Heart Block and Conduction Abnormalities


  • abnormalities may occur at any part of the conduction system


1st degree block

  • prolongation of PR interval (>0.2s)

2nd degree Mobitz type I (Wenckebach) block

  • progressive lengthening of PR interval with eventual dropped ventricular conduction

2nd degree Mobitz type II (Hay) block

  • intermittent dropping of ventricular conduction

2nd degree (2:1 type) block

  • alternate p-wave not conducted to ventricles

3rd degree block (complete heart block)

  • complete dissociation between atria and ventricular

Left Anterior Fascicular Block (LAFB) (Left anterior hemiblock)

  • LAD, Q waves in I and aVL, small R in III (and absence of LVH)

Left Posterior Fascicular Block (LPFB) (Left posterior hemiblock)

  • RAD, small R in I, small Q in III (and absence of RVH)

Right bundle branch block (RBBB)

  • RSR in V1 (‘M’), and ‘W’ in V6 (MARROW), normal axis

Left bundle branch block (LBBB)

  • septal depolarisation reversed so there is a change in initial direction of QRS (WILLIAM), normal axis

Bifascicular block

  • RBBB + block of either left anterior or posterior fascicle.
  • RBBB + left anterior fascicle block -> LAD
  • RBBB + left posterior fascicle block -> RAD

Trifascicular block – 3 types:

  1. Prolonged PR interval + RBBB + LAD
  2. LBBB + RAD
  3. AF + RBBB + LAD


By diagnosis

  • 1st degree
    – nothing unless symptomatic and other causes of symptoms excluded
  • 2nd degree (Mobitz type I)
    – nothing unless symptomatic and other causes of symptoms excluded
  • 2nd degree (Mobitz type II)
    – pacemaker
  • 3rd degree
    – pacemaker
  • branch blocks
    – nothing unless progresses or symptomatic -> pacemaker
    — if sympatomatic -> pacemaker
    — trifascicular block -> pacemaker
  • may need temporary pacing wire or external pacing
  • also if rates too slow and unresponsive to drugs -> pace

Emergency management of bradycardia

  • check blood pressure
  • atropine 25microgram/kg or glycopyrolate 0.2mg
  • isoprenaline 1-10mcg/min
  • adrenaline 0.1-1.0mcg/kg/min
  • temporary pacing – tranthoracic, transoesophageal, transvenous

References and Links


CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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