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PHYSL 404 - Cardiovascular Physiology > 14- electrocardiogram > Flashcards

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

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2
Q

P wave on the ECG represents:

A

Atrial depolarization (contraction)

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3
Q

What does the QRS complex on the ECG represent?

A

Ventricular Depolarization (contraction)

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4
Q

What does the T-wave on an ECG represent?

A

Ventricular repolarization (relaxation)

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5
Q

What does the T-wave on an ECG represent?

A

Ventricular repolarization (relaxation)

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6
Q

What are the 12 leads in the ECG machine connected to?

A

3 limb leads (unipolar)

3 bipolar leads

6 chest leads

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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

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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
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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

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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
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11
Q

What are the left-sided leads?

A
  • Lead I (bipolar), aVL (unipolar) and V5, V6 (chest leads)
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12
Q

What are the Right-sided leads?

A
  • V1, V2, and aVR
  • V1, V2 = anterior chest leads
  • aVR = right unipolar lead
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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
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14
Q

What are the four Anterior leads?

A

V1, V2, V3, V4

Anterior chest leads

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15
Q

Which leads do A, B, C of the ECG refer to?

A
  • A = bipolar leads
  • B = Limb leads
  • C = Chest leads
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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

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17
Q

1 small box on the y-axis of ECG is equivalent to

A

0.1 mV

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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

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19
Q

What are five electrophysiological pathologies illustrated by a 12-lead ECG

A
  1. Atrial/Ventricular Synchrony (AV block, Atrial fibrillation)
  2. Depolarization
  3. Repolarization
  4. Hypertrophy
  5. Myocardia Ischemia/infarction (St-T wave abnormalities)
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20
Q

What are the four basic characteristics of ECG recordings

A
  • Rate
  • Rhythm
  • Axis
  • Intervals
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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

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22
Q

Normal rhythm is called ________

A

Normal rhythm is called sinus rhythm

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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
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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
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25
Q

What is normal HR?

A

60-100 bpm

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26
Q

A HR <60 bpm is indicative of:

A

Sinus bradycardia

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27
Q

A HR greater than 100bpm is indicative of:

A

Sinus tachycardia

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28
Q

QRS Axis Determination

What does the hexaxial reference (aka Cabrera) system determine?

A

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

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29
Q

What is a normal QRS axis?

A

-30 to +90 (or +100)

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30
Q

A QRS axis of -30 to -90 represents:

A

Left axis deviation

LAD block, inferior MI, LV hypertrophy

31
Q

What does a QRS axis of +90 (or +100) to +180 represent?

A

Right axis deviation:

High lateral MI, RV hypertrophy or strain pattern

32
Q

What does a QRS of +180 to -90 represent?

A

Undetermined (extreme right axis deviation) rare

33
Q

What do numbers 1 through 4 of QRS axis indicate?

A
  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
Q

How do you calculate corrected QT?

A

QTc = QT/ (sqrt(R-R))

35
Q

What does P-R interval show:

A

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
Q

QRS interval shows:

Normal duration?

A

The time required for ventricular cells to depolarize. The normal duration is 0.06 to 0.12 seconds

37
Q

What does the QT interval show?

A

The time required for depolarization and repolarization of the ventricles (faster HR, shorter QT interval)

38
Q

Prolonged PR-interval indicates:

A

A-V block

39
Q

_________: PR interval is prolonged >0.20 sec

A

First degree AV block: PR interval is prolonged >0.20 sec

40
Q

What are the two types of a second degree AV block?

A
  • 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
Q

Diagnosis:

Progressive prolongation of PR interval with dropped beats (the PR interval gets long and longer; finally one beat drops)

A
  • 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
Q

Diagnosis:

PR interval remains unchanged prior to the P wave which suddenly fails to conduct to the ventricles

A
  • 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
Q

What is a third degree AV block?

A

No association between P waves and QRS complexes

44
Q

What is the normal PR interval?

A

3-5 small boxes (120-200ms)

In the image:

PR interval = 4 small boxes (1mm = 0.04s)

4x0.4 = 0.16sec = 160ms

45
Q

PR INTERVAL:

The image shows:

A

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
Q

PR INTERVAL

What does the image show?

A

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
Q

PR-INTERVAL

What does the image show?

A

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
Q

How long is a normal QRS interval?

Recall: what does QRS interval represent?

A

Normal QRS interval = 2 small boxes

2x0.04 = 0.08 sec

Normal range: 0.06 - 0.12 seconds

QRS interval represents Ventricular Depolarization

49
Q

What are 3 possible causes of prolonged QRS interval?

A
  • Right bundle branch block
  • Left bundle branch block
  • Metabolic (hyperkalemia (↑K+)
50
Q

The image shows?

A

Right bundle branch block

51
Q

How would Right Bundle Branch Block appear on an ECG

  • At V1, V2
  • At V5, V6
A

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
Q

The image shows:

A
  • 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
Q

The image shows:

A

Left bundle branch Block

54
Q

How can you recognize a left bundle branch block on ECG?

At V1

At V6

A
  • 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
Q

The image shows:

A

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
Q

How would hyperkalemia appear on ECG?

A
  • Loss of P-wave
  • Prolonged (widened) QRS interval
  • Peaked T-waves
57
Q

Fill in the table:

A
58
Q

How does cardiac action potential during hyperkalemia relate to ECG?

A
  • The slow membrane depolarization (phase 0) upstroke slows down conduction through the myocardium and prolongs membrane depolarization, resulting in prolonged QRS wave
59
Q

What does the image show?

A

Moderate Hyperkalemia (K+ = 6.5mM)

  • Widened QRS wave
  • Tall slender T-wave
  • Ectopic beats and escape rhythms
60
Q

What does the image show?

A
  • 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
Q

What is the QT interval and what does it represent?

A
  • 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
Q

Generally, QT is how long (cardiac cycle)

R-R interval?

A

Generally QT is < half of the cardiac cycle = QT < 50% of R-R interval

63
Q

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 ________

A

If QT < ½ cardiac cycle (R-R) = NormalQT

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
Q

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 ________

A

If QT < ½ cardiac cycle (R-R) = NormalQT

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
Q

Why does QT need to be corrected for HR?

A

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
Q

How do you correct for QT for HR?

A
  • Bazett’s formula
    • QT (corrected) = QT/ (sqrt (R-R interval(s)))
66
Q

If HR=60 and R-R interval is 1, will the QTc be less than, equal to or greater than the QTabsolute

A

HR=60bpm

R-R interval = 1 (sqrt(1)) =1 → QTc = QTabsolute

66
Q

If HR=60 and R-R interval is 1, will the QTc be less than, equal to or greater than the QTabsolute

A

HR=60bpm

R-R interval = 1 (sqrt(1)) =1 → QTc = QTabsolute

67
Q

If HR>60 and R-R interval is < 1, will the QTc be less than, equal to or greater than the QTabsolute

A

HR > 60bpm

R-R interval <1 (sqrt(RR)) <1 → QTc>QTabsolute

68
Q

If HR<60 and R-R interval is >1, will the QTc be less than, equal to or greater than the QTabsolute

A

HR < 60bpm

R-R interval >1 (sqrt(RR)) >1 → QTcabsolute

69
Q

What is the normal QTc in males? Females?

A

Males: <450ms

Females: <460ms

70
Q

What is the QTc in the image?

A
  • 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
Q

What is the electrophysiological basis for LQT syndrome?

A

Loss of K+ current during cardiac action potential

PHYSL 404 - Cardiovascular Physiology (17 decks)

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