Characterized by an interrupted or delayed conduction between the atria and the ventricles

1st Degree Heart Block

• PR interval greater than 0.2 seconds (5 small squares)

Causes

• High vagal tone (e.g. athletes)
• Acute inferior MI
• Electrolyte abnormalities (e.g. hyperkalaemia)
• Drugs: NHP-CCBs, beta-blockers, digoxin, cholinesterase inhibitors

Management

• First degree heart block itself is benign and does not need treating
• Underlying pathological cause should be reversed
• Long term follow-up recommended

2nd Degree Heart Block

• Intermittent absence of QRS complexes - indicates there is a blockage between the AV node and the ventricles
• Split into Mobitz type I and Mobitz type II

Mobitz type 1

• Type of second degree heart block that is usually due to reversible conduction block at the AV node
• It is characterised by progressive lengthening of the PR interval which results in a P wave that fails to conduct a QRS

Causes

• MI (mainly inferior)