Pathology of cardiomyopathy

While I am preparing for my master degree exam - 1st part, I noticed the topic of cardiomyopathy is much frequently encountered in pathology exams. I also noticed that our Egyptian pathology books are very deficient when dealing with this important topic. So, I decided to write it myself collecting data from different Pathology texts. It was "Robin's basic pathology, 8th ed" which I found most informative and well-organized and most of data here are derived from it.

Cardiomyopathy

Definition

Group of diseases that primarily involve the myocardium and produce myocardial dysfunction (or intrinsic disease of the cardiac muscle)

Types of cardiomyopathy

1. Dilated (congestive)

2. Hypertrophic

3. Restrictive

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Dilated cardiomyopathy

1. Epidemiology
1. Incidence: Most common cardiomyopathy (90% of cases)

The incidence of this disorder in Europe and North America is 2-8 cases per 100 000 per year. The median age at presentation is about 50 years but young adults may be affected.

2. Etiology:
1. Idiopathic (most common)
2. Genetic causes (25-35%)
3. Myocarditis (usually postviral myocarditis with coxsackievirus B)
4. Toxic: e.g., doxorubicin(adriamycin), cocaine and cobalt.
5. Postpartum state
6. Alcoholism:can cause thiamine deficiency in addition to the acetaldehyde (alcohol metabolite) which is toxic to the myocardium.
1. Pathophysiology
1. Decreased contractility with a decreased EF (<40%)>
2. Systolic dysfunction type of left ventricular failure
   
2. Gross picture:
1. Global enlargement of the heart (the heart is 2-3 times the normal size and flobby)
1. All chambers are dilated.
2. Echocardiography shows poor contractility and mural thrombi may be present.
3. No significant 1ry valvular disease (except for functional regurgitation 2ry to ventricular chamber enlargement)
4. No significant affection of the coronary arteries.
3. Microscopic picture:

The histologic abnormalities in DCM are nonspecific. Microscopically most myocytes are hypertrophied with enlarged nuclei, but many are attenuated, stretched, and irregular. There is variable interstitial and endocardial fibrosis; scattered scars are also often present, probably marking previous myocyte ischemic necrosis caused by reduced perfusion (due to poor contractile function) and increased demand (due to myocyte hypertrophy). The extent of the changes frequently does not reflect the degree of dysfunction or the patient's prognosis.

5. Complications:
1. Biventricular CHF
2. Bundle branch blocks
3. Atrial and ventricular arrhythmias
4. Mural thrombi and systemic embolisation
6. Prognosis: poor and only 50-60% of patients survive 2 years after presentation.

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Hypertrophic cardiomyopathy

1. Epidemiology
1. Most common cause of sudden death in young individuals
2. Familial form (autosomal dominant) in young individuals (majority of cases)
• Due to mutations in heavy chain of β-myosin and in the troponins
3. Sporadic form in elderly people
2. Pathophysiology
1. Hypertrophy of the myocardium
• Disproportionately greater thickening of the interventricular septum than of the free left ventricular wall
2. Obstruction of blood flow is below the aortic valve
• Anterior leaflet of the mitral valve is drawn against the asymmetrically hypertrophied septum as blood exits the left ventricle.
3. Aberrant myofibers and conduction system in the interventricular septum
• Conduction disturbances are responsible for sudden death.
4. Decreased diastolic filling: Muscle thickening restricts filling.
3. Gross picture:

- massive myocardial hypertrophy without ventricular dilation

- disproportionate thickening of the ventricular septum relative to the left ventricle free wall

- On longitudinal sectioning, the ventricular cavity loses its usual round-to-ovoid shape and is compressed into a "banana-like" configuration

- an endocardial plaque in the left ventricular outflow tract is often present with thickening of the anterior mitral leaflet. This is correlated to contact between the anterior mitral valve leaflet and the septum during late systole (dynamic obstruction)

4. Microscopic picture:

- severe myocyte hypertrophy

- myocyte (and myofiber) disarray

- interstitial and replacement fibrosis

5. Complications and Prognosis:
1. Heart failure: due to impaired diastolic filling and dynamic outflow tract obstruction (in 25% of cases).
2. Arrythmias: atrial and ventricular arrhythmias and heart block.
3. Infective endocarditis of the mitral valve.
4. Sudden cardiac death: the most common cause of SCD in young adults.

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Restrictive cardiomyopathy

1. Etiology
1. Tropical endomyocardial fibrosis: the most common cause worldwide
2. Infiltrative diseases
• Examples-Pompe's glycogenosis, amyloidosis, hemochromatosis
3. Endocardial fibroelastosis in a child (thick fibroelastic tissue in the endocardium), sarcoidosis
2. Pathophysiology

a. Decreased ventricular compliance

b. Usually secondary to infiltrative disease of the myocardium

c. Diastolic dysfunction type of LHF

3. Gross picture:

- The ventricles are of approximately normal size or slightly enlarged, the cavities are not dilated, and the myocardium is firm.

- Biatrial dilation is commonly observed.

4. Microscopic picture:

- interstitial fibrosis, varying from minimal and patchy to extensive and diffuse

- disease-specific features can be seen on endomyocardial biopsy (e.g., amyloid, iron overload, sarcoid granulomas).

5. Prognosis and complications: CHF and Arrhythmias (conduction defects)