AV Node Block for NP
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AV Node Block for the Nurse Practitioner Licensing Exam
Overview of AV Node Block
Atrioventricular (AV) node block refers to delayed or impaired conduction of electrical signals from the atria to the ventricles, often resulting in bradycardia. AV blocks vary in severity from mild (first-degree) to complete (third-degree), impacting clinical presentation and management.
Classification of AV Node Blocks
- First-Degree AV Block:
- Characterized by a PR interval >200 ms, with each atrial impulse successfully conducted to the ventricles.
- Usually asymptomatic and often detected incidentally on ECG.
- Common causes include medications (e.g., beta-blockers, calcium channel blockers), increased vagal tone, and aging.
- Generally benign and does not require treatment unless symptomatic.
- Second-Degree AV Block:
- Some atrial impulses fail to reach the ventricles, causing dropped QRS complexes.
- Mobitz Type I (Wenckebach): Progressive lengthening of the PR interval until a QRS is dropped. Often benign and related to reversible factors.
- Mobitz Type II: Intermittent dropped QRS complexes without prior PR prolongation, often indicating structural heart disease and with a higher risk of progression to complete block. Symptomatic cases typically require a pacemaker.
- Third-Degree (Complete) AV Block:
- Complete dissociation between atrial and ventricular rhythms, with no conduction through the AV node.
- Ventricular rhythm is sustained by an escape rhythm, often very slow, leading to symptoms such as dizziness, syncope, or fatigue.
- Requires immediate treatment with temporary pacing if unstable, followed by permanent pacemaker placement.
Etiology
- Intrinsic Causes:
- Age-related fibrosis, ischemic heart disease, inflammatory disorders (e.g., myocarditis, Lyme disease), and congenital conditions (e.g., neonatal lupus).
- Extrinsic Causes:
- Medications, electrolyte imbalances (hyperkalemia), and increased vagal tone, particularly in athletes.
Key Points
- Types: AV block includes first-degree, second-degree (Mobitz I and II), and third-degree (complete) blocks.
- Etiology: Common causes are medications, aging, ischemic heart disease, and increased vagal tone.
- Diagnosis: Identified by ECG, with first-degree block showing prolonged PR interval and second- and third-degree blocks showing progressively dropped or dissociated QRS complexes.
- Management: First-degree and Mobitz I generally do not require intervention; Mobitz II and complete heart block often require pacemaker placement.