Cardiomyopathies
Objectives - Differentiate dilated, restrictive, and hypertrophic cardiomyopathies.
Definition
Cardiomyopathies are a heterogeneous group of diseases of the myocardium associated with mechanical and/or electrical dysfunction. They usually show inappropriate ventricular hypertrophy or dilation and are due to a variety of causes that are frequently genetic.
The source groups cardiomyopathies into:
| Type | Simple source cue |
|---|---|
| Dilated | Too thin. |
| Restrictive | Stiffen. |
| Hypertrophic | Thicken. |
Cardiomyopathies can lead to dysrhythmias, backup of blood into the lungs or the rest of the body, and heart failure.
Causes
Cardiomyopathy causes can be genetic or acquired/secondary to another disease or condition.
Listed causes include:
- Chronic hypertension
- Myocardial damage from a heart attack
- Chronic tachycardia
- Heart valve problems
- Infections that cause heart inflammation
- Metabolic disorders, obesity, thyroid disease, and diabetes
- Granulomas from sarcoidosis
- Iron buildup in the myocardium from hemochromatosis
- Buildup of abnormal proteins in organs from amyloidosis
- Pregnancy complications
Dilated Cardiomyopathy
Dilated cardiomyopathy is a dilated chamber with systolic dysfunction that is not caused by ischemic or valvular heart disease.
It often begins in the left ventricle, causing it to dilate and stretch. This thins the muscle fibers in the walls. As the left ventricle fails, the rest of the heart tries to compensate for left-sided failure. This leads to further dilation and weakening of the other chambers and outflow tracts.
Symptoms include:
- Dyspnea
- Fatigue
- Edema of the feet, legs, abdomen, and jugular veins
- Weight gain
- Cough and congestion related to fluid retention
- Heart arrhythmias
- Dizziness
- Syncope
Diagnosis may include ECG, chest x-ray, echocardiography or TEE, and cardiac magnetic resonance imaging.
Restrictive Cardiomyopathy
Restrictive cardiomyopathy is the rarest form of cardiomyopathy. It is a condition in which the ventricular walls are abnormally rigid and lack flexibility to expand as the ventricles fill.
Systolic function may be normal, but diastolic function is abnormal. The ventricles have more difficulty filling with blood, and over time the heart loses the ability to pump properly, leading to heart failure.
Causes are often unknown and not usually inherited. Known causes include:
- Scar tissue buildup, listed as idiopathic and most common
- Amyloidosis, with abnormal proteins in the heart muscle
- Chemotherapy or chest radiation exposure
- Excess iron in the heart from hemochromatosis
- Other systemic diseases such as sarcoidosis
Infiltrative Cardiomyopathy
Infiltrative cardiomyopathy is characterized by deposition of abnormal substances that cause ventricular walls to become progressively rigid, impeding ventricular filling.
The source describes it as a type of restrictive cardiomyopathy. It can be characterized by thickened walls and occasional dilation.
Hypertrophic Cardiomyopathy
Hypertrophic cardiomyopathy involves hypertrophy or thickening of the ventricles. It is associated with left ventricular stiffness, mitral valve changes, myocardial cellular changes, and the source label "athletes' heart."
The myocardium thickens most commonly at the septum. The thickened septum narrows flow from the left ventricle to the aorta. This is called outflow tract obstruction. The ventricles must pump harder to overcome the narrowing. The source terms this hypertrophic obstructive cardiomyopathy, or HOCM.
Left ventricular stiffness results from cellular changes in the myocardium due to hypertrophy. The left ventricle cannot relax and fill with blood normally. Less end-diastolic blood means less oxygenated blood is pumped to organs and muscles.
Mitral Valve and Cellular Changes in HCM
Narrowing of the left ventricular outflow tract disrupts mitral valve function. Obstruction occurs when the mitral valve strikes the septum. This can cause mitral regurgitation, with blood going back into the left atrium.
Myocytes can appear disorganized and irregular instead of organized and parallel. This can change electrical signals through the lower chambers and lead to ventricular arrhythmia.
Diagnostics for hypertrophic cardiomyopathy include echocardiography and cardiac magnetic resonance imaging.
Symptoms of heart failure may develop unpredictably at any age. Functional limitation can occur from exertional dyspnea or fatigue. Symptoms may include orthopnea or paroxysmal nocturnal dyspnea.