If the axis is RUQ, it could be extreme RAD or extreme LAD. To determine which, we look at the loop of QRS. There are two types of loops - clockwise (q in II. III. A VF) and counter clockwise (q in I. aVL). If in RUQ axis QRS is clockwise it is extreme RAD and if it is counter clockwise it is extreme LAD.

ST Segment

Point of end of S wave and beginning of ST segment is called J point. From J point to beginning of T wave is called ST segment. The most important information is regarding its deviation from base line (T-P segment). Normally, it should be always <1mm. In precordial leads some ST elevation is seen in the young in V1-V3. Any ST depression in precordial leads is abnormal.

T Wave

It represents ventricular repolarisation. The polarity is that of QRS complex. Upto 3 days of life T is upright in V3R, V1, V2. After the 3rd day it is inverted in V3R, V1 and can be so even up to V3. In older children inverted T is rare in V3. Maximum height of T is 6mm in limb leads and 10 mm in precordial leads.

QTc (Corrected QT Interval)

It represents the duration of ventricular electrical systole. It is measured from beginning of QRS to end of T wave. QT varies with heart rate, so corrected QT is calculated. For this divide QT in mille seconds obtained by square root of R-R interval in seconds. Normal QTC is < 440 msec.

U Wave

It probably represents repolarisation of His Purkinje system. It has one fourth amplitude of T wave and is positive.

Abnormal EGG

Having described a Normal ECG we shall go into abnormal pattern. First we take up chamber enlargement.

1. Left Atrial Enlargement

Best seen in lead II. V1.

a. Morris criteria - Negative deflection of P wave in V1 is more than 1 mm in depth and width.

b. P wave duration > 120 msec.

c. In a bifid P wave, inter peak distance > 40 msec.

d. Macruz index - P duration / PR segment is > 1.6.

e. P axis - < 30o.

2. Right Atrial Enlargement

Best seen in II. V1.

a. Tall, peaked P wave, > 3mm, in lead II.

b. P axis > 60o.

c. P initial force in V1 > 1.5 mm.

Previously LAE was called as P mitrale and RAE was called as P pulmonale and congenitale. These terms are no longer in current use.

3. Left Ventricular Hypertrophy

(Modified Lyon - Sokolow criteria)

a. R in V5/V6 + S in V1 > 45 mm

b. R in V5/V6 > 35 mm

c. R in aVL, aVF > 20 mm

d. Additional criteria - prolonged QRS, LAD, LAE.

Estes scoring is other criteria to diagnose LVH incorporating QRS amplitude, strain pattern, LAE, LAD, QRS duration

LVH may be

a. Volume overload

1. Prominent q in 1, aVL. V5-V6

2. Tall R in V5-V6

3. Tall symmetrical upright T in V5-V6

b. Pressure overload

1. No significant q in aVL. V5-V6

2. Slurred upstroke of R in Left precordial leads.

3. Asymmetrical T inversion with sagging ST segment in V5-V6

4. Right Ventricular Hypertrophy

a. Upright T in V1-V3 R after 3 days of life.

b. R/S in V1 > 1 after 6 years.

> 1.5 between 3-6 years

> 3 between 6 months - 3 years

> 5 in infants (<6 months)

c. qR in V3 R or V1.

d. R in V1 > 7 mm in child above 6 years.

e. R in V1 + S in V6 > 11 mm.

f. R in AVR > 5 mm

g. RAD > + 110o

There can be three morphological types of RVH.

1. Type A RVH - monophasic R in V1 or qR (Pressure overload)

2. Type B RVB - rSR in V1 or V3R (Volume overload)

3. Type C RVH - rS in V1-V6.

5. Biventricular Hypertrophy

1. Independently RVH + LVH

2. LVH + RAD

3. LVH + Clockwise loop

4. RVH + LAD

5. Katz - Wachtel Phenomenon - tall R and deep S in mid precordial leads measuring > 60 mm.

Heart Blocks

Can be divided into SA blocks

AV Blocks

Bundle Branch Blocks

1. SA Block

SA Blocks are uncommon in children except in postoperative patients. It is divided into I, II, III. degree heart blocks. 1o is not detected on surface ECT and in 11o block there is presence of long cycle between P waves. In IIIo SA Block, only an escape rhythm is evident on surface ECG.

2. AV Block

Can also be of three types - 1o, 11o, 111o. (CHB).

Io AV Block : All atrial impulses are conducted to ventricles with AV delay. So PR interval is prolonged (> 200 msec.).

IIo AV Block : Not all atrial impulses are conducted to ventricles. There are two types of blocks.

a. Mobitz Type I (Wenckebach) - There is gradual prolongation of PR interval in successive beats followed by dropping of QRS complex.

b. Mobitz Type II - There is no preceding PR prolongation. QRS is abruptly dropped. The ratio of P to QRS may be 2:1 or 3:1 or so.

IIIo AV Block (complete heart block) : No impulse from atrium reaches the ventricle so that both atrium and ventricle have their own rates - AV dissociation.

3. Bundle Branch Block

Can be RBBB or LBBB

RBBB : 1. QRS duration > 120 m sec.

2. R > r in rSR

3. VAT is > 80 msec

4. ST depression and T inversion.

LBBB : 1. QRS duration > 120 msec

2. VAT . 80 msec.

3. Characteristic M pattern or monophasic tall R in V5V6

4. Absence of Q in V5-V6

5. ST depression and T inversion

Note : rSR pattern is found in

a. Normal

b. Pectus, Straight Back Syndrome

c. RV volume overload

d. Cor pulmonale

e. WPW syndrome


1. Atrial Ectopics

1. Premature P wave

2. Premature P wave is abnormal and different from sinus P wave

3. Variable PR interval

4. Narrow QRS

5. Less than full compensatory pause.

2. Ventricular Ectopics

1. Premature QRS complex

2. No proceeding P wave

3. QRS is abnormal and wide

4. Secondary ST-T changes.

5. Full compensatory pause

6. Constant coupling interval.

3. WPW Syndrome

It is not an uncommon situation in Pediatric ECG. Characteristic features are

1. PR interval < 120 msec.

2. Delta wave

3. Abnormal QRS with width > 110 msec.

4. Additional ST-T changes.

5. Associated SVT complicating.

4. Supraventricular Tachycardia

It is an important rhythm abnormality in children. Rate is around 180-220/mt. with Narrow QRS complexes. P wave is either submerged in QRS or retrograde. It can be commonly due to AV Nodal re-entrant tachycardia, WPW and concealed bypass tract.

5. Ventricular Tachycardia

Uncommon rhythm inn children. Can occur in long QT syndromes.


Age Group


PR interval in m sec.

QRS axis degree

QRS dur. In m sec.

R/s in V1

R/S V6

R in V1

R in V6

0-7 Days









7 D -6 MO









6 MO - 1 Yr









1-4 YRS









5-7 YRS









8-12 YRS









> 12 YRS