What are the principal types of cardiomyopathy?

Types of Cardiomyopathy

The principal types of cardiomyopathy are five distinct morphological and functional phenotypes: dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy (RCM), arrhythmogenic right ventricular cardiomyopathy (ARVC), and unclassified cardiomyopathies (including left ventricular noncompaction). 1

The Five Primary Phenotypes

1. Dilated Cardiomyopathy (DCM)

• Characterized by ventricular dilation and depressed myocardial performance
• Occurs in the absence of hypertension, valvular disease, congenital heart disease, or ischemic heart disease
• Enlarged, dilated left and/or right ventricle with or without decreased systolic function 2
• Prevalence approximately 1:250 to 1:500 in adults 3

2. Hypertrophic Cardiomyopathy (HCM)

• Abnormally thickened ventricular myocardium without identifiable cause (excluding hypertension, coarctation, aortic stenosis)
• Most common primary cardiomyopathy with prevalence of 1:250 to 1:500 3
• Reported as the most common cause of sudden cardiac arrest and sudden cardiac death in young athletes 2

3. Restrictive Cardiomyopathy (RCM)

• Normal to thickened ventricular walls with normal ventricular size
• Impaired diastolic function with often dilated atria 2
• Much less common than DCM or HCM 4

4. Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

• Enlarged, dilated right ventricle with or without decreased systolic function
• Associated with frequent arrhythmias
• Can also affect the left ventricle 2
• Prevalence approximately 1:2,000 to 1:5,000 3

5. Unclassified Cardiomyopathies

• Includes left ventricular noncompaction (LVNC)
• Left ventricular myocardium shows abnormal hypertrabeculation and crypts 2

Classification Framework Evolution

The classification has evolved significantly over time. The European Society of Cardiology (ESC) Working Group uses a clinically oriented classification grouping heart muscle disorders into specific morphological and functional phenotypes, with each subclassified into familial and nonfamilial forms 1.

Primary vs. Secondary Cardiomyopathies

Primary cardiomyopathies are genetic, nongenetic, or acquired forms solely or predominantly confined to heart muscle 1.

Secondary cardiomyopathies involve myocardial involvement as part of systemic (multiorgan) disorders including:

• Amyloidosis
• Hemochromatosis
• Sarcoidosis
• Autoimmune/collagen vascular diseases
• Toxins and cancer therapy
• Endocrine disorders (diabetes mellitus) 1

Clinical Pitfalls

Common diagnostic error: The term "nonischemic cardiomyopathy" is often used interchangeably with DCM, but this fails to recognize that nonischemic cardiomyopathy can include cardiomyopathies caused by volume or pressure overload (hypertension, valvular disease) that are not conventionally accepted under the DCM definition 1.

Important distinction: Inflammatory and viral cardiomyopathies were added as distinct entities by the WHO/International Society and Federation of Cardiology classification in 1996, recognizing these as separate from the five primary morphological types 1.

Modern Diagnostic Approach

The MOGE(S) nosology system provides comprehensive classification incorporating:

• Morphofunctional phenotype
• Organ(s) involvement
• Genetic inheritance pattern
• Etiologic annotation (genetic defect or underlying disease)
• Status (functional status using ACC/AHA HF stages and NYHA class)

This system is endorsed by the World Heart Federation and assists in describing cardiomyopathy in both symptomatic and asymptomatic patients and family members in the context of genetic testing 1.