14- electrocardiogram Flashcards
1
Q
What is an ECG?
A
Electrocardiogram:
Non-invasive transthoracic recording of the electrical activity of the heart, externally recorded by skin electrodes (indirect)
- useful tool to detect altered electrical activities of the heart
2
Q
P wave on the ECG represents:
A
Atrial depolarization (contraction)
3
Q
What does the QRS complex on the ECG represent?
A
Ventricular Depolarization (contraction)
4
Q
What does the T-wave on an ECG represent?
A
Ventricular repolarization (relaxation)
5
Q
What does the T-wave on an ECG represent?
A
Ventricular repolarization (relaxation)
6
Q
What are the 12 leads in the ECG machine connected to?
A
3 limb leads (unipolar)
3 bipolar leads
6 chest leads
7
Q
What do the unipolar (limb) leads of the ECG measure
A
Unipolar/limb leads measure the electrical activity in the Vertical plane
aVR = Augmented vector Right (position: rt wrist or shoulder)
aVL = Augmented vector Left (position: Left wrist or shoulder)
aVF = Augmented vector foot (position = left foot
8
Q
What information comes from the Bi-polar leads and where are they positioned?
A
- Information gathered between the three unipolar leads is known as the bipolar leads
- Lead I = information between aVR and aVL
- Lead II = information between aVR and aVF
- Lead III = information between aVL and aVF
9
Q
Electrical signal moving _______ a lead results in a positive deflection
Electrical signal moving ______ a lead results in a negative deflection
A
Electrical signal moving towards a lead results in a positive deflection
Electrical signal moving away from a lead results in a negative deflection
10
Q
What do the chest leads (precordial leads) of the ECG measure
Positions?
A
- Measure electrical activity in the horizontal plane
- V1-V4 = anterior chest leads
- V5 & V6 = left lateral leads
11
Q
What are the left-sided leads?
A
- Lead I (bipolar), aVL (unipolar) and V5, V6 (chest leads)
12
Q
What are the Right-sided leads?
A
- V1, V2, and aVR
- V1, V2 = anterior chest leads
- aVR = right unipolar lead
13
Q
What are the three inferior leads?
A
- Lead II, Lead III, aVF
- Lead II and III are bipolar leads
- aVF = unipolar left lead
14
Q
What are the four Anterior leads?
A
V1, V2, V3, V4
Anterior chest leads
15
Q
Which leads do A, B, C of the ECG refer to?
A
- A = bipolar leads
- B = Limb leads
- C = Chest leads
16
Q
On an ECG one small box on the x-axis is equivalent to ____ seconds and 5 Large boxes = ___
A
On an ECG one small box on the x-axis is equivalent to 0.04 seconds (40ms) and 5 Large boxes = 1 second
17
Q
1 small box on the y-axis of ECG is equivalent to
A
0.1 mV
18
Q
The x axis of the ECG measures:
The y-axis of the ECG measures:
A
The x-axis of the ECG measures: Time
The y-axis of the ECG measures: Voltage
19
Q
What are five electrophysiological pathologies illustrated by a 12-lead ECG
A
- Atrial/Ventricular Synchrony (AV block, Atrial fibrillation)
- Depolarization
- Repolarization
- Hypertrophy
- Myocardia Ischemia/infarction (St-T wave abnormalities)
20
Q
What are the four basic characteristics of ECG recordings
A
- Rate
- Rhythm
- Axis
- Intervals
21
Q
How do you determine Heart rate using ECG?
A
- eg
- 30 large boxes = 6 seconds
- Multiply the number of beats in 6 seconds by 10 (60sec/1min = beats per minute bpm)
- recall: 5 large boxes = 25mm = 1 sec
- eg. 8 beats in 6 seconds = 80beats/60secs = 80bpm
particulary useful for irregular rhythms
22
Q
Normal rhythm is called ________
A
Normal rhythm is called sinus rhythm
23
Q
Sinus rhythm (normal rhythm) is present if which qualities are present on ECG:
A
- Every p-wave followed by QRS wave
- Every QRS preceded by 1 P-wave
- P-wave uprint in I, II and III
- PR interval >0.12 sec (0.12-0.20 sec)
- recall one small box = 0.04 sec
24
Q
******SLIDE 16*****
What kind of rhythm is shown in the image? How do you know?
A
Sinus Rhythm
- Every P-wave followed by QRS
- Every QRS preceded by 1 P-wave
- P-wave upright in I, II, III
- PR interval >0.12 sec
25
What is normal HR?
60-100 bpm
26
A HR \<60 bpm is indicative of:
Sinus bradycardia
27
A HR greater than 100bpm is indicative of:
Sinus tachycardia
28
QRS Axis Determination
What does the hexaxial reference (aka Cabrera) system determine?
