Dilated Cardiomyopathy Overview

Dilated Cardiomyopathy (DCM)

• Definition: DCM is a heart muscle disease characterized by enlarged, weakened heart chambers that struggle to pump blood effectively.
• Etiology:
  • Idiopathic (most common)
  • Familial/Genetic
  • Inflammatory:
    • Infectious (Viral): Coxsackievirus A & B, parvovirus B19, adenovirus, ECHO, HIV, CMV, influenza
    • Nonviral: Trypanasoma cruzi (Chagas Disease), Trichinella spiralis (Trichinosis), Toxoplasma gondii (Toxoplasmosis), Borrelia burgdorferi (Lyme Disease), Corynebacterium diphtheriae (Diptheria)
  • Noninfectious: Hypersensitivity myocarditis, Giant cell myocarditis
  • Toxic: Chronic alcohol ingestion, chronic cocaine use, chemotherapeutic agents
• Pathological Features:
  • Gross Appearance: Heavy, large, flabby heart with dilation of all chambers. May be limited to one side.
  • Microscopic Appearance:
    • Enlarged nuclei and irregular hypertrophy of myocytes
    • Attenuated, stretched, irregular, degenerated, and atrophic myocytes
    • Interstitial, endocardial, and perivascular fibrosis
• Pathophysiology:
  • ** Impaired myocyte contractility:** Decreases ventricle stroke volume (SV) and cardiac output (CO)
  • Compensatory mechanisms:
    • Frank-Starling Mechanism: Increased end-diastolic volume (EDV) leads to increased myofiber stretch, which increases contractile force and SV.
    • Neurohormonal Activation:
      • Decreased CO results in decreased renal perfusion, triggering the renin-angiotensin-aldosterone system (RAAS) activation.
      • Sympathetic stimulation increases heart rate and contractility, further increasing CO.
    • RAAS Activation:
      • Angiotensin II increases systemic vascular resistance (SVR), making it difficult for a weakened LV to pump.
      • Aldosterone increases intravascular/EDV, leading to fluid backup and pulmonary/systemic congestion.
• Clinical Features:
  • Slow, progressive signs/symptoms of congestive heart failure (CHF):
    • Cool extremities, low arterial pressure, tachycardia
    • Pulmonary venous congestion leading to auscultatory crackles
    • Left and upward displacement of the point of maximal impulse (PMI)
    • Enlarged heart
    • Third heart sound (S3)
  • Complications: Mitral/Tricuspid regurgitation, atrial fibrillation, mural thrombus/thromboembolism
• Prognosis:
  • High mortality rate
  • Death typically occurs from progressive cardiac failure or arrhythmia

Hypertrophic Cardiomyopathy (HCM)

• A heart muscle disease characterized by thickening of the heart muscle, particularly in the left ventricle.

• Etiology: Primarily genetic, caused by mutations in genes responsible for cardiac proteins.

• Pathogenesis:

  • Increased wall stress: Due to increased myocardial oxygen demand.
  • Hypertrophy: Squeezes down on small coronary branches, impairing myocardial perfusion.
  • Outflow obstruction: The thickened heart muscle can obstruct blood flow from the left ventricle, leading to a reduction in CO.

• Pathological Features:

  • Gross Appearance: Enlarged heart, particularly the left ventricle
  • Microscopic Appearance: Hypertrophic myocytes with disorganized arrangement.

• Pathophysiology:

  • Aberrant myocytes: Within the conduction system, leading to abnormal conduction and arrhythmias.

• Clinical Features:

  • Symptoms:
    • Chest pain
    • Dyspnea
    • Syncope
    • Arrhythmias
  • Physical exam findings:
    • Hyperdynamic precordium
    • A fourth heart sound (S4)

• Treatment:

  • Medical: Beta-blockers, calcium channel blockers, antiarrhythmics
  • Surgical: Septal myectomy, alcohol septal ablation
  • Devices: Implantable cardioverter-defibrillator (ICD)

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

• A rare heart muscle disease characterized by the replacement of heart muscle with fat and fibrous tissue.
• Etiology: Primarily genetic, associated with mutations in genes involved in desmosome formation.
• Pathogenesis:
  • Genetic: Leads to abnormalities in the cell-to-cell connections of heart muscle cells, making them more prone to damage and death.
  • Replacement of muscle with fat and fibrosis: This disrupts the normal electrical activity of the heart, leading to arrhythmias.
• Clinical Features:
  • Symptoms: Arrhythmias, palpitations, syncope, sudden cardiac death
  • Physical exam findings: May have a heart murmur.

Comparison of Dilated and Hypertrophic Cardiomyopathy

Hypertrophic Cardiomyopathy

• 19-year-old college student with a family history of sudden death, collapses suddenly during basketball
• EKG shows ventricular tachycardia and ventricular fibrillation
• Patient resuscitated and hospitalized, but dies suddenly 3 years later
• Echocardiogram reveals thickened left ventricular wall and small chamber
• Interventricular septum markedly thickened
• Most likely mutation in a sarcomeric protein, causing hypertrophic cardiomyopathy

Hypertrophic Cardiomyopathy Pathophysiology

• Genetic condition, often inherited
• Mutation in sarcomeric proteins leads to impaired energy transfer from mitochondria to the sarcomere
• Results in excessive hypertrophy of the left ventricle muscle
• Thickened ventricular septum can obstruct blood flow out of the left ventricle.
• Impaired muscle function and blood flow can lead to arrhythmias like ventricular tachycardia and fibrillation.
• Sudden death is a major risk due to cardiac arrhythmias.