| Intrinsic causes | Associated clinical and laboratory findings |
| Structural congenital heart disease |
| Atrial septal defect | - Infants with a large ASD present with signs of heart failure (eg, tachypnea and dyspnea, poor feeding, failure to thrive)
- Physical exam findings may include fixed S2 split and/or midsystolic pulmonary flow or ejection murmur
- ECG may show incomplete right bundle branch pattern
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| Atrioventricular canal | - Typically presents in early infancy with signs of heart failure (eg, tachypnea and dyspnea, poor feeding, failure to thrive)
- Physical exam findings may include hyperactive precordium with inferior and laterally displaced precordial impulse, increased P2, and systolic ejection murmur due to increased blood flow across the pulmonary valve
- ECG shows leftward and superior QRS axis
|
| Heritable arrhythmia syndromes |
| Long QT syndrome | - ECG shows prolonged QTc for age, often with biphasic or notched T wave
- Suggestive family history (family member with LQTS or sudden cardiac death)
|
| Brugada syndrome | - ECG shows shortened right ventricular conduction delay with abnormal ST segments in anterior precordial leads
- May be associated with sinus bradycardia and/or atrioventricular block in some cases
|
| Collagen vascular disease |
| Systemic lupus erythematosus | - Involvement of other organs, including skin, joints, kidneys, lungs, nervous system, serous membranes
- Elevated inflammatory markers (ESR and CRP)
|
| Surgical trauma |
| Sinus node dysfunction | - Surgical closure of ASD
- Fontan
- Atrial switch operation
|
| Atrioventricular block | |
| Extrinsic causes | Associated clinical and laboratory findings |
| Medications* | - History of exposure (either via prescribed medication or accidental ingestion)
|
| Beta-adrenergic blockers | - Also may cause hypotension and hypoglycemia
|
| Calcium channel blockers | - Also causes hypotension, which may be severe in large overdoses
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| Clonidine | - Also may cause hypotension and sedation; in large overdoses may cause hypertension
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| Opioids | - Constricted pupils, CNS depression, respiratory depression
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| Hypothermia | - Bradycardia may occur with core temperature <35°C
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| Elevated intracranial pressure | - Associated with hypertension, abnormal respirations, and abnormal pupillary response
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| Hypervagotonia/neurally mediated (reflex) syncope | - Usually triggered by a precipitating event (eg, nasopharyngeal or esophageal stimulation, breath-holding spell, coughing, vomiting)
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| Sleep | - Heart rates during sleep can be as low as 60 to 80 bpm in infants and young children; 40 to 50 bpm in school-aged children; and 30 to 40 bpm in adolescents
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