ECG 1: The Basics Flashcards
Basic Electric Stuff, Waveforms, Origins of Activity, Rhythm Diagnostic Criteria. Based on TeachingMedicine.com modules.
1
Q
What is moving in the process of depolarization?
A
Positive ion into cell
Negative ion out of cell
2
Q
What is moving in the process of depolarization?
A
Positive ion out of cell
Negative ion into cell
3
Q
What is the baseline electrical state of myocytes?
A
Negatively charged
4
Q
What direction is the voltage change in depolarization?
A
Postitive
5
Q
What direction is the voltage change in repolarization?
A
Negative
6
Q
What do the electrodes detect?
A
Change in polarization, ie charges that are moving (not still)
7
Q
What makes a lead (ECG)?
A
2 electrodes; voltage is compared between them
One is designated + and one - by convention
8
Q
What is voltage?
A
Electrical potential difference
Voltage is what makes electric charges move. It is the ‘push’ that causes charges to move in a wire or other electrical conductor.
9
Q
What direction does the reading deflect when a positive charge moves toward the positive electrode?
A
Upward
10
Q
What direction does the reading deflect when a positive charge moves away from the positive electrode?
A
Downward
11
Q
What direction does the reading deflect when a positive charge moves diagonally toward the positive electrode?
A
Upward, but smaller (than if it were moving directly toward it)
12
Q
If a charge is moving roughly perpendicular to the lead, what is the deflection on ECG?
A
Extant but tiny
13
Q
Where are the limb electrodes placed?
A
One on each shoulder, and one on a leg
14
Q
What does Lead I measure?
A
Electrical current from right to left (at level of shoulders)
15
Q
What does Lead II measure?
A
Electrical current from R shoulder to feet
16
Q
What does Lead III measure?
A
Electrical current from L shoulder to feet
17
Q
What are the aVF, aVR, and aVL leads based on?
A
One electrode & average of the two others
Electrode end is +, averaged end is -
18
Q
What plane do the limb leads assess current in?
A
All limb leads assess electrical activity in the coronal plane
Measure activity that is up-down or right-left, but NOT front-back
19
Q
What do aVF, aVL, and aVR stand for?
A
augmented Vector Foot, Left, and Right
The F/L/R indicates the + end, and is the non-calculated one (- end of this lead is the average between the other two electrodes)
20
Q
What does “augmented” mean, in the limb leads?
A
Historical note: these leads have a little “a” in the name to mean “augmented”. The word “augmented” arose because originally the active electrode was compared to an average of all three electrodes. When they removed the active electrode from the “averaged electrodes” the electrical deflection became greater and thus “augmented”
21
Q
What is the positive end of the precordial leads?
A
Theoretical ground, from sum of the 3 limb electrodes
Theoretically corresponds to centre of chest
22
Q
What are bipolar vs unipolar leads?
A
Bipolar: limb leads. Based on 2 electrodes, or 1 & avg of the other 2
Unipolar: precordial leads. Based on 1 electrode, & avg of limb leads
23
Q
What plane do precordial leads measure activity in?
A
Coronal plane: front-back, and right-left
24
Q
Describe the pattern of electrical movement in the heart
A
Starts in the RA, spreads to LA
SA node activated
Charge starts down bundle of His as atria start repolarizing
Charge is at end of septum and starts travelling up walls around when atria are done repolarizing
Signal travels through myocardium; depolarizes
Myocardium slowly repolarizes
25
Which bundle branch depolarizes the septum?
Left bundle branch
26
Which depolarizes first, endocardium or epicardium?
Endocardium: Purkinje fibres are close to the endocardium
| Inside before outside
27
Which repolarizes first, endocardium or epicardium?
Epicardium
| Heart depolarizes outside-in
myocytes near outside have shorter plateau phase
28
How big is a small square of ECG paper?
1mm
29
How big is a large square of ECG paper?
5mm
30
What speed are ECGs recorded?
25mm/s
31
How many big squares correspond to 1 second?
5
32
How many big squares correspond to 1 minute?
300!
33
How can you calculate HR based on ECG paper?
HR = 300 / (# of big squares between 2 QRS's)
34
How can you calculate HR based on ECG paper?
Full tracing is 10s long
HR = # of QRS complexes on the page x 6
35
What are the 4 rhythm categories on ECG?
regular
regular with random extra or missing beats
irregular with a pattern (regularly irregular)
irregular without a pattern (irregularly irregular)
36
What feature of the ECG should always be regular?
P waves
| If you think it's a P wave, check if there are others, comparably spaced out -- if not, it's probably not a P wave
37
How long is 1 little square on the ECG strip?
.04s = 40ms
38
What are the PR interval options?
```
normal
too short
too long, constant
too long, changing
not applicable (in other words, does not exist--eg if it changes every time)
```
39
what is the normal PR interval?
