Heart Block

Exam Cram

• Heart block refers to conduction defects within the cardiac systolic cycle,

• Types

  • First degree: long PR- benign

  • Mobitz 2:1: increasing distance between P & QRS complex resulting in missed QRS complex

  • Mobitz 2:2: consistent distance between P & QRS complex with missed QRS

  • 3rd Degree: p & QRS not in sync

• Management: Mobitz 2:2 & 3rd Degree requires pacemaker

Classification

First Degree Heart Block

• Definition: PR > 200

• Slow conduction between atria and ventricle, not associated with asystole or adverse outcomes

• Presentation: asymptomatic

• Management: nil

• Note bi-fasicular block + PR enlongation, doesn't equal tri-fasicular block, partly because this combination isn't associated with an increased risk of asystole

Mobitz 2:1- Wenckebach

• Increasing distance between p wave and QRS complex, resulting in a missed QRS complex

• Not associated with a high rate of asystole and doesn't require emergency pacemaker

Mobitz 2:2

• Consistent distance between p wave and QRS complex, however sporadically or consistency there is a missed QRS complex

• Associated with asystole and requires pacemaker

Complete Heart Block (3rd Degree)

• P wave and QRS complex out of sync

• Associated with asystole and requires pacemaker

Med Reg Notes

Indications for a pacemaker

• Mobitz 2:2 or 3rd degree heart block

• Trifasicular block

• Pauses > 3s

• Symptomatic bradycardia: syncope, hypotension, chest pain, heart failure

Resources & References

Written in 2025