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					         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.
                 ECG
                       3. Ventricular
                       repolarization




1. Atrial
depolarization
                 Electrocardiography (ECG)

2. Ventricular                 3. Ventricular repolarization
depolarization




1. Atrial
depolarization
 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
Amplitude
      P     0.25 mv

     R      1.6 mv

     Q      25 % of R wave

      T     0.1 to 0.5 mv
 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
      Diagnosis of cardiac diseases
      the the heart rate – 60- 100 beats/ min
 First
                            ( Normal value)
 Slower than this ( bradycardia)
 Higher than this ( Tachycardia )
 Check whether the cycle is evenly spaced – If not
  Arrhythmia
 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
 Device – Electrocardiograph
 Advantage
   Can provide several diagnostic information
Disadvantage
    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
            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.
 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
EINTHOVEN TRIANGLE
 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
 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
 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.
               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 )
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.