AV Blocks: Diagnosis and Management

Types of AV Blocks and Their Characteristics

First-degree AV block is defined as a prolonged PR interval >200 ms, typically occurring at the AV node level, and is generally benign, according to the American Heart Association 1, 2
Mobitz Type I second-degree AV block is characterized by progressive PR interval prolongation until a P wave fails to conduct, usually associated with narrow QRS complexes, and often transient and asymptomatic, as stated by the American College of Cardiology 1, 3
Mobitz Type II second-degree AV block is characterized by constant PR intervals before and after blocked P waves, usually associated with wide QRS complexes, and often symptomatic, requiring permanent pacing, as recommended by the European Society of Cardiology 1, 3
Third-degree AV block is characterized by complete absence of AV conduction with atrial and ventricular activity completely dissociated, and may occur at any anatomical level, according to the American Heart Association 1, 3

The American College of Cardiology recommends permanent pacing for symptomatic third-degree AV block and Mobitz Type II second-degree AV block, while first-degree and Mobitz Type I blocks often require only monitoring unless symptomatic 1, 3
For symptomatic bradycardia, atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg) is recommended as first-line treatment for AV nodal blocks, as stated by the American Heart Association 4, 5
Transcutaneous pacing is recommended for unstable patients not responding to medications, and transvenous temporary pacing is considered for persistent symptomatic bradycardia, according to the European Society of Cardiology 4, 5
Permanent pacing is indicated for all symptomatic patients with third-degree AV block, and for asymptomatic patients with average awake ventricular rates <40 bpm or with cardiomegaly/LV dysfunction, as recommended by the American College of Cardiology 6

In acute myocardial infarction, inferior MI often causes AV block at the supra-Hisian level, which is usually transient and responds to atropine, while anterior MI usually causes AV block at the infra-Hisian level, carrying a worse prognosis and often requiring pacing, as stated by the European Society of Cardiology 7
Permanent pacing is recommended regardless of symptoms for patients with neuromuscular diseases, such as myotonic muscular dystrophy and Kearns-Sayre syndrome, due to unpredictable progression of conduction disease, according to the American College of Cardiology 6

The American Heart Association recommends that Mobitz Type I second-degree AV block, which is often benign and asymptomatic, requires observation only, with no permanent pacing indicated 8, 9
For Mobitz Type II second-degree AV block, which carries a high risk of progression to complete heart block, permanent pacemaker implantation is indicated regardless of symptoms 8, 9, 10

The American College of Cardiology recommends permanent pacemaker implantation for third-degree AV block in symptomatic patients, including those with heart failure, presyncope, syncope, or ventricular arrhythmias presumed due to block 8, 9, 10
Asymptomatic third-degree AV block with documented asystole ≥3.0 seconds while awake, escape rate <40 bpm while awake, or escape rhythm below the AV node (wide QRS) also warrants permanent pacemaker implantation 8, 9, 10
The American Heart Association suggests that third-degree AV block after catheter ablation of AV junction, postoperative third-degree AV block not expected to resolve, and third-degree AV block requiring medications that cause symptomatic bradycardia are indications for permanent pacemaker implantation 8, 9, 10

In patients with exercise-induced AV block not due to ischemia, permanent pacing is indicated due to the poor prognosis associated with His-Purkinje disease 8, 9
For sleep apnea-related AV block, treatment of the underlying sleep apnea is recommended, and permanent pacing is only considered if the patient is symptomatic 8, 9
In patients with neuromuscular diseases such as myotonic dystrophy, Kearns-Sayre syndrome, Erb dystrophy, or peroneal muscular atrophy, permanent pacing may be considered for any degree of AV block due to the unpredictable progression of the disease 8