Atrioventricular (AV) Heart Block - Cardiovascular

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