How to read ECG report?

 ELECTROCARDIOGRAPHIC GRID

The paper that is used for recording ECG is called ECG paper. ECG machine amplifies the electrical signals produced from the heart and records these signals on a moving ECG paper.

Electrocardiographic grid refers to the markings (lines) on ECG paper. ECG paper has horizontal and vertical lines at regular intervals of 1 mm. Every 5th line (5 mm) is thickened.

How to read ECG report?


DURATION

Time duration of different ECG waves is plotted horizontally on X-axis.

On X-axis

1 mm = 0.04 second

5 mm = 0.20 second

AMPLITUDE

Amplitude of ECG waves is plotted vertically on Y-axis.

On Y-axis

1 mm = 0.1 mV

5 mm = 0.5 mV

SPEED OF THE PAPER

Movement of paper through the machine can be adjusted by two speeds, 25 mm/second and 50 mm/

second. Usually, speed of the paper during recording is fixed at 25 mm/second. If heart rate is very high,

speed of the paper is changed to 50 mm/second.

ECG LEADS

ECG is recorded by placing series of electrodes on the surface of the body. These electrodes are called ECG leads and are connected to the ECG machine. Electrodes are fixed on the limbs. Usually, right arm,

left arm and left leg are chosen. Heart is said to be in the center of an imaginary equilateral triangle drawn by connecting the roots of these three limbs. This triangle is called Einthoven triangle.

Einthoven Triangle and Einthoven Law

Einthoven triangle is defined as an equilateral triangle that is used as a model of standard limb leads used to record electrocardiogram. Heart is presumed to lie in the center of Einthoven triangle.

Electrical potential generated from the heart appears simultaneously on the roots of the three limbs, namely the left arm, right arm and the left leg.

ECG is recorded in 12 leads, which are generally classified into two categories.

I. Bipolar leads

II. Unipolar leads.

BIPOLAR LIMB LEADS

Bipolar limb leads are otherwise known as standard limb leads. Two limbs are connected to obtain these

leads and both the electrodes are active recording electrodes, i.e. one electrode is positive and the other

one is negative.

Standard limb leads are of three types:

a. Limb lead I

b. Limb lead II

c. Limb lead III.

Lead I

Lead I is obtained by connecting right arm and left arm. Right arm is connected to the negative terminal of the instrument and the left arm is connected to the positive terminal.

Lead II

Lead II is obtained by connecting right arm and left leg. Right arm is connected to the negative terminal of the instrument and the left leg is connected to the positive terminal.

Lead III

Lead III is obtained by connecting left arm and left leg. Left arm is connected to the negative terminal of the instrument and the left leg is connected to the positive terminal.

UNIPOLAR LEADS

Here, one electrode is active electrode and the other one is an indifferent electrode. Active electrode is

positive and the indifferent electrode is serving as a composite negative electrode.

Unipolar leads are of two types:

1. Unipolar limb leads

2. Unipolar chest leads.

1. Unipolar Limb Leads

Unipolar limb leads are also called augmented limb leads or augmented voltage leads. Active electrode is connected to one of the limbs. Indifferent electrode is obtained by connecting the other two limbs through a resistance.

Unipolar limb leads are of three types:

i. aVR lead

ii. aVL lead

iii. aVF lead.

i. aVR lead

Active electrode is from right arm. Indifferent electrode is obtained by connecting left arm and left leg.

ii. aVL lead

Active electrode is from left arm. Indifferent electrode is obtained by connecting right arm and left leg.

iii. aVF lead

Active electrode is from left leg (foot). Indifferent electrode is obtained by connecting the two upper limbs.

2. Unipolar Chest Leads

Chest leads are also called ‘V’ leads or precardial chest leads. Indifferent electrode is obtained by connecting the three limbs, viz. left arm, left leg and right arm, through a resistance of 5000 ohms. Active electrode is placed on six points over the chest. This electrode is known as the chest electrode and the six points over the chest are called V1, V2, V3, V4, V5 and V6. V indicates vector, which shows the direction of current flow.

Position of chest leads:

V1 : Over 4th intercostal space near right sternal

margin

V2 : Over 4th intercostal space near left sternal

margin

 (V1 to V6)

V3 : In between V2 and V4

V4 : Over left 5th intercostal space on the mid

clavicular line

V5 : Over left 5th intercostal space on the anterior

axillary line

V6 : Over left 5th intercostal space on the mid

axillary line.

 

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