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Block C - Circulation > Cardiology Lectures 1 and 2 -- EKG > Flashcards

Cardiology Lectures 1 and 2 -- EKG Flashcards

1
Q

Define EKG

A

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

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2
Q

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

A
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3
Q

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

A

Peak

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4
Q

Single cell model: voltmeter reading for a fully depolarized cell

A

Returned to baseline (since no more current)

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5
Q

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

A

Flips wave upside down

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6
Q

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

A
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7
Q

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

A

Last cells to depolarize are actually the first cells to repolarize

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8
Q

General location of chest electrodes

A

In 4th and 5th intercostal spaces

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9
Q

Define a lead

A

A recording electrical activity between 2 points on the body

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10
Q

Number of leads in a complete ECG

A

12

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11
Q

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

A

Upward (positive) deflection

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12
Q

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

A

Downward (negative) deflection

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13
Q

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

A

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

(NOTE: not very helpful)

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14
Q

Number of limb leads

A

6

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15
Q

Plane of measurement of limb leads

A

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

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16
Q

Number of precordial (chest) leads

A

6

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17
Q

Plane of chest leads

A

Transverse plane (i.e. provides depth perception)

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18
Q

Directionality of unipolar limb leads

A

Towards the limbs from the heart

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19
Q

Names of unipolar leads and locations

A

aVR = right arm

aVF = left leg/foot

aVL = left arm

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20
Q

Name and directionality of bipolar limb leads

A

I = right arm –> left arm

II = right arm –> left leg

III = left arm –> left leg

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21
Q

Result of overlaying the 6 limb leads

A

Axial Reference System is established

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22
Q

Location relative to the heart of the 6 chest leads

A

On the anterior and left lateral aspect of the chest

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23
Q

3 major deflections that represent a heartbeat

A

P wave

QRS complex

T wave

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24
Q

The first chambers to depolarize

A

Right and left atria

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25
Q

What event does the P wave represent

A

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

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26
Q

What event does the QRS complex represent?

A

Ventricular contraction

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27
Q

5 different possible shapes of the QRS complex

A
  1. QRS
  2. RS
  3. R only
  4. QS
  5. RSR’
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28
Q

Define the Q wave

A

The first downward deflection of the QRS

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29
Q

Define the R wave

A

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

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30
Q

Define the S wave

A

Any downward reflection following the R wave

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31
Q

Normal resting state

A

Surfaces of myocardial cells homogenously charged

No electrical activity detected by ECG leads

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32
Q

First portion of ventricle to depolarize

A

Left side of mid portion of interventricular septum

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33
Q

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

A

Toward the right ventricle and interiorly

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34
Q

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

A

aVL

aVF

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35
Q

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

A

Q wave (initial downward deflectoin)

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36
Q

What wave does aVF detect upon left mid interventricular septum depolarization

A

R wave (initial upward deflection

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37
Q

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

A

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

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38
Q

What phase does the T wave represent?

A

Ventricular repolarization

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39
Q

Define the ST segment

A

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

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40
Q

When may the ST segment move up or down?

A

When the heart is lacking oxygen

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41
Q

Define the P-R interval

A

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

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42
Q

Define the QT interval

A

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

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43
Q

Vertical axis of an ECG

A

Voltage in mV

1 mm = 0.1 mV

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44
Q

Horizontal axis of an ECG

A

Time (ms)

1 small box = 40 ms

1 large box = 0.2 sec

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

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45
Q

8 steps in the sequence of analysis of an EKG

A
  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
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46
Q

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

A

Hypertrophy

Bundle branch block

Infarction

47
Q

How to calibrate ECG voltage

A

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
Q

When is doubling the calibration of the ECG useful?

A

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

49
Q

4 criteria to have a normal sinus rhythm

A
  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
Q

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

A

There is an arrhythmia

51
Q

First method of determining HR from an ECG

A

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
Q

Use method1 to determine the HR of this ECG

A

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

53
Q

Method 2 of determining HR from an ECG

A

“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
Q

Advantage and disadvantage of Method 2 for determining HR

A

Advantage = faster (most commonly used in busy wards)

Disadvantage = less accurate than method 1

55
Q

Method 3 of determining HR from an ECG

A

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
Q

Normal PR interval

A

0.12 - 0.20 sec

(3 - 5 small boxes)

57
Q

2 conditions that may cause PR interval decrease

A

Preexcitation syndrome

Junctional rhythm

58
Q

One condition that may cause PR interval increase

A

First degree AV block

59
Q

What does the QT interval indicate?

