16. Pediatric Myopericardial and Inflammatory Diseases
Inflammatory myocardial and pericardial diseases in pediatric patients produce acute repolarization abnormalities, low voltage complexes, and life-threatening ventricular arrhythmias.
Figure 16.1: 12-lead ECG of Acute Pericarditis displaying diffuse upward concave ST-segment elevation and PR-segment depression in inferolateral leads with reciprocal ST depression in lead aVR. Rendered with solid white background.
1. Clinical Presentation & Physical Examination
| Disease Entity | Cardinal Bedside Signs | Auscultation & Physical Findings |
|---|---|---|
| Acute Myocarditis | Unexplained sinus tachycardia out of proportion to fever, gallop rhythm ($S_3$), poor peripheral perfusion, hepatomegaly. | Soft $S_1$, $S_3$ gallop, mitral regurgitation murmur, muffled heart sounds. |
| Acute Pericarditis | Sharp, pleuritic precordial chest pain relieved by sitting forward and worsened by lying supine. | Pericardial friction rub (triphasic: atrial systole, ventricular systole, early diastolic filling). |
| Kawasaki Disease | High fever $>5$ days, bilateral non-purulent conjunctivitis, strawberry tongue, polymorphous rash, cervical lymphadenopathy. | Tachycardia, hyperdynamic precordium, muffled heart sounds if pericardial effusion present. |
| MIS-C (Post-COVID) | Multiorgan inflammation, shock, abdominal pain, conjunctival injection. | Hypotension, tachycardia, peripheral edema, low cardiac output state. |
2. Electrocardiographic Hallmarks
- Acute Pericarditis Stages:
- Stage 1 (Acute): Diffuse upward concave ST elevation in I, II, aVF, $V_2 - V_6$; PR segment depression in inferolateral leads; reciprocal ST depression and PR elevation in lead aVR.
- Stage 2 (Days): Return of ST and PR segments to baseline; flattening of T waves.
- Stage 3 (Weeks): Diffuse, symmetrical T-wave inversions without pathological Q waves.
- Stage 4 (Months): Normalization of the ECG.
- Acute Myocarditis:
- Diffuse Low Voltage QRS complexes ($<5\text{ mm}$ total amplitude across all limb leads).
- Unexplained persistent Sinus Tachycardia, prolonged $QTc$, frequent PVCs, ventricular tachycardia, variable AV blocks.
- Kawasaki Disease & Coronary Aneurysms:
- Subacute/Late Phase: Development of deep pathological $Q$ waves ($>4\text{ mm}$), ST elevation or T inversion indicating coronary artery aneurysm thrombosis and acute myocardial infarction.
3. Multimodality Diagnostic Investigations
- Cardiac Biomarkers: High-sensitivity Troponin-I and NT-proBNP (markedly elevated in active myocarditis and MIS-C).
- Echocardiography (TTE): Assesses global LV systolic function, regional wall motion abnormalities, pericardial effusion/tamponade, and Coronary Artery Z-scores (LAD and RCA dimensions in Kawasaki).
- Cardiac MRI (CMR): Lake Louise Criteria for myocarditis (T2-weighted myocardial edema + early/late gadolinium enhancement representing necrosis/fibrosis).
4. Evidence-Based Clinical Management Protocols
- Acute Pericarditis:
- First-line: High-dose NSAIDs (Ibuprofen $30-40\text{ mg/kg/day}$ or Indomethacin) + Colchicine ($0.5-1.0\text{ mg/day}$ adjusted for weight) to prevent recurrent pericarditis.
- Kawasaki Disease:
- Immediate Intravenous Immunoglobulin (IVIG) ($2\text{ g/kg}$ single infusion over $10-12\text{ hr}$) within the first $10$ days of fever plus High-Dose Aspirin ($30-50\text{ mg/kg/day}$ until afebrile $\to$ low-dose $3-5\text{ mg/kg/day}$ for $6-8$ weeks).
- Fulminant Myocarditis:
- Inotropic support (Milrinone, Epinephrine), mechanical circulatory support (Extracorporeal Membrane Oxygenation / ECMO), avoidance of cardiac glycosides.