Cardiac Electrophysiology Flashcards
1
Q
What is excitable tissue?
A
nerves and muscle
2
Q
How do excitable tissue communicate?
A
through AP
3
Q
What is an action potential?
A
brief, rapid, large change in membrane potential
4
Q
What are the 2 types of APs in heart muscle?
A
- pacemaker cell AP
- contractile cell AP
5
Q
What is pacemaker cell AP?
A
cells can fire AP on their own
6
Q
What is contractile cell AP?
A
cells cannot fire AP on their own
7
Q
What is a contractile cell?
A
ventricular myocyte
8
Q
What is EK?
A
-90 mV
9
Q
What is ENa?
A
+60 mV
10
Q
What is ECa?
A
~ +60 mV, or more positive
11
Q
What heart cells have contractile cell AP?
A
99% of heart cells
- most cells are contractile – in ventricles especially (but atrium also has them)
- much lower amount of conduction tissue
12
Q
What does the stable resting membrane potential depend on?
A
K+
13
Q
What does the sharp fast rising phase of AP depend on?
A
Na+
14
Q
What does the plateau phase of AP depend on?
A
Ca2+ and K+
15
Q
What is the absolute refractory period?
A
second AP can’t be fired while membrane potential is changed (during previous AP) – must wait until membrane potential returns to resting
16
Q
What regulates the absolute refractory period?
A
Na+ state
- Na+ channels inactivate when AP reaches peak
- as long as Na+ cannot be fired, next AP cannot be fired
17
Q
What is a muscle twitch?
A
muscle contraction when Ca2+ enters
18
Q
What is tetanus?
A
sustained muscle contraction evoked when APs are emitted at very high rate
19
Q
Compare the duration of a muscle twitch to duration of AP.
A
equal duration
20
Q
Can twitches in skeletal muscles be summated?
A
yes
21
Q
Can twitches in cardiac muscles be summated?
A
no – therefore, cannot tetanize heart
22
Q
Why is tetanization of the heart bad?
A
if muscle contracted and was able to fire more APs, muscle will be constantly contracted
heart needs to beat regularly to fill and pump
23
Q
What is the SA node?
A
(tissue) cells that can contract/fire on their own
24
Q
Pacemaker Cell Action Potential – SA Node
A
- slight depolarization
- Na+ enters slowly (first rise)
- few different channels potentially responsible for allowing Na+ entry - depolarization
- Ca2+ enters through Ca2+ channels
- don’t open as quickly - hyperpolarization
- K+ enters through open K+ channels
25
What are cells in the heart connected by?
gap junctions (ion channels)
26
What happens once AP is initiated?
current produced moves across heart, causing contraction of atria and then ventricles
27
What determines heart rate?
rate of pacemaker APs (SA node)
28
What happens to HR when slope of pacemaker potential is increased?
increase rate
29
What happens to HR when slope of pacemaker potential is decreased?
decrease rate
30
What is the primary way to increase/decrease heart rate?
ANS release of:
- noradrenaline/adrenaline from SNS
- acetylcholine from PSNS
31
What do sympathetic nerves do?
increase slope of pacemaker potential to speed up heart rate
32
SNS
What does noradrenaline and adrenaline do?
increases slope of pacemaker depolarization
33
Where is noradrenaline from?
nerve
34
Where is adrenaline from?
adrenal gland
35
What does PSNS do?
decreases slope of pacemaker potential to slow down heart rate
36
PSNS
What does acetylcholine do?
- decreases slope of pacemaker depolarization (takes longer to reach threshold before Ca2+ channels open and AP fires)
37
PSNS
What receptors does acetylcholine act on?
muscarinic (M2) receptor on SA node cells
38
SNS
What receptor does noradrenaline and adrenaline act on?
𝛽1-adrenergic receptor on SA node cells
39
SNS
Noradrenaline and Adrenaline in Nodal Cells
- receptor
- result
receptor:
- 𝜷1 receptors
result:
- increase phase 4 slope
- increase heart rate
40
PSNS
Acetylcholine in Nodal Cells
- receptor
- result
receptor:
- muscarinic M2 receptors
result:
- decreases phase 4 slope
- decreases heart rate
41
SNS
Noradrenaline and Adrenaline in Ventricular Muscle Cells
- receptor
- result
receptor:
- 𝜷1 receptors
result:
- increase Ca2+
- increase stroke volume
42
PSNS
Acetylcholine in Ventricular Muscle Cells
- receptor
- result
no direction action
43
SNS
Noradrenaline in Vascular Smooth Muscle Cells
- receptor
- result
receptor:
- 𝛼1 receptors
result:
- increase Ca2+
- vasoconstriction
44
SNS
Adrenaline in Vascular Smooth Muscle Cells
- receptor
- result
receptor
- 𝜷2 receptors
result:
- decrease MLCK activity
- vasodilation
45
PSNS
Acetylcholine in Vascular Smooth Muscle Cells
- receptor
- result
limited direct action
46
What is phase 4?
