Cardiomyopathies

Cardiomyopathies

Overview

Cardiomyopathies are diseases of the heart muscle that can cause mechanical and/or electrical dysfunction. Can produce heart failure or fatal arrhythmias.

Four key types based on cardiac morphology: Dilated, Hypertrophic, Restrictive, Arrhythmogenic Right Ventricular Cardiomyopathy

Be aware that some authors specifically exclude cardiac dilation or hypertrophy caused by cardiac disorders such as hypertension or ischemia, but other authors do not make this distinction. For clarity, in this tutorial, we will use the limited definition of cardiomyopathy and exclude, for example, cardiac hypertrophy that occurs as a physiologic response to valvular disease, etc.

Cardiomyopathies are caused by both genetic and non-genetic factors, though, in many cases, underlying causes are not identified.

Diagnosis of cardiomyopathy includes chest x-rays, ECGs, and echocardiograms.

Treatments are focused on addressing the underlying causes, where appropriate, and the management of heart failure and arrhythmias.

Normal heart anatomy

Dilated Cardiomyopathies

Dilated Cardiomyopathies are characterized by dilation and contractile impairment; think of a "ballooning" heart, because "dilated" means to become wider or more open.

Gross Morphology:

Dilated cardiomyopathies produce systolic dysfunction with reduced ejection fractions (typically defined as 40 - 45% less than normal). The dilated heart is characterized by "ballooning" of the left ventricular, which often leads to dilation in the other chambers, as well. The dilated heart is heavy, and is often described as "baggy" due to contractile impairment.

Wall thickness is often reduced, and functional mitral valve regurgitation is possible (due to sagging and lack of structural support). Mural thrombi formation is also possible.

Histology:

Hypertrophied cells and loss of myofibrils with interstitial fibrosis in histological samples.

Symptoms:

Left ventricular dilation is associated with dyspnea and fatigue, and that right ventricle dilation can lead to peripheral edema.

Causes:

Dilated cardiomyopathies can be caused by several factors, including: Genetic mutations, which often lead to defects in the cardiac myocyte cytoskeleton, sarcolemma, and nuclear envelope. Various infections, including Coxasackievirus, Chagas Disease, and HIV; Toxins and drugs, especially alcohol abuse, cocaine, and some cancer drugs. Metabolic disorders, including diabetes, hyper- or hypo-thyroidism, hyper- or hypo-kalemia, and various nutritional deficiencies. Neuromuscular diseases, such as Friedreich ataxia and muscular dystrophy. Pregnancy (the cardiomyopathy becomes apparent in late pregnancy or postpartum period). Myocarditis.

Arrhythmogenic Right Ventricular Cardiomyopathy

Characterized by muscle cell loss with fibrofatty replacement in the wall of the right ventricle.

Genetic mutations that cause desmosome defects.
Especially likely to cause ventricular arrhythmias.

Hypertrophic Cardiomyopathy

Characterized by hypertrophy, which means that the myocardium grows abnormally thick, (think of a hyper-muscular body builder who can't relax); Reduced compliance produces diastolic dysfunction. Ejection fraction is increased or normal; recall that this is a measure of how much blood the left ventricle pumps in a single contraction. Diastolic filling is impaired (due to reduced compliance), so stroke volume is reduced.

Gross Morphology:

We show a hypertrophic heart with a significantly thickened left ventricular wall and septal myocardium. The patterns of hypertrophy vary; in some cases, the hypertrophy is asymmetrical and includes only the septum or a portion of the ventricular wall.

In many cases, myocardial hypertrophy leads to obstructive myopathy (HOCM), in which systolic blood flow through the aorta is impaired. Abnormalities in the mitral valve apparatus (including abnormally positioned papillary muscles and elongated valve leaflets) are associated with systolic anterior motion (SAM), which produces the dynamic left ventricular obstruction, and, possibly, mitral valve regurgitation.

Hypertrophic obstructive cardiomyopathy is often characterized by a systolic ejection murmur as well as abnormal P-wave and septal Q-waves.

Histology:

Myocardial cell hypertrophy and disarray (note the "swirling" pattern, instead of the normal parallel branching pattern), with interstitial and replacement fibrosis.

Symptoms:

Many patients are asymptomatic, but others experience dyspnea, chest pain, and syncope.

Causes:

Almost exclusively caused by genetic mutations, particularly those that cause defects in the sarcomere and those that cause glycogen storage diseases.

Restrictive Cardiomyopathy

Restrictive cardiomyopathy is a rare disorder that causes diastolic dysfunction. Characterized by rigid, but not hypertrophic, heart walls. Ejection fraction is normal, but diastolic filling is impaired due to very low compliance (we draw our heart as if its ventricles are comprised of concrete, which has no elasticity!). The heart walls may be slightly thickened, but not always.

Several causes of restrictive cardiomyopathy include: post-radiation fibrosis, amyloidosis, sarcoidosis, Loeffler endocarditis, endomyocardial fibrosis, and hemochromatosis.

For References, see Cardiomyopathies tutorial

Cardiomyopathies

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