Cardiac Path Online
Pathology of Cardiomyopathy
Cardiomyopathies are diseases characterised by cardiac dysfunction in which the main abnormality lies in the myocardium.
It is expressed as diastolic and /or systolic ventricular dysfunction.
Such abnormalities may directly affect one or both ventricles in a diffuse or multifocal fashion and in many patients produce myocardial failure or arrhythmias.
Cardiomyopathies have been traditionally divided into two main categories:
(I) Primary - (idiopathic "heart muscle disease of unknown causes") and
(II) Secondary - ("heart muscle diseases of known cause" or associated with disorders of other systems).
- Dilated Cardiomyopathy : Familial ; Idiopathic.
- Hypertrophic cardiomyopathy : Obstructive ; Nonobstructive ; Familial ; Nonfamilial.
- Restrictive cardiopathy : Endomyocardial fibrosis ; Idiopathic.
II Secondary cardiomyopathy:
-Inflammatory ; Metabolic ; Toxic ; Infiltrative ; Physical agents ; Neuromuscular disorders ; Primary tumour of the myocardium ; Hematologic ; Immunologically mediated cardiomyopathy ; Miscellaneous.
Based on pathophysiology there are three major groups :
1.Dilated ; 2.Hypertrophic ; 3.Restrictive
A. Normal ;
B. Dilated type - Hypertrophy & dilation of left ventricle with normal left atrium. ;
C. Hypertrophic type - Thick left ventricle with small cavity but dilated left atrium. ;
D. Restrictive type -Normal left ventricle but dilated left atrium.
It is characterized by slow, progressive hypertrophy and dilation of four chambers and contractile (systolic) dysfunction.
Age: This may occur at any age (most common 20-60 years).
Clinical presentation: Ineffective ventricular systolic contraction causes congestive heart failure, followed by embolic complications.
Etiology: The cause is unknown. May be related to the effect of alcohol toxicity, pregnancy or genetic defect.
Heavy metal ingestion and some cytotoxic drugs give an identitical picture.
Idiopathic cases may be late sequela of viral infection.
Gross: The heart is enlarged & flabby.
Poor contractile function and stasis can lead to the formation of mural thrombi.
-An increase in total heart weight due to increase in left ventricular mass ;
-Increase in Left ventricular cavity dimension ;
-Normal or reduced Left ventricular wall thickness ;
-Left ventricular endocardial thickening and mural thrombi in atria or ventricles may or may not be present.
Microscopic features: The features include permutations of the following features:
1. Myocyte nuclear enlargement (polypoidy).
2. Reduction myocyte width (attenuation)
3. Loss of myofibrils in myocytes.
4. Diffuse interstitial fibrosis.
5. Increased numbers of interstitial lymphocytes.
It is also termed as idiopathic hypertrophic subaortic and hypertrophic obstructive cardiomyopathy.
The term hypertrophic cardiomyopathy is used clinically to denote thick walled left ventricle with a small cavity in which systolic contraction is early and discordinated, leading to outflow obstruction.
Diastolic relaxation is also impaired.
Clinical presentation: This lesion is usually detected in young healthy adults.
Most patients remain stationary and asymptomatic for years, but some progressively worsen with major complications.
Outflow obstruction is seldom a major problem.
1) Atrial fibrillation with mural thrombosis ;
2) Embolization ;
3) Infective endocarditis ;
4) Congestive heart failure.
Arrhythmias represent the major cause of death in these patients causing sudden death.
Gross: In hypertrophic cardiomyopathy, the hypertrophy is not associated with ventricular dilation.
Disproportionate thickness of interventricular septum and free wall of left ventricle cause bulging of the interventricular septum into left ventricle forming “banana-like” configuration of left ventricle.
NOTE: An increase in left ventricle mass with a thick wall and normal or reduced cavity can occur in 3 separate conditions - these cannot be separated without histology and knowledge of the clinical details.
1. Appropriate left ventricle hypertrophy - there is a defined plausible cause i.e. aortic valve stenosis or hypertension.
The hypertrophy is microscopically normal.
