ECG

Question 1

Causes of 1st and 2nd degree heart block

Answer 1

Prolonged PR interval: coronary artery disease, acute rheumatic carditis, digoxin toxicity, electrolyte disturbance

Question 2

Types of 2nd degree heart block

Answer 2

1. Wenckeback or Mobitz I
2. Mobitz type II
3. 2:1, 3:1, 4:1

Question 3

Define Wenckeback or Mobitz type 1

Answer 3

Progressive lengthening of the PR interval followed by non-conduction of a p wave; benign

Question 4

Define Mobitz type 2

Answer 4

Constant PR interval with non-conduction of a p wave

Question 5

PR interval in 2:1 or 3:1 block: constant or prolonged?

Answer 5

Constant

Question 6

Define 1st degree heart block

Answer 6

Prolonged PR interval (>6 small squares)

All p waves are followed by a QRS complex

Question 7

Define 3rd degree heart block

Answer 7

Complete non-conduction of p waves; no relationship between p waves and QRS complexes; ventricular escape rhythm takes over

Question 8

Causes of complete heart block

Answer 8

1. MI (usually transient)
2. Fibrosis around Bundle
   of His
3. Block of both bundle branches

Question 9

Causes of RBBB

Answer 9

1. Normal heart
2. Pulmonary conditions causing right heart strain (e.g. PE)
3. Congenital heart disorders (e.g. atrial septal defect)

Question 10

Causes of LBBB

Answer 10

Conduction defect > LVH

1. Left anterior fascicular block/hemiblock
2. Ischaemia
3. Aortic stenosis
4. HTN
5. Cardiomyopathy

Question 11

Pneumonic for left and right bundle branch block

Answer 11

WILLIAM

MORROW

Question 12

When is left axis deviation significant?

Answer 12

When the average depolarisation in both leads II and III are negative

Question 13

Define bifascicular block

Answer 13

RBBB with left anterior fascicular block –> causes left axis deviation

Question 14

When to consider a pacemaker in conduction abnormalities?

Answer 14

1. 2nd degree HB - 2:1, 3;1
2. Complete heart block
3. RBBB with left axis deviation (concurrent left anterior hemiblock) –> indicates severe conducting tissue disease

Question 15

Define sinus arrhythmia

Answer 15

All p waves conducted; changes in HR from beat to beat, associated with respiration; normally seen in young people

Question 16

Define supraventricular and ventricular rhythms and their corresponding QRS complexes

Answer 16

Supraventrocular:
1. Sinus rhythm
2. Atrial escape
3. Junctional escape (AVN)
Normal QRS complex

Ventricular escape rhythms has abnormally shaped and wide QRS; T wave also abn due to abn repolarisation

Question 17

When might supraventricular rhythms have wide QRS complexes?

Answer 17

With concurrent left or right bundle branch block or the Wolff-Parkinson-White syndrome

Question 18

Effect of carotid sinus pressure on tachyarrhythmias

Answer 18

Activates a reflex that leads to vagal stimulation of the SA and AV nodes
Reduced frequency of SAN discharge and increase the delay of conduction in the AV node –> can abolish some supraventricular arrhythmias

Question 19

Diagnosis of Wolff-Parkinson-White syndrome on ECG

Answer 19

1. Short PR interval (less than 3 small squares)
2. Wide and abnormal QRS complex that may or may not have delta waves (= slurred upstroke) due to pre-excitation of the ventricles

Question 20

Define WPW syndrome and its types

Answer 20

• Extra (“accessory”) conduction bundle directly linking the atrium and ventricle
• No AV node to delay conduction
• Type A: LA to LV; R wave in V1
• Type B: RA to RV; S wave in V1