Aaaaaaand yes it's another pathology lecture! Believe it or not, we still have another sneaky cardiac pathology lecture coming up in the middle of the renal block for some reason...
Cardiomyopathy
Cardiomyopathy is defined as heart disease that results from an abnormality in the myocardium.
Classification
Cardiomyopathy, which is often diagnosed via biopsy, is usually classified into four broad categories: dilated, hypertrophic, restrictive, and arrhythmogenic. I will discuss them in more detail later.
Aetiology
Cardiomyopathy may be primary, meaning that it only affects the heart (often idiopathic or due to some genetic cause), or secondary, meaning that it is secondary to some other cause (such as a neuromuscular disease or connective tissue disorder).
Pathogenesis, morphological changes, clinical features, and clinical sequelae
Dilated cardiomyopathy is the most common type of cardiomyopathy, making up around 90% of cardiomyopathies. As you may guess from the name, in dilated cardiomyopathy, all of the chambers are dilated (the heart can be up to 3x the size of normal), resulting in progressive cardiac dilation and systolic dysfunction. Patients with dilated cardiomyopathy often present between 20-50 years of age with shortness of breath and fatigue. Roughly 20-50% of dilated cardiomyopathies are thought to be genetic.
Hypertrophic cardiomyopathy involves left ventricular hypertrophy without an obvious external cause. It is pretty much always due to an autosomal dominant mutation, often in the beta-myosin heavy chain. Since the left ventricle is hypertrophied, diastolic filling is impaired and there may be blocking of the outflow tract (which is why this type of cardiomyopathy is sometimes called HOCM- Hypertrophic Obstructive Cardiomyopathy). The septum is particularly thickened (this is in contrast to hypertensive heart disease, which has an evenly thickened wall), resulting in a ventricular lumen that looks like a banana. Under a microscope, the myocytes look bigger and the fibres are disorganised.
Restrictive cardiomyopathy involves a rigid left ventricular wall which results in impaired diastolic filling. It is often idiopathic but may be due to diseases that affect the myocardium. Up close, there may be patchy or diffuse fibrosis. The ventricles are usually normal size or slightly enlarged. Restrictive cardiomyopathy may be confused with other conditions in which there is fibrosis of the endocardium, such as endocardial fibroelastosis, endomyocardial fibrosis, and Loeffler's endomyocarditis.
Myocarditis
Myocarditis is inflammation of the myocardium.
Aetiology
Myocarditis may be due to infections or immune-mediated reactions. There are also other miscellaneous causes of myocarditis, such as radiation therapy. Myocarditis can even affect generally healthy people.
Clinical features and everything else
In the active phase of myocarditis, the heart may be either normal or dilated. As the disease advances, the ventricular myocardium may become flabby and mottled. Myocarditis may be patchy, i.e. not affecting everywhere in the heart, so biopsies may turn up with false negatives, which might be problematic as myocarditis can result in cardiac failure or even sudden death.
Pericarditis
Pericarditis is inflammation of the pericardium (outer covering of the heart).
Aetiology
Pericarditis may be due to infections, or due to a variety of non-infectious causes ranging from aortic dissection to uraemia (high levels of urea in the blood). There are also some autoimmune conditions that might result in pericarditis, such as rheumatic fever and rheumatoid arthritis.
Pathogenesis
One type of pericarditis is effusive pericarditis, in which there is effusion of fluid into the pericardium. The more rapid the effusion occurs, the worse the outcome. Slowly-accumulating effusions generally do not interfere greatly with heart function, but rapid accumulation of fluid may lead to a condition called cardiac tamponade, in which the fluid presses against the heart and restricts its filling, which may result in death from restrictive heart failure.
Classification etc.
Pericarditis can be classified according to the length of time that it lasts. Acute pericarditis lasts for less than 6 weeks, chronic pericarditis lasts for longer than 6 months, and subacute pericarditis is in between. Chronic pericarditis can be further divided into several subtypes. Adhesive pericarditis rarely interferes with cardiac function. Adhesive mediastinopericarditis, on the other hand, can cause issues as the heart is tethered to surrounding structures and it may pull on the structures that it is tethered to. In constrictive pericarditis, there is dense fibrosis and possibly calcification as well, reducing filling. Some of the pericardium may have to be removed in constrictive pericarditis.
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