Electrocardiography (ECG)

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ECG Machines

An electrocardiogram (ECG) is a record of the voltages created by the wave of depolarization and repolarization in the heart.

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The heart

  • The heart is made up of four chambers, the top two being atriums, the bottom two being ventricles.
  • The right and left atria receive blood from the body and lungs, respectively, and pump the blood into the ventricles.
  • The right and left ventricles, in turn, pump blood through the lungs and the rest of the body, respectively.
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  • Depolarization of the heart muscle causes it to contract. After contraction, it is repolarized to ready it for the next beat.
  • The ECG measures components of depolarization and repolarization of the heart muscle.
  • An ECG can give us a lot of information about if the heart is functioning well.

ECG Waveform

The heartbeat and polarization waves create a characteristic waveform.

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P wave

  • The major features of an ECG wave are labelled P, Q, R, S, and T.
  • The P wave is from the depolarization and contraction of the atria as they pump blood into the ventricles.
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QRS wave

  • The QRS part of the wave is created by the depolarization of the ventricles as they pump blood to the lungs and body.
  • The QRS complex has this typical shape and time span.
  • The QRS signal also masks the repolarization of the atria, which occur at the same time.
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T wave

  • Finally, the T wave is generated by the repolarization of the ventricles.
  • The T wave is followed by the next P wave in the next heartbeat.

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