Dilated Cardiomyopathy Definition
Dilated cardiomyopathy (DCM) is a heart muscle disease characterized by left ventricular or biventricular dilatation and systolic dysfunction in the absence of abnormal loading conditions (hypertension, valvular disease) or coronary artery disease sufficient to cause global systolic impairment. 1
Core Diagnostic Criteria
The definition requires three essential components to be present simultaneously:
- Ventricular dilatation: Left ventricular or biventricular chamber enlargement beyond normal reference values 1
- Systolic dysfunction: Reduced left ventricular ejection fraction, typically below 50% 1
- Exclusion of secondary causes: Absence of hypertension, significant valvular disease, congenital heart disease, or coronary artery disease sufficient to explain the ventricular changes 1
Evolving Diagnostic Concepts
The traditional definition has been recognized as overly restrictive, as left ventricular hypokinesis without dilation can represent the initial presentation of DCM 2. This has led to recognition of intermediate phenotypes within the DCM spectrum, including:
- Isolated left ventricular dilation without overt systolic dysfunction 1
- Hypokinetic non-dilated cardiomyopathy (left ventricular dysfunction without chamber enlargement) 1
- Early arrhythmogenic features without structural abnormalities 1
- Isolated myocardial scar on advanced imaging 1
Pathophysiological Features
DCM is characterized by specific structural and functional abnormalities:
- Ventricular remodeling: Progressive chamber dilation with increased diastolic and systolic wall stress 1
- Myocyte changes: Myocyte hypertrophy with increased cell length (eccentric hypertrophy pattern) 1
- Valvular consequences: Annular dilatation of mitral and tricuspid valves, apical displacement of papillary muscles, and secondary atrioventricular valve regurgitation 1
- Biventricular involvement: Both left and right ventricular enlargement with biatrial enlargement and elevated filling pressures 1
Etiological Classification
DCM encompasses heterogeneous causes that must be considered in the diagnostic workup:
- Genetic/familial: Accounts for 30-50% of cases, with 30-40% attributable to identifiable genetic mutations in cytoskeletal, sarcomeric, sarcolemmal, and nuclear envelope proteins 1, 3
- Acquired causes: Include myocarditis (especially viral), toxins (alcohol, chemotherapeutic agents like anthracyclines), endocrinopathies, pregnancy, tachyarrhythmias, autoimmune disorders, and nutritional deficiencies 1, 2
- Idiopathic: Up to 50% of patients have no identifiable cause despite comprehensive evaluation 4
A critical caveat: 5-15% of patients with acquired DCM harbor pathogenic gene variants, meaning genetic and acquired factors can coexist and both must be evaluated 2.
Epidemiology
- Prevalence: Ranges from 1:250 to 1:400 individuals in the general population, though earlier estimates suggested 1:2500 1
- Clinical significance: DCM is a major cause of heart failure with reduced ejection fraction and the leading indication for heart transplantation worldwide 1
- Prognosis: Mortality remains approximately 40% at 10 years despite modern therapy 4
Distinction from Related Terminology
The term "nonischemic cardiomyopathy" is often used interchangeably with DCM but is imprecise, as it can include cardiomyopathies from volume or pressure overload (hypertension, valvular disease) that do not meet DCM criteria 1. True DCM specifically excludes these secondary loading conditions by definition 1.