29 - Electrical activity during cardiac performance. Origin, registration, and evaluation of the ECG.

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7 Terms

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sectiosn

electrocardiography

leads of electrocardiography

electrodes of ECG (electrocardiography)

PQRS complex

depolarisation

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electrocardiography

Method for recording the summated bioelectrical activity of a beating heart

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leads of electrocardiography

  1. 1. Limb Leads (Frontal Plane) – 6 leads:

    • These look at the heart from front to back.

      • Bipolar limb leads:

        • Lead I: Right arm (–) to Left arm (+)

        • Lead II: Right arm (–) to Left leg (+)

        • Lead III: Left arm (–) to Left leg (+)

      • Augmented unipolar limb leads:

        • aVR: Right arm

        • aVL: Left arm

        • aVF: Left leg (foot)

      2. Chest (Precordial) Leads – 6 leads (Unipolar):

      These look at the heart from a horizontal view (across the chest).

      • V1: 4th intercostal space, right of sternum

      • V2: 4th intercostal space, left of sternum

      • V3: Between V2 and V4

      • V4: 5th intercostal space, midclavicular line

      • V5: Same level as V4, anterior axillary line

      • V6: Same level as V4, midaxillary line

    • ……………………………………………………………………

ECG since it includes 12 leads – is obtained using 10 electrodes.

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electrodes of ECG (electrocardiography)

ECG since it includes 12 leads – is obtained using 10 electrodes.

  • Electrodes:

  • yellow - left arm

  • red - right arm

  • green - left leg

  • black - right leg (ground electrode).

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how to calculate cardiac axis

ECG and the hexaxial reference system, picture attached

<p>ECG and the hexaxial reference system, picture attached </p>
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PQRST complex

  • The P wave is caused by the atrial depolarization prior to contraction.

  • The QRS complex is caused by currents generated when the ventricles depolarize prior to contraction.

  • Therefore, both P wave and the components of the QRS complex are depolarization waves.

  • The T wave is caused by currents generated as the ventricles recover from the state of depolarization.

  • P-Q interval (normally approximately 0.16 s).

  • Q-T interval and ordinarily is approximately 0.35 s.

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depolarisation

  • Depolarisation of the cells of the SAN → right atrium → AVN → Bundle of His → Purkinje fibres