The myocardium is the muscular tissue of the heart that, by contracting, sustains the pumping function and ensures the delivery of an adequate amount of blood at sufficient pressure. It constitutes the largest part of the cardiac wall and is especially developed at the ventricular level, particularly in the left ventricle, which must ensure systemic perfusion and overcome greater peripheral resistance compared to 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 wall's distensibility.
Contractility: the ability of the myocardial fiber to develop force and shorten.
Afterload: the force that must be generated to pump blood, determined by the sum of all resistances opposing ