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2288 pages added, reviewed or updated during the last month (last updated: 19/4/2021)


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electrocardiography

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The ECG is an record of the electrical activity of the heart. Its utility stems from the specific changes in the trace caused by various pathologies.

The P waves represent atrial depolarisation. The PR interval is caused by the slow propagation of the depolarisation through the AVN; this allows time for the ventricles to fill. PR is measured from the start of P to the start of R. Once the depolarisation reaches the ventricles, conduction must be fast. The impulse passes though the following hierarchy of structures:

  • AVN then:
    • bundle of His then:
      • right bundle branch
      • left bundle branch then:
        • anterior fascicle of the left bundle branch
        • posterior fascicle of the left bundle branch

Ventricular depolarisation is recorded as the QRS complex. In practice, the Q, R and S waves are not always present.

The Q wave is defined as any initial downward deflection. The R wave is defined as any deflection upwards. The S wave is defined as any down deflection that is not Q. The T wave is the repolarisation.

Teams of Leads Inferior: II, III, aVF Anterior: I, aVL, V1, V2, V3

Last reviewed 01/2018

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