Cardiomyopathies

Introduction and Classification

• Cardiomyopathies are defined as a heterogeneous group of diseases of the myocardium associated with mechanical and/or electrical dysfunction that usually exhibit inappropriate ventricular hypertrophy or dilation and are due to a variety of causes that frequently are genetic.
• These conditions are either confined to the heart or are part of generalized systemic disorders, often leading to cardiovascular death or progressive heart failure-related disability.
• The American Heart Association (AHA) classifies cardiomyopathies as primary (predominantly involving the heart, such as genetic or idiopathic forms) or secondary (associated with systemic disease).
• The contemporary clinical standard utilizes the MOGE(S) classification system, which comprehensively characterizes the disease by integrating Morphofunctional phenotype (M), Organ involvement (O), Genetic inheritance pattern (G), Etiological annotation (E), and the functional Status (S) using the AHA stage and New York Heart Association (NYHA) functional class.
• Pediatric cardiomyopathies are broadly categorized into five major morphofunctional phenotypes: Dilated Cardiomyopathy (DCM), Hypertrophic Cardiomyopathy (HCM), Restrictive Cardiomyopathy (RCM), Left Ventricular Noncompaction (LVNC), and Arrhythmogenic Cardiomyopathy (ACM/ARVC).

Dilated Cardiomyopathy (DCM)

• Dilated cardiomyopathy is the most common form of pediatric cardiomyopathy, accounting for over 50% of cases, with an annual incidence of 0.57 cases per 100,000 children.
• It is morphologically characterized by dilation of the left ventricle (LV) or both ventricles, accompanied by minimal or no wall thickening, resulting in significantly impaired systolic contractility.

Etiopathogenesis and Genetics

• The etiology in children is highly diverse, though the majority of cases are considered idiopathic or secondary to viral myocarditis.
• Genetic forms account for a significant percentage and typically display autosomal dominant inheritance, though autosomal recessive, X-linked, and mitochondrial patterns exist.
• Pathogenic variants primarily affect the sarcomere (force generation), the cytoskeleton (force transmission), gene expression, protein processing, and calcium cycling.
• Common genetic mutations include TTN (titin, accounting for up to 25% of familial DCM), MYH7 (beta-myosin heavy chain), TNNT2 (cardiac troponin T), LMNA (lamin A/C, highly associated with conduction disease), and RBM20 (an RNA-binding protein associated with aggressive DCM and arrhythmias).
• X-linked variants include DMD (dystrophin), seen in Duchenne and Becker muscular dystrophies, and TAZ (tafazzin), seen in Barth syndrome.

Clinical Manifestations

• Infants typically present with severe congestive heart failure, manifesting as tachypnea, poor feeding, diaphoresis with feeds, failure to thrive, and irritability.
• Older children may present with exertional dyspnea, fatigue, orthopnea, or syncope.
• Patients are at a significantly elevated risk for severe arrhythmias (both atrial and ventricular) and systemic thromboembolism secondary to blood stasis in the dilated chambers.

Diagnostic Investigations

• Auscultation: Examination typically reveals resting tachycardia, a soft first heart sound (S1), and a prominent protodiastolic third heart sound (S3) gallop. A holosystolic murmur of functional mitral regurgitation is frequently audible at the apex due to annular dilation.
• Electrocardiogram (ECG): Findings include sinus tachycardia, left atrial enlargement, left ventricular hypertrophy (often voltage criteria without strain), and non-specific ST-segment and T-wave abnormalities. Intraventricular conduction delays or high-grade atrioventricular block may be present, particularly pointing toward LMNA or DES mutations.
• Chest Radiograph (CXR): Demonstrates marked cardiomegaly resulting from severe left ventricular and left atrial dilation, accompanied by signs of pulmonary venous congestion or frank pulmonary edema.
• Echocardiography: The definitive diagnostic modality. It reveals a significantly enlarged, spherical (remodeled) left ventricular cavity with normal or thinned myocardial walls. Systolic function is profoundly depressed, indicated by a markedly reduced ejection fraction (EF) and fractional shortening. Color Doppler often shows secondary mitral and tricuspid valve regurgitation.
• Cardiac Magnetic Resonance (CMR): Utilized to evaluate for myocardial inflammation (edema/hyperemia) and fibrosis. Late gadolinium enhancement (LGE), particularly mid-wall or subepicardial enhancement, indicates replacement fibrosis and carries a worse prognosis.
• Cardiac Catheterization: Primarily utilized in advanced cases to determine candidacy for heart transplantation. Hemodynamics reveal elevated left ventricular end-diastolic pressure (LVEDP), elevated pulmonary capillary wedge pressure (PCWP), and low cardiac output. Endomyocardial biopsy may be performed to rule out active myocarditis or infiltrative disease.

