Cardiology Lectures 1 and 2 -- EKG Flashcards Preview

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Flashcards in Cardiology Lectures 1 and 2 -- EKG Deck (113):
1

Define EKG

A voltmeter that records electrical voltages at the skin surface generated by the depolarization of heart muscle

2

Single cell model: voltmeter reading for a cell that has initially depolarized

3

Single cell model: voltmeter reading for a cell that has depolarizaed halfway

Peak

4

Single cell model: voltmeter reading for a fully depolarized cell

Returned to baseline (since no more current)

5

Single cell model: effect of switching polarity of the voltmeter on the reading

Flips wave upside down

6

Voltmeter reading (in theory) for myocyte repolarization of a single cell

7

Why is the voltmeter curve for repolarization upright in an actual voltmeter?

Last cells to depolarize are actually the first cells to repolarize

8

General location of chest electrodes

In 4th and 5th intercostal spaces

9

Define a lead

A recording electrical activity between 2 points on the body

10

Number of leads in a complete ECG

12

11

Deflection recorded when a depolarization current is directed towards the + electrode of a lead

Upward (positive) deflection

12

Deflection recorded when a depolarization current is directed away from the positive electrode 

Downward (negative) deflection

13

Wave recorded when the wave of depolarization moves perpendicularly to the lead in question

Biphasic (partially positive and partially negative) waveform or a straight line

(NOTE: not very helpful)

14

Number of limb leads

6

15

Plane of measurement of limb leads

Frontal plane (i.e. no depth perception; only up-down and lateral)

16

Number of precordial (chest) leads

6

17

Plane of chest leads

Transverse plane (i.e. provides depth perception)

18

Directionality of unipolar limb leads

Towards the limbs from the heart

19

Names of unipolar leads and locations

aVR = right arm

aVF = left leg/foot

aVL = left arm

20

Name and directionality of bipolar limb leads

I = right arm --> left arm

II = right arm --> left leg

III = left arm --> left leg

21

Result of overlaying the 6 limb leads

Axial Reference System is established

22

Location relative to the heart of the 6 chest leads

On the anterior and left lateral aspect of the chest

23

3 major deflections that represent a heartbeat

P wave

QRS complex

T wave

24

The first chambers to depolarize

Right and left atria

25

What event does the P wave represent

Atrial depolarization (right, quickly followed by left; superimposed)

26

What event does the QRS complex represent?

Ventricular contraction

27

5 different possible shapes of the QRS complex

  1. QRS
  2. RS
  3. R only
  4. QS
  5. RSR'

28

Define the Q wave

The first downward deflection of the QRS

29

Define the R wave

The first upward deflection whether or not a Q wave is present

30

Define the S wave

Any downward reflection following the R wave

31

Normal resting state

Surfaces of myocardial cells homogenously charged

No electrical activity detected by ECG leads

32

First portion of ventricle to depolarize

Left side of mid portion of interventricular septum

33

Direction of electrical current from left side of mid portion of interventricular septum during ventricular depolarization

Toward the right ventricle and interiorly

34

Leads that perceive the depolarization through the left side of the mid portion of the interventricular septum

aVL

aVF

35

Wave that aVL detect upon depolarization of the left mid portion of the interventricular septum

Q wave (initial downward deflectoin)

36

What wave does aVF detect upon left mid interventricular septum depolarization

R wave (initial upward deflection

37

Directionality of the overall charge as the lateral walls of the ventricles are depolarized

Forces of the thicker LV outweigh those of the right, so the arrow's orientation is increasingly directed towards the LV

38

What phase does the T wave represent?

Ventricular repolarization

39

Define the ST segment

The line between the QRS complex and the T wave that should normally be isoelectric (same as baseline)

40

When may the ST segment move up or down?

When the heart is lacking oxygen

41

Define the P-R interval

Time from start of P wave to the start of the QRS complex

42

Define the QT interval

Time from start of the QRS complex to the end of the T wave

43

Vertical axis of an ECG

Voltage in mV

1 mm = 0.1 mV

44

Horizontal axis of an ECG

Time (ms)

1 small box = 40 ms

1 large box = 0.2 sec

NOTE: assuming a normal paper speed of 25 mm/sec

45

8 steps in the sequence of analysis of an EKG

  1. Check voltage calibration
  2. Heart rhythm
  3. Heart rate
  4. Intervals (PR and QT)
  5. Mean QRS axis
  6. Abnormalities of the P wave
  7. Abnormalities of the QRS
  8. Abnormalities of the ST segment and T wave

46

3 examples of abnormalities that can arise in an abnormal QRS complex

Hypertrophy

Bundle branch block

Infarction

47

How to calibrate ECG voltage

1.0 mV (i.e. 10 small boxes) vertical signal at the beginning and/or end of the tracing to document normal voltage calibration has been used

48

When is doubling the calibration of the ECG useful?

