Atrioventricular blocks
Atrioventricular block is impaired conduction between atria and ventricles, graded first-degree, second-degree (Mobitz I and II), and third-degree (complete). The key distinction is nodal versus infranodal disease: Mobitz I is usually benign, whereas Mobitz II and complete block are infranodal, unstable, and require pacing.
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What this article covers
- Overview
Definition: atrioventricular (AV) block is delayed or failed conduction of atrial impulses to the ventricles, graded as first-degree, second-degree (Mobitz I and Mobitz II), and third-degree (complete) block.
- Epidemiology
First-degree and Mobitz I are common and often benign, including in athletes and during sleep.
- Risk factors
Age-related conduction system fibrosis (Lenegre and Lev disease).
- Pathophysiology
Nodal block: delay in the AV node, vagally influenced and atropine-responsive, with a stable junctional escape.
- Clinical features
First-degree and Mobitz I: usually asymptomatic.
- Differential diagnosis
Sinus node dysfunction: impulse-formation rather than conduction failure (sinus node dysfunction).
- Diagnosis
Establish and grade with an ECG defining the P-wave to QRS relationship: the diagnostic basis is a 12-lead ECG classifying the block as first-degree (PR over 200 ms, all conducted), Mobitz I…
- Management
First-line, assess stability and grade: asymptomatic first-degree block and Mobitz I usually need only observation and removal of offending drugs.
- Complications
Syncope, falls, and sudden death from asystole or a failed escape rhythm.
- Prognosis
Excellent for first-degree and Mobitz I, which rarely progress.
- Prevention
Minimize combinations of nodal-blocking drugs, especially in older patients.
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