A-V Blocks

Atrioventricular Blocks

Written by Dr Andrew Lam

First Degree Heart Block 

• Prolongation of the PR interval (>200ms)
• Benign as an isolated entity that doesn’t cause haemodynamic instability. Intervention generally not required

Second Degree Heart Block (Mobitz Type 1 – Wenckebach)

• Progressive prolongation of the PR interval, followed by non-conductive p-wave
• Usually benign, low risk of haemodynamic instability or progression to complete heart block 
• Rarely require pacemaker insertion and asymptomatic patients don’t require intervention

Second Degree Heart Block (Mobitz Type 2)

• Consistent PR interval followed by sudden “dropped beat” with failure to conduct p-wave
• Higher risk of haemodynamic instability, asystole and progression to complete heart block
• Usually requires admission for cardiac monitoring and pacemaker insertion.

Third Degree (Complete) Heart Block

• Complete AV dissociation (no relationship between p-waves and QRS complexes)
• At risk of sudden cardiac death and ventricular standstill
• Require admission for cardiac monitoring and pacemaker insertion

References: 

Nickson, C. (2020). Heart Block and Conduction Abnormalities, Life in the Fast Lane. Retrieved 23rd November 2021 from https://litfl.com/heart-block-and-conduction-abnormalities/