ECGs

Question 1

What does the P wave represent?

Answer 1

Atrial depolarisation (electrical signal spreading from the SA node through the atria).

Question 2

What does the PR segment represent?

Answer 2

Time taken for the electrical signal to travel through the AV node.

Question 3

What does the PR interval include?

Answer 3

P wave + PR segment.

Question 4

What is the normal PR interval?

Answer 4

120–200 ms.

Question 5

What does the Q wave represent?

Answer 5

Depolarisation of the interventricular septum.

Question 6

What does the R wave represent?

Answer 6

Depolarisation of the bulk of the ventricles.

Question 7

What does the S wave represent?

Answer 7

The final phase of ventricular depolarisation

Question 8

What does the ST segment represent?

Answer 8

The plateau phase of the myocardial action potential (ventricular contraction).

Question 9

What does the T wave represent?

Answer 9

Ventricular repolarisation.

Question 10

What is the QT interval made up of?

Answer 10

QRS complex + ST segment + T wave.

Question 11

What is the normal QT interval rule?

Answer 11

QT should be less than half the RR interval.

Question 12

hat is the RR interval?

Answer 12

Time between two consecutive R waves (one cardiac cycle).

Question 13

What is the TP segment?

Answer 13

The segment between the end of the T wave and start of next P wave; used as the ECG baseline.

Question 14

What is an ECG lead?

Answer 14

A view of the voltage between two points (poles) over time.

Question 15

What is the positive pole?

Answer 15

The single recording electrode.

Question 16

What are the standard limb leads?

Answer 16

I, II, III.

Question 17

What are the augmented limb leads?

Answer 17

aVR, aVL, aVF.

Question 18

What are the chest (precordial) leads?

Answer 18

V1–V6.

Question 19

What is the hexaxial system used for?

Answer 19

Determining the QRS axis in the frontal plane.

Question 20

What does an ECG represent?

Answer 20

The voltage of the heart as a function of time from various chest locations.

Question 21

How long is 1 small box on ECG paper?

Answer 21

40 ms (1 mm).

Question 22

How long is 1 large box?

Answer 22

200 ms (5 mm).

Question 23

How many large boxes equal 1 second?

Answer 23

5 large boxes (25 mm).

Question 24

How do you calculate heart rate from a 10-second ECG strip?

Answer 24

Count beats in 10 seconds × 6.

Question 25

Example: 16 beats in 10 seconds = ?

Answer 25

96 bpm (16 × 6).

Question 26

What does the QRS axis represent?

Answer 26

The average direction of ventricular depolarisation in the frontal plane.

Question 27

What is the first step in the quadrant method?

Answer 27

Look at QRS in lead I and lead aVF.

Question 28

If QRS is positive in lead I and positive in aVF, what is the axis?

Answer 28

Normal axis.

Question 29

If positive in lead I but negative in aVF, what should you check next?

Answer 29

Lead II.

Question 30

What can axis deviation indicate?

Answer 30

- Chamber enlargement - Conduction abnormalities - Myocardial infarction - Arrhythmia origin

Question 31

Non-pathological causes of axis variation?

Answer 31

- Short/obese → axis closer to 0° - Tall/thin → axis closer to +90° - Neonates → right axis deviation

Question 32

Causes of left axis deviation?

Answer 32

- Left anterior fascicular block - Left bundle branch block - LV hypertrophy - Inferior MI

Question 33

Other causes of abnormal axis?

Answer 33

- Ventricular ectopy - Paced rhythm - Wolff-Parkinson-White syndrome

Question 34

What causes Acute Coronary Syndromes (ACS)?

Answer 34

Oxygen supply–demand mismatch in myocardial tissue.

Question 35

What defines NSTEMI?

Answer 35

Troponin positive without ST elevation.

Question 36

What defines STEMI?

Answer 36

ST elevation meeting diagnostic criteria.

Question 37

What does the LAD supply?

Answer 37

- Anterior LV wall - Intraventricular septum - Apex

Question 38

What does the Circumflex artery supply?

Answer 38

- Left atrium - Lateral LV wall

Question 39

What does the RCA supply?

Answer 39

- Right atrium - Right ventricle - Usually inferior & posterior LV

Question 40

What percentage of people are right dominant?

Answer 40

80%.

Question 41

Inferior leads?

Answer 41

II, III, aVF.

Question 42

Lateral leads?

Answer 42

I, aVL, V5, V6.

Question 43

Anterior leads?

Answer 43

V3, V4.

Question 44

Septal leads?

Answer 44

V1, V2.

Question 45

Which artery is usually responsible for large anterior MI?

Answer 45

LAD (ST elevation V2–V5+).

Question 46

What is the J point?

Answer 46

Junction between QRS complex and ST segment.

Question 47

STEMI criteria (limb leads)?

Answer 47

ST elevation >1 mm in ≥2 contiguous limb leads.

Question 48

STEMI criteria (chest leads)?

Answer 48

ST elevation >2 mm in ≥2 contiguous chest leads.

Question 49

What ECG change can also diagnose STEMI?

Answer 49

New LBBB.

Question 50

ST elevation >1 mm in aVR suggests what?

Answer 50

Left Main Stem (LMS) lesion.

Question 51

What are Sgarbossa criteria (for MI in LBBB)?

Answer 51

a) Concordant ST elevation >1 mm b) Concordant ST depression >1 mm in V1–V3 c) Discordant ST elevation >5 mm

Question 52

ECG sign of isolated posterior MI?

Answer 52

ST depression >0.05 mV in V1–V3.

Question 53

How is posterior MI confirmed?

Answer 53

ST elevation in posterior leads V7–V9.