Management

• Medical therapy focuses on reducing cardiac work, augmenting contractility, and controlling volume overload.
• Angiotensin-converting enzyme (ACE) inhibitors (or Angiotensin Receptor Blockers) and loop diuretics are the first-line therapies for afterload reduction and volume management.
• Beta-blockers (e.g., Carvedilol) are initiated once the patient is hemodynamically stable to prevent pathological remodeling and decrease catecholamine-induced vasoconstriction.
• For acute, fulminant heart failure or cardiogenic shock, intravenous inotropes (milrinone, dobutamine) are indicated.
• Refractory cases require mechanical circulatory support via Extracorporeal Membrane Oxygenation (ECMO) or Ventricular Assist Devices (VAD) as a bridge to recovery or orthotopic heart transplantation.

Hypertrophic Cardiomyopathy (HCM)

• Hypertrophic cardiomyopathy is defined by increased ventricular wall thickness in the absence of a hemodynamic cause (such as aortic stenosis or systemic hypertension).
• It is the most common genetic cardiovascular disease and the leading cause of sudden cardiac death (SCD) in adolescent athletes in the United States.

Etiopathogenesis and Genetics

• Primary HCM is primarily caused by pathogenic "gain-of-function" mutations in genes encoding components of the cardiac sarcomere, demonstrating autosomal dominant inheritance with variable penetrance.
• The most commonly implicated genes are MYH7 (beta-myosin heavy chain) and MYBPC3 (myosin-binding protein C), which together account for 60-70% of genotype-positive cases. Other genes include TNNT2, TNNI3, and TPM1.
• Secondary forms of HCM (phenocopies) present in the context of systemic diseases, such as inborn errors of metabolism (Pompe disease, Danon disease), neuromuscular disorders (Friedreich ataxia), or malformation syndromes (Noonan syndrome and other RASopathies).
• Pathologically, the disease is characterized by massive myocyte hypertrophy, extensive myofibrillar disarray, and interstitial fibrosis.
• Hemodynamically, it is characterized by profound diastolic dysfunction (impaired relaxation) due to the thick, non-compliant ventricle. In about 25% of cases, dynamic left ventricular outflow tract (LVOT) obstruction develops, exacerbated by systolic anterior motion (SAM) of the anterior mitral valve leaflet.

Clinical Manifestations

• The clinical spectrum ranges from asymptomatic (discovered on screening) to exertional dyspnea, fatigue, atypical chest pain (angina), and palpitations.
• Syncope or near-syncope, particularly occurring during or immediately after physical exertion, is a highly ominous symptom reflecting exercise-induced dynamic LVOT obstruction or life-threatening ventricular arrhythmias.
• Sudden cardiac arrest may be the primary and only presentation.

