What is Dilated Cardiomyopathy (DCM)

What is Dilated Cardiomyopathy (DCM)?

Dilated cardiomyopathy (DCM) is a heart muscle disease characterized by left ventricular or biventricular chamber enlargement and reduced systolic function (ejection fraction typically <50%) that occurs in the absence of hypertension, significant coronary artery disease, valvular disease, or congenital heart disease sufficient to explain the cardiac dysfunction. 1, 2

Core Diagnostic Features

DCM requires three essential components to be present simultaneously 2:

• Ventricular dilatation: Left ventricular or biventricular chamber enlargement beyond normal reference values 2
• Systolic dysfunction: Reduced left ventricular ejection fraction, typically below 50% 2
• Exclusion of secondary causes: Absence of abnormal loading conditions (hypertension, valvular disease) or coronary artery disease sufficient to cause the observed global systolic impairment 1, 2

Pathophysiology

The disease involves specific structural and functional abnormalities 2:

• Progressive ventricular remodeling with chamber dilation and increased diastolic and systolic wall stress 2
• Myocyte hypertrophy with increased cell length, creating an eccentric hypertrophy pattern 2
• Impaired myocardial contractility leading to heart failure symptoms 1

Etiology

DCM represents a heterogeneous spectrum of myocardial disorders with multiple causes 1:

Genetic/Familial causes (30-50% of cases) 2, 3:

• Identifiable genetic mutations in cytoskeletal, sarcomeric, sarcolemmal, and nuclear envelope proteins account for 30-40% of DCM 2
• Familial DCM may account for 20-48% of all DCM cases 3

Acquired causes 2, 4:

• Myocarditis (viral or inflammatory) 1, 2
• Toxins (alcohol, chemotherapy agents) 2, 4
• Endocrinopathies 2, 4
• Pregnancy (peripartum cardiomyopathy) 2, 5
• Tachyarrhythmias 2, 4
• Autoimmune/collagen vascular diseases 1, 2
• Nutritional deficiencies 2

Important caveat: 5-15% of patients with acquired DCM harbor a likely pathogenic gene variant, so both genetic and acquired factors should always be considered in the diagnostic workup 4.

Epidemiology and Clinical Significance

• Prevalence: 1 in 250 to 1 in 400 individuals in the general population 2
• Incidence: Approximately 7 per 100,000 per year (though likely underdiagnosed) 3
• DCM is a major cause of heart failure with reduced ejection fraction and the leading indication for heart transplantation worldwide 2
• Mortality remains approximately 40% at 10 years despite modern therapy 6

Clinical Terminology Clarification

In clinical practice, the term "nonischemic cardiomyopathy" is often used interchangeably with DCM, though this is imprecise 1. This terminology fails to recognize that nonischemic cardiomyopathy can include conditions caused by volume or pressure overload (such as hypertension or valvular disease) that are not conventionally accepted under the strict definition of DCM 1. The term "ischemic cardiomyopathy" specifically refers to ventricular dilation and depressed myocardial contractility caused by ischemia or infarction 1.

Prognosis and Complications

Patients with DCM face multiple risks 3:

• Progressive heart failure with symptoms including dyspnea, orthopnea, paroxysmal nocturnal dyspnea, fatigue, and edema 7
• Ventricular and atrial arrhythmias 3, 5
• Sudden cardiac death 7, 3
• Thromboembolic events 3
• Need for advanced therapies including cardiac resynchronization therapy, implantable cardioverter-defibrillators, left ventricular assist devices, or heart transplantation 7, 3