A

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
Q

Effect of high HR on QT interval

A

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

61
Q

Effect of low HR on QT interval

A

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

62
Q

2 methods to correct for QT interval for HR

A

Bazett’s formula

Rapid rule

63
Q

Bazett’s formula for QT interval correction

A

QTc = “Qtcorrected (for heart rate)”

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

64
Q

Normal QTc

A

Normal QTc ≤ 0.44 sec

65
Q

Rapid rule for QT interval correction for HR determination

A

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
Q

What is the danger of an abnormally long QT interval?

A

May predispose patients to lethal cardiac rhythm disturbances

67
Q

2 conditions that cause a decrease in QT interval

A

Hypercalcemia

Tachycardia

68
Q

6 conditions that can cause an increase in the QT interval

A
  • Hypocalcemia
  • Hypokalemia
  • Hypomegnesemia
  • Myocardial ischemia
  • Congenital QT interval increase
  • Toxic drug effect (i.e. certain anti-arrhythmic drugs)
69
Q

What is the mean QRS axis?

A

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
Q

Effect of heart orientation on QRS axis

A
71
Q

Effect of ventricular hypertrophy on QRS axis

A

Shift towards the hypertrophied side

72
Q

Effect of myocardial infarction on QRS axis

A

Points away from the infarction

73
Q

3 causes of left axis deviation

A
  • Inferior wall myocardial infarction
  • Left anterior fascicular block
  • Left ventricular hypertrophy (sometimes)
74
Q

3 causes of right axis deviation

A
  • Right ventricular hypertrophy
  • Acute right heart strain (i.e. massive pulmonary embolism)
  • Left posterior fascicular block
75
Q

First step for determining QRS axis

A

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
Q

Second stop for determining QRS axis

A

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
Q

What is normal range ofr QRS axis

A

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

78
Q

Leads that see P wave best

A

Leads II and V1

79
Q

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

A

Height greater than 2.5 mm in lead II

80
Q

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

A

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

81
Q

4 important abnormalities of QRS complex

A
  1. Ventricular Hypertrophy
  2. Bundle branch blocks
  3. Fascicular Blocks
  4. Pathologic Q waves in Myocardial Infarction
82
Q

Effect of right ventricular hypertrophy on ECG waves

A

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

83
Q

Effect of right ventricular hypertrophy on QRS axis

A

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

84
Q

Effect of left ventricular hypertrophy on ECG waves

A

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
Q

Effect of left ventricular hypertrophy on QRS axis

A

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

86
Q

Define a bundle branch block and its potential cause

A

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

87
Q

Effect of bundle branch blockage on electrical activity and QRS complex

A

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
Q

Normal QRS duration

A

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

89
Q

Effect on QRS duration by a complete bundle branch block

A

QRS > 0.12 sec (> 3 small boxes)

90
Q

Effect on QRS duration by an incomplete bundle branch block

A

QRS between 0.10 - 0.12 sec

91
Q

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

A

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

92
Q

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

A

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

93
Q

Effect of fascicular blockage on mean axis

A

Marked alteration (no details)

94
Q

How is myocardial necrosis represented in an ECG

A

Pathologic Q waves

95
Q

In what leads do pathologic Q waves develop

A

In leads overlying the infarcted tissue

96
Q

Reason why pathologic Q waves occur

A
  • 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
Q

Where can Q waves be physiological

A

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

98
Q

How are physiological Q waves represented in an ECG

A

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

99
Q

ECG representation of a pathological Q wave

A

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

100
Q

Leads involved in anteroseptally-localized infarction

A

V1

V2

101
Q

Leads involved in anteroapically-localized infarction

A

V3

V4

102
Q

Leads involved in anterolaterally-localized infarction

A

I

aVL

V5

V6

103
Q

Leads involved in inferiorly-localized infarction

A

II

III

aVF

104
Q

Why isnt aVR involved in readings for infarctions?

A

Electrical forces are normally directed away from the right arm

105
Q

How to detect posteriorly-localized infarction

A
  • 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
Q

3 ST-segment and T-wave abnormalities

A
  • Transient Myocardial Ischemia
  • Acute ST segment Elevation MI (STEMI)
  • Acute Non-ST Segment Elevation MI (NSTEMI)
107
Q

Common ECG manifestations of transient myocardial ischemia

A

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

108
Q

Sequence of ECG changes in acute ST-segment elevation MI

A

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
Q

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

A

When the thrombus is only partially occlusive

110
Q

ECG manifestations of non-ST-segment elevation MI

A

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
Q

ECG manifestations of pericarditis

A

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

112
Q

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

A

Reflects inflammation of adjacent myocardium

113
Q

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

A

Reflects abnormal atrial repolarization

Block C - Circulation (26 decks)

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