ELECTROCARDIOGRAM [ECG] DISCOVERED by Einthoven willem

ELECTROCARDIOGRAM [ECG]

Generally we all heared term "ECG" most of the time but most of you don't know what exact it is and why it is so important. 

Let's know about it ! 

DISCOVERED by the Dutch Physiologist Einthoven willem( The father of ECG). 

Electrocardiogram[ECG] is the graphical registration of electrical activities of the heart, which occure prior to the onset of mechanical activity of the heart. 

The technique by which the electrical activities of the heart are studied called Electrocardiography and the instrument (machine) is called Electrocardiograph. 

ECG is the summed electrical activity of all cardiac muscle fibers recorded from the body. 

HOW IT IS RECORDED 

The paper that is used for recording ECG is called ECG paper and Electrocardiographic grid refers to the markings on ECG paper. 

ECG paper has horizontal and vertical lines at regular intervals of 1mm.

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

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

ECG LEADS

ECG is recorded by placing series of electrodes on the surface of the body of the subject. 

Electrodes  are usually fixed on right limb(arm), left limb(arm) and left leg. 

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

1) Bipolar leads

2) unipolar leads

Let's know first about each leads

•BIPOLAR LIMB LEADS

It is otherwise known as standard limb leads. Two limbs are connected to obtain these leads in which one electrode is positive and other one is negative. 

    Standard limb leads are three types

 LIMB LEAD I

Lead l is obtained by connecting right arm to negative terminal of electrode and left arm to positive terminal of electrode. 

LIMB LEAD ll

Lead ll is obtained by connecting right arm to negative terminal of electrode and left leg to positive terminal of electrode. 

LIMB LEAD lll

Lead lll is obtained by connecting left arm to negative terminal of electrode and left leg ro positive terminal of electrode. 

                

  

•unipolar leads

Here, one electrode is active and other one is an indifferent electrode. Active electrode is positive and indifferent serving as composite negative electrode. 

Unipolar leads are of two types

1) unipolar limb leads 

2) unipolar chest leads

•Ground Or Earth Electrode

While recording ECG in each lead. A ground electrode is connected to right leg of subject to prevent any artifact from machine. 

∆USES OF ECG

1) DETERMINING HEART RATE 

2) DETERMINING HEART RHYTHM

3) USEFUL IN DIAGNOSIS OF

       • Abnormal electric conduction of                  heart. 

        • poor blood flow to heart muscle. 

        • Heart attack

        • Coronary artey ( heart own artey)                disease. 

         • Hypertrophy of heart chambers. 

*WAVES OF NORMAL ECG

Normal ECG consists of waves, complexes, intervals and segments. 

Complex in ECG

•'p' wave, the atrial complex. 

•'QRS' wave, the initial ventricular complex. 

•'T'wave, the final ventricular  complex. 

*'P' WAVE

'P' wave is produced due to the Depolarization of atrial musculature (Depolarization - changes within the cell which cause less negativity inside the cell, when contraction of heart muscle occurs) 

•DURATION OF 'P' WAVE

0.1 SECOND

•AMPLITUDE OF 'P' WAVE

0.1 TO 0.12 mV. 

*'QRS' WAVE

QRS wave is due to depolarization of ventricular musculature. 

•DURATION

0.08 TO 0.10 SECOND

•AMPLITUDE

'Q'wave=0.1to 0.2 mV

'R'wave = 1mV 

'S'wave = 0.4 mV

*'T' WAVE

T wave is  due to the repolarization of ventricular musculature. 

•DURATION

0.2 SECOND

•AMPLITUDE

0.3 mV

( Repolarization is a changes within the cell when relaxation of heart muscle occurs) 

'U' WAVE 

U WAVE IS NOT ALWAYS SEEN. IT IS ALSO AN INSIGNIFICANT WAVE IN ECG. IT IS DUE TO REPOLARIZATION OF PAPILLARY MUSCLE AND PURKINJE FIBERS OF HEART. IT SEEN WHEN ANY TYPE OF CLINICAL CONDITIONS OCCUR. 

*clinical conditions like 

1) Bradycardia

2) Hypercalcemia

3) Myocardial Ischemia

*INTERVALS AND SEGMENTS OF ECG

•'P-R' Interval

P-R interval  represent duration of conduction of impluse from SA node to AV node. 

•'Q-T' Interval

Q-T interval represent interval between the ventricular contraction to ventricular relaxation. 

•'S-T'Interval

S-T interval represent isoelectric period of heart. 

•'R-R'Intervala

R-R interval is the time interval between two consecutive 'R'waves. It signifies the duration of one cardiac cycle. 

It's mainly help to diagnose Heart Rate and Heart Rate Variability. 

*SOME ABNORMAL ECG WAVES 

1) SINUS TACHYCARDIA

2) SINUS BRADYCARDIA

3) SA NODE BLOCK WITH A-V NODAL RHYTHM DURING THE BLOCK PERIOD. 

4) PROLONGED P-R INTERVAL CAUSED BY FIRST DEGREE A-V HEART BLOCK

5) COMPLETE A-V BLOCK

So,it's all about ECG .