Lecture Notes: Types of AV Blocks

Introduction

Purpose: Understanding the three types of AV blocks, crucial for Step One exams.
Relevance: AV blocks are high-yield topics because they are frequently tested.
Focus: Emphasis on the PR interval on the EKG.

Components: P-wave, QRS complex, T-wave.
PR Interval:
- Normal duration: less than 200 milliseconds (5 little boxes on an EKG).
- Example shown: 3.5 to 4 boxes.

Definition: Long PR interval (> 200 milliseconds or > 5 boxes), but constant.
Presentation:
- Symptoms: Dizziness, syncope, slow heartbeat due to inefficient heart contractions.
- Clinical vignette example: Normal rhythm but prolonged PR interval.

Characteristics:
- PR interval progressively lengthens until a QRS is dropped.
- Pattern: "Longer, longer, longer, drop".
Mnemonic: "Wenckebach gives you warning" with progressively lengthened PR intervals.

Characteristics:
- Constantly prolonged PR interval (> 200 milliseconds).
- Regular dropped beats.
Comparison: Similar to first-degree AV block with occasional dropped beats.

Definition: Complete dissociation between atrial and ventricular contractions.
EKG Characteristics:
- Constant P-P intervals and constant Q-Q intervals.
- P-waves may be buried within QRS complexes, making detection difficult.
Clinical Presentation: Bradycardia, dizziness, potential fainting.
Diagnosis Tips: Look for constant intervals even if waves are hard to discern.

AV Blocks Overview:
- Conduction abnormalities affecting heart efficiency.
- Recognition of specific patterns crucial for Step One exams.
Types Recap:
- First-degree: Prolonged PR interval.
- Second-degree: Mobitz Type 1 (Wenckebach) with progressively longer intervals; Mobitz Type 2 with constant but prolonged intervals and dropped beats.
- Third-degree: Complete dissociation, difficult EKG interpretation.
Importance: High-yield for exams; recommended to review several times.

This summary is intended as a study aid to help remember the key points about AV blocks and their characteristics on an EKG.