What is cardiomyopathy?

Cardiomyopathy: Definition and Classification

Cardiomyopathy is 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

Types of Cardiomyopathy

The American Heart Association and American College of Cardiology classify cardiomyopathies into several main types:

1. Dilated Cardiomyopathy (DCM)

   • Characterized by dilated ventricle and global systolic dysfunction 1
   • Prevalence: 1:250 to 1:500 in adults 1
   • Approximately 50% of cases are idiopathic, more common in younger patients 1
   • Presents with symptoms of heart failure and systolic dysfunction

2. Hypertrophic Cardiomyopathy (HCM)

   • Characterized by massive ventricular hypertrophy without obvious cause 1
   • Prevalence: 1:250 to 1:500 1
   • Features impaired diastolic and systolic function 1
   • High risk for sudden cardiac death, especially in young athletes 1

3. Restrictive Cardiomyopathy (RCM)

   • Characterized by restriction to ventricular filling due to restrictive forces in the endomyocardium 2
   • Less common than DCM and HCM
   • Often associated with infiltrative diseases like amyloidosis

4. Arrhythmogenic Cardiomyopathy (ACM)

   • Prevalence: 1:2,000 to 1:5,000 in adults 1
   • Primarily caused by desmosomal protein mutations 1
   • Associated with high risk of arrhythmias and sudden cardiac death

5. Left Ventricular Non-Compaction Cardiomyopathy (LVNC)

   • Characterized by prominent trabeculations and deep intertrabecular recesses 1

Etiology

Cardiomyopathies can be primary (genetic, mixed, or acquired) or secondary (infiltrative, toxic, inflammatory) 3:

• Genetic causes: Account for approximately 50% of DCM cases 1

  • Mutations in MYBPC3 and MYH7 genes are most common in HCM 1
  • Desmosomal protein mutations in ACM 1

• Metabolic disorders: Anderson-Fabry disease, glycogen storage diseases, lysosomal storage diseases 1

• Inflammatory and infectious causes: Myocarditis, atrial fibrillation 1

  • Tachycardia-induced cardiomyopathy (TIC) can develop from prolonged tachycardia, leading to dilatation and systolic dysfunction 4

• Toxic and medication-related causes: Hydroxychloroquine, steroids, alcohol 1

• Other causes: Pheochromocytoma, acromegaly, diabetes, muscular dystrophies 1

Clinical Presentation

Although cardiomyopathy may be asymptomatic in early stages, common symptoms include:

• Shortness of breath
• Fatigue
• Cough
• Orthopnea
• Paroxysmal nocturnal dyspnea
• Edema 3

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in patients with cardiomyopathies, with varying prevalence among different subtypes. The presence of AF indicates increased risk for thromboembolism, heart failure, and cardiovascular morbidity and mortality 5.

Diagnosis

Diagnostic approach includes:

• Clinical evaluation and family history
• Electrocardiography (ECG)
• Echocardiography
• Cardiac MRI (particularly useful for tissue characterization in non-ischemic cardiomyopathies) 1
• Genetic testing (recommended for both primary and secondary cardiomyopathies) 1
• Endomyocardial biopsy in selected cases

Treatment

Treatment aims to:

• Reduce symptoms
• Prevent complications
• Improve quality of life 1

Treatment options include:

• Medications: Based on cardiomyopathy subtype and symptoms
• Implantable devices: Cardioverter-defibrillators for high-risk patients
• Cardiac resynchronization therapy: For eligible patients with heart failure
• Heart transplantation: For end-stage disease 1

Important Lifestyle Modifications

• Limiting alcohol consumption
• Maintaining healthy weight
• Regular appropriate exercise
• Smoking cessation
• Following a low-sodium diet
• Managing stress
• Regular medical follow-up 1

Prognosis and Complications

The overall prevalence of cardiomyopathy is approximately 0.02% in the general population, with an annual death rate of 25,000 in the United States 1. Complications include:

• Heart failure
• Arrhythmias (particularly AF)
• Thromboembolism
• Sudden cardiac death (particularly in HCM, which is the most common cause of sudden cardiac arrest in young athletes) 1

The prognosis varies significantly based on the type of cardiomyopathy, genetic factors, and response to treatment.