ECG RECORDERELECTROCARDIOG RAPH ECG SIGNAL An ECG is

ECG RECORDERELECTROCARDIOG RAPH

ECG SIGNAL An ECG is a recording of the electrical activity of the heart Different “views” of the heart can be recorded using different electrodes

ECG SIGNAL Electrodes are able to measure the voltages of the cardiac current

ELECTROCARDIOGRAPH

LIMB LEADS Electrodes Right arm Left leg Right leg (ground)

LEAD I LA = electrical voltages of the heart that are transmitted to the left arm RA = electrical voltages of the heart that are transmitted to the right arm The electrocardiograph subtracts RA from LA and the difference appears as lead I.

LEAD I Lead one ‘travels’ horizontally. Ø Its left pole (LA) is positive and its right pole (RA) is negative. Ø Therefore, lead I = LA minus RA Ø Shows a positive wave when an impulses moves towards the left arm, negative wave when an impulse moves away from the left arm. Ø

LEAD II Lead II points downward diagonally Lower pole (LL) is positive and upper pole (RA) is negative. Lead II = LL minus RA

LEAD III Lead III points downward diagonally Lower pole (LL) is positive and upper pole (LA) is negative. Lead III = LL minus LA

BIPOLAR LEADS

UNIPOLAR OR AUGMENTED LIMB LEADS Record the electrical voltages at one location rather than relative to the voltage at another electrode

UNIPOLAR OR AUGMENTED LIMB LEADS a. VR + a. VL + a. VF = 0

LIMB LEADS Bipolar leads & Uni-polar (or augmented) leads Frontal plane

LIMB LEADS

Functional blocks of electrocardiograph 30

ECG Amplifier instrumentation amplifier HPF non-inverting amp This ECG amplifier has a gain of 25 in the dc-coupled stages. The high-pass filter feeds a noninverting-amplifier stage that has a gain of 32. The total gain 800. When m. A 776 op amps were used, the circuit was found to have a CMRR of 86 d. B at 100 Hz and a noise level of 40 m. V peak to peak at the output. The frequency response was 0. 05 to 106 Hz for 3 d. B and was flat over 4 to 40 Hz. A single op-amp chip, the LM 324, that contains four individual op amps could also be used in this circuit reducing the total parts 32 count.

Electrodes

LEADS 12 possible leads Six limb (extremity) leads Bipolar leads: I, II, and III Unipolar leads: a. VR, a. VL, a. VF Six chest (precordial) leads

CHEST LEADS V 1 to V 6 unipolar horizontal plane front to back

Chest Leads

ALL 12 leads Frontal Plane Horizontal Plane

HOLTER MONITORS