“PQRST”

ECG INTERPRETATION

Dr PalanikumarPediatrics department

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Cardiac cells, in their resting state, are electrically polarized, that is, their insides arenegatively charged with respect to their outsides.

Lead I is created by making the left arm positive and the right arm negative.

Lead II is created by making the legs positive and the right arm negative.

Lead III is created by making the legs positive and the left arm negative.

Lead AVL is created by making the left arm positive and the other l imbs negative.

Lead AVR is created by making the right arm positive and the other limbsnegative.

Lead AVF is created by making the legs positive and the other limbs negative.

1. Standardization “Usually two big squares”

2. Rhythm “From the strip usually lead II”3. Rate “Regular and irregular”4. Axis “Direction and Degree”5. Waves “5 Physiologic & 5 Pathologic”6. Intervals “Segment!”7. Chamber size “Hypertrophy!”

Standardization

A full standard “Height of 2 big squares at the beginning of each line” means that the ECG was not reduced in size so as to fit on the paper.

If the ECG is half standard, then the rectangle will be one large square high. If the ECG is half standard you MUST multiply all waves by 2 to normalize them

Rhythm

Normal rhythm should be within physiological rate and regular pattern “Constant Ps & Rs interval”.

Sinus arrhythmia is a physiological phenomenon particularly in young. “Respiration effect”

Dysrrhythmia means abnormally faster, slower or irregular intervals.

Heart rate

Regular: Count the number of big squares between two

consecutive R waves (RR duration). Now divide 300 by the number of squares counted. That's the heart rate.

It can be more accurate by counting the number of small squares, then dividing 1,500 by that number.

For irregular Rhythm: count the number of R waves in a 6-second (30 big

square) and multiply by 10.

AXIS

Normal AxisNeonate & infant: 90-150 child: 60-120 elder: “>12 years” 30-90

Waves

Physiological waves:P-wave:Best seen in Lead II Normally 2-3 small squares (0.08-

0.12 sec) duration &height “Simple 2.5X2.5”.

Wide or bifid P waves indicate left atrial enlargement “P-Mitrale”.

Tall or peaked P wave indicate right atria enlargement “P-Pulmonale”.

QRS-waves:Look for 4 parameters1. Duration: <3 small squares2. Amplitude: Variable but equal in same lead,

< 2.0 mV or 4 big squ. in aVF lead is normal.3. Q wave: <3 small squares depth if present

“right leads”4. Progression:A. Right to left: From mainly S in V1 to mainly

R in V6B. Age: From RV dominance in neonates to LV

dominance after age of 3 years.

T-wave:In V6 is always upright. If inverted

indicate LVH.In V1 it is inverted from age of 1

week up to puberty “16 years”; upright after birth & after puberty.

Pathological waves1. Delta-wave: Slurred upstroke of R waveThis is present in WPW “with short P-R interval”

2. J-wave (Osborne wave): Hump at the end ofR wave “at J point”This is present in Hypothermia

3. R’ -wave: Extra R waves (RSRK) This indicates BBB

4. U-wave: Extra up wave after T waveThis is present in Hypokalemia “with depressed

S-T segment & flat or inverted T wave”

Intervals

P-R Interval: Normally, 2-5 small squares (average 0.08-0.2)

Long P-R >5: in first degree AV block, Digoxin effect, Hypokalemia or myocardial depression.

Short P-R <2: interval is one criterion of WPW or less commonly LGL syndrome “Ganong”.

S-T segment: Normally at “isoelectric” base line but,not flat.

Abnormal if flat, elevated or depressed by 0.5-1 mm “small square”

Elevated ST segment: PericarditisDepressed ST segment: Ischemia,

Digoxin effect “reversed tick sign √”, Hypokalemia.

Q-T Interval: is the duration from the beginning of the QRS complex to the end of the T wave. Count the number of small squares, then multiply by 0.04 seconds, that the QT in seconds. Normal QT should be corrected to the HR

“QTc”. Correction is done by Bazett Formula.

Bazett Formula: QTc = QT/square root of RR“RR: are the small squares between 2 R waves”

Crude normal value: 0.35-0.45 at rate between 60-100Short Q-T: HypercalcemiaLong Q-T: 5 HYPOs “Thermia, Thyroidism, Calcemia, Magnisemia &

Kalemia”2 Syndromes: Romano–Ward & Jervell and Lange–Nielson “+Deafness”Drugs: e.g. Tricyclic Antidepressant

Right Atrial Enlargement: Tall P- wave “P pulmonale” Lead II & V2

The P wave is taller than two small squares (>0.08 sec) in infants and small children and more than

three small squares (> 0.12 sec) in older children and adults.

Left Atrial Enlargement: Wide P- wave “P mitrale” Lead II & V6

The P waves are wide, more than two small squares (> 0.08 sec) in infants and small children and

more than three small squares (> 0.12 sec) in older children and adults.

Right Ventricular Hypertrophy: One of FOUR Criteria (V1 R & V6 S away from each other)

In lead V1, the R wave is larger than the S wave.

In lead V6, the S wave is larger than the R wave

With Right axis deviation

Left Ventricular Hypertrophy: ONE Criterion (V1 S & V6 R looking to each other)

The R wave amplitude in lead V5 or V6 plus the S wave ampl itude in lead V1 or V2 exceeds 35 mm.

The R wave amplitude in lead V5 exceeds 26 mm.

The R wave amplitude in lead V6 exceeds 18 mm.

The R wave amplitude in lead V6 exceeds the R wave amplitude in lead V5.

Bi-Ventricular Hypertrophy One of 2 criteria Picture of both ventricular hypertrophy

1. Sum of Rs in V1 & V6 > 352. Sum of Rs in V3 & V4 > 60

P wave

Right atrial dilatation

Left atrial dilatation

RVH

RVH

LVH