Cardiac Conduction Flashcards
Explain the cardiac conduction pathways of the heart (SA & AV nodes, Bundle of His, & Purkinje Fibers). Describe action potential and refractory periods. Identify the various components on the electrocardiogram (P wave, PR interval, QRS complex, ST segment, and T wave). Discuss the differences among atrial and ventricular conduction disorders related to rate and rhythm. Compare first, second degree (Wenckebach and Mobitz) and third-degree heart blocks.
1
Q
what node is considered the pacemaker cell?
A
SA node
2
Q
what is the intrinsic rate of the SA node?
A
60 -100 bpm
3
Q
Heart cells are special because they can
A
Initiate and spread electrical activity without external influence
4
Q
what is the cardiac conduction pathway?
A
- SA node
- internodal tracts
- AV node/bundle of his
- purkinje fibers
5
Q
Why is there a delay with the AV node?
A
it allows for the atria to fully contract and empty blood into ventricles
6
Q
what does the AV node do?
A
conduct impulse from atria to ventricles
7
Q
what is the intrinsic rate of the AV node?
A
40 - 60 bpm
8
Q
what conducts the impulse through the venticles?
A
purkinje fibers
9
Q
what is the intrinsic rate of purkinje fibers?
A
15 - 40 bpm
10
Q
what valve is the bundle of his close to?
A
aortic valve
11
Q
what are the 3 phases of APs?
A
resting state
depolarization
repolarization
12
Q
how are cells depolarized?
A
efflux of K
influx of Na
(Na/K pump)
13
Q
normally inside of cells are _______ and outside of cells are ________
A
negative
positive
14
Q
how are cells repolarized?
A
K+ influx
Na efflux
(Na/K pump)
15
Q
contraction = __________
A
depolarization
16
Q
relaxation = ____________
A
repolarization
17
Q
if there are 80 APs/min, what is the HR?
A
80 bpm
18
Q
what occurs during phase 0?
A
upstroke or rapid depolarization
Na enters
19
Q
what occurs during phase 1?
A
rapid repolarization period
peak of AP/ QRS
Na comes in but stop at the end
20
Q
what occurs during phase 2?
A
plateau
permeability of Na/K stops
SLOW Ca influx (for contraction)
21
Q
what occurs during phase 3?
A
final, rapid repolarization period
Ca influx stops
sharp rise in K+ into cell
22
Q
what occurs during phase 4?
A
diastolic depolarization
ultimate rest
Na/Ca out
K+ in
23
Q
phase 0 is associated with ______ on an EKG
A
P wave
24
Q
phase 1 is associated with ______ on an EKG
A
QRS wave
25
phase 2 is associated with ______ on an EKG
ST segment
26
phase 3 is associated with ______ on an EKG
T wave
27
P wave
depolarization of atria
28
QRS complex
depolarization of ventricles
repolarization of atria
29
T wave
repolarization of ventricles
30
what is absolute refractory period?
Cell cannot be depolarized no matter the strength of the stimulus
31
What is the relative refractory period? and what phase is it in?
cell is capable of responding to a stronger than normal stimulus
3
32
what is the supernormal excitatory period? and when does it occur?
a WEAK stimulus can evoke a response, time for arryhtmias to develop
immediately following relative refractory period; terminal period of phase 3 until beginning of phase 4
33
Pumping of heart requires ______ contraction and relaxation --> __________ of additional action potential to prevent _____ beats
alternating
protection
extra
34
if the SA node stops working, what will I see on the ekg
no P wave
wider than normal QRS (bc AV node takes over)
35
what is the PR segment?
delay from SA to AV node
36
what is the ST segment?
end of ventricular depolarization to repolarization
37
reason for 5/6 lead EKG
tele
continuous monitoring
38
10/12 lead EKG
10 = stickers
get 12 visuals
39
inverted waves on an EKG means ...
away from
40
EKG: The shape of the recorder
tracing is determined by the
__________ the impulse spreads
through the heart muscle in
relation to _________ placement
direction
electrode
41
what are the 4 chracteristics of heart muscle cells?
automaticity
excitability
conductivity
refractioriness
42
what are the causes of rhythm/impulse conduction disorders? (6)
congenital defects
degenerative changes in conduction
myocardial ischemia
myocaridal infarction
lyte imbalance
meds
43
why is tachycardia dangerous?
heart beats too fast so there is not enough time for the chambers to fill with enough blood, so the heart is not pumping out enough blood
44
why is bradycardia dangerous?
heart is pumping too slow, so not all of the blood gets out before more blood enters
45
what is automatcity?
spontanously initiate impulses (on own)
46
what is excitability?
ability of cell to repond to impulse and generate own
(get, do, send to friend)
47
what is conductivity?
cells ability to conduct impulses
do
48
what is refractoriness?
the extent to which a cell is able to respond
able to go back and be ready to do it again
49
what causes reentry tachyarrythmias? (3)
ischemia
infarction
hyperkalemia
50
REENTRY TACHYARRHYTMIAS
Normally multiple conductions are sent out on opposite sides and they meet in the middle to ______ out
cancel
51
REENTRY TACHYARRHYTMIAS
When a partial conduction block occurs, the impulse on the unblocked side travels until it ____ the other one and this leads to a _____ HR
meets
fast
52
what are the 3 forms of reentry tachyarrhythmias?
