Heart Block

Question 1

Define heart block

Answer 1

Impaired conduction from atria -> ventricles

Question 2

What are the different types of heart block?

Answer 2

1st degree – fixed prolongation of PR interval

2nd degree
• Mobitz Type 1/Wenckeback’s phenomenon – progressive prolongation of PR interval
with eventual loss of AV conduction for one beat followed by repetition of the cycle
• Mobitz Type 2 – fixed prolongation of PR interval with intermittent/regular loss of
AV conduction for one beat e.g. 2:1 or 3:1 block

3rd degree/complete heart block – complete loss of synchronisation of atrial and ventricular
contraction (marching p waves)

Question 3

What are the causes/risk factors of heart block?

Answer 3

• MI or IHD
• Infection e.g. rheumatic fever, infective endocarditis
• Drugs e.g. digoxin, beta-blockers, CCBs
• Metabolic e.g. hyperkalaemia, cholestatic jaundice, hypothermia
• Infiltration of conducting system e.g. sarcoidosis, neoplasm, amyloidosis

Question 4

What are the symptoms of heart block?

Answer 4

1st degree and Mobitz Type 1/Wenckeback’s phenomenon
• Asymptomatic

Mobitz Type 2 and 3rd degree
• Stoke-Adams attack (syncope)
• Palpitations
• Dizziness
• Chest pain

Question 5

What are the signs of heart block?

Answer 5

1st degree and Mobitz Type 1/Wenckeback’s phenomenon
• Nil of note

Mobitz Type 2 and 3rd degree
• Hypotension
• Heart failure

3rd degree
• Slow large volume pulse
• JVP cannon a waves

Question 6

What investigations are carried out for heart block?

Answer 6

• ECG - GOLD STANDARD
- First Degree - fixed prolonged PR interval (> 0.2 s)
- Mobitz Type I (Wenckebach) - progressively prolonged PR interval, culminating in a P wave that is NOT followed by a QRS complex. The pattern then begins again. ‘Going, going, gone’.
- Mobitz Type II - intermittently a P wave is NOT followed by a QRS. There may be a regular pattern of P waves not followed by QRS (e.g. 2:1 or 3:1)
- Complete Heart Block - no relationship between P waves and QRS complexes. If QRS is initiated in the:
> Bundle of His - narrow complex
> More distally - wide complex and slow rate (~ 30 bpm)

• CXR - Cardiac enlargement, pulmonary oedema
• Bloods
- TFTs
- Digoxin level
- Cardiac enzymes
- Troponin
• Echocardiogram - Wall motion abnormalities, aortic valve disease, vegetations

Question 7

What is the management for heart block?

Answer 7

Chronic Block - permanent pacemaker is recommended in:
• Complete heart block
• Advanced Mobitz Type II
• Symptomatic Mobitz Type I

Acute Block - if associated with clinical deterioration use IV atropine
- Consider temporary (external) pacemaker

Question 8

What are the complications of heart block?

Answer 8

• Asystole
• Cardiac arrest
• Heart failure
• Complications of any pacemaker inserted