Diagnostic Investigations

• Auscultation: The arterial pulse has a sharp upstroke with a classic bisferiens (double-peaked) character. A harsh, crescendo-decrescendo ejection systolic murmur is audible at the left sternal border. The hallmark of this murmur is its dynamic nature: interventions that decrease LV volume (standing, Valsalva maneuver) increase the intensity of the murmur, while maneuvers that increase venous return (squatting, passive leg raise) decrease the murmur. An S4 gallop is frequently present due to atrial contraction against a stiff ventricle.
• Electrocardiogram (ECG): Demonstrates severe left ventricular hypertrophy. Deep, narrow Q waves in the lateral and inferior leads (pseudoinfarction pattern) are common. Severe repolarization abnormalities, including marked ST-segment depression and deep T-wave inversions, are classic. In Pompe disease, the ECG pathognomonically shows a very short PR interval accompanied by massive QRS voltages. WPW patterns with short PR and delta waves are seen in Danon disease and PRKAG2 deficiency.
• Echocardiography: Reveals asymmetric septal hypertrophy (or concentric hypertrophy), dynamic LVOT narrowing, and characteristic Systolic Anterior Motion (SAM) of the mitral valve. Continuous-wave Doppler quantifies the dynamic LVOT gradient.
• Cardiac Magnetic Resonance (CMR): Provides precise anatomical delineation and is essential for identifying myocardial crypts, apical aneurysms, and quantifying fibrosis. The presence and extensive distribution of Late Gadolinium Enhancement (LGE) serves as an independent marker for sudden cardiac death risk and arrhythmogenicity.

Management

• Patients must be strictly restricted from competitive sports and strenuous physical activity to mitigate the risk of sudden cardiac death.
• Negative inotropic agents, specifically beta-adrenergic blockers (e.g., propranolol, nadolol) or non-dihydropyridine calcium channel blockers (e.g., verapamil), are the mainstays of medical therapy. They decrease heart rate, prolong diastolic filling, and decrease myocardial contractility, thereby reducing the dynamic LVOT gradient.
• Vasodilators, ACE inhibitors, and Digoxin are strictly contraindicated in obstructive HCM as they decrease afterload or increase contractility, acutely worsening the LVOT obstruction.
• Patients with a history of aborted sudden cardiac arrest, unexplained syncope, massive extreme hypertrophy, or extensive LGE on CMR meet Class I indications for Implantable Cardioverter-Defibrillator (ICD) placement.
• For patients with severe, medically refractory LVOT gradients, surgical septal myectomy or alcohol septal ablation is indicated.

Restrictive Cardiomyopathy (RCM)

• Restrictive cardiomyopathy is an extremely rare and rapidly lethal form of pediatric cardiomyopathy, accounting for approximately 2.5% to 5% of all cases.
• It is defined by normal or near-normal ventricular chamber dimensions and wall thickness, with profoundly impaired diastolic function resulting in restrictive ventricular filling and massive biatrial enlargement.

Etiopathogenesis and Genetics

• In children, most cases of RCM are primary/idiopathic or genetic. Mutations in sarcomeric genes strongly overlap with HCM and DCM, notably including TNNI3, TNNT2, MYH7, and ACTC1. Non-sarcomeric mutations include DES (desmin) and BAG3.
• Secondary (infiltrative) causes are exceptionally rare in children but include amyloidosis, hemochromatosis, and endomyocardial fibrosis (EMF).
• Pathophysiologically, the extremely stiff ventricular walls resist passive diastolic filling. This rapidly leads to a massive, retrograde increase in atrial pressures, severe biatrial dilation, and subsequent reactive pulmonary arterial hypertension.

Clinical Manifestations

• Patients usually present with signs of advanced right and left-sided heart failure. Symptoms include severe fatigue, exertional dyspnea, orthopnea, ascites, and marked pedal edema.
• Syncope or near-syncope with exertion is common due to the inability to increase cardiac output.
• The massive dilation of the atria predisposes patients to highly symptomatic atrial fibrillation and catastrophic systemic thromboembolic events.

