EZMed Lecture: Heart Blocks Overview

Introduction

• Channel: EZMed
• Topic: Tricks to remember different types of heart blocks
• Purpose: To provide a concise reference video for studying exams and career use.

Atrioventricular Heart Block

Conduction System Review

• SA Node: Produces action potentials (heart rate)
• Pathway:
  • Atria (Internodal pathway and Bachmann's bundle) → Atrial contraction
  • Impulse travels to ventricles: AV node → Bundle of His → Right and Left Bundle Branches → Purkinje Fibers → Ventricular contraction
• AV Heart Block: Delay/blockage in transmission from atria to ventricles, usually in the AV node, Bundle of His, or Bundle Branches.

Types of AV Heart Blocks

1. First Degree
2. Second Degree
   • Mobitz Type 1 (Wenckebach)
   • Mobitz Type 2
3. Third Degree

Heart Block Poem

• First Degree: "If the R is far from the P, then it must be a first degree."
• Second Degree:
  • Type 1 Wenckebach: "If PR gets longer, then a QRS drop, then it must be a type 1 Winkybok."
  • Type 2 Mobitz: "If PR stays normal and QRS quits, then it must be a type 2 Mobitz."
• Third Degree: "If P and QRS beat independently, then it must be a complete third degree."

Simplified Tricks

• First Degree: "Far away P"
• Wenckebach (Type 1): "Longer than drop"
• Second Degree (Type 2): "Drop randomly"
• Third Degree: "Beat independently"

Detailed Breakdown of Heart Blocks

First Degree Heart Block

• Phrase: Far away P
• Description: Prolonged PR interval (>200 ms)
  • Impulse delayed but QRS follows each P wave
  • Occurs at AV node

Second Degree Heart Blocks

Mobitz Type 1 (Wenckebach)

• Phrase: Longer than drop
• Description: Progressive PR interval lengthening, followed by a dropped QRS
  • PR interval gets longer with each beat until a QRS is dropped
  • Known as Wenckebach phenomenon

Mobitz Type 2

• Phrase: Drop randomly
• Description: Constant PR interval with random QRS drops
  • Impulse is blocked suddenly, leading to dropped QRS
  • Occurs in bundle of His, branches or AV node

Third Degree Heart Block

• Phrase: Beat independently
• Description: Complete block, no communication between atria and ventricles
  • Atria and ventricles generate own action potentials independently
  • Junctional escape rhythms maintain cardiac function

Conclusion

• Review: Importance of understanding heart blocks
• Resources: Free notes and blogs available via EasyMed
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