Most heart muscle diseases are secondary to some other condition, like coronary artery disease, hypertension or valvular disease. These diseases are not cardiomyopathies. A cardiomyopathy (CMP) is defined as a primary (!) heart muscle disease, meaning that it doesn’t occur secondary due to any other disease. Specifically, we must exclude ischaemic, hypertensive and valvular heart diseases, to establish the presence of a cardiomyopathy.
Pathophysiology department has a different definition, where a cardiomyopathy is any abnormality of the myocardium, either primary or secondary. Robbins also has a slightly different definition. Keep this in mind.
We have three major types of cardiomyopathies:
- Dilatative/congestive cardiomyopathy
- Hypertrophic cardiomyopathy
- Restrictive cardiomyopathy
Let’s look at them.
Any dilatative cardiomyopathy (DMP) will, as the name suggests, lead to severe dilation of the heart. All four chambers dilate, but perhaps most notably the left ventricle. The most important causes are:
- Genetic mutations
- Alcohol consumption
- Peripartum (around labour)
The most common consequences are:
- Systolic heart failure
- Turbulent flow in the ventricles -> Mural thrombus formation -> Embolization
- Functional mitral or tricuspid valve insufficiency
When the left ventricle dilates significantly will the walls go further away from each other. This dilation causes the mitral valve to be unable to close completely, causing blood to regurgitate into the left atrium during systole. There’s nothing wrong with the valve itself, which is why it’s called functional insufficiency.
Histology of a dilatative cardiomyopathy doesn’t show anything specific, only hypertrophy and fibrosis. DMP hearts will progressively dilate, which slowly leads to a progressive congestive heart failure. Dyspnoea and early fatigue are common symptoms, and eventually the dilation causes the systole to become ineffective. 50% of patients die within 2 years.
In hypertrophic cardiomyopathy (HCM) is the whole heart thick-walled, heavy and hypercontractile, due to concentric hypertrophy of all parts of the myocardium. However, the hypertrophy is disproportional because the septum is 3x as hypertrophied as the rest of the myocardium. This causes the septum to bulge into the left ventricle, which gives the left ventricle lumen a banana-shape.
It’s mostly caused by missense mutations in either the β-myosin heavy chain gene (most common), myosin-binding protein C or troponin T.
The most common consequences are:
- Diastolic heart failure due to impaired filling of the left ventricle and decreased compliance
- Obstruction of left ventricular outflow by the anterior leaflet of the mitral valve and septum -> syncope
- Increased risk for ischaemia, angina and AMI due to the hypertrophy
The decreased lumen of the left ventricle markedly reduces the stroke volume, although the ejection fraction is actually increased because of the strong heart muscle. The hypertrophic myocardium is more stiff, which reduces the compliance which further causes decreased left ventricular filling. These factors lead to diastolic heart failure.
The anterior cusp of the mitral valve enlarges as well. During some heart cycles can this cusp come in contact with the enlarged septum and completely block the outflow of the left ventricle. During this heart cycle will the mean arterial pressure drop significantly, which can lead to syncope. Occasional syncope is a characteristic symptom of HCM.
Other diseases that produce similar symptoms and must be excluded during differential diagnosis of HCM are:
- Also leads to reduced compliance of ventricles
- Hypertensive heart disease
- Also leads to hypertrophy
- Valvular aortic stenosis
- Also leads to hypertrophy
For histology of HCMP check the slide.
Restrictive cardiomyopathy (RCM) is the rarest of the three. It’s characterized by a decrease in ventricular compliance, which causes impaired ventricular filling. The ventricles have normal morphology, but the atria are dilated because of the increased end-diastolic pressure in the ventricles.
Common causes include:
- Idiopathic (no known cause)
- Radiation fibrosis
- Metastatic tumor invasion
Secondary restrictive heart conditions
These diseases are not cardiomyopathies but are secondary to some other condition. They are:
- Endomyocardial fibrosis is an endemic condition of children in tropical areas. Fibrosis of the endocardium and inner myocardium, with involvement of tricuspid and mitral valves is common.
- Löffler’s endomyocarditis is the late stage of a condition called Löffler’s endocarditis. Löffler’s endocarditis is characterized by endocardial fibrosis with large thrombi that takes up large portions of the ventricular lumen. In the late stage of this disease will the myocardium also be inflamed, and the thrombi may become organized into scar tissue. At this point is the disease called Löffler’s endomyocarditis, and the myocardial fibrosis causes the myocardium to become restrictive. Löffler’s endocarditis is associated with elevated eosinophils in the blood (hypereosinophilia)
- Endocardial fibroelastosis is characterized by diffuse fibroelastic thickening of the left ventricular endocardium. It’s a congenital heart disease.
Tumors inside the heart is very uncommon, due to the low turnover of cells in the heart. Only about 5% of cancer-related deaths present with metastatic invasion into the heart. Some cancers have a higher tendency to metastasize into the heart. Here are some of them, from most to least common:
- Lung cancer
- Breast cancer
80-90% of primary heart tumors are benign. Let’s talk about some of them.
Cardiac myxomas are the most common. They mostly occur in the atria, and mostly the left atrium. They can be anywhere from 1 – 10 cm, and are soft and translucent masses.
They are often loose and can swing like a wrecking ball into the AV valve to cause damage. They can also loosen and become emboli. Histology shows a type of cell called lepidic cells, which are similar to endothelial cells. It can be diagnosed with echocardiography.
Cardiac fibromas are most common in childhood and rarely occurs in adults. They’re associated with arrhythmias, heart failure and sudden death, mostly by compressing the conducting system of the heart. It’s usually seen in Gorlin syndrome, a condition where naevoid basal cell carcinomas are common. Histology shows collagen, elastic fibres and fibroblasts.
Cardiac rhabdomyomas are the most common cardiac neoplasms in infants. It’s often seen in a condition called tuberous sclerosis. It commonly causes outflow tract obstruction and tachyarrhythmias and can lead to heart failure. Like many neoplasms in infants does it frequently regress spontaneously, with no obvious reason.
Cardiac haemangiomas and cardiac lipomas should also probably be known.
Several types of malignant cardiac tumors exist, but remember that they’re rare. They are:
- Angiosarcoma (most common)
Cardiac metastases are more common than primary tumors. The most common origins are:
70. Pathology of the valvular disorders (inflammatory and degenerative ones)
72. Myocarditis. Pathology of the pericardium.