## Congenital vs Acquired Complete Heart Block ### Congenital CHB **Key Point:** Congenital CHB is associated with maternal anti-Ro/La (SSA/SSB) antibodies that cross the placenta and damage the fetal AV node, typically presenting in the neonatal period or discovered incidentally. - Maternal autoimmune disease (SLE, Sjögren syndrome) is the primary risk factor - Maternal anti-Ro/La antibodies cross placenta and cause AV nodal inflammation and fibrosis - Usually diagnosed prenatally (fetal bradycardia) or in neonatal period - Often asymptomatic in childhood; may present with syncope or heart failure later - Escape rhythm is typically narrow QRS (junctional), rate 40–60 bpm - No acute precipitant; patient has always had CHB ### Acquired CHB **Key Point:** Acquired CHB develops acutely in response to myocardial damage, ischemia, or degeneration of the conduction system. - Common causes: acute MI (anterior > inferior), infiltrative disease, cardiomyopathy, Lyme disease (in endemic areas), medications - Acute anterior MI is the most common cause in acute care settings - Escape rhythm may be narrow (nodal) or wide (ventricular), depending on site of block - Hemodynamically unstable; requires urgent pacing - Develops acutely over hours to days - May be preceded by progressive AV block (first → second → third degree) ### Comparison Table | Feature | Congenital CHB | Acquired CHB | |---------|----------------|---------------| | **Etiology** | Maternal anti-Ro/La antibodies | MI, degeneration, infiltration | | **Onset** | Prenatal/neonatal | Acute (hours to days) | | **Clinical presentation** | Often asymptomatic; incidental finding | Symptomatic; hemodynamically unstable | | **Escape rate** | 40–60 bpm (narrow QRS) | Variable; often < 40 bpm (wide QRS) | | **Associated findings** | Maternal SLE/Sjögren; neonatal lupus | ECG evidence of MI or conduction disease | | **Prognosis** | Generally good if asymptomatic | Poor without pacing | | **Pacing** | Elective (if symptomatic) | Emergent | **High-Yield:** The **history of maternal anti-Ro/La antibodies and neonatal lupus** is the single most specific discriminator of congenital CHB. This is a classic board question. **Clinical Pearl:** In an acute MI setting (anterior wall), CHB is acquired and indicates extensive conduction system damage. The presence of a maternal autoimmune history and long-standing bradycardia would suggest congenital disease, not acute MI-related block. **Mnemonic:** **"Congenital = Antibodies; Acquired = Acute"** — Congenital CHB is tied to maternal antibodies; acquired CHB is tied to acute tissue damage. **Warning:** Do not confuse the narrow escape rhythm of congenital CHB (which is benign and long-standing) with the wide escape rhythm of acquired infra-His block (which is dangerous and requires urgent pacing). [cite:Harrison 21e Ch 226]
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