Cardiac Conduction and ECG Flashcards Preview

CVPR Exam 1 > Cardiac Conduction and ECG > Flashcards

Flashcards in Cardiac Conduction and ECG Deck (39):
1

What happens after the pacemaker cells in the SA node generate an action potential?


• It propogates rapidly through the gap junctions
• From SA node, high in right atrium, depolarization (through gap junctions) continues through right and left atria
• This generates the P wave

2

As far as action potentials go, what is the difference between Purkinje cells and contractile myocytes

• Faster action potential propagation and longer duration in purkinje cells than contractile myocytes

3

How are the right and left bundles from the AV node different?

• Right bundle is one entity and services the whole right atrium
• Left bundle splits into left andterior and left posterior

4

Where does the depolarization wave spread after the AV node deploarizes?

• Through the bundle of His and into the left and right bundle branches
• The bundles then divide into fibers made up of Purkinje cells
• Purkinje fibers radiate toward the contractile cardiac myocyets and induce contraction
• The depolarization spreads through myocytes due to gap junctions

5

Where in the heart is the AV node?

• Between the fibrous tricuspid and mitral valve rings that separate the atria from the ventricles

6

What is the P wave on the ECG?

• Atrial depolarization

7

What does the QRS complex reflect?




• Depolarization in the ventricles

8

Which direction is the T-wave?

• It moves in the same direction as the QRS complex even though in an individual myocyte depolarization and repolarization are in opposite directions

9

Why is atrial repolarization not generally seen in the ECG?

• Occurs during the QRS complex and it's relatively minor in the scheme of electric propagation

10

What does the T wave reflect?

• Repolarization of the ventricles

11

What number/phase of the ventricular action potential matches up with the QRS complex?

• Phase 0, or upstroke, and phase 1

12

What does the T wave reflect?

• Repolarization, phase 3 of the action potential
• Rapid decrease in voltage as potassium efflux continues and Calcium influx dies off

13

What does the isoelectric ST segment reflect?

• Phase 2 of the action potential, or the long plateau with little change in voltage
• Calcium influx and potassium efflux are pretty balanced at this point

14

What is the normal time course of QRS through T on an ECG?

• 400 ms

15

What number/phase of the ventricular action potential matches up with the T wave?

• Repolarization or phase 3

16

What number/phase of the ventricular action potential matches up with the ST wave?

• Plateu phase or phase 2

17

The R wave of the QRS complex reflects what?

• The upstroke, or phase 0 of the ventricular action potential
• Due to the fast sodium current

18

Which depolarizes first, the endocardium or the epicardium?

• Endocardium depolarizes earlier than epicardium
• However, there is a transmural repolarization gradient and epicardial cells repolarize earlier than endocardial cells because they have a shorter action potential

19

Which REPOLARIZES first, the endocardium or epicardium?

• Epicardium repolarizes first, even though they depolarize second

20

What does the discordance of repoloarization mean in the ECG?

• The T wave should be in the same direction as the QRS complex
• If there is discordance, this reflects pathology, like ischemia or ventricular hypertrophy

21

What does the PR interval reflect?




• Conduction time across the AV node

22

How many leads are in an ECG?

• 12 separate leads
• Shape of QRS is dependent on lead placement, in particular the postive electrode

23

Using the red boxes, you can determine that which complexes or intervals are abnormal?

• PR interval
○ Normal is 0.12-0.2 seconds
• P
○ Normal is 0.08 - 0.1 seconds
• QRS
○ Normal is 0.06 - 0.1 seconds
• Q-Tc interval
○ Normal is less than 0.44 seconds

24

What do the square red boxes in the ECG represent?

• "y-axis" is 10mm = 1mV
• "x-axis" every line is 0.04 seconds.

25

What does the QT interval reflect?

• Total duration of depolarization and repolarization

26

When will you see a positive deflection on an ECG?

• Positive deflection is UPWARD
• This happens when activation wave is moving towards a sensing electrode
What makes a deflection larger or smaller?
• Muscle mass. The more mass, the larger the deflection

27

Where is the SA node and where does the depolarization wave move?

• SA node is high in right atrium and depolarization sweeps downward and leftward
• Thus, a lead with a positive electrode near the right arms normally has negative QRS
• Lead with positive electrode near left leg has positive QRS

28

What are the 4 steps of deploarization in the heart?

• One - upper portion of septum is depolarized from left to right
• Two - depolarization downward in the septum to apex
• Three - depolarization moves from endocardium to epicardium
• four - depolarization moves upward from apex in the free walls of both ventricles
• FINAL - depolarization of bass of ventricles

29

Where can blocks in the conduction occur?


• SA block and sinus arrest - A
• AV block - B
• Right bundle branch block - C
• Left bundle branch block - C
• Posterior fascicular block - D
• Anterior fascicular block - D

30

What's up with the AV block?

• Three types
○ First degree
§ Conduction delayed but all P waves conduct to ventricles
○ 2nd degree
§ Some P waves conduct but other do not
○ 3rd degree
§ None of the P waves conduct and ventricular pacemaker takes over

31

What's up with SA node abnormalities?

• 'sick sinus syndrome'
• Slow sinus rates or takeover by other pacemakers which may be fast or slow

32

What happens when the right bundle is blocked?


• QRS widening with delayed conduction to the right ventricle

33

What happens when the left bundle fascicles are blocked?

• Shifts in the direction of depolarizaiton but no QRS widening

34

What happens when the left bundle is blocked?

• QRS widening with delayed conduction to the left ventricle

35

Where can abnormal reentry pathways be present?




• In the atria, ventricles or the junctional tissue

36

What happens in triggered activity?

• Deals with abnormal afterpolarizations
• Can be triggered by the preceding action potential
• Looks like the triggering of an action potential before full repolarization has happened
• Can also be longer than normal after repolarization, leading to a different arrhythmia
○ These are seen usually with a long QT interval

37

What are ectopic foci?

• Occur when a focus of myocardium outside the conduction system acquires automaticity and if the rate of depolarization exceeds that of the sinus node an abnormal rhythm occurs
• Can be isolated ectopic beats or sustained tachyarrhythmias

38

What is the most common mechanism of serious tachycardias?

• Abnormal reentry pathways due to slowed or unidirectionally blocked conduction pathways

39

What's up with reentry?

• Occurs when there is a unidirectional block and slowed conduction thorugh the reentry pathway
• After the slow reentry the previously depolarized tissue has recovered and reentry into it will occur
• Most common mechanism of serious tachycardias
• Looks like an action potential started before full repolarization