A First Look at the ECG

Question 1

Augmented limb leads

Answer 1

I, II, III, aVR, aVL, aVF

- Frontal plane

Question 2

Precordial limb leads

Answer 2

V1-6

- Transverse plane

Question 3

P wave

Answer 3

Atrial depolarisation

• Is each QRS complex preceded by a P wave?
• Small because most blood travels due to gravity

Question 4

QRS complex

- Normal time

Answer 4

Ventricular depolarisation (and atrial repolarisation)

• 0.08s
• Is the QRS complex too wide (>0.12s)

Question 5

Q wave

Answer 5

Interventricular septal depolarisation (left to right)

- prominent: characteristic of MI

Question 6

R wave

Answer 6

Ventricular depolarisation

• endocardial to epicardial surface
• axis deviation in left rotation, right hypertrophy or atrophy

Question 7

S wave

Answer 7

Purkinje fibre and upper part of inter ventricular septum depolarisation
- negative as fibre spread from top to bottom

Question 8

T wave

Answer 8

Ventricular repolarisation
- positive going because AP is longer in endocardial than epicardial cells, so the wave of repolarisation runs in the opposite direction

Question 9

PR interval

- normal time

Answer 9

Time for atrial depolarisation to ventricular depolarisation
- 120-200ms
- Is PR interval too short or too long?
<120 ms: pre-excitation or AV nodal rhythm
>200 ms: first degree heart block

Question 10

ST segment

Answer 10

Interval between ventricular depolarisation and repolarisation

• STEMI
• NSTEMI

Question 11

QT interval

- normal time

Answer 11

Time for ventricular activity

• 0.36 - 0.44 sec: varies with age, gender, HR (0.42s at 60bpm)
• Is the QT interval too long?

Question 12

HR from an ECG

Answer 12

• 30 large squares = 6 seconds

Question 13

Normal sinus rhythm

Answer 13

60-100 bpm

Question 14

Sinus tachycardia

Answer 14

> 100 bpm

Question 15

Sinus bradycardia

Answer 15

<60 bpm