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EKG Midterm > 3 Electrical Axis and Chamber Enlargment > Flashcards

3 Electrical Axis and Chamber Enlargment Flashcards

1
Q

The heart’s normal axis is …

A

Down and to the patient’s left

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2
Q

Vectors of the left ventricle are …

A

Larger and persist longer than those of the right ventricle

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3
Q

The mean QRS axis can be approximated by looking at…

A

The QRS complexes in Leads I and aVf

If the predominant direction is positive in both of these leads, the axis is normal

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4
Q

Normal Axis range extends from ______ to ______

A

0˚ to 90˚

3 o’clock to 6 o’clock

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5
Q

In Left Axis Deviation (LAD), the mean QRS axis is ….

A

Between 0˚ and -90˚ (pointing toward left shoulder)

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6
Q

In Right Axis Deviation (RAD), the mean QRS axis is …

A

Between +90˚ and +180˚ (pointing toward right foot)

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7
Q

If the mean QRS deflection is positive in Lead I, the axis is…

A

Between -90˚ and + 90˚

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8
Q

If mean QRS deflection is positive in aVf, the axis is …

A

Between 0˚ and +180˚

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9
Q

If mean QRS deflection is positive in both Lead I AND aVF, the axis is…

A

In the normal range (0˚ to +90˚)

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10
Q

Besides the Four Quadrant method, what’s another way to estimate the axis?

A

Identify the tallest QRS complex in the frontal plane
—> axis points in the direction of that lead

Find a lead with an EQUIPHASIC QRS complex
—> axis is perpendicular to that lead

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11
Q

How to use an equiphasic lead to determine the axis

A

Find an equiphasic lead (positive component = negative component on QRS)

The axis is perpendicular to that lead

Locate a positive lead to determine which direction along the perpendicular line corresponds with the axis

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12
Q

What is the Hexaxial Reference System?

A

For normal axis (upright QRS in both Leads I and aVF), the relative deflection of Lead I and aVF determines a closer approximation of the axis

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13
Q

Positive QRS deflection of Lead I = Lead aVF

A

Mean QRS axis is ~ +45˚

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14
Q

Positive QRS deflection of Lead I > Lead aVF

A

Mean QRS lies closer to Lead I (0˚to 45˚)

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15
Q

Positive QRS deflection of Lead I < Lead aVF

A

Mean QRS axis lies closer to Lead aVF (+45˚ to +90˚)

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16
Q

Normal P wave axis should be…

A

0˚ to 75˚

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17
Q

Normal T wave axis should be …

A

Close to the QRS axis

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18
Q

If the R wave in aVL > R wave in Lead 1….

A

STRONG LAD (associated with LAHB)

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19
Q

If R wave in Lead III > R wave in aVF

A

STRONG RAD (associated with LPHB)

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20
Q

What are some causes of Left Axis Deviation?

A

Left anterior hemiblock
Left ventricular hypertrophy
Q waves of inferior myocardial infarction
Chronic coronary artery disease
Diffuse myocardial disease (ie cardiomyopathy, amyloidosis, myocarditis)
Some cases of hyperkalemia
Wolff-Parkinson-White Syndrome with a right-sided accessory pathway

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21
Q

What are some causes of Right Axis Deviation?

A

Normal finding in children and tall then adults
Right ventricular hypertrophy
Chronic lung disease even without pulmonary hypertension
Anterolateral myocardial infarction
Left posterior hemiblock
Pulmonary embolus
Dextrocardia

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22
Q

RAD can be normal in…

A

Children and tall thin adults

23
Q

Tall, thin individuals may have a more ______ heart

A

Vertical - with a shift in the QRS axis toward +90˚

24
Q

Obese or pregnant individuals may have a more ______ heart

A

Horizontal - the mean QRS axis shifted more leftward (close to 0˚)

25
Q

Thickening of the wall(s) of a cardiac chamber

A

Hypertrophy

26
Q

Hypertrophy is usually due to…

A

Increased work of the heart against higher pressure (ie - HTN, aortic stenosis)

27
Q

Stretching of the wall(s) of the cardiac chamber

A

Enlargement (dilation)

28
Q

Enlargement/dilation of a chamber of the heart often occurs as a result of…

A

Volume overload (ie LAE due to mitral insufficiency/regurg

29
Q

_____ tend to dilate rather than hypertrophy

A

Atria

30
Q

______ is more common in the ventricles

A

Hypertrophy

31
Q

______ provide evidence for Atrial Enlargement

A

P waves

Tall p waves —> RAE

Wide p waves —> LAE

32
Q

________ provides evidence for ventricular hypertrophy

A

QRS complex

33
Q

Leads ____ and _____ are used to assess Atrial Enlargement

A

Leads II and V1

34
Q

P wave amplitude > 2.5mm

A

RAE (P pulmonale)

35
Q

P wave duration > 0.10s

A

LAE (P mitrale)

36
Q

Increased P wave amplitude and duration

A

Biatrial Enlargement

37
Q

Criteria for RAE

A

P wave is >2.5 mm tall

OR

IF V1 P wave is BIPHASIC, the initial component of the P wave is larger than the terminal component (upward deflection > downward deflection)

38
Q

Clinical conditions with RAE

A

Pulmonic stenosis
Tricuspid stenosis
Tricuspid regurgitation

Clues:
• Presence of RVH
• RAE

39
Q

Criteria for LAE

A

P wave > 0.10s

OR

The terminal portion of a biphasic P wave in V1 is NEGATIVE with a duration ≥0.04s and depth ≥1mm (one small block)

40
Q

Clinical conditions with LAE

A

Mitral stenosis

Mitral regurgitation

41
Q

Ventricular hypertrophy is assessed by …

A

Viewing the QRS complex in several leads

42
Q

Normal ventricular depolarization moves…

A

Downward, to the left, and posteriorly in the direction of the thicker left ventricular muscle

It moves away from Lead V1, which is the reason the R wave in V1 is small

43
Q

Why is the R wave usually small in V1?

A

Because normal ventricular depolarization moves downward, to the left and posteriorly — AWAY from Lead V1

44
Q

With ventricular hypertrophy, the direction of _____ may change

A

Depolarization

45
Q

Large negative R wave in V1 and large positive R wave in V6

A

LVH

46
Q

Equiphasic RS complex in V1

A

RVH

47
Q

Common causes of LVH

A

Hypertension

Valvular heart disease

48
Q

______ leads are more sensitive and helpful in diagnosing LVH

A

Precordial

49
Q

LVH criteria

A

Sum of the deepest S in V1 or V2 plus the tallest R in V5 or V6 >35mm

OR

R in aVL >11mm

OR

R in Lead I plus S in Lead III >25mm

50
Q

Which is more common: RVH or LVH

A

LVH

51
Q

RVH is most often due to …

A

Pulmonary HTN or pulmonic stenosis

52
Q

With normal hearts, the R waves get ______ when comparing V1-V6

A

Progressively more positive

53
Q

In RVH, what happens to the R waves when comparing V1-V6?

A

They get progressively smaller rather than getting progressively more positive

54
Q

RVH Criteria

A

Right axis deviation (> +90˚)

OR

R wave > S wave in V1 (R wave usually 7mm tall)

OR

S wave > R wave in V6

EKG Midterm (4 decks)

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