diastolic depolarization / slow depolarization / pacemaker potential
47
When does phase 4 occur?
occurs once heart relaxes... eventually leads to next contraction
48
What are the conduction tissues of the heart? (5)
- SA node
- AV node
- bundle of His
- left and right bundle branches
- Purkinje fibres
49
Pathway of AP
1. Starts at SA node
2. Passes through AV node
3. Passes through Bundle of His
- slows down when travelling here to regulate timing of contraction – allows atria to contract before ventricles
4. Passes through left and right bundle branches (large pieces of conduction tissue)
5. Passes through Purkinje fibres in right and left ventricles
- moves from cell to cell via gap junctions
6. Ventricle contracts
50
How can AV node cells produce AP?
- AP arrives from SA node (60-100 beats/min)
| - if not, it self-depolarizes (40-50 beats/min)
51
How does the AV node compare to SA node?
has similar properties to SA node
beats on its own
52
Does AV node or SA node beat faster?
on their own: AV node beats slower
in the heart: both beat at same rate
53
How does the SA node and AV node beat at same rate (60 bpm) in the heart?
- SA node fires before AV node
| - AV node becomes stimulated to fire before it would normally fire itself
54
When is the only time AV node would beat on its own?
if something happens to SA node (ie. in disease) – would be acting as pacemaker
55
What is an electrocardiogram (ECG)?
using recording electrodes placed on body surface to produce tangible record of electrical changes
method of measuring wave of depolarization and repolarization occurring in heart (starting from SA node)
- pattern of electrical depolarization (and repolarization) repeats itself over and over again
56
What do bipolar limb leads do?
measure wave of depolarization
57
What is Lead I?
right arm (-) to left arm (+)
58
What is Lead II?
right arm (-) to left leg (+)
59
What is Lead III?
left arm (-) to left leg (+)
60
Einthoven's Triangle
–
61
When does ECG pen deflect upwards?
when depolarization moves to positive end of lead
62
When does ECG pen deflect downwards?
when depolarization moves away from positive end of lead
63
What is the P wave?
atrial depolarization
- wave of atrial depolarization travels downward and left
- as it moves down, leads pick it up as upward deflection (atrial depolarization)
64
What is the QRS wave?
ventricular depolarization
- more complex than atria (takes place in several stages)
65
In ventricle, which cells repolarize first?
last cells to depolarize are first to repolarize
wave of repolarization is in opposite direction of depolarization
66
What is depolarization?
upstroke of AP in ventricle
picked up outside of heart by leads
67
What is repolarization?
down phase of ventricular AP
when it’s going back down to RMP
68
What is the T wave?
ventricular repolarization
- wave of depolarization moves away from positive end of lead
- ECG pen deflects upward
- produces relatively simple waveform on ECG
69
What are the 2 things that have changed when repolarization begins?
- direction of change in membrane voltage (depolarization → repolarization) that’s picked up from outside
- changed direction – depolarization towards positive end = positive deflection
**if repolarization and direction changes, it’s still in upwards direction
70
What is a positive deflection?
depolarization towards positive end
71
3 Frontal Leads – Perspectives
–
72
What is a regular (normal) heart rate?
60-100 beats/min
73
What is paper speed?
25 mm/s
74
What is the time that each large sqaure represents?
0.2 seconds
75
What is the rate of normal sinus rhythm?
~75 beats/min [300/4 on paper]
between 60-100 beats/min
76
What is the rhythm of normal sinus rhythm?
regular
77
Are there P waves in normal sinus rhythm?
yes
- all facing upwards
- 1:1 with QRS (every QRS is preceded by P wave)
78
What is sinus bradycardia?
elongated period between beats
79
What is sinus tachycardia?
fast beating, not much time between beats
80
What is paroxysmal atrial fibrillation?
- atrial depolarization and repolarization are disorganized
- AV node is receiving random rapid volleys of APs
- APs proceed to ventricle depending on whether AV node is refractory or not
81
What is the danger of paroxysmal atrial fibrillation?
- hypotension: high irregular ventricular rate will decrease heart’s cardiac output
- embolisms: blood flow within atria becomes stagnant and can produce clots