If a condition, such as PC effusion, muffles the signal to produce small voltage waves (need to see them better)

49

4 criteria to have a normal sinus rhythm

  1. Every P wave is followed by a QRS complex
  2. Every QRS complex is preceded by a P wave
  3. P wave is upright in leads I, II, III
  4. PR interval is >0.12 sec (3 small boxes)

50

What happens if not all 4 criteria for a sinus rhythm are fulfilled?

There is an arrhythmia

51

First method of determining HR from an ECG

Count the number of boxes between two adjacent QRS complexes (i.e. between two beats).

Note that the standard paper speed is 25 mm/sec, so use this equation

52

Use method1 to determine the HR of this ECG

HR = (25 mm/sec x 60 sec/min) / 23 mm per beat = 1500 mm/min / 23 mm/beat = 65 bpm

53

Method 2 of determining HR from an ECG

"Count off method" = memorize this sequence:

300 - 150 - 100 - 75 - 60 - 50

Start at an R wave that is on a dark line and assign each subsequent dark line to the right with a number from this descending sequence. Where the next R wave falls is the HR.

54

Advantage and disadvantage of Method 2 for determining HR

Advantage = faster (most commonly used in busy wards)

Disadvantage = less accurate than method 1

55

Method 3 of determining HR from an ECG

There is usually a 3 sec marker on the ECG. Count the number of QRS complexes in this interval and multiply by 20 to get the HR.

56

Normal PR interval

0.12 - 0.20 sec

(3 - 5 small boxes)

57

2 conditions that may cause PR interval decrease

Preexcitation syndrome

Junctional rhythm

58

One condition that may cause PR interval increase

First degree AV block

59

What does the QT interval indicate?

Represents the time for ventricular depolarization and repolarization.
Estimates the duration of the cardiac action potential (so increased action potential duration = increased QT interval)

60

Effect of high HR on QT interval

At high heart rates, the heart needs to repolarize faster so the QT interval tends to shorten

61

Effect of low HR on QT interval

At low heart rates, the heart does not need to rush so it takes its time repolarizing and the QT tends to lengthen

62

2 methods to correct for QT interval for HR

Bazett's formula

Rapid rule

63

Bazett's formula for QT interval correction

QTc = “Qtcorrected (for heart rate)”


QTc = QT interval in ms / √ R-R interval (in sec)

64

Normal QTc

Normal QTc ≤ 0.44 sec

65

Rapid rule for QT interval correction for HR determination

If the QT interval is less than ½ the R-R interval, then the QT is within normal range
This technique only works at normal heart rates (60-100bpm)

66

What is the danger of an abnormally long QT interval?

May predispose patients to lethal cardiac rhythm disturbances

67

2 conditions that cause a decrease in QT interval

Hypercalcemia

Tachycardia

68

6 conditions that can cause an increase in the QT interval

  • Hypocalcemia
  • Hypokalemia
  • Hypomegnesemia
  • Myocardial ischemia
  • Congenital QT interval increase
  • Toxic drug effect (i.e. certain anti-arrhythmic drugs)

69

What is the mean QRS axis?

A vector that represents the average of the instantaneous electrical forces generated during the sequence of ventricular depolarization as measured in the frontal plane (the limb leads)

Blue section = normal area of axis

70

Effect of heart orientation on QRS axis

71

Effect of ventricular hypertrophy on QRS axis

Shift towards the hypertrophied side

72

Effect of myocardial infarction on QRS axis

Points away from the infarction

73

3 causes of left axis deviation

  • Inferior wall myocardial infarction
  • Left anterior fascicular block
  • Left ventricular hypertrophy (sometimes)

74

3 causes of right axis deviation

  • Right ventricular hypertrophy
  • Acute right heart strain (i.e. massive pulmonary embolism)
  • Left posterior fascicular block

75

First step for determining QRS axis

Start with lead I:
Is the QRS + or - ?
If + then the vector of depolarization is heading towards the + electrode of lead I (so between -90°and + 90°) = good (no right axis deviation)

If - then the vector of depolarization is heading towards the - electrode of lead I = right axis deviation

76

Second stop for determining QRS axis

Move on to lead II:
Is the QRS + or - ?
If + then the vector of depolarization is heading towards the + electrode of lead II (so between -30°and + 150°)

If -, then left axis deviation

77

What is normal range ofr QRS axis

If QRS is + in both I and II, then the axis vector must lie between -30° and + 90°

78

Leads that see P wave best

Leads II and V1

79

Define right atrial enlargement representation on an ECG and which lead best perceives it

Height greater than 2.5 mm in lead II

80

Define left atrial enlargement representation on an ECG and which lead perceives it best