Determines the direction that the maximal ECG vector is “pointing” (in which lead there are most positive amplitude)
Tells us the direction the depolarization is headed in the ventricles
29
What is a normal QRS axis?
-30 to +90 (or +100)
30
A QRS axis of -30 to -90 represents:
Left axis deviation
LAD block, inferior MI, LV hypertrophy
31
What does a QRS axis of +90 (or +100) to +180 represent?
Right axis deviation:
High lateral MI, RV hypertrophy or strain pattern
32
What does a QRS of +180 to -90 represent?
Undetermined (extreme right axis deviation) rare
33
What do numbers 1 through 4 of QRS axis indicate?
1. -30 to +90 (or +100) = normal
2. -30 to -90 = Left axis deviation (LAD block, inferior MI, LV hypertrophy)
3. +90 (or +100) to +180 = Right axis deviation (High lateral MI, RV hypertrophy or strain pattern)
4. +180 to -90 = undetermined (extreme Right Axis deviation), rare
34
How do you calculate corrected QT?
QTc = QT/ (sqrt(R-R))
35
What does P-R interval show:
The time required for completion of atrial depolarization
Conduction through AV node, bundle of His, and bundle branches
Arrival at the ventricular myocardial cells
0.12-0.20 seconds
36
QRS interval shows:
Normal duration?
The time required for ventricular cells to depolarize. The normal duration is 0.06 to 0.12 seconds
37
What does the QT interval show?
The time required for depolarization and repolarization of the ventricles (faster HR, shorter QT interval)
38
Prolonged PR-interval indicates:
A-V block
39
\_\_\_\_\_\_\_\_\_: PR interval is prolonged \>0.20 sec
_First degree AV block_: PR interval is prolonged \>0.20 sec
40
What are the two types of a second degree AV block?
* Type 1 (or Mobitz 1): Progressive prolongation of PR interval with dropped beats (the PR interval gets long and longer; finally one beat drops)
* Type 2 (Mobitz 2): PR interval remains unchanged prior to the P wave which suddenly fails to conduct to the ventricles
41
Diagnosis:
Progressive prolongation of PR interval with dropped beats (the PR interval gets long and longer; finally one beat drops)
* Type 1 (or Mobitz 1) of Second degree AV block: Progressive prolongation of PR interval with dropped beats (the PR interval gets long and longer; finally one beat drops)
42
Diagnosis:
PR interval remains unchanged prior to the P wave which suddenly fails to conduct to the ventricles
* **Type 2 (Mobitz 2) of Second degree AV block**: PR interval remains unchanged prior to the P wave which suddenly fails to conduct to the ventricles
43
What is a third degree AV block?
No association between P waves and QRS complexes
44
What is the normal PR interval?
3-5 small boxes (120-200ms)
In the image:
PR interval = 4 small boxes (1mm = 0.04s)
4x0.4 = 0.16sec = 160ms
45
PR INTERVAL:
The image shows:
1st degree AV block (prolonged PR interval)
* PR interval = 7 small boxes → 7x0.4s = 0.28s (normal interval 0.16s)
* 280ms PR indicates delay in AV node: 1st degree AV block
46
PR INTERVAL
What does the image show?
2nd Degree AV block
Mobitz II = PR interval remains unchanged until a P-wave suddenly fails to conduct in the ventricles
* AV block at level of bundle of His or at bilateral bundle branches or trifascicular
47
PR-INTERVAL
What does the image show?
3rd degree AV block: No association between P waves and QRS complexes ie No association between atria and ventricles
Atria and Ventricles are depolarizing independently
48
How long is a normal QRS interval?
Recall: what does QRS interval represent?
Normal QRS interval = 2 small boxes
2x0.04 = 0.08 sec
Normal range: 0.06 - 0.12 seconds
QRS interval represents Ventricular Depolarization
49
What are 3 possible causes of prolonged QRS interval?
* Right bundle branch block
* Left bundle branch block
* Metabolic (hyperkalemia (↑K+)
50
The image shows?
Right bundle branch block
51
How would Right Bundle Branch Block appear on an ECG
* At V1, V2
* At V5, V6
How would Right Bundle Branch Block appear on an ECG
* At V1, V2
* ‘bunny ears’ on right = right bundle branch
* Late RV firing = late forces coming toward Vq → R'
* At V5, V6
* Also → fat, wide S wave on left leads I, aVL, V6
52
The image shows:
* Right bundle branch block:
* V1 (&V2) leads:
* Late M-shaped QRS (RSR')
* Sometimes wide notched R or qR
* I, aVL, V5, and V6 leads: wide S wave
* Late depolarization of RV
* Slow, via ‘back alley’ cell conduction
* Late positive right forces
* R' in V1, V2
53
The image shows:
Left bundle branch Block
54
How can you recognize a left bundle branch block on ECG?
