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ElectrocardiogramElectrocardiogram

The tracing made by an electrocardiograph

Electrocardiograph

an instrument for recording thechanges of electrical potential occurring

during the heartbeat used especially in

diagnosing abnormalities of heart action

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Sinoatrial Node (SA)the impulse generating tissue

located in the right atrium of theheart

 Atrioventricular Node (AV)the tissue between the atria and the

ventricles of the heart, conducts thenormal electrical impulse from the atria

to the ventricles

Cardiac conduction systemCardiac conduction system

SA AV His bundle Purkinje fibers

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Electrocardiogram (ECG) (cont.)Electrocardiogram (ECG) (cont.)

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ECG Waves and IntervalsECG Waves and Intervals

P wave: the sequential activation (depolarization) of the right and

left atria QRS complex: right and left ventricular depolarization

ST-T wave: ventricular repolarization

U wave: probably represents "afterdepolarizations" in theventricles

PR interval: time interval from onset of atrial depolarization (P

wave) to onset of ventricular depolarization (QRS complex)

QRS duration: duration of ventricular muscle depolarization

QT interval: duration of ventricular depolarization andrepolarization

RR interval: duration of ventricular cardiac cycle (an indicator ofventricular rate)

PP interval: duration of atrial cycle (an indicator of atrial rate)

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ECG Signal CharacteristicsECG Signal Characteristics

Signal is generated in the heart

 Amplitude range: -5 mV to +5 mV (usually thepacked up signal on the body surface is 1 mV)

Frequency range: 0.05 to 1500 Hz Acquisition by surface electrodes

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Lead configurations for ECG AcquisitionLead configurations for ECG Acquisition

1. Bipolar limb leads (Einthoven)

2. Unipolar limb leads or  Augmented limb

leads (Goldberg)

3. Unipolar chest leads (Wilson)

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Bipolar limb leads (Einthoven)Bipolar limb leads (Einthoven)

Lead I Lead II Lead III

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Signal shape of Bipolar l imb leadsSignal shape of Bipolar l imb leads

(Einthoven)(Einthoven)

Lead I

Lead II

Lead III

U i l li b l d A t d li b l d

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Unipolar Unipolar limb leads or limb leads or  Augmented limb leads Augmented limb leads

(Goldberg)(Goldberg)

Lead aVR Lead aVL Lead aVF

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Signal shape ofSignal shape of Unipolar Unipolar limb leadslimb leads

Lead aVR

Lead aVL

Lead aVF

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Signal processing of ECGSignal processing of ECG