USMLE Step 1 Physiology Review 55 10 Normal EKG

USMLE Step 1 Physiology Review 55 10 Normal EKG

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Play USMLE Audio MP3 55 10 Normal EKG Below

Begin 55 10 Normal EKG Transcription

Now we will talk about normal EKGs, What are EKGs?

  • They’re the tracing of surface cardiac potentials recorded against time.

What is the standard recording speed for these tracings?

  • 25mm per second

What is the standard amplification on EKG?

  • 1mm equals 1cm deflection on the graph paper

In two words describe what causes the P wave?

  • Atrial depolarization

What immediately follows atrial depolarization?

  • Atrial contraction or systole.

Is this visible on EKG?

  •  No, Atrial systole is not visible on EKG

What causes the QRS complex?

  •  Ventricular depolarization

What follow the ventricular depolarization?

  • Ventricular contraction or Systole

Is this visible on EKG?

  • No

What also occurs on the QRS complex which is not visible on EKG?

  • Atrial repolarization.

Student doctor please pause the tape and summarize the information discuss thus far on EKG.

  • EKGs are the tracing of surface cardiac potentials recorded against time. The standard recording speed for these tracings is 25mm per second with the standard amplification of 1mV equals 1cm deflection on the graph paper. Atrial depolarization causes the P wave. Atrial contraction or systole immediately follows atrial depolarization but Atrial systole is not visible on EKG. Ventricular depolarization causes the QRS complex. Ventricular contraction or Systole follows the ventricular depolarization. Ventricular systole like atrial systole is not visible on EKG. Atrial repolarization also occurs during the QRS complex and is not visible on EKG.

What causes the T wave?

  • Ventricular repolarization

What is the PR interval?

  •  It is the measure of the AV conduction timing including the delay through the AV node

How is it measured or defined on the EKG?

  • You may want to pause the tape here, From the SA node signal release…

Which is, what wave?

  • The P

To the start of the ventricular depolarization, which is, what wave?

  • the Q wave

In order words, it is defined from the P wave to the start of the Q wave.

And what is the QT interval?

  • It is the entire period of ventricular depolarization and repolarization

How is it defined on the EKG?

  • From the beginning of the Q which is the beginning of ventricular depolarization to the end of the T wave which is the end of ventricular repolarization

What is the ST segment?

  • The period during which ventricles are entirely depolarized

And how is it measured on the EKG?

  • It is the period between the end of the S wave and the beginning of the T wave

In the EKG where does each new cycle start?

  • With the P wave

Student doctor please pause the tape and summarize the information discussed since the last summary on EKGs.

  • The first question was about the T waves. Ventricular repolarization causes the T wave. The PR interval is the measure of the AV conduction timing including the delay through the AV node. It is measured or defined on the EKG from the SA node signal release, which is the P, to the start of the ventricular depolarization, which is the Q wave. In order words, it is defined from the P wave to the start of the Q wave. The QT interval is the entire period of ventricular depolarization and repolarization. The QT defined on the EKG from the beginning of the Q which is the beginning of ventricular depolarization to the end of the T wave which is the end of ventricular repolarization. So in order words, from the beginning of the Q wave to the end of the T wave. The ST segment is the period during which ventricles are entirely depolarized.  The period between the end of the S wave and the beginning of the T wave. In the EKG, each new cycle start with the P wave.

****END OF TRANSCRIPTION****

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