What is cardiomyopathy?

Definition of Cardiomyopathy

Cardiomyopathy refers to a spectrum of heterogeneous myocardial disorders characterized by structural and functional abnormalities of the heart muscle that lead to mechanical or electrical dysfunction in the absence of coronary artery disease, hypertension, valvular disease, or congenital heart disease as the primary cause. 1

Classification of Cardiomyopathies

Cardiomyopathies are classified into five major morphological and functional phenotypes:

1. Dilated Cardiomyopathy (DCM):

   • Characterized by ventricular dilation and depressed myocardial performance
   • Most common type and leading cause for cardiac transplantation 2
   • Typically presents with heart failure symptoms due to systolic dysfunction

2. Hypertrophic Cardiomyopathy (HCM):

   • Abnormally thickened ventricular myocardium without an identifiable cause
   • Most common cause of sudden cardiac arrest and death in young athletes 1
   • Often associated with left ventricular outflow tract obstruction

3. Restrictive Cardiomyopathy (RCM):

   • Normal to thickened ventricular walls with normal ventricular size
   • Impaired diastolic function with often dilated atria 1
   • Characterized by restrictive filling and reduced diastolic volume

4. Arrhythmogenic Cardiomyopathy (ACM):

   • Includes arrhythmogenic right ventricular cardiomyopathy (ARVC)
   • Enlarged, dilated right ventricle (can also affect left ventricle)
   • Often associated with frequent arrhythmias 1

5. Left Ventricular Non-Compaction Cardiomyopathy (LVNC):

   • Characterized by hypertrabeculation and deep recesses in the left ventricle
   • Considered an "unclassified cardiomyopathy" in some classification systems 1

Etiological Classification

Cardiomyopathies can also be classified based on etiology:

1. Primary Cardiomyopathies:

   • Genetic: Caused by inherited gene mutations affecting sarcomeric proteins, ion channels, or structural proteins 1
   • Non-genetic: Acquired forms without clear genetic basis
   • Mixed: Combination of genetic predisposition and environmental factors

2. Secondary Cardiomyopathies:

   • Infiltrative diseases (e.g., amyloidosis, hemochromatosis)
   • Inflammatory conditions (myocarditis)
   • Toxic (alcohol, chemotherapy)
   • Metabolic disorders
   • Neuromuscular diseases
   • Endocrine disorders 1

Epidemiology

• The prevalence of cardiomyopathy is approximately 0.02% in the general population 1
• Annual death rate of about 25,000 in the United States 1
• Specific prevalence rates:
  • Hypertrophic cardiomyopathy: 1:250 to 1:500
  • Dilated cardiomyopathy: 1:250 to 1:500
  • Arrhythmogenic right ventricular cardiomyopathy: 1:2,000 to 1:5,000 1

Clinical Manifestations

Cardiomyopathies can present with a range of symptoms:

• Heart failure (dyspnea, edema, fatigue)
• Arrhythmias and palpitations
• Syncope or presyncope
• Sudden cardiac death
• Chest discomfort
• Asymptomatic (detected incidentally) 1, 3

Genetic Considerations

• Over 100 genes have been associated with various cardiomyopathy subtypes 4
• Many cardiomyopathies show autosomal dominant inheritance pattern
• Genetic testing is recommended for both primary and secondary cardiomyopathies 1
• First-line genetic testing typically involves targeted gene panels specific to the cardiomyopathy subtype
• Cascade screening of family members is recommended when a pathogenic variant is identified 1

Diagnostic Approach

Diagnosis of cardiomyopathy typically involves:

• Clinical evaluation and family history
• Electrocardiography (ECG)
• Echocardiography (first-line imaging)
• Cardiac MRI (for tissue characterization)
• Genetic testing
• Endomyocardial biopsy (in selected cases) 1, 3

Management Considerations

Treatment strategies focus on:

• Relieving heart failure symptoms
• Reducing hospitalization rates
• Preventing sudden cardiac death
• Specific therapies based on cardiomyopathy subtype
• Device therapy (implantable cardioverter-defibrillators, cardiac resynchronization)
• Heart transplantation in advanced cases 3

Evolution of Cardiomyopathy Definition

The definition of cardiomyopathy has evolved over time:

• Originally defined as "heart muscle diseases of unknown cause"
• In 1995, the WHO/ISFC task force redefined cardiomyopathies as "diseases of the myocardium associated with cardiac dysfunction" 5, 2
• Modern classifications incorporate genetic, morphological, and functional characteristics 1, 4

The understanding of cardiomyopathies continues to evolve with advances in genetic testing and molecular biology, offering new insights into pathophysiology and potential therapeutic targets.