USMLE Step 1 Physiology Review 55 06 Heart Function & Heartbeat (2_2)

USMLE Step 1 Physiology Review 55 06 Heart Function & Heartbeat (2_2)

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Play USMLE Audio MP3 55 06 Heart Function & Heartbeat (2_2) Below

Begin 55 06 Heart Function & Heartbeat (2_2) Transcription

How does the wave of depolarization travel from the SA node to the AV node? (Please pause the tape)

  • Via gap junction between myocytes during myocardial contraction of both atria.

Where is the AV node?

  • The AV node is the interatrial septum.

What are the cells of the AV node similar to?

  • They are similar to the SA cells and the cells of the AV node also conduct slowly.

What is the overall purpose of the slow conduction of the AV node?

  •  To delay the signal so that atrial may fill the ventricles.

How does the AV node send the signal along?

  • It sends the wave along via the atrial ventricular bundle.

Student please pause the tape and summarize the information discussed on Heart function discussed since the last summary.

  • The wave of depolarization travels, from the SA node to the AV node, via gap junction between myocytes during myocardial contraction of both atria. The AV node is the inter-atrial septum. The cells of AV node are similar to SA cells and the cells of the AV node also conduct slowly. The slow conduction in the AV node, delay the signal so that atrial may fill the ventricles. The AV node sends the signal along via the atrial ventricular bundle.

What is another term for the atrial ventricular bundle?

  • The bundle of His

At its terminal branches in the ventricles, what are the fibers called?

  • Purkinje fibers

What is the bridge between the ventricular and atria myocardial cells?

  • The bridge is the atrial ventricular bundle that is the AV bundle.

Do atrial tachycardia and fibrillation increase ventricular rate?

  • No

Why not?

  • Because the AV node is unable to transmit all of the atrial impulses

Is atrial tachycardia immediately life-threatening?

  • Not immediately

Why not?

  • Because the AV node still allows adequate time for ventricular filling.

Student please pause the tape and summarize the information discussed on Heart function discussed since the last summary.

  • The first question was about the bundle of His. Another term for the atrial ventricular bundle is the bundle of His. At its terminal branches in the ventricles, are the Purkinje fibers. The bridge between the ventricular and atria myocardial cells is the atrial ventricular bundle that is the AV bundle. Atrial tachycardia and fibrillation do not increase ventricular rate because the AV node is unable to transmit all of the atrial impulses. Atrial tachycardia is not immediately life-threatening because the AV node still allows adequate time for ventricular filling.

Okay now for some more questions. What effect does digoxin have on AV node?

  • Digoxin slows the AV node down.

How does the slowing down of the AV node affect heart function during atrial tachycardia or fibrillation? (Please pause the tape)

  • In atrial tachycardia or fibrillation the slowing down of the AV node improves heart function by allowing more filling time at the ventricle

What can digoxin do to atrial flutter?

  • It may convert it to fibrillation by slowing the SA node.

What kind of fibrillation is life-threatening?

  •  Ventricular fibrillation

Why is ventricular fibrillation life-threatening?

  • There is inadequate time for ventricular filling.

Student please pause the tape and summarize the information discussed on Heart function discussed since the last summary.

The first question was about the effect of digoxin on AV node. Digoxin slows the AV node down. In atrial tachycardia or fibrillation, the slowing down of the AV node improves heart function by allowing more filling time at the ventricle. Digoxin may convert atrial flutter to fibrillation by slowing the SA node. Ventricular fibrillation is life-threatening because there is inadequate time for ventricular filling.

****END OF TRANSCRIPTION****

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