ECG 1 and 4 - Theory and recognising normal/ abnormal ECGs

Question 1

What is the name for a recording of the potential differences between distant sites on the body surface?

Answer 1

Electrocardiogram (measured by an electrocardiograph)

Question 2

What is the wave of depolarisation across the heart and what does this create?

Answer 2

Positive charge moving towards the ventricles leaving behind a negative chargeCreates an electric dipole (which generates an electrical field) - the dipole represents an electrical vector

Question 3

In terms of leads, when is the measured potential difference greater?

Answer 3

When lead axis is parallel to the direction of the dipole- zero when perpendicular

Question 4

What determines the magnitude of the electrical vector?Direction?

Answer 4

Magnitude = mass of cardiac muscleDirection = overall activity of the heart

Question 5

Where does each of the standard limb leads (I, II, III) run?At what degree does each lead look at the heart?

Answer 5

I = RA (-) - LA (+) (0 degrees = 3 o’clock)II = RA (-) - LL (+) (+60 degrees = 5 o’clock)III = LA (-) - LL (+) (+120 degrees = 7 o’clock)RL = earthed

Question 6

In terms of depolarisation, what causes an upwards deflection on the ECG and what causes a downwards deflection?

Answer 6

Upwards = deflection moving towards recording electrodeDownwards = deflection moving away from recording electrode

Question 7

What causes the P wave? Duration?

Answer 7

Action potential upstroke through the atrial muscle 0.08 - 0.1 secs

Question 8

What causes QRS complex? durationWhat causes each of the separate waves?

Answer 8

Action potential upstroke throughout the ventricular muscle

Question 9

T wave cause?

Answer 9

Ventricular repolarisation moving in a direction opposite to that of depolarisation accounts for the usually observed upwards deflection

Question 10

What causes the PR interval? Duration

Answer 10

Largely AV nodal delay (0.12 - 0.2 secs) - different from PR segment

Question 11

What causes the ST segment?

Answer 11

Maintained ventricular depolarisation

Question 12

What causes the TP interval?

Answer 12

Diastole

Question 13

What are the augmented limb leads and where does each link?

Answer 13

aVR = RA (+) to [LA and LF] (-)aVL = LA to [RA and LF]aVF = LF to [RA and LA]

Question 14

What cause the direction of the Q wave on an ECG?

Answer 14

Left to right depolarisation of the inter-ventricular septum moving slightly away from the recording electrode

Question 15

What causes the direction of the R wave on an ECG?

Answer 15

Depolarisation of the main ventricular mass moving towards the recording electrode

Question 16

What causes the direction of the S wave on an ECG?

Answer 16

Depolarisation of ventricles at the base of the heart moving away from the recording electrode

Question 17

What causes the direction of the T wave on an ECG?

Answer 17

Ventricular repolarisation moving in a direction opposite to that of depolarisation

Question 18

What is another name for the standard limb leads?What is another name for augmented limb leads?What is another name for chest (precordial) leads?

Answer 18

Bipolar limb leadsUnipolar limb leadsUnipolar leads (wilson’s leads)

Question 19

What type of polarity do the augmented limb leads have?

Answer 19

Goldberger’s method: one +ve electrode, 2 others linked as -ve electrodes

Question 20

How do the augmented limb leads differ in direction to the standard limb leads?

Answer 20

30 degrees away

Question 21

What is the name given to the normal triangle that the standard limb leads are arranged in?

Answer 21

Einthoven’s triangle

Question 22

How does the appearance of II and aVR compare?

Answer 22

aVR is practically an upside down version of II

Question 23

What degrees are classified as a normal axis for the heart? (between)

Answer 23

-30 - +90

Question 24

What range of degrees are classified as a left axis?

Answer 24

-30 to -90

Question 25

What range of degrees are classified as a right axis?

Answer 25

+90 to 180

Question 26

What range of degrees are classified as a far right axis?

Answer 26

-90 o 180

Question 27

At what degree is aVL present at?

Answer 27

-30

Question 28

At what degree is aVR present at?

Answer 28

-150

Question 29

At what degree is aVF present at?

Answer 29

+90

Question 30

Where is V1 placed?

Answer 30

Right sternal edge, 4th intercostal space

Question 31

Where is V2 placed?

Answer 31

Left sternal edge, 4th intercostal space

Question 32

Where is V3 placed?

Answer 32

Halfway between V2 and V4

Question 33

Where is V4 placed?

Answer 33

Apex beat

Question 34

Where is V5 placed?

Answer 34

Anterior axillary line

Question 35

Where is V6 placed?

Answer 35

Mid-axillary line

Question 36

What lead are the ECG waves best seen in?

Answer 36

Lead II

Question 37

What happens during the ST segment?

Answer 37

Ventricles contract (systole)

Question 38

What happens during the TP segment?

Answer 38

Ventricles relax (diastole)

Question 39

What is the normal QT interval?

Answer 39

0.36-0.44 seconds at a heart rate of 60 (needs to be corrected for heart rate)

Question 40

How many seconds does each small block represent when the paper speed = 25mm/sec?

Answer 40

0.04 seconds (and 1mm of amplitude)

Question 41

Equation for calculating HR from ECG?

Answer 41

300/number of large squares between beats

Question 42

What is the ECG strip?

Answer 42

Prolonged recording of one lead (usually lead II) which allows you to detect rhythm disturbances

Question 43

How many wires does an ECG have?

Answer 43

10 (despite there being 12 leads)

Question 44

What test should be done if stable angina is suspected?

Answer 44

An exercise ECG (ECG changes are usually absent during rest)

Question 45

How to calculate the heart rate from an ECG if the heart rate is irregular?

Answer 45

Count the number of QRS complexes in 30 large squares and multiply by 10