17. Pediatric Cardiomyopathies
Pediatric cardiomyopathies encompass primary disorders of the myocardium leading to mechanical dysfunction and electrophysiological instability.
1. Classification & Electrocardiographic Features
| Cardiomyopathy Type | Primary Pathophysiology | 12-Lead Electrocardiographic Hallmarks |
|---|---|---|
| Dilated Cardiomyopathy (DCM) | Impaired systolic ejection $\to$ spherical ventricular dilation. | Left ventricular hypertrophy with strain, Left Atrial Enlargement, Left Bundle Branch Block, frequent multifocal PVCs. |
| Hypertrophic Cardiomyopathy (HCM) | Asymmetrical septal or apical myofibrillar hypertrophy. | Dagger-like, deep narrow septal Q waves in I, aVL, $V_5-V_6$; massive precordial QRS voltage; giant negative T waves; shortened PR interval. |
| Restrictive Cardiomyopathy (RCM) | Impaired diastolic ventricular filling with rigid walls. | Massive Biatrial Enlargement (Giant P waves) with relatively normal or paradoxically low QRS voltage; variable AV blocks. |
| Left Ventricular Non-Compaction (LVNC) | Arrest of myocardial compaction with prominent hypertrabeculation. | High precordial voltage, repolarization abnormalities, bundle branch blocks, WPW pre-excitation. |
| Arrhythmogenic RV Dysplasia (ARVD) | Fibrofatty replacement of the right ventricular myocardium. | Epsilon waves in $V_1-V_2$, localized precordial QRS prolongation ($V_1-V_3$), T-wave inversions beyond age 14. |
2. Multimodality Diagnostic Investigations
- Echocardiography (TTE): Measures left ventricular mass index Z-score, asymmetrical septal to posterior wall ratio ($>1.3-1.5$), non-compaction ratio (Non-compacted to compacted myocardium $>2.0$ in end-systole), and diastolic filling velocities ($E/A$ ratio, tissue Doppler $E/e'$).
- Cardiac Magnetic Resonance (CMR): Quantifies Late Gadolinium Enhancement (LGE) indicating myocardial fibrosis and arrhythmogenic risk.
- Genetic Panels: Comprehensive sarcomeric multigene testing ($MYH7, MYBPC3, TNNT2$).
3. Evidence-Based Clinical Management Protocols
- Pharmacotherapy for Obstructive HCM: Non-vasodilating Beta-Blockers (Propranolol, Atenolol) as first-line to reduce LVOT dynamic obstruction. Calcium channel blockers (Diltiazem) in older children without obstruction.
- Heart Failure Guideline-Directed Medical Therapy (GDMT) in DCM: ACE inhibitors / ARNI (Sacubitril/Valsartan), Beta-blockers (Carvedilol), Mineralocorticoid receptor antagonists (Spironolactone), and SGLT2 inhibitors (Dapagliflozin).
- Primary Sudden Death Prevention (ICD): Implantable Cardioverter-Defibrillator indicated for severe unexplained syncope, massive LV wall thickness ($Z\text{-score} \ge 6$ or $\ge 30\text{ mm}$), extensive LGE on CMR ($>15\%$ of LV mass), or family history of early sudden cardiac death.