Cardiac Conduction System & ECG (complete) Flashcards

1
Q

Describe the relationship between ventricular APs of individual cardiac myocytes and the surface electrocardiogram

A
  • R wave => phase 0
  • ST segment => phase 2
  • T wave => phase 3
  • Segment after T wave => phase 4
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2
Q

What is the sequence of the activation of the cardiac electrical conduction system?

A
  • Upper portion of septum is depolarized from left to right
  • then depolarization downward in the septum to the apex
  • Depolarization from endocardium to epicardium
  • Depolarization moves upward from apex in the free walls of both ventricles
  • Depolarization of the base of the ventricles

OVERALL GOAL: to help push the blood in the correct direction!

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3
Q

Describe the P wave

A
  • Represents atrial depolarization
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4
Q

Describe the QRS complex

A
  • Represents depolarization of ventricles
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5
Q

Describe the T wave

A
  • Represents repolarization of ventricles

- When K+ channel takes over

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6
Q

Describe the PR interval

A
  • Index of conduction time across the AV node

- Depolarization pauses at the bundle of His after depolarization of atria and before that of ventricles

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7
Q

Describe the QT interval

A
  • Represents total duration of depolarization and repolarization
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8
Q

Describe the effects of left or right bundle branch block on cardiac conduction

A

Right: QRS widening w/ delayed conduction to RV

Left: QRS widening w/ delayed conduction to LV

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9
Q

What are the three major mechanisms by which disturbances in cardiac conduction cause tachyarrhythmias?

A

1) Abnormal reentry pathways
2) Ectopic foci
3) Triggered activity

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10
Q

Describe abnormal reentry pathways as a mechanism leading to arrhythmia

A
  • Most common cause of severe tachycardias

- Reentry occurs w/ unidirectional block and slowed conduction

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11
Q

Describe ectopic foci as a mechanism leading to arrhythmia

A
  • when cells outside conduction system acquire automaticity
  • and if depolarization rate exceeds that of SA node => abnormal rhythm
  • Can be isolated ectopic beats or sustained arrhythmias
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12
Q

Describe the concept of triggered activity as a mechanism leading to arrhythmia

A
  • abnormal afterdepolarizations may be triggered by the preceding AP
  • Early afterdepolarization before AP => tachyarrhythmia
  • Delayed afterdepolarizations appear after an AP => also triggers arrhythmias
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13
Q

What are the three types of atrioventricular block?

A

1) First Degree
2) Second Degree
3) Third Degree

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14
Q

Describe first degree AV block

A
  • Conduction is delayed

- BUT all P waves conduct to the ventricles

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15
Q

Describe second degree AV block

A

Some P waves conduct — not all

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16
Q

Describe third degree AV block

A
  • No P waves conduct

- Ventricular pacemaker now needed