What are the potential causes of 1 degree atrioventricular (AV) block in an adolescent patient presenting with acute chest pain?

Potential Causes of First-Degree AV Block in an Adolescent with Acute Chest Pain

In an adolescent presenting with acute chest pain and first-degree AV block on EKG, the most important causes to consider are myocarditis/pericarditis, medication effects (particularly beta-blockers or calcium channel blockers), congenital heart disease, and infectious etiologies such as Lyme disease. 1, 2

Immediate Diagnostic Considerations

Inflammatory/Infectious Cardiac Causes (Most Critical in This Context)

• Myocarditis and pericarditis are primary considerations when an adolescent presents with chest pain and conduction abnormalities, as these conditions can cause both symptoms and AV conduction delays 3, 4
• Myopericarditis can present with markedly elevated troponin levels (>15,000 ng/L), chest pain, and non-specific ECG changes including PR segment depression, which may be subtle but points toward pericardial inflammation 3
• Look specifically for PR segment depression on the EKG, as this finding suggests pericardial involvement rather than ischemic disease 3
• Infectious causes, particularly Lyme disease, can affect the cardiac conduction system and cause first-degree AV block in adolescents 1, 2

Medication-Induced Causes

• Beta-blockers are a common reversible cause of first-degree AV block by slowing AV nodal conduction 1, 2, 5
• Beta-blockers can cause bradycardia, including first-degree AV block, with metoprolol specifically causing first-degree heart block (PR ≥0.26 sec) in 5.3% of patients versus 1.9% in placebo groups 5
• Non-dihydropyridine calcium channel blockers, digoxin, and antiarrhythmic medications can similarly cause first-degree AV block 1, 2
• Always obtain a complete medication history, including any recent additions or dose changes 1, 2

Congenital Heart Disease

• Congenital heart disease is a significant cause of first-degree AV block in adolescents, including conditions such as repaired tetralogy of Fallot, ventricular septal defects, and congenitally corrected transposition of the great arteries 6, 1
• Congenitally corrected transposition can present with first-degree AV block and minimal other physical findings, making it easily missed 1
• Approximately 30% of congenital AV blocks remain undiscovered until adolescence or adulthood 1

Structural Heart Disease with Ischemia (Less Common but High-Risk)

• While acute coronary syndromes are rare in adolescents (0.6% of chest pain presentations), they must be considered, particularly anomalous coronary arteries, which are the second most common cause of sudden cardiac death after hypertrophic cardiomyopathy 6, 4
• Anomalous coronary arteries can present with syncope or atypical chest pain (pain that raises alarm for cardiac causes, not typical musculoskeletal pain) 6
• Myocardial infarction, particularly inferior wall MI, is commonly associated with first-degree AV block, with the site of AV delay usually located above the bundle of His 1

Electrolyte and Metabolic Disturbances

• Check potassium and magnesium levels, as electrolyte abnormalities can cause or worsen AV conduction delays 1
• These are reversible causes that should be identified and corrected 1, 2

Critical Diagnostic Algorithm

Step 1: Assess PR Interval Duration and Symptoms

• PR interval 0.20-0.30 seconds: Usually asymptomatic and requires no treatment unless other concerning features present 1, 2
• PR interval >0.30 seconds: May cause symptoms due to inadequate timing of atrial and ventricular contractions (pseudo-pacemaker syndrome) 1, 7

Step 2: Evaluate for Acute Cardiac Pathology

• Obtain troponin levels: Markedly elevated troponin (>15,000 ng/L) in a young patient should raise suspicion of myopericarditis rather than ischemic disease 3
• Perform urgent echocardiography to assess ventricular function, regional wall motion abnormalities, and structural heart disease 3, 4
• Examine EKG carefully for:
  • PR segment depression (suggests pericarditis) 3
  • ST-segment changes or T-wave inversions (may indicate ischemia or myocarditis) 6, 3
  • QRS width (wide QRS suggests infranodal disease with worse prognosis) 1

Step 3: Rule Out Reversible Causes

• Review all medications for AV node-blocking agents (beta-blockers, calcium channel blockers, digoxin, antiarrhythmics) 1, 2, 5
• Check electrolytes (potassium, magnesium) 1
• Consider Lyme disease testing if epidemiologically appropriate 1, 2

Step 4: Risk Stratification for Structural Disease

• Patients with evidence of structural heart disease require more intensive monitoring 1
• Consider cardiac MRI as the gold standard to provide detailed structural information, rule out ischemic heart disease, and confirm inflammatory processes 3
• In adolescents with chest pain and cardiac disease, arrhythmia is the most common cardiac-related etiology (9 of 24 cases in one large cohort), followed by pericarditis (6 cases) and myocarditis (4 cases) 4

Important Clinical Pitfalls

• Do not assume first-degree AV block is benign in the setting of acute chest pain - it may indicate underlying myocarditis, pericarditis, or structural disease 1, 3, 7
• A completely normal EKG does not exclude acute coronary syndrome - approximately 5% of patients with normal EKGs who were discharged were ultimately found to have acute myocardial infarction or unstable angina 6
• Subtle PR segment depression may be the only EKG finding pointing to pericardial inflammation and should not be overlooked 3
• In adolescents, 92% of cardiac-related chest pain cases received EKGs compared to 27% without cardiac disease, emphasizing the importance of EKG evaluation in this population 4
• Chronic first-degree AV block at the AV node level has a good prognosis and is frequently drug-related and reversible, but this should only be concluded after excluding acute pathology 6, 1, 2