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.
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.
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
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 )