anatomic
functional
spiral
53
what is anatomic reentry?
anatomic obstacle that the circulating current must pass
54
what do we see with anatomic reentry? (5)
supraventricular tachycardias
atrial fibrillation
atrial flutter
AV nodal reentry
some ventricular tachycardias
55
what is functional reentry?
depends on local differences in conduction velocity and refractoriness among neighboring fibers that allow an impulse to circulate around an area
56
what do we see with spiral reentry? (1)
atrial fibrillation
57
what is spiral reentry?
initiated by current that does not proceed down regular pathway;
breaks away, curls, rotates
58
what are the 4 types of sinus node arrhythmias?
sinus bradycardia
sinus pasue/arrest
sinus tachycardia
sick sinus syndrome
59
what is sinus bradycardia? and what causes it? (2)
decrease of the firing rate of
SA node and conduction through AV node = decrease in HR
vagal stimulation, some medication
60
what is sinus pause/arrest? and what causes it? (8)
failure of SA node to discharge = impulse fails to proceed through AV node = escape rhythm develops (AV pacemaker takes over)
disease of SA node
digitalis toxicity stroke
MI
acute myocarditis
excessive vagal tone
sleep apnea
medications
hyper- or hypo-kalemia
61
when you feel your pulse you are only feeling the ______ function
ventricular
62
what is sinus tachycardia? and what causes it? (4)
HR greater than 100 bpm
d/t enhanced automaticity
related to sympathetic stimulation or withdrawal of vagal tone
congestive heart failure, MI, hyperthyroidism, medications
63
what is sick sinus syndrome?
term that describes a # of forms of cardiacimpulse formation and intra- atrial and AV conduction abnormalities
result of total or subtotal destruction of SA node, areas of nodal-atrial discontinuity, inflammatory or degenerative changes, changes in atrial
wall
64
what are the 5 atrial arrhythmias?
premature atrial contractions
atrial tachycardia
atrial flutter
atrial fibrillation
paroxysomal supraventciualr tachy
65
what are premature atrial contractions?
contractions that originate in the atrial conduction pathways that occur before the next expected SA node impulse
66
what are paroxysmal supraventricular tachycardia?
tachyarrhythmias that originate above the bifurcation of the
bundle of His and have sudden onset & termination
67
what is the most common arrhythmia?
atrial fibrilaltion
68
what is atrial fibrillation?
rapid disorganized atrial activation and uncoordinated contraction by the atria
in most cases = small reentrant circuits are constantly arising in atria = fibrillatory waves
Paroxysmal, persistent, permanent
69
what are atrial flutters?
rapid atrial ectopic tachycardia (aka SA and other area also fires, not in sync
typical (most common, AKA Type I) vs atypical
70
what is the difference between focal and multifocal atrial tachycardia?
focal: too fast, REGULAR rhythm
multi: too fast with IRREGULAR rhythm
71
what causes premature atrial contractions? (5)
K+ imbalance
stress
coffee
alcohol
hypoxia
72
What causes atrial tachycardia? (5)
caffeine
hypoxia
lyte imblance
alcohol
meds
73
with atrial flutter and fibrillation, not every contraction passes into the _______
ventricles
74
what are premature ventricular contractions (PVCs)?
caused by ventricular ectopic
pacemaker that leads to the inability for the ventricle to repolarize and respond to next electrical impulse
75
what causes PVCs?
ischemia
infection
venticular hypertrophy
lyte imbalance
meds
76
what is ventricular tachycardia?
rhythm originating distal to the bifurcation of the bundle of His or in specialized conduction system in ventricular muscle or both
77
what is a ventricular flutter/fibrillation?
ventricle quivers but does not
contract (no pulse)
78
What is first-degree AV block
?
EKG:
E:
M:
? Indicates delayed AV conduction, but all atrial impulses are conducted to the
ventricles, Regular atrial and ventricular rhythm
EKG: Prolonged PR interval (>0.20 second)
E: ischemia, infarction, infections such as rheumatic fever or myocarditis
M: usually asymptomatic if isolated
79
what are the 2 types of 2nd degree AV block?
type I: wenckebach
type 2: mobitz II
80
what is 2nd degree AV block?
Intermittent failure of conduction of one or more impulses from the atria to ventricles
81
what is type I 2nd AV block?
progressive lengthening of the PR interval until an impulse is blocked and sequence begins again
Etiology: inferior wall MI
82
what is type II 2nd AV block?
intermittent block of atrial impulses (no QRS) with a constant PR interval
Etiology: anterior wall MI
83
what is 3rd AV node?
Occurs when the conduction link between the atria and the ventricles is lost
Results in atrial and ventricular depolarization being controlled by separate pacemakers
Atria continue to beat at normal rate & ventricles develop their own rate (usually 30-40 beats/minute)
84
manifestations of 3 AV block? (5)
Stokes-Adams attack (pd of dec CO and syncope), dizziness, fatigue, exercise intolerance,
episodes of acute heart failure
85