3-5 little squares
= 0.12-0.20 seconds
= 120-200ms
40
What is the criterion for wide vs normal QRS?
Normal: 120ms or less (3 little squares)
Wide: > 120ms
41
What are two important causes of slow conduction (wide QRS)?
diseased conducting fibers, typically called conduction delay, aberrancy, or bundle branch block.
electrical signal STARTS in the ventricle muscle: conduction is much slower (myocyte conduction v slow compared to purkinje fibers)
42
What is the conduction pattern in bundle branch block?
Slow: signal moves down one bundle branch, but to get to other side of heart, must be conducted via myocytes. Thus, slow.
43
Where can electrical activity start in the heart?
Sino-atrial (SA) node
Atria
Atrio-ventricular (AV) node
Ventricles
44
Where do upright P waves orginate?
SA node (>95%)
45
Where do inverted P waves originate?
atria, AV node, or ventricles
46
If there are no P waves, what does that rule out?
SA node, Atria
47
Where is the rarest origin of a P wave?
Ventricles
48
Why is the P wave inverted when it comes from the AV node (or ventricles, or some spots in the atria)
The electrical activity is moving in the opposite direction
49
Which focus/pacemaker does a normal or long PR interval rule out?
AV node & ventricles
AV node creates the PR interval: if there is one, it's doing its job, and not originating the activity
If focus is in ventricles, there may be a P wave, but it will be at the same time as the QRS (won't see it) or will come after -- still no PR interval
50
If you see P waves and QRS complexes, but no consistent PR interval, what does that mean?
2 pacemakers
51
What does "no PR interval" mean?
There is not a consistent interval between the P wave and the QRS complex (there may be intervals, but they vary)
52
What will you see when there is a ventricular origin as well as the SA node for the atria?
P waves with different rate from QRS
May appear to occasionally have normal PR interval, but is actually just chance
53
What two things cause "random wavy garbage" (as this module puts it)?
```
fibrillation
muscle tremors (or patient movement)
```
54
What do regular consistent P waves and regular QRS complexes rule out?
Atrial fibrillation and ventricular fibrillation, respectively
55
Wavy baseline + regular P waves + QRS complexes =
No fibrillation (movement artifact)
56
Wavy baseline + no P waves + QRS complexes =
Atrial fibrillation, probably (atrial origin)
57
Wavy baseline with no QRS complexes =
ventricular fibrillation (ventricular origin)
58
Does a wide QRS rule out SA node, atria, or AV node pacemakers?
No
| Slow conduction through diseased purkinje fibres --> wide QRS
59
Which pacemaker does a narrow QRS rule out?
Ventricles
60
Why is the term "supraventricular tachycardia" convenient?
Sometimes hard to tell the difference between the SA node, the atria, and the AV node on a fast ECG: all we know is it's not the ventricle (bc of the narrow complex)
61
What is a rare origin for wide QRS?
AVRT (atrio-ventricular re-entry tachycardia) due to WPW
62
What is the normal pace limit for the SA node?
200 BPM
63
Which pacemaker(s) does a HR > 200 rule out?
SA node
64
Which pacemaker(s) does a ventricular rate > 200 rule out?
SA node or atria
(bc of AV node)
Exceptions: babies & v young children, WPW
65
Ventricular rate > 200 + narrow QRS = (which pacemaker)
AV node pacemaker (junctional)
66
When might you see more P waves than QRS complexes?
```
AV node is diseased (not conducting the signals)
Atrial flutter (too many P waves), and AV node is blocking signal (normal physiological block)
```
67
P waves not all same size and shape =
more than one origin for the P waves
| possible combination of sinus, atrial or junctional beats
68
What are the diagnostic criteria for normal sinus rhythm?
```
Rate: 60-100
Rhythm: regular
P waves: upright, all same size and shape
PR interval: normal (3-5 little squares)
QRS: narrow (< 3 little squares)
```
69
What are the diagnostic criteria for sinus bradycardia?
Rate: < 60
Rhythm: regular
P waves: normal
PR interval: normal (3-5 little squares)
QRS: narrow (< 3 little squares)
70
What can cause sinus bradycardia?
healthy cardiovascular fitness level
negative chronotropes (drugs that slow down the sinus node such as beta blockers and calcium channel blockers)
toxins that increase parasympathetic tone: some insecticides (also called organophosphates)
myocardial ischemia
71
How is sinus bradycardia treated?
atropine intravenous bolus
dopamine intravenous infusion
epinephrine intravenous infusion
artificial electronic pacemaker
72
What are the diagnostic criteria for sinus tachycardia?
Rate: > 100
Rhythm: regular
P waves: normal
PR interval: normal (3-5 little squares)
QRS: narrow (less than 3 little squares)
73
When should sinus tachycardia not be treated?
