Electrocardiogram

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 ELECTROCARDIOGRAM

     An electrocardiogram records the electrical signals in the heart. It's a common and painless test used to quickly detect heart problems and monitor the heart's health.

     Electrical signals from the heart characteristically precede the normal mechanical function and monitoring of these signals has great clinical significance.

    ECG provides valuable information about wide range of cardiac disorders such as the presence of an inactive part(infarction) or an enlargement (cardiac hypertrophy) of the heart muscle.


ECG WAVEFORM






P Wave: Atrial depolarization

 

       T Wave: Ventricular repolarization

 

                                     QRS Complex: Ventricular depolarization

 

ECG BLOCK DIAGRAM


 

     Lead selector

 In the lead selector, the electrodes are selected two by two according to the lead program.

 By means of capacitive coupling to the differential preamplifier.

·      Preamplifier

 The preamplifier is usually a three or four stage differential  amplifier.

 Preamplifier are having large negative current feedback from end stage to first stage which gives a stabilizing effect.

·     Power amplifier

 Push-pull differential type

 The base of one input transistor of this amplifier is driven by pre amplified signal.

 The base of the others transistor is driven by the feedback signal resulting from the pen position and connected via frequency selective network.

·     Frequency selective network

 R-C network

 Which provides necessary damping of the pen motor and is preset by the manufacturer.

·    Auxiliary circuits

              Provides a 1mv calibration signal and automatic blocking of the amplifier of the lead switch.

             It may include a speed control circuit for the chart drive motor.

 

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