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PHSL232 Cardiovascular and Respiratory > Lab 1 - ECG > Flashcards

Lab 1 - ECG Flashcards

1
Q

What is an ECG?

A

Electrocardiogram - measures the electrical activity of the heart

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2
Q

What event in the cardiac cycle does the T wave represent?

A

Ventricular repolarisation

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3
Q

What event in the cardiac cycle does the P wave represent?

A

Depolarisation of the atria

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4
Q

What event in the cardiac cycle does the QRS complex represent?

A

Depolarisation of the ventricles

Q wave: The initial negative deflection following the P wave.

R wave: The subsequent large positive deflection.

S wave: The negative deflection following the R wave.

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5
Q

Why is ventricular repolarisation a positive deflection?

A

Because repolarisation is when it gets more negative and when going towards the negative lead (negative + negative = positive).

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6
Q

Explain why the amplitude and polarity of the P, QRS and T waves vary in recordings of 6 different limb leads?

A

Polarity is to do with the nature in change in membrane potentials but also to do with the orientation and direction - therefore when we change the leads and this the orientation/direction the recordings will vary.

Amplitude also depends on orientation - how parallel it is to the electrode - the more parallel the larger the amplitude.

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7
Q

If the amplitude is towards positive lead is it depolarisation or repolarisation?

A

Depolarisation - it is depolarisation when they match e.g., when towards positive lead or away from the negative lead.

It is repolarisation when they don’t match e.g., away from positive and towards negative.

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8
Q

What deflection its shown when depolarisation is towards a positive electrode?

A

Positive deflection

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9
Q

What deflection is shown when repolarisation is away from a positive electrode?

A

Positive deflection

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10
Q

If there is poor alignment of lead and electrical activity will the amplitude be large or small?

A

Small

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11
Q

Why does the recording of the aVR lead appear to be an inversion of the recording of standard limb lead 2?

A

Because the electrodes are reversed for lead 2 and aVR which means they look at the heart from the opposite direction thus the ECG is inverted

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12
Q

What prevents depolarisation of skeletal muscle every time the heart beats?

A

Isolation of the hearts electrical activity from the body by pericardium and cartilage around the valve. This prevents depolarisation of skeletal muscle very time the heart beats.

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13
Q

What is Mean Electrical Axis?

A

MEA is the average direction of all the electrical activity occurring during depolarisation of the ventricles.

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14
Q

What ECG lead will have the largest R wave?

A

The one that is more aligned with the direction of ventricular depolarisation - which is typically lead 2 (right arm and left leg)

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15
Q

What is the normal range of MEA?

A

-30 to +120 degrees

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16
Q

The MEA of individuals with a shorter and broader torso will likely be:

A

More horizontal

17
Q

The MEA of individuals with a tall and thin torso will likely be:

A

More vertical

18
Q

Why is the MEA effect by height?

A

Because it changes the thorax space for the heart e.g., shorter people have less thorax space and therefore heart sits in a more horizontal position

19
Q

How does fitness effect MEA?

A

Left Ventricular hypertrophy - muscle growth will mean that it sits more horizontally

20
Q

Is the MEA of heart more horizontal during inspiration or expiration?

A

Expiration (heart rises in chest due to the diaphragm relaxing and expanding)

21
Q

What happens to the diaphragm as we inspire?

A

it contracts and flattens

22
Q

What factors effect MEA?

A

Height
LV hypertrophy
gastric distension
obesity
pregnancy
myocardial infarction on right side

23
Q

What three things cause LV hypertrophy?

A

Fitness
Aortic stenosis (increases aortic pressure = increase afterload)
Hypertension (age)

24
Q

What causes RV hypertrophy?

A

Pulmonary hypertension
High altitude

25
Q

What direction does the heart move for LV and RV hypertrophy respectively?

A

LV = moves horizontally (anti clockwise)
RV = move vertically (clockwise)

26
Q

What is the consequence of a missed QRS complex?

A

NO QRS = no ventricular depolarisation or contraction which means a missed heart beat

It means that no blood have been pumped into the body and lungs for that cardiac cycle.

27
Q

Is every P wave followed by a QRS complex in 2nd degree AV block?

A

No - there is no R wave after the 5th P wave.

28
Q

IS the PR interval consistent during 2nd degree AV block?

A

No there PR interval gets progressively longer

PHSL232 Cardiovascular and Respiratory (12 decks)

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