It is physiological (eg when exercising) or compensatory (eg anemia, hemorrhage)
74
When should sinus tachycardia be treated?
- it is driven by a pathological process such as an over active thyroid gland (hyperthyroidism)
- you have coronary artery disease and will experience myocardial ischemia at high(er) heart rates
75
How can sinus tachycardia be treated?
- treating the underlying cause of the tachycardia (treat hyperthyroidism or anemia for example)
- give a negative chronotrope: beta blocker or calcium channel blocker
76
Name 6 rhythms/patterns that re-entrant circuits are responsible for
```
atrial fibrillation
atrial flutter
atrial tachycardia
AVNRT (AV node re-entry tachycardia)
AVRT (atrio-ventricular re-entry tachycardia)
ventricular tachycardia
```
77
What are the diagnostic criteria for atrial fibrillation?
Rate: any
* Rhythm: irregular with no pattern
* P waves: none - a wavy chaotic baseline is present
* PR interval: no P waves
(* indicates imp criteria)
QRS: narrow
78
What conditions are associated with an increase in atrial fibrillation?
```
any structural heart abnormalities, especially valve diseases and enlarged atria
hypertension
acute myocardial infarction
hyperthyroidism
alcohol consumption
```
79
How is atrial fibrillation treated?
- convert back to sinus rhythm with anti-arrhythmic drugs or electrical cardioversion
- reduce the ventricular heart rate if too fast, using drugs that reduce AV node conduction (beta blockers, calcium channel blockers, and digoxin)
- anti-coagulate because the atria do not mechanically contract and therefore blood can pool and clot in the atria
80
What are the diagnostic criteria for atrial flutter?
Rate: any (usually fast)
* Rhythm: regular or irregular
* P waves: more P waves than QRS, non-stop "flutter" waves
* PR interval: sometimes normal, sometimes appears random
(* = important)
QRS: narrow
81
Does atrial flutter have a regular or irregular ventricular rhythm?
Either: depends on how many flutter waves are being conducted through the AV node, and whether that rate changes
Eg might conduct 1 of 2, 1 of 3, 1 of 4, or switch between
82
Which leads are the best to see P waves?
II and V1
83
What "clue" should point you to atrial flutter?
Regular HR of 150:
| atrial flutter is commonly 300 and 2:1 conduction gives regular ventricular rate of 150
84
What is first degree heart block?
conduction through AV node is slower than normal
| 100% of P waves are conducted to ventricles... but PR interval is long
85
What effect does 1st degree block have on HR?
None: 1st degree block does not change HR
86
What are the diagnostic criteria for first degree heart block?
Rate: any
Rhythm: regular
P waves: all normal
* PR interval: long (> 5 little squares which is > 200 ms), and constant
QRS: narrow
87
What should the presence of a first degree heart block do?
Raise your suspicion for other problems with the heart
| often occurs when there are other problems in the heart
88
What is second degree heart block generally?
some, but not all of the P waves are conducted to the ventricles
89
What are the diagnostic criteria for 2nd degree heart block, type 1?
Rate: any
* Rhythm: regular with occasional missing beats
P waves: all normal
* PR interval: increasing with each heartbeat, resetting after missing QRS
QRS: narrow
90
What is type I second degree heart block (Mobitz type 1)
PR interval is not constant: grows, until AV node cannot conduct and a ventricular beat is skipped
91
What is type II second degree heart block (Mobitz type 2)?
PR interval is constant, and QRS complexes are randomly dropped
92
Where is the location of the bock, in type 1 2nd degree block?
Usually AV node, sometimes bundle of His
93
Name 4 causes of 2nd degree Type 1 heart block
- ischemia (the AV node branch of the right coronary artery supplies the AV node)
- high vagal tone in athletes
- heart surgery
- medications that suppress the AV node (beta blockers, calcium channel blockers, other anti-arrhythmics)
94
What are the diagnostic criteria for 2nd degree heart block, type 2?
Rate: any
* Rhythm: regular with occasional missing beats
P waves: all normal
PR interval: constant
QRS: narrow
95
Where do 2nd degree heart block, type 2 occur?
Usually occur BELOW the AV node
20% are in the Bundle of His
80% are in the bundle branches (note that both branches would need to be blocked at same time)
96
Which second degree heart block is temporary?
Type 1
| Type 2 is permanent
97
Which second degree heart block sometimes progresses to a third degree block?
Type 2
| Type 1 rarely progresses
98
What medications can cause or worsen heart block?
Beta blockers, calcium channel blockers, or any other medications that inhibit the AV node
99
Name 3 causes of second degree type 2 heart block
ischemia (the AV node branch of the right coronary artery supplies the AV node)
fibrosis in the conducting system
heart surgery
... and, others
100
What feature makes it impossible to distinguish between type 2 and type 1 second-degree block?
