An electrocardiogram (ECG) records the electrical activity of the heart over time via electrodes placed on the skin. It displays the P wave, QRS complex, and T wave, which correspond to atrial depolarization and repolarization and ventricular depolarization and repolarization, respectively. The ECG is used clinically to diagnose cardiac conditions by examining intervals, amplitudes, and other characteristics. It provides important diagnostic information but cannot assess heart valves like angiography and echocardiography can.

1. ELECTROCARDIOGRAM
DEFENITION
 Electrocardiogram is a graphic recording of the time
invariant voltage produced by the myocardium during the
cardiac cycle.
 P, QRS and T waves – de-polarization
& Re polarization
 Clinical use – Diagnosis of diseases & conditions
associated with heart.

2. ECG 3. Ventricular
repolarization
1. Atrial
depolarization

3. Electrocardiography (ECG)
2. Ventricular 3. Ventricular repolarization
depolarization
1. Atrial
depolarization

4.  Sum of all cardiac action potentials
 Amplitude: 1-5 mV
 Bandwidth: 0.05-100 Hz

5.  Cardiologists looks critically
 At various time intervals
 Polarities and amplitudes

6. Normal values of ECG parameters
Amplitude
P 0.25 mv
R 1.6 mv
Q 25 % of R wave
T 0.1 to 0.5 mv

7.  Duration
 P-R interval 0.12 to 0.20 sec
 Q- T interval 0.35 to 0.44 sec
 SW- T segment 0.05 to 0.15 sec
 P wave interval 0.11 sec
 QRS interval 0.09 sec

8. Diagnosis of cardiac diseases
 First
the the heart rate – 60- 100 beats/ min
( Normal value)
 Slower than this ( bradycardia)
 Higher than this ( Tachycardia )
 Check whether the cycle is evenly spaced – If not
Arrhythmia

9.  If PR interval > 0.2 sec ---BLOCKAGE OF AV
node
 If one or more of the basic features of ECG are
missing -----indicate HEART BLOCK

10.  Device – Electrocardiograph
 Advantage
Can provide several diagnostic information
Disadvantage
Can not provide information about the disorders
involving heart valves.
Angiography and Echocardiography

11. Electrodes and leads
 Lead --- The particular electrodes selected and the
way in which they are connected to the amplifier
are called lead
 For the individual lead wire, as well as the
physical connection to the body of the patient, the
term electrode will be used.

12. 3- Bipolar Limb lead --- Einthoven

13. Einthoven Postulated
 1. At any instant of the cardiac cycle, the frontal
plane representation of the electrical axis of the
heart is a two dimensional vector.
 2.Einthoven also made the assumption that the
heart is near the centre of an equilateral triangle,
the apexes of which are the right and left shoulders
and the crotch.

14.  3. By assuming that the ECG potentials at the at
the shoulders are same as the wrists and the
potential at the crotch differ little from those at
either ankle, he let the points of this triangle
represents the electrode positions for the 3- limb
leads.
 THIS TRIANGLE IS KNOWN AS EINTHOVEN
TRIANGLE

15. EINTHOVEN TRIANGLE

16.  The sides of the triangle represents the lines along which
the three projections of the ECG vector are measured.
 Based on this Einthoven showed that , the instantaneous
voltage measured from any one of the three limb lead
positions is approximately equal to the algebraic sum of
the other two.
 THE VECTOR SUM OF THE PROJECTIONS ON ALL
THREE LINES IS EQUAL TO ZERO.

17. 12-Lead ECG Measurement
Most widely used ECG measurement setup in
clinical environment
Signal is measured non-invasively with 9
electrodes
Lots of measurement data and international
reference databases
Well-known measurement and diagnosis practices
This particular method was adopted due to

18. 12 Lead ECG Measurement
Einthoven leads: I, II & IIIGoldberger augmented leads: Precordial leads: V1-V6
V R, V L & V F

19. Voltage generated by the pumping
action of the heart
 Is a vector – Magnitude as well as spatial
orientation changes with time.
 ECG signal is measured from electrodes applied to
the surface of the body.
 Waveform of ECG signal is depended on the
placement of electrode.

20. ELECTRODES
 Einthoven – Record ECG from electrodes placed
vertically as well as horizontally to the body.
 Experiments with immersion electrodes---
Placed electrodes not only on the arm but also on
one leg.– Left Leg.
Electronic amplifiers ----Ground reference. ( RL )

21. ECG Recording set up

22. SPECIFICATIONS OF ECG
 Frequency response – Upper 100Hz, Lower 50 Hz
 Sensitivity – 20 mm/mV
 Input impedance 5 Mega ohms
 Output impedance Less than 100 ohms
 Standardization signal 1 mv
 CMRR 10,000: 1
 Recording – heated stylus and heat sensitive paper

23.  Paperspeed 25 mm/sec or 50 mm/sec
 Frequency response 0.1 to 60 Hz.