Negative P in V1 > 1 mm wide and 1 mm deep

81

4 important abnormalities of QRS complex

  1. Ventricular Hypertrophy
  2. Bundle branch blocks
  3. Fascicular Blocks
  4. Pathologic Q waves in Myocardial Infarction

82

Effect of right ventricular hypertrophy on ECG waves

Chest leads V1 and V2 (which overlie the RV) record greater than normal upward deflections (R wave greater than S wave)

83

Effect of right ventricular hypertrophy on QRS axis

Increased RV mass shifts the mean axis to the right --> Right axis deviation

84

Effect of left ventricular hypertrophy on ECG waves

V5 and V6 (which overlie the LV) record greater than normal upward deflections (Taller than normal R waves)
Other side of the heart (V1 and V2) demonstrate the opposite (deeper than normal S waves

85

Effect of left ventricular hypertrophy on QRS axis

Increased LV mass may shift the mean axis to the left = Left axis deviation

86

Define a bundle branch block and its potential cause

Interruption of conduction through the right or left bundle branches
May develop from ischemic or degenerative damage

87

Effect of bundle branch blockage on electrical activity and QRS complex

Cells of that ventricle must rely on relatively slow myocyte to myocyte spread of electrical activity traveling from the unaffected ventricle


Prolongs depolarization and widens the QRS complex

88

Normal QRS duration

Less than or equal to 0.10 sec (2.5 small boxes)

89

Effect on QRS duration by a complete bundle branch block

QRS > 0.12 sec (> 3 small boxes)

90

Effect on QRS duration by an incomplete bundle branch block

QRS between 0.10 - 0.12 sec

91

Give the progression of the directionality of the electrical activity during a left bundle branch blockade

Complete depolarization of the right ventricle --> slow myocyte to myocyte depolarization towards the left ventricle

92

Give the progression of the directionality of the electrical activity during a right bundle branch blockage

Complete depolarization of the left ventricle --> slow myocyte to myocyte depolarization towards the right ventricle

93

Effect of fascicular blockage on mean axis

Marked alteration (no details)

94

How is myocardial necrosis represented in an ECG

Pathologic Q waves

95

In what leads do pathologic Q waves develop

In leads overlying the infarcted tissue

96

Reason why pathologic Q waves occur

  • Necrotic muscle does not generate electrical forces
  • ECG electrode over the necrotic region picks up electrical currents from the healthy tissue on the opposite region of the ventricle
  • Therefore, Q waves are permanent evidence of an old trans-mural infarction

97

Where can Q waves be physiological

It is normal to have small Q waves in leads V6 and aVL (from normal septal depolarization)

98

How are physiological Q waves represented in an ECG

Physiologic Q waves are short in duration (<0.04 sec) and are not deep (< 25% of the total QRS height)

99

ECG representation of a pathological Q wave

Width ≥ 1 small square
Depth > 25% to total height of QRS complex

100

Leads involved in anteroseptally-localized infarction

V1

V2

101

Leads involved in anteroapically-localized infarction

V3

V4

102

Leads involved in anterolaterally-localized infarction

I

aVL

V5

V6

103

Leads involved in inferiorly-localized infarction

II

III

aVF

104

Why isnt aVR involved in readings for infarctions?

Electrical forces are normally directed away from the right arm

105

How to detect posteriorly-localized infarction

  • Chest leads V1 and V2 are directly opposite the posterior wall --> record the inverse of what leads placed on the back would record
  • Taller than normal R waves in leads V1 and V2 are the equivalent of pathologic Q waves in the diagnosis of posterior MI

106

3 ST-segment and T-wave abnormalities

  • Transient Myocardial Ischemia
  • Acute ST segment Elevation MI (STEMI)
  • Acute Non-ST Segment Elevation MI (NSTEMI)

107

Common ECG manifestations of transient myocardial ischemia

Reversible deviations of the ST segments (usually ST depression) and T waves (usually inversions)

108

Sequence of ECG changes in acute ST-segment elevation MI

Note: These changes are recorded in the leads overlying the zone of infarction
Typically, reciprocal changes are observed in the leads opposite that site

109

When does acute non-ST-segment elevation MI occur?

When the thrombus is only partially occlusive

110

ECG manifestations of non-ST-segment elevation MI

ST-segment depressions and/or T wave inversions in the leads overlying the affected myocardium
Q waves do not develop as typically only the sub-endocardium is involved

111

ECG manifestations of pericarditis

Diffuse ST segment elevation in most leads except aVR and V1
PR segment depression

112

What does diffuse ST segment elevation signify in the event of pericarditis?

Reflects inflammation of adjacent myocardium
 

113

What does PR segment depression reflect in the event of pericarditis?

Reflects abnormal atrial repolarization