Idiopathic DCM: No known etiology, classified as idiopathic dilated cardiomyopathy.
Clinical Features of DCM
Typically affects individuals aged 20-50 years.
Symptoms: Progressively worsening congestive heart failure (CHF), secondary mitral regurgitation, rhythm disturbances, potential for death due to progressive cardiac failure, arrhythmias, or embolism.
Enlarged and heavy (2-3 times normal weight, typical = 280-350g with gender differences).
Appearance: Dilated and flabby, often globular.
Four-chamber dilation, particularly in the left ventricle.
Left ventricular wall:
Thickened, with a minimum wall thickness of ≥ 15 mm, and a septal/posterior wall thickness ratio > 1.3 in normotensive patients.
Mural thrombi which may be embolic sources.
Associated mitral regurgitation due to left ventricular dilatation.
Histopathology of DCM
Pathological features:
Abnormalities are generally non-specific.
Myocyte hypertrophy with possible atrophy.
Enlarged nuclei (variation in size and shape, some attenuated, stretched, irregular).
Myofibrillary loss.
Interstitial and endocardial fibrosis observed.
Small subendocardial scars detectable.
Hypertrophic Cardiomyopathy (HCM)
Characteristics:
Disorder characterized by myocardial hypertrophy.
Causes rigid and poorly compliant left ventricular myocardium leading to abnormal diastolic filling.
In one-third of patients, intermittent ventricular outflow obstruction occurs.
Pathogenesis of HCM
Genetic factors:
Condition is typically autosomal dominant with variable penetrance.
Mutations are identified in genes encoding sarcomeric proteins:
Over 400 different mutations found in nine distinct genes.
Major genes affected: β-myosin heavy chain (β-MHC), cardiac TnT, α-tropomyosin, myosin-binding protein C (MYBP-C).
Clinical Features of HCM
Consequences of reduced stroke volume:
Impaired diastolic filling due to reduced chamber size and decreased compliance of the hypertrophied left ventricle.
Obstruction of left ventricular outflow can lead to increased pulmonary venous pressure, leading to exertional dyspnea.
Additional symptoms include:
Angina, atrial fibrillation, mural thrombus formation resulting in possible embolisms, cardiac failure, ventricular arrhythmias, and sudden death.
Often presents with a harsh systolic ejection murmur due to left ventricular outflow obstruction.
Mitral leaflet dynamics during systole result in movement toward the ventricular septum.
Major clinical risks involve thrombus formation leading to embolic strokes, intractable cardiac failure, and fatal arrhythmias.
Notably high incidence of sudden death in young athletes due to HCM.
Gross Pathology of HCM
Features:
Left ventricular hypertrophy without ventricular dilatation.
Asymmetric septal hypertrophy leading to disproportionate thickening of the ventricular septum (ratio of septum to free wall > 3:1).
Characteristic “banana-like” configuration of the left ventricular cavity upon longitudinal sectioning.
Fibrous endocardial plaques can develop along with anterior mitral leaflet thickening resulting from direct contact during systole.
Histopathology of HCM
Pathological features:
Extensive myocyte hypertrophy.
Myofiber disarray observed: myocytes form disorganized crisscross bundles rather than organized, parallel structures.
Increased presence of interstitial cells.
Presence of abnormal small intramural coronary arteries may be detected.
Restrictive Cardiomyopathy (RCM)
Characteristics:
Primarily results in decreased ventricular compliance, impairing filling during diastole; however, contractile function (systolic) is generally preserved.
Types of RCM:
Idiopathic or associated with distinct diseases that affect myocardium.
Examples of associated conditions:
Radiation-induced fibrosis
Amyloidosis
Sarcoidosis
Metastatic tumors
Inborn errors of metabolism.
Clinical Features of RCM
Presentation: Clinical features can depend on the underlying cause.
Possible confusion with constrictive pericarditis or hypertrophic cardiomyopathy since contractility remains relatively intact.
Gross Pathology of RCM
Key Features:
Normal or enlarged ventricles.
No dilation of ventricular cavities with a firm and noncompliant myocardium.
Possible biatrial dilation evident.
Histopathology of RCM
Abnormalities include:
Non-specific findings
Myocyte hypertrophy
Patchy or diffuse interstitial fibrosis
Myofiber disarray.
Amyloidosis
A significant cause of secondary restrictive cardiomyopathy.
Defined by the infiltration of the myocardium with amyloid.
Staining for Amyloidosis
Lugol's iodine:
Imparts a mahogany brown color to amyloid deposits.
Important for identifying sections of myocardium infiltrated with amyloid fibers.
Features of cardiac amyloidosis include ventricular hypertrophy.
Amyloid appears as an extracellular pink-hyaline amorphous deposit consisting of fibrillar material.
References
Robbins & Cotran. Pathological Basis of Disease. 9th ed. Vinay Kumar, Abul K. Abbas, Jon C. Aster.