Conduction blocks ( intraatrial, AV- nodal and intraventricular) – etiology, pathogenesis, and clinical manifestations
Conduction blocks are disturbances in the propagation of electrical impulses through the heart's conduction system, leading to delayed or completely blocked activation of certain chambers.
1 Intra- atrial block
Etiology
- Atrial enlargement (e.g., from mitral stenosis or hypertension).
- Ischemic heart disease.
- Fibrosis or scarring (age- related or after inflammation).
- Infiltrative diseases (e.g., amyloidosis).
Pathogenesis
- Slowed or blocked conduction within atrial muscle fibers.
- Can lead to interatrial conduction delay, resulting in abnormal or prolonged P- wave morphology.
Clinical manifestations
- Usually asymptomatic.
- Can predispose to atrial arrhythmias (e.g., atrial fibrillation).
- On ECG: prolonged P-wave (>120 ms), sometimes biphasic ("notched") in lead II.
2 AV nodal (atrioventricular) block
Etiology
- Ischemic heart disease (especially inferior MI involving AV node).
- Degenerative changes ( Lenègre- Lev disease).
- Increased vagal tone (e.g., during sleep, athletes).
- Drugs (beta- blockers, digoxin, calcium channel blockers).
- Myocarditis, Lyme disease.
Pathogenesis
Impaired conduction through the AV node, classified as:
Clinical manifestations
- First- degree: usually asymptomatic.
- Second- degree:
- Mobitz I: may have dizziness or minimal symptoms.
- Mobitz II: higher risk of syncope, may progress to complete block.
- Third- degree:
- Severe bradycardia.
- Fatigue, dizziness, syncope (Stokes-Adams attacks).
- Risk of sudden cardiac arrest.