Updated: 4/4/2020

Atrioventricular (AV) Heart Block

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Topic
Snapshot
  • A 20-year-old man presents to his primary care physician for an annual exam. He is currently feeling well. Medical history is unremarkable and he takes a daily multivitamin. He denies any alcohol or smoking history. He is a college student and part of the school's track team, which he continued since he was a student in high school. He is concerned because a classmate of his passed out during practice and ended up dying due to sudden cardiac death. He is requesting an electrocardiogram (ECG) to ensure his heart is healthy. An ECG demonstrates a PR interval of 0.25 sec and is otherwise unremarkable. (First-degree heart block)
Introduction
  • Clinical definition
    • an impairment of the electrical transmission from the atria to the ventricles
  • Etiology
    • idiopathic (most common)
      • e.g., fibrosis and sclerosis of the conduction system
    • ischemic heart disease (2nd most common)
    • ↑ vagal tone
    • familial causes
    • iatrogenic
      • medications
        • e.g., β-blockers, calcium channel blockers, adenosine, digoxin, and amiodarone
      • cardiac procedures
        • e.g., cardiac surgery and transcatheter aortic valve implantation
Atrioventricular (AV) Block
 
AV Blocks
Types
Electrocardiogram Findings
Treatment Comments
First degree AV block
  • ↑ PR interval (> 0.2 secs)
  • No treatment is required
  • Typically seen in young patients with a ↑ vagal tone
  • Well-trained athletes
Second degree AV block (Mobitz type I)
  • Progressive ↑ PR interval until a P wave is not followed by a QRS complex (Wenckebach phenomenon)
    • the sequence then repeats
    • QRS complex is narrow
  • Treatment is unnecessary unless the patient is symptomatic
    • use atropine or a temporary pacemaker in symptomatic cases
  • Patients are typically asymptomatic
  • Can be seen in patients with
    • drug intoxication (e.g., β-blockers and digitalis)
    • ↑ vagal tone
Second degree AV block (Mobitz type II) 
  • Fixed PR intervals with occasional dropped QRS complexes
    • QRS complex is typically wide
  • Permanent pacemaker
  • May progress to a third-degree heart block
Third degree (complete) AV block 
  • Atria and ventricles depolarize independently
    • P waves and QRS complexes are not rhythmically synchronized
 
  • Permanent pacemaker unless the cause is reversible 
 
  • Can be a complication of Lyme disease
 
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(M1.CV.12.8) A 29-year-old computer programmer presents to the general medicine clinic complaining of dizziness, fatigue, and shortness of breath. One month ago, the patient went on a camping trip in northern Connecticut. On assessment, vital signs are temperature 36.9°C, blood pressure 100/65, heart rate 41, and respiratory rate 16 with an oxygen saturation of 99%. A print of the EKG strip is shown below (Figure A). What is the most likely diagnosis? Tested Concept

QID: 100524
FIGURES:
1

Wolff-Parkinson-White syndrome

6%

(16/247)

2

Second degree Mobitz type I AV block

13%

(32/247)

3

Second degree Mobitz type II AV block

13%

(31/247)

4

First degree AV block

9%

(23/247)

5

Third degree (complete) AV block

57%

(141/247)

M 2 E

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