Arrythmias - Heart Block

Question 1

ESSENCE

Answer 1

Impairment of electrical transmission from atria to ventricles

Question 2

AETIOLOGY

Common causes

Answer 2

• Idiopathic (most common)
• Ischaemic heart disease (2nd most common)
• Increased vagal tone
• Familial
• Iatrogenic

Question 3

AETIOLOGY

Medication

Answer 3

• Beta blockers, CCB, adenosine, digoxin and amiodarone

Question 4

DIFFERENTIALS

Key differential

Answer 4

Sick sinus syndrome

Question 5

CLASSIFCATION

Answer 5

• 1st degree AV block
• 2nd degree AV block (Mobitz type I)
• 2nd degree AV block (Mobitz type II)
• 2:1 block
• 3rd degree AV block

Question 6

1st degree block ECG findings

Answer 6

• Increased PR interval (>0.2s)
• 1:1 p waves and QRS complex

Question 7

2nd degree block mobitz type I ECG findings

Answer 7

• Progressive increasing PR interval until P wave not followed by QRS complex
• Sequence then repeats
• QRS complex is narrow

Question 8

2nd degree block mobitz type II ECG findings

Answer 8

• Fixed PR intervals with occasional dropped QRS complexes
• QRS complex typically wide

Question 9

3rd degree block ECG findings

Answer 9

• Atria and ventricles depolarise independently
  
  • P waves and QRS complex not synchronised

Question 10

MANAGEMENT

General principles

Answer 10

• If stable then observe
• If unstable or risk of asystole (Mobitz type II, 3rd degree or previous asystole) then treat

Question 11

MANAGEMENT

Asystole risk lines

Answer 11

• 1) Atropine 500mcg IV
• 2) If no improvement
  
  • Atropine 500mcg IV repeated (up to 6 doses for total 3mg)
  • Other inotropes (such as noradrenaline)
  • Transcutaneous cardiac pacing (using defibrillator)