6. Cardiac Conduction System & ECG Flashcards Preview

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Flashcards in 6. Cardiac Conduction System & ECG Deck (54):
1

Cells in the sinoatrial node and AV node are capable of _____.

spontaneous depolarization

2

How are SA and AV node cells able to spontaneously depolarize?

their phase 4 periods have slow depolarization due to the funny current and are thereby unstable

3

What kind of channels are absent in the SA and AV node cells?

sodium

4

Why is the SA node the usual cardiac pacemaker?

its cells have the fastest spontaneous depolarization rate, and the AV node cells' delay allows the atrium to contract first

5

Why do Purkinje cells have such fast APs?

they have a large # of Na channels

6

What makes up a gap junction?

connexins

7

What is automaticity?

the ability to spontaneously depolarize

8

What is the P wave?

depolarization of the R and then L atrium

9

Where is the AV node located?

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

10

What is found between the fibrous tricuspid and mitral valve rings that separate the atria from the ventricles?

the AV node

11

Where does the depolarization wave go after the AV node?

through the bundle of His into the left and right bundle branches

12

What do the bundle branches divide into?

Purkinje fibers

13

What does the right Purkinje bundle divide into?

it doesn't- it's a single entity supplying the R ventricle

14

What does the left Purkinje bundle divide into?

anterior and posterior branches or fascicles

15

What does the QRS complex represent?

depolarization of the ventricles

16

What is the T wave?

repolarization of the ventricles

17

What is phase zero of the ventricular AP?

the fast sodium current causes rapid depolarization

18

What does phase two of the ventricular AP look like?

a long plateau and little change in voltage

19

What does the T wave on the EKG correspond to in the ventricular AP?

phase 3- a rapid decrease in voltage as potassium efflux continues

20

If the _____ is positive the T wave should be positive.

QRS

21

If the QRS is positive the _____ should be positive.

T wave

22

If the QRS is negative the _____ should be negative as well.

T wave

23

if the _____ is negative the T wave should be negative as well

QRS

24

Discordance between the ___ and ____ in any lead is pathological, reflecting abnormalities such as ischemia or ventricular hypertrophy.

QRS and T waves

25

Discordance between the QRS and T waves in any lead is pathological, reflecting abnormalities such as _____ or _____.

ischemia; ventricular hypertrophy

26

What is the PR interval?

index of conduction time across the AV node

27

What is the index of conduction time across the AV node?

the PR interval

28

What is the QT interval?

total duration of depolarization and repolarization

29

What is total duration of depolarization and repolarization called?

the QT interval

30

How long is a normal P wave?

0.08-0.10 s

31

How long is a normal QRS interval?

0.08-0.10 s

32

How long is a normal PR interval?

0.12-0.2 s

33

How long is a normal Q-Tc interval?

less than 0.44 s

34

Where is atrial depolarization in the EKG?

it's buried in the QRS (the larger signal)

35

Where can conduction be delayed or blocked with clinical consequences?

1. SA node block 2. AV node block (3 types) 3. bundle branch blocks (R, L, L bundle fascicles)

36

What does SA node block commonly cause?

sick sinus syndrome- slow sinus rates or takeover by other pacemakers

37

What are the 3 types of AV block?

1. first degree- conduction delayed but all P waves conduct 2. 2nd degree- some P waves conduct but others not 3. 3rd degree- none of the P waves conduct and a ventricular pacemaker takes over

38

What is a first degree AV block?

conduction delayed but all P waves conduct to the ventricles

39

What is a second degree AV block?

some P waves conduct but others do not

40

What is a third degree AV block?

none of the P waves conduct & a ventricular pacemaker takes over

41

What are the different types of bundle branch blocks?

1. right bundle branch block 2. left bundle branch block 3. left bundle fascicles block

42

What is a right bundle branch block?

QRS widening with delayed conduction to the right ventricle

43

What is a left bundle branch block?

QRS widening with delayed conduction to the left ventricle

44

What is a left bundle fascicles block?

shifts in direction of depolarization but no QRS widening.

45

What are 3 common mechanisms leading to arrhythmia?

1. abnormal re-entry 2. ectopic foci 3. triggered activity

46

Where can abnormal re-entry occur?

in the atria, ventricles, or junctional tissue

47

Reentry occurs when there is a _____ and slowed conduction through the reentry pathway.

unidirectional block

48

What is the most common cause of serious tachycardias?

abnormal re-entry pathways

49

____ occur when a focus of myocardium outside the conduction system acquires automaticity.

Ectopic foci

50

Ectopic foci occur when a focus of myocardium outside the conduction system acquires _____.

automaticity

51

When does an abnormal rhythm occur?

when the rate of depolarization exceeds that of the SA node

52

What is triggered activity?

abnormal “afterpolarizations” are triggered by the preceding action potential

53

What are abnormal “afterpolarizations” triggered by the preceding action potential called?

triggered activity

54

How does a triggered activity look on an EKG?

a long QT interval