2:1 block -- because the beat is dropped after every other P wave (ie there is only QRS and thus 1 PR interval between dropped beats), it is impossible to determine if the PR interval is increasing or not
101
Describe 3rd degree block
AV node does not conduct any electrical signals
Ventricular pacemaker is what causes contractions -- thus very slow rate
102
What is AV dissociation?
P waves at regular rate
QRS complexes at regular rates
Not consistently associated (though some QRS may follow P waves by change)
103
What is another name for third degree heart block?
Complete heart block
| A-V dissociation
104
What are the diagnostic criteria for third degree heart block?
* Rate: ventricular rate is almost always slow
* Rhythm: usually regular but sometimes irregular
* P waves: more P waves than QRS, P waves not associated with QRS complexes
* PR interval: not applicable because the P waves are not associated with QRS complexes
QRS: narrow or wide
105
How can you tell where the block is in third degree block?
QRS complex:
- narrow: signal coming from Bundle of His -- so block is in AV node or Bundle of His
- wide: pacemaker signal coming from ventricles -- so block is at level of bundle branches
106
In third degree block, which rate is faster?
P wave rate is faster than QRS complex rate
107
What is an important clue that should make you think about third degree heart block?
Absence of a PR interval
108
Name 4 causes of third degree heart block
ischemia or infarction (the AV node branch of the right coronary artery usually supplies the AV node)
fibrosis or sclerosis of the conducting fibers (many causes)
heart surgery
cardiomyopathy (a generic term to describe disease of heart muscle ... many causes of this as well)
109
What is a junctional rhythm?
Rhythm originating from AV node
110
What are the 3 typical junctional rhythms? Where does the rhythm start for each? What is the appearance of the P wave for each?
P wave before QRS: signal starts at top of AV node. P wave is inverted.
P wave simultaneous with QRS: signal starts near middle of AV node. P wave is not seen (overpowered by QRS).
P wave after QRS: signal starts near bottom of AV node. P wave is in ST segment, and is typically inverted.
111
What are the diagnostic criteria for junctional rhythms?
* Rate: typically 40-60
Rhythm: regular
* P waves: present, usually inverted or absent
* PR interval: short (if P wave is in front of QRS), or "not applicable" if P wave is AFTER QRS
QRS: narrow
112
What are the diagnostic criteria for SVT?
* Rate: > 100, but typically > 150
Rhythm: regular
* P waves: not easily identified (but they could be present)
* PR interval: no P waves identified
QRS: narrow
113
Name 2 similarities between SVT and VT
both rhythms are very fast
| P waves are usually NOT seen in both rhythms
114
Name 3 differences between SVT and VT
SVT is a narrow QRS and VT is a wide QRS
SVT originates from either the SA node, atria or AV node, while VT always originates from the ventricle
VT is more dangerous than SVT
115
What are the diagnostic criteria for VT?
* Rate: > 100
Rhythm: regular
* P waves: not easily identified (but they could be present)
* PR interval: if P waves are present, they are not associated with QRS
* QRS: wide (> 3 little squares = 120ms)
116
Name and describe two subtypes of VT
Monomorphic: all the QRS's are the same size and shape and all come from the same pacemaker
Polymorphic: QRS's are different size and shape and come from different pacemakers in the ventricle
117
What are the three main reasons CO is reduced in VT?
- fill time is short so ventricle underfills
- contraction is slow, because activation travels via myocytes (not conducting fibres)
- contraction is abnormal, because of abnormal pattern of activation, and thus less efficient
118
Name 3 causes of VT
myocardial ischemia or infarction
dilated cardiomyopathy
myocarditis
many others
119
What are the diagnostic criteria for VF?
* Rate: 0
* Rhythm: indeterminant (not applicable)
* P waves: none
* PR interval: not applicable
* QRS: none
120
What is the appearance of the QRS complex in VF?
None: there is no QRS in VF
121
Name 4 causes of VF
- ischemia (lack of oxygen changes the electrical properties of the heart)
- infarction (produces scars and the region around the scar often have abnormal electrical properties)
- heart failure (a strained heart will be electrically abnormal)
- dilated cardiomyopathy (a stretched out heart will have some fibrosis and abnormal conduction)
122
When might the P wave have slightly different shapes?
If the R or L atrium is enlarged
123
What is the approach to diagnosing rhythm?
1. Ventricular rate
2. Ventricular rhythm
3. Are any P waves seen?
4. Ratio of P waves to QRS
5. Are P waves all the same shape?
6. P waves conducted to ventricles?
7. PR interval
8. QRS width
9. Origin(s) of waves? (P waves and QRS, if separate)
10. Diagnosis!
