Cardiomyopathy

• Any disease that affects the myocardium
• Cardiomyopathies constitute a group of diseases in which the dominant feature is involvement of the heart muscle

Two classification systems:

1)Primary or Secondary disease process

• The cause is often unknown or obscure but may be identified with a primary or secondary process:

i) Primary cardiomyopathy:

• Are not the result of ischaemic*, hypertensive, congenital, valvular or pericardial diseases [dx of primary cardiomyopathy requires exclusion of these aetiologies]
• involvement of myocardium alone [exclude valves & other cardiac structures]
• cause is known or unknown (idiopathic)

ii) Secondary cardiomyopathy:

• cardiomyopathy is associated with dysfunction of other organ systems
• may develop secondary to any condition of pressure or fluid overload
• compensatory hypertrophy mechanisms eventually cause degenerative changes in cardiac muscle

2)Functional classification

• The pathophysiology of cardiomyopathies may be classified into three groups:

i) Congestive/ dilated cardiomyopathy

• - most common
• - systolic dysfunction
• - contractile dysfunction -> ventricular dilatation -> congestive heart failure

ii) Hypertrophic cardiomyopathy

• - second most common
• - obstructive process -> left ventricular hypertrophy
• - preserved/increased contractility

iii) Restrictive cardiomyopathy

• rarest form
• diastolic dysfunction
• - abnormal ventricular compliance -> impairment of diastolic filling->increased filling pressures

• note that the three functional categories frequently overlap
• The functional & aetiological classifications may be combined eg: primary hypertrophic cardiomyopathy
• Ischaemic cardiomyopathy: ischaemic heart dx—> diffuse fibrosis & multiple infarctions—> heart failure
• There is a decreased exercise capacity and an inability to respond to postoperative stresses caused by increasing cardiac output

Ætiology of Cardiomyopathy

1) Dilated Cardiomyopathy

Pathophysiology

• Myocardium is pale with areas of fibrosis but no significant hypertrophy
• Heart is globular with poor contraction & low ejection fraction
• See markedly dilated left ventricle, low cardiac output and poor systolic function
• Mild to moderate regurgitation may be present

Aetiology

• The dilated cardiomyopathy may be a common expression of myocardial damage that has been produced by a variety of myocardial insults
• At least 4 major conditions appear to lower the threshold for the development of dilated cardiomyopathy:

i) Toxic

eg) ETOH due to:

- direct toxic effect of alcohol

- thiamine deficiency

- cobalt additive in beverage

ii) Infectious

eg) viral myocarditis 2° to autoimmune reaction -> dilated cardiomyopathy

include: poliovirus & influenza virus

iii) Metabolic

eg) hyperthyroidism, pheochromocytoma, beriberi & kwashiorkor

iv) Hypertension

v) Pregnancy

ie) peripartum or postpartum dilated cardiomyopathy

- unknown cause

2) Hypertrophic Cardiomyopathy

Pathophysiology

• •see inappropriate myocardial hypertrophy, often involving interventricular septum of a non dilated left ventricle
• •diastolic dysfunction: abnormal stiffness of left ventricle during diastole-> impaired ventricular filling -> increased left ventricular filling pressures -> pulmonary congestion

Aetiology

• A familial form of inheritance may be involved in which individuals inherit a susceptibility to the development of hypertrophic cardiomyopathy
• •Other aetiologies include: subaortic stenosis, increased cardiac response to catecholamines; abnormal coronary arteries -> impaired dilatation response -> ischaemia & compensatory hypertrophy; collagen abnormality; abnormal handling of Ca2+ by myocardium

3) Restrictive Cardiomyopathy

Pathophysiology

• Myocardium & endocardium are infiltrated with fibroelastic tissue
• See abnormal ventricular compliance & increased ventricular diastolic pressures
• This infiltration results in a rigid heart that does not distend well during diastole nor completely contract in systole
• Results in low cardiac output and congestive heart failure
• May resemble restrictive pericarditis

Aetiology

• •Amyloidosis -> secondary restrictive cardiomyopathy
• a common cause of death in amyloidosis
• due to abnormal protein deposition
• •Sarcoidosis
• granulomatous disorder
• •Hemochromatosis & hemosiderosis
• -excessive deposition of iron in various parenchymal tissues including heart

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