Cardiovascular System - Lecture 5 Flashcards
1
Q
What is an electrocardiogram?
A
a recording of the electrical activity of the heart
2
Q
What is an electrocardiograph?
A
the device that records the electrical activity of the heart
3
Q
What kind of recordings are ECGs?
A
extracellular
4
Q
When do ECGs appear?
A
when there is a potential difference
5
Q
What are the 3 parts of the ECG set-up?
A
- patient cable + electrode
- lead-selector switch
- voltmeter
6
Q
What is found on the electrode to allow free flowing of ions?
A
salt solution
7
Q
All waves start and end at ___.
A
baseline
8
Q
What are the 8 steps of an ECG wave?
A
- sinus node fires
- P-wave
- AV node activation
- His bundle
- left bundle and septum (Q-wave)
- Purkinje fibres and ventricles (R-wave)
- late activation (S-wave)
- ventricle repolarize (T-wave)
9
Q
What direction does the ECG wave move?
A
right to left
10
Q
Does the sinus node firing show up on the ECG?
A
no
11
Q
What does the P-wave represent?
A
the atrial activation
12
Q
Which node activation propagates very slowly?
A
the AV node
13
Q
Is the His bundle activation visible?
A
no
14
Q
Is the left bundle activation visible?
A
no
15
Q
Is the septum activation visible?
A
yes
16
Q
What does the Q-wave represent?
A
the activation of the septum
17
Q
What is the sign of the Q-wave?
A
negative
18
Q
What is the direction of the Q-wave?
A
left to right
19
Q
Is the activation of Purkinje fibres visible?
A
no
20
Q
Is the activation of the ventricles visible?
A
yes
21
Q
What does the R-wave represent?
A
activation of the ventricles
22
Q
What does the S-wave represent?
A
some parts of the ventricle that activate a bit later
23
Q
What does the T-wave represent?
A
the ventricles repolarizing (recovering)
24
Q
What does the QRS complex represent?
A
depolarization of the ventricles
25
When is the P-R segment?
end of P to start of Q
26
When is the P-R interval?
start of P to start of Q
27
What is the P-R segment?
the time delay between atrial and ventricular activation
28
What does the P-R segment define?
the reference line for the ECG
29
What is the reference line for ECGs?
the P-R segment
30
The P-R interval is mostly a measure of ___ transit time.
AV
31
What happens when there are long P-R intervals?
AV block
32
What is the S-T segment?
the end of S to the start of T
33
What is the Q-T interval?
the start of Q to the end of T
34
The S-T segment is the time between ventricular ___ and ___.
depolarization and repolarization
35
What happens to tissues when S-T segment is elevated?
some will have abnormal APs (typical of an infarction)
36
What is the Q-T interval proportional to?
AP duration
37
Long QT causes problems with repolarization, what can this lead to?
arrhythmias
38
What is the QRS interval?
start of Q to the end of S
39
What would happen if the QRS interval is longer than 100 ms?
slow excitation, possible problems in His Purkinje or slow conduction in cardiac muscle (ischemia)
40
Case 1: cell A is depolarized (active). B is hyperpolarized (resting). Propagation is going from left to right.
Will the Voltage be positive or negative? Why?
+
positive electrode senses + ions, negative electrode senses - ions
41
Case 2: cell A is hyperpolarized (resting) . B is polarized (active) Propagation is going from right to left.
Will the Voltage be positive or negative? Why?
-
positive electrode senses - ions, negative electrode senses + ions
42
Case 3: cell A is hyperpolarized (resting). B is polarized (active). A repolarization (relaxation) wave is going from left to right.
Will the Voltage be positive or negative? Why?
-
positive electrode senses - ions, negative electrode senses + ions
43
What is V if the depolarization is going towards the positive electrode?
+ve
44
What is V if the depolarization is going towards the negative electrode?
-ve
45
What is V if the repolarization is going towards the positive electrode?
-ve
46
What is V if the repolarization is going towards the negative electrode?
+ve
47
Why is the T wave positive?
because the depolarization wave moves in the opposite direction as the repolarization wave, and this is due a difference in AP duration from the inside to outside of the heart
48
How many limb leads are there?
6
49
How many chest leads are there?
6
50
What plane do the limb leads look at the heart?
vertical
51
What plane do the chest leads look at the heart?
horizontal
52
What are leads?
12 electrical views of the heart from 12 different angles
53
What are the 3 bipolar limb leads?
right arm, left arm, left foot
54
What is lead I attached to?
right arm (-) to left arm (+)
55
What is lead II attached to?
right arm (-) to left foot (+)
56
What is lead III attached to?
left arm (-) to left foot (+)
57
What kind of electrode is the right foot?
it is an Earth electrode
58
What kind of loop does the RLF limb lead form?
closed loop
59
What does the voltage across each limb lead equal to?
zero
60
What are the 3 unipolar limb leads?
aVR, aVL, aVF
61
Where does aVR look at the heart from?
the upper right side
62
Where does the aVL look at the heart from?
the upper left side
63
Where does the aVF look at the heart from?
inferior wall
64
How many unipolar chest leads are there?
6
65
What are the 4 stages of ventricular action potential?
1. resting potential
2. upstroke
3. plateau
4. repolarization
66
What is the permeability of K, Ca and Na at rest?
P(K)>>P(Ca) and P(Na)
67
What is Vrest close to?
Ek
68
What happens at I(Na)?
there is a fast inward Na+ current
69
What do both sinus nodes and purkinje fibres both have in their action potentials?
pacemaker potential
70
What is a pacemaker potential?
spontaneous diastrolic depolarization
71
Since the sinus node doesn't have sodium channels, what is the upstroke driven by?
the flux of calcium
72
What is the rate of flow of ions in the sinus node and AV node? What does this cause?
slow, it causes slow depolarization
73
What kind of channels do the purkinje fibres have?
sodium channels
74
What is the rate of flow of ions in the purkinje fibres? What does this cause?
fast, it causes fast depolarization
75
Which structures have slow APs?
SA and AV nodes
76
Which structures have fast APs?
ventricular muscle
atrial muscle
bundle of His
bundle branches
Purkinje fibres
77
What happens before the ventricles beat?
there is a delay in the AV node after the atria beats
78
(T or F) The left bundle branch is blocked. This will lead to a long QRS, and no Q wave.
True. The septum is activated early by the left bundle branch, which gives the Q. And the left ventricle will contract more slowly as the His system can't trigger synchronous contract.
79
(T or F) The left bundle branch block can result in a change of direction of the R wave.
Both true and false.
True: the left ventricle isn't going to contract synchronously and this could result in a change of the waves direction relative to the electrodes
False: R wave is a positive deflection
80
(T or F) A repolarization wave deflecting in the same direction as an activation wave on the same lead means that the direction of the repolarization wave changed.
True. If that didn't happen, the direction would reverse as the charge at the two electrodes has switched.
81
(T or F) The sinus node beats twice in a row, 50 milliseconds apart. We therefore see two P waves.
False. The sinus doesn't have enough cells in it to cause a deflection in the ECG. To do so, it would have to trigger the atria. But the atrial action potential is 150 ms, and it wouldn't be possible to do that so quickly