Diagnostic Investigations

• Auscultation: A prominent gallop rhythm (S3 or S4) is characteristically present. If severe pulmonary hypertension has developed, a loud, palpable pulmonary component of the second heart sound (P2) and an active right ventricular heave are evident.
• Electrocardiogram (ECG): Uniquely demonstrates massive biatrial enlargement. The QRS voltage is typically normal or low (unlike HCM). Arrhythmias, including atrial fibrillation, atrial flutter, and varying degrees of atrioventricular block, are frequently noted.
• Chest Radiograph (CXR): Heart size may appear normal or massively enlarged; massive cardiomegaly on CXR in RCM is driven entirely by extreme biatrial enlargement rather than ventricular dilation. Pulmonary venous congestion is prominent.
• Echocardiography: Demonstrates normal or slightly reduced left and right ventricular volumes, normal myocardial wall thickness, and preserved systolic ejection fraction. The diagnostic hallmark is massive enlargement of both the left and right atria. Doppler echocardiography reveals a classic "restrictive" transmitral filling pattern characterized by a tall, narrow E-wave, a diminutive A-wave, and an abnormally high E/A ratio.
• Cardiac Catheterization: Mandatory to differentiate RCM from constrictive pericarditis and to assess pulmonary vascular resistance. In RCM, the Left Ventricular End-Diastolic Pressure (LVEDP) exceeds the Right Ventricular End-Diastolic Pressure (RVEDP) by >4 mmHg, and the Right Ventricular Systolic Pressure (RVSP) is severely elevated (>50 mmHg).

Management

• Medical therapy for RCM is palliative and generally highly ineffective. Judicious use of loop diuretics is utilized to manage pulmonary and systemic venous congestion, but over-diuresis will precipitously drop ventricular preload and cause catastrophic cardiovascular collapse.
• Rigorous systemic anticoagulation (e.g., Warfarin) is strictly indicated to prevent intra-atrial thrombus formation and stroke.
• Antiarrhythmic therapy and pacemaker placement may be required for conduction disease.
• Because of the rapidly progressive nature of the disease, the high risk of sudden death, and the irreversible progression to pulmonary vascular disease, early evaluation and listing for orthotopic heart transplantation is the only definitive therapy.

Left Ventricular Noncompaction (LVNC)

• Left ventricular noncompaction is characterized by an arrest of normal embryological myocardial compaction, resulting in a distinctly hypertrabeculated, spongy-appearing left ventricle with deep intertrabecular recesses communicating with the ventricular cavity.

Etiopathogenesis and Genetics

• LVNC can be isolated or occur in conjunction with structural congenital heart disease, DCM, or HCM phenotypes.
• Genetic etiologies are diverse. In the pediatric population, X-linked and syndromic associations are frequent, heavily implicating the TAZ gene (Barth syndrome, characterized by neutropenia, growth delay, and 3-methylglutaconic aciduria). Other implicated genes include sarcomeric mutations (MYH7, MYBPC3) and mitochondrial DNA abnormalities.

Clinical Manifestations

• The clinical presentation is characterized by a classic triad: (1) congestive heart failure due to depressed systolic or diastolic function, (2) ventricular and atrial tachyarrhythmias (including WPW), and (3) systemic thromboembolic events originating from thrombi formed within the deep, sluggish intertrabecular recesses.

Diagnostic Investigations

• Electrocardiogram (ECG): Nonspecific but frequently demonstrates ventricular hypertrophy, ST-T wave changes, and occasionally pre-excitation (WPW pattern) or heart block.
• Echocardiography: The primary diagnostic tool. Diagnosis relies on identifying a two-layered myocardium featuring a thickened, noncompacted (NC) endocardial layer and a thin, compacted (C) epicardial layer. The diagnostic criterion requires an NC/C ratio > 2 measured at end-systole in the parasternal short-axis view. Color Doppler demonstrates blood flow penetrating deeply into the intertrabecular recesses.
• Cardiac Magnetic Resonance (CMR): Provides superior anatomical definition of the trabeculae and apex, utilizing an NC/C ratio > 2.3 in end-diastole for diagnosis. LGE can identify underlying fibrosis.