At V1
At V6
* At V1
* ‘bunny ears’ on Left = left bundle branch
* also → fat, wide S wave on right leads = V1
* At V6
* Late LV firing = late forces coming toward V6 → R'
55
The image shows:
Left bundle Branch Block:
* V1 leads: QS or RS (instead of QRS)
* I, aVL and V6 leads:
* Late R peak, no Q waves, notched wide R
* Late depolarization of LV
* slow via ‘back alley’ cell conduction
* Late positive left forces
* R' or wide R in I, a VL, V5, V6 (left leads (red))
* Wide S wave in V1 (grean)
56
How would hyperkalemia appear on ECG?
* Loss of P-wave
* Prolonged (widened) QRS interval
* Peaked T-waves
57
Fill in the table:
58
How does cardiac action potential during hyperkalemia relate to ECG?
* The slow membrane depolarization (phase 0) upstroke slows down conduction through the myocardium and prolongs membrane depolarization, resulting in **prolonged QRS wave**
59
What does the image show?
Moderate Hyperkalemia (K+ = 6.5mM)
* Widened QRS wave
* Tall slender T-wave
* Ectopic beats and escape rhythms
60
What does the image show?
* Severe hyperkalemia (K+ = 8.5mM)
* Loss of P-wave
* Progressive widening of QRS wave (slurred)
* Tall T = sine wave
* Further elevation of K+ can lead to ventricular tachycardia and or atrial fibrillation
61
What is the QT interval and what does it represent?
* Time from between the start of the Q wave and the end of the T wave in the heart's electrical cycle
* The QT interval represents electrical depolarization and repolarization of the ventricles
62
Generally, QT is how long (cardiac cycle)
R-R interval?
Generally QT is \< half of the cardiac cycle = QT \< 50% of R-R interval
63
If QT \< ½ cardiac cycle (R-R) = \_\_\_\_\_\_QT
If QT \> ½ cardiac cycle (R-R) = ______ QT
HOWEVER:
With **faster HR** heart still needs a certain length of time to complete systole→systole \> ½ cardiac cycle → QT \> \_\_\_\_\_\_RR
Therefore QT needs to be \_\_\_\_\_\_\_\_
If QT \< ½ cardiac cycle (R-R) = **_Normal_**QT
If QT \> ½ cardiac cycle (R-R) = _Abnormal_ QT
HOWEVER:
With **faster HR** heart still needs a certain length of time to complete systole→systole \> ½ cardiac cycle → QT \> _0.5_RR
Therefore QT needs to be _corrected for HR_
63
If QT \< ½ cardiac cycle (R-R) = \_\_\_\_\_\_QT
If QT \> ½ cardiac cycle (R-R) = ______ QT
HOWEVER:
With **faster HR** heart still needs a certain length of time to complete systole→systole \> ½ cardiac cycle → QT \> \_\_\_\_\_\_RR
Therefore QT needs to be \_\_\_\_\_\_\_\_
If QT \< ½ cardiac cycle (R-R) = **_Normal_**QT
If QT \> ½ cardiac cycle (R-R) = _Abnormal_ QT
HOWEVER:
With **faster HR** heart still needs a certain length of time to complete systole→systole \> ½ cardiac cycle → QT \> _0.5_RR
Therefore QT needs to be _corrected for HR_
64
Why does QT need to be corrected for HR?
With **faster HR** heart still needs a certain length of time to complete systole→systole \> ½ cardiac cycle → QT \> _0.5_RR
Therefore QT needs to be _corrected for HR_
65
How do you correct for QT for HR?
* Bazett's formula
* QT (corrected) = QT/ (sqrt (R-R interval(s)))
66
If HR=60 and R-R interval is 1, will the QTc be less than, equal to or greater than the QTabsolute
HR=60bpm
R-R interval = 1 (sqrt(1)) =1 → QTc = QTabsolute
66
If HR=60 and R-R interval is 1, will the QTc be less than, equal to or greater than the QTabsolute
HR=60bpm
R-R interval = 1 (sqrt(1)) =1 → QTc = QTabsolute
67
If HR\>60 and R-R interval is \< 1, will the QTc be less than, equal to or greater than the QTabsolute
HR \> 60bpm
R-R interval \<1 (sqrt(RR)) \<1 → QTc\>QTabsolute
68
If HR\<60 and R-R interval is \>1, will the QTc be less than, equal to or greater than the QTabsolute
HR \< 60bpm
R-R interval \>1 (sqrt(RR)) \>1 → QTcabsolute
69
What is the normal QTc in males? Females?
Males: \<450ms
Females: \<460ms
70
What is the QTc in the image?
* QT interval = 8 (small boxes) x 0.04 = 0.32s
* R-R interval = 19 x 0.04 = 0.76s
* QTc = 0.32/ (sqrt(0.76)) = 0.36sec = normal QTc
71
What is the electrophysiological basis for LQT syndrome?
Loss of K+ current during cardiac action potential
