ECG analysis

Question 1

How to calculate rate

Answer 1

If regular:
300/no. of large squares

If irregular:
no. of QRS complexes within 30 large squares x 10

Question 2

Rythmn

Answer 2

Sinus - every P wave followed by QRS

AF - no P waves and irregularly irregular QRS

Atrial flutter: saw-toothed baseline

Nodal rhythm: regular QRS but no P waves

Question 3

Axis

Answer 3

II most +ve = normal axis

AVL most +ve = Left axis deviation

AVF most +ve = right axis deviation

Question 4

Systematic analysis of ECG

Answer 4

1. Rate
2. Rhythm
3. Axis
4. P waves and PR interval
5. QRS
6. ST segment
7. T waves

Question 5

P waves

Answer 5

Atrial depolarisation

• Absent: AF, SAN block, nodal rhythm
• Dissociated: complete heart block

• Bifid P waves = LA hypertrophy
- HTN, Aortic stenosis, Mitral regurgitation or stenosis

• Peaked P waves= RA hypertrophy
- pulmonary HTN, COPD

Question 6

QRS

Answer 6

Ventricular initiation depolarisation

• Wide QRS >120ms - more than 3 small squares

• Conduction defect
• WPW
• Broad complex tachycardia

• Pathological Q wave
- Full Thickness MI

• RVH: Dominant R wave in V1 + deep S wave in V6
• LVH
• R wave in tall V6
• R wave in V5/V6 + S wave in V1

Question 7

PR interval

Answer 7

PR interval (3-5 small sq)
Start of P wave to start of QRS

• Long: heart block
•Short
- Accessory conduction: e.g. WPW
- Nodal rhythm

Question 8

Long QT

Answer 8

QTc - Start of QRS to end of T wave

> 420ms

Question 9

ST Segments

Answer 9

Elevated
• STEMI
• Pericarditis: saddle-shaped
• Aneurysm: ventricular

Depressed
• NSTEMI
• Unstable angina

Question 10

T-waves

Answer 10

• Peaked in ↑K+

* Flattened in ↓K+

Question 11

U waves

Answer 11

Hypokalaemia

Question 12

1st Degree Heart Block

Answer 12

Constantly extended PR interval with no absent QRS complexes

PR > 200ms (more than 1 large sq)

Question 13

2nd Degree Heart Block

- Wenckebach /Mobitz I

Answer 13

Progressive lengthening of
PR interval

Absence of QRS complex

Next conducted beat has
shorter PR interval

Question 14

2nd Degree Heart Block

- Mobitz II

Answer 14

Constant PR
Occasional absent QRS

• block is usually in bundle
  branches of Purkinje fibres

Question 15

2nd Degree Heart Block

- 2:1 Block

Answer 15

Two P waves per QRS
Normal consistent PR
intervals

Question 16

3rd Degree Heart Block

Answer 16

P waves and QRS are dissociated

Question 17

RBBB

Answer 17

Broad complex QRS 
Bunny ear V1 
Slurred S wave 
Causes:
• Infarct – Inferior MI
• Normal variant
• Congenital – ASD, VSD, Fallot’s
• Hypertrophy – RVH (PE, Cor Pulmonale)

Question 18

Left BBB

Answer 18

Broad complex QRS
-ve V1
+ve at V6
Left axis deviation

Causes:
• Fibrosis
• LVH – AS, HTN
• Infarct – Inf. MI
•Coronary HD

Question 19

Bifascicular Block

Answer 19

RBBB + axis deviation

Question 20

Trifascicular Block

Answer 20

RBBB + axis deviation + 1st

degree AV block

Question 21

Bradycardia

Answer 21

Less than 50bpm

Question 22

TAchycardia

Answer 22

More than 100 bpm

Question 23

Atrial escape

Answer 23

Missed P wave as SAN fails to depolarise

Normal QRS

Question 24

Atrial Flutter

Answer 24

Saw-toothed baseline as
atria contract at 300bpm

2:1 - 150bpm

Question 25

Ventricular tachycardia

Answer 25

Leads to cardiac arrest - requires defibrillator

No P waves
Regular, wide QRS
No T waves

Question 26

VF

Answer 26

Shapeless, rapid
oscillations and no
organised complexes

• Electrical cardioversion

Question 27

Torsades de Pointes

Answer 27

VT where QRS become taller and smaller

Broad complex tachycardia

Question 28

Wolf Parkinson White

Answer 28

Accessory conducting bundle
Short PR interval
Slurred upstroke of QRS -
delta wave

Question 29

Pericarditis

Answer 29

Saddle shaped ST

Question 30

Hyperkalaemia

Answer 30

Tall tented T waves
Widened QRS
Absent P waves
Sine wave appearance

Question 31

Hypokalaemia

Answer 31

Small T waves
ST depression
Prolonged QT interval
Prominent U waves

Question 32

SVT

Answer 32

Sinus tachycardia
AF
Atrial flutter
AV re-entry tachycardia

Question 33

Broad complex tachycardia

Answer 33

VT

Torsades de points