Management

• Management is strictly targeted toward the specific clinical phenotype and complications.
• Standard heart failure regimens (ACE inhibitors, beta-blockers, diuretics) are utilized for patients exhibiting a dilated phenotype with systolic dysfunction.
• Routine prophylactic systemic anticoagulation is strongly recommended due to the exceptionally high risk of mural thrombus formation within the trabecular recesses.
• Aggressive screening and treatment with antiarrhythmic drugs or ICD implantation are required for those with a high burden of ventricular arrhythmias or syncope.

Arrhythmogenic Cardiomyopathy (ACM / ARVC)

• Arrhythmogenic Cardiomyopathy (historically Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy) is characterized by the progressive replacement of normal ventricular myocardium with fibrofatty tissue, predisposing patients to malignant ventricular arrhythmias and sudden cardiac death.

Etiopathogenesis and Genetics

• ACM is recognized as a disease of the cardiac desmosomes. It is primarily inherited in an autosomal dominant pattern with incomplete penetrance.
• The most frequently implicated genes encode desmosomal proteins, prominently including PKP2 (Plakophilin-2), DSP (Desmoplakin), DSG2 (Desmoglein-2), and JUP (Plakoglobin).
• Disruption of desmosomes causes mechanical detachment of myocytes under mechanical stress (especially right ventricular stress during exercise), leading to cell death, inflammation, and subsequent fibrofatty scar replacement that acts as a highly arrhythmogenic substrate.
• Naxos disease (recessive JUP mutation) and Carvajal syndrome (DSP mutation) are rare cardiocutaneous syndromes combining ACM with woolly hair and palmoplantar keratoderma.

Clinical Manifestations

• Patients are frequently asymptomatic until they present with life-threatening ventricular arrhythmias (ventricular tachycardia or fibrillation), often triggered by vigorous physical exertion or competitive sports.
• Progressive disease leads to right ventricular dilation and failure, progressing eventually to biventricular heart failure.

Diagnostic Investigations

• Electrocardiogram (ECG): Resting ECG reveals classic depolarization abnormalities, notably the Epsilon wave (a small positive deflection buried in the terminal QRS complex) in leads V1-V3. Repolarization abnormalities include inverted T waves in V1-V3 in patients beyond adolescence. Holter monitoring frequently captures non-sustained ventricular tachycardia exhibiting a Left Bundle Branch Block (LBBB) morphology with an inferior axis, localizing the origin to the Right Ventricular Outflow Tract (RVOT).
• Echocardiography: Demonstrates regional right ventricular akinesia, dyskinesia, or aneurysmal bulging, alongside global RV dilation and reduced fractional area change.
• Cardiac Magnetic Resonance (CMR): Highly sensitive for identifying structural and functional RV/LV abnormalities, regional wall motion defects, and confirming the presence of fibrofatty replacement and late gadolinium enhancement within the ventricular walls.
• Cardiac Catheterization: Endomyocardial biopsy can yield a definitive diagnosis if it demonstrates transmural fibrous replacement of myocardium with or without fatty tissue, but is limited by sampling error and the risk of RV perforation.

Management

• Complete restriction from competitive and high-intensity endurance sports is absolutely essential, as exertion accelerates desmosomal disruption, disease progression, and the likelihood of sudden cardiac death.
• Beta-blockers are the first-line therapy to reduce adrenergic tone, prevent exercise-induced arrhythmias, and reduce right ventricular wall stress.
• Implantable Cardioverter-Defibrillator (ICD) placement is the definitive therapy for the primary and secondary prevention of sudden cardiac death in high-risk individuals.
• Radiofrequency catheter ablation may be utilized for patients with frequent, drug-refractory ventricular tachycardia, but it is rarely curative due to the progressive nature of the fibrofatty infiltration.

Summary Comparison of Cardiomyopathies