General Overview of Cardiomyopathies

The Myocardium and Cardiac Pump Function

The myocardium is the muscular tissue of the heart that, through contraction, supports its pump function, ensuring the adequate delivery of blood at sufficient pressure. It constitutes the majority of the heart wall and is particularly developed at the ventricular level, especially in the left ventricle, which must provide systemic perfusion and overcome greater peripheral resistance than the right ventricle.

The main mechanical determinants of myocardial function are:

• Preload: the initial length of the myocardial fiber, which depends on ventricular filling and the compliance of the ventricular wall.
• Contractility: the ability of the myocardial fiber to develop force and shortening.
• Afterload: the force that must be developed to pump blood, determined by the total resistance opposing ventricular emptying.

The heart's pump function is influenced not only by the intrinsic capacities of the myocardium but also by volume and pressure. Myocardial tissue has a limited ability to proliferate and adapts to chronic volume and pressure overloads through the mechanism of hypertrophy.

In response to chronic volume overload, the myocardium develops eccentric hypertrophy, characterized by the addition of sarcomeres in series and an enlargement of the ventricular cavity.
In response to chronic pressure overload, the myocardium develops concentric hypertrophy, characterized by the addition of sarcomeres in parallel and thickening of the ventricular wall, with a reduction in cavity volume.

The myocardium is involved in all major cardiac diseases. Heart diseases that significantly alter cardiac function always result, to some extent, in an increase in volume and/or pressure, to which the myocardium responds with hypertrophy. In addition, ischemic heart disease causes necrosis of muscle tissue, replacing it with fibrotic tissue, and myocardial involvement can occur in endocardial or pericardial processes.

Myocardial Diseases: Myocarditis and Cardiomyopathies

Myocardial diseases, characterized by primary alterations of the muscle tissue, are classified into myocarditis and cardiomyopathies, depending on whether they are caused by inflammatory processes or not.

• Myocarditis: inflammation of the myocardium, primarily caused by viral, bacterial, fungal, or parasitic infections, but also due to autoimmune, toxic, or reactive causes.
• Cardiomyopathies: primary diseases of the myocardium that are not a direct consequence of other cardiovascular conditions (hypertension, valvular heart diseases, ischemic heart disease).

Definition and Classification of Cardiomyopathies

According to the European Society of Cardiology (ESC), cardiomyopathies are defined as "diseases of the myocardium associated with mechanical and/or electrical dysfunction, usually presenting with ventricular hypertrophy or dilation, and which may be hereditary or acquired." The current classification distinguishes cardiomyopathies into:

• Primary cardiomyopathies: of genetic or idiopathic origin, without a clear systemic cause.
• Secondary cardiomyopathies: resulting from systemic, metabolic, toxic, or infectious diseases.

Based on morphology and pathophysiology, cardiomyopathies are further classified into:

• Dilated cardiomyopathy (DCM): characterized by ventricular dilation and systolic dysfunction.
• Hypertrophic cardiomyopathy (HCM): myocardial thickening, often with obstruction of the left ventricular outflow tract.
• Restrictive cardiomyopathy (RCM): reduced ventricular compliance with impaired diastolic filling.
• Arrhythmogenic right ventricular cardiomyopathy (ARVC): fibro-fatty replacement of the myocardium with a predisposition to arrhythmias.
• Unclassified cardiomyopathies: including Takotsubo cardiomyopathy and other rare forms.

Conclusions

Cardiomyopathies represent one of the leading causes of heart failure and sudden cardiac death. Early recognition and appropriate management can significantly improve prognosis. Ongoing research continues to provide new therapeutic perspectives, including innovative drugs and gene therapy approaches for hereditary forms.

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