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  • Electrical activities of the heart can be picked up on the skin via electrodes.

  • An ECG machine records these activities and displays them graphically.

  • The graphs show the heart's OVERALL electrical potential, or voltage, as it changes over

  • time during a cardiac cycle.

  • The 12 leads of the ECG represent 12 electrical views of the heart from 12 different angles.

  • The conventional 12-lead procedure involves attaching 10 electrodes to the body: one to

  • each limb and six across the chest.

  • There are 6 limb leads and 6 chest leads.

  • The 6 limb leads look at the heart in a vertical plane and are obtained from three electrodes

  • attached to the right arm, left arm, and left leg.

  • The electrode on the right leg is an earth electrode.

  • The measurement of a voltage requires 2 poles: negative and positive.

  • The ECG machine uses the negative pole as zero reference.

  • Thus, the position of the positive pole is thepoint of view”, and the line connecting

  • the 2 poles is theline of sight”.

  • Leads I, II, and III are BI-polar - they measure electrical potential between 2 of the 3 limb

  • electrodes: Lead I represents the voltage between the right armnegative pole - and

  • the left armpositive pole, and thus looks at the heart from the left.

  • Lead II sees signal movements between the right armnegative - and the left leg

  • positive - forming the INFERIOR LEFT view.

  • Similarly, lead III measures electrical potential between the left armnegative - and the

  • left legpositive, looking at the heart from an INFERIOR RIGHT angle.

  • Leads aVR, aVL, and aVF, oraugmented limb leads”, are UNIpolar.

  • They use ONE limb electrode as the positive pole, and take the average of inputs from

  • the OTHER two as the zero reference.

  • Hence, aVR looks at the UPPER RIGHT side of the heart; aVL looks at the UPPER LEFT side

  • of the heart; and aVF looks at the INFERIOR wall of the heart.

  • The chest leads, or precordial leads, view the heart in a HORIZONTAL plane.

  • These are unipolar leads.

  • The corresponding chest electrodes serve as the positive poles.

  • The reference negative value is the same for all chest leads and is calculated as the average

  • of inputs from the three limb electrodes.

  • DE-polarization TOWARD a lead produces a POSITIVE deflection; DE-polarization AWAY from a lead

  • gives a NEGATIVE deflection.

  • The REVERSE is true for RE-polarization.

  • Thus, leads that look at the heart from different angles may have waves pointing in different

  • directions.

Electrical activities of the heart can be picked up on the skin via electrodes.

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12 リード心電図の説明、アニメーション (12 Lead ECG Explained, Animation)

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    楊瑋珊 に公開 2021 年 01 月 14 日
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