2. Inappropriate left ventricle hypertrophy - there is either no cause or a cause (mild hypertension) insufficient in degree to responsible for the degree of hypertrophy.
The hypertrophy is microscopically normal. Examples are renal hypertension, athletes hearts and the hearts of infants of diabetic mother.
3. Hypertrophic cardiomyopathy - In this condition there is a histological abnormality characterized by myocardial disarray with bundles running in all directions and interstitial fibrosis.
The condition is now recognised to be due to 5 different genes (heavy chain myosin , Tropinin T , myosin binding protein C , tropomyosin and preexcitation associated gene).
The 4 known genes are concerned with myofibrillary organisation within the myocyte and disorganisation leads to misshapen myocytes running in whorls.
These genes are dominant negatives in which the mutant protein interferes with the wild type protein function.
All the genes carry a risk of sudden unexpected death.
Cases with a large heavy thick walled Left ventricle which may, or may not, be asymmetric are relatively easy to recognise.
About 30% of cases have a pathognomic subaortic mitral impact lesion.
Pathologists should be aware that a proportion of cases have normal or mild increase in left ventricle mass and macroscopically look normal.
Microscopy to identify these cases is needed.
Restrictive Cardiomyopathy :
In this form of cardiomyopathy the abnormality of function is in LV diastolic relaxation.
The left atrial pressure rises in an effort to achieve ventricular filling.
This in turn leads to pulmonary hypertension.
The LV remains normal macroscopically, while the right ventricle hypertrophies. The commonest cause is amyloid.
Primary disease of the ventricle results in impaired ventricular filling during diastole, resulting in reduced cardiac outflow.
This may be of the following types:
This is typically seen in children and young adults in Africa.
This is characterized by ventricular subendocardial fibrosis, often with mural thrombus formation.
Reduced ventricular filling is due to reduced ventricular chamber volume.
This is characterized by endo-myocardial fibrosis with large mural thrombi and is found in temperate zone.
Eosinophilic infiltration is seen in multiple organs including the heart. There may be associated peripheral eosinophilia. Cationic proteins released from activated eosinophils in the circulation damage the endocardium.
These lesions are rapidly fatal.
This uncommon disorder is characterized by focal-to-diffuse cartilage-like fibroelastic thickening of the endocardium, mostly of left ventricle.
Mostly affected patients are younger than two years old.
Problems with Cardiomyopathy:
In some patients arrythmias and sudden death predominate and contractile function is normal, the subjects have normal exercise tolerance in life.
Several forms exist.
- Arrhythmogenic right ventricular cardiomyopathy: (arrhythmogenic right ventricular dysplasia). Image Link
This is a familial disorder, most commonly associated with right-sided heart failure and various rhythm disturbances, particularly ventricular tachycardia and sudden death.
Morphologically, the dilated right ventricular wall is severely thinned, with extensive fatty infiltration, loss of myocytes and interstitial fibrosis.
Death occurs due to congestive heart failure, embolism of mural thrombi or fatal arrhythmias
- In other subjects there is idiopathic fibrosis in the left ventricle with a distribution and pattern unlike ischaemic disease.
It is not known whether this is acquired (? post viral) or familial.
- In the long QT syndrome (often referred to as cardio-myopathy) now known to be due to genetic defects in sodium and potassium channels in the myocyte, sudden death is common.
The heart is normal structurally (macro and micro).
Inflammatory Cardiomyopathy- Myocarditis:
Acute non-specific myocarditis usually produces the rapid onset of fever, palpitations and arrhythmia with cardiac failure and a high risk of sudden death.
Pericarditis may or may not be present.
Acute myocarditis is not an entity recognised by macroscopic examination alone.
Microscopy shows individual myocyte necrosis and a heavy T- lymphocyte infiltrate.
Most cases are due to viral infection with a Coxsackie group predominant.
In infants adenoviruses can cause disproportionate myocyte necrosis with scanty lymphocytes.
In adults a particularly florid acute myocarditis is associated with serpigenous areas of necrosis at the margins of which are numerous macrophage giant cells and eosinophils.
The cause is unknown.
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