Electrocardiogram is a graphic recording of the time
invariant voltage produced by the myocardium during the
P, QRS and T waves – de-polarization
& Re polarization
Clinical use – Diagnosis of diseases & conditions
associated with heart.
2. Ventricular 3. Ventricular repolarization
Sum of all cardiac action potentials
Amplitude: 1-5 mV
Bandwidth: 0.05-100 Hz
Cardiologists looks critically
At various time intervals
Polarities and amplitudes
Normal values of ECG parameters
P 0.25 mv
R 1.6 mv
Q 25 % of R wave
T 0.1 to 0.5 mv
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
Diagnosis of cardiac diseases
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
If PR interval > 0.2 sec ---BLOCKAGE OF AV
If one or more of the basic features of ECG are
missing -----indicate HEART BLOCK
Device – Electrocardiograph
Can provide several diagnostic information
Can not provide information about the disorders
involving heart valves.
Angiography and Echocardiography
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.
3- Bipolar Limb lead --- Einthoven
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.
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
THIS TRIANGLE IS KNOWN AS EINTHOVEN
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.
12-Lead ECG Measurement
Most widely used ECG measurement setup in
Signal is measured non-invasively with 9
Lots of measurement data and international
Well-known measurement and diagnosis practices
This particular method was adopted due to
historical reasons, now it is already rather obsolete
12 Lead ECG Measurement
Einthoven leads: I, II & III Goldberger augmented leads: VR, VL & VF Precordial leads: V1-V6
Voltage generated by the pumping
action of the heart
Isa 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.
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 )
ECG Recording set up
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
Paperspeed 25 mm/sec or 50 mm/sec
Frequency response 0.1 to 60 Hz.