21.1: Cardiomyopathy I: Introduction and Classification

Cardiomyopathy, or CMP, is a group of diseases affecting the myocardial structure, impairing its ability to pump blood effectively. This condition can lead to arrhythmias, heart failure, or sudden cardiac death.

Cardiomyopathies are classified into primary and secondary categories:

• Primary Cardiomyopathy refers to conditions involving only the heart muscle that are often idiopathic (of unknown cause) or genetic. They primarily affect the myocardium without the involvement of other systemic conditions.
• Secondary Cardiomyopathy occurs when other disease processes, such as valvular heart disease, hypertension, coronary artery disease, or systemic conditions like amyloidosis, impact the myocardium.

The common types of cardiomyopathies are as follows:

Dilated Cardiomyopathy (DCM)

DCM is marked by ventricular enlargement and systolic dysfunction, decreasing ejection fraction. This condition may be idiopathic or caused by genetic mutations, alcohol abuse, chemotherapy drugs, or other toxins, muscular dystrophy, or myocarditis.

Hypertrophic Cardiomyopathy (HCM)

HCM involves thickening of the heart muscle, especially the interventricular septum, which can obstruct blood flow and impair diastolic function. Often inherited in an autosomal dominant pattern, HCM is caused by gene mutations encoding sarcomere proteins.

Restrictive Cardiomyopathy (RCM)

RCM is characterized by a rigid heart muscle that restricts ventricular filling during diastole while maintaining normal systolic function. Common causes include amyloidosis, sarcoidosis, hemochromatosis, and fibrosis due to radiation or chemotherapy.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

ARVC occurs when the myocardium is progressively replaced by fibrous scar and adipose tissue, primarily affecting the right ventricle. This condition is often genetic, involving mutations in genes encoding desmosomal proteins.

Unclassified Cardiomyopathies

These include cardiomyopathies that do not neatly fit into the other classifications. For instance, Takotsubo Cardiomyopathy (Stress-Induced Cardiomyopathy) is a transient heart syndrome that causes apical ballooning and mimics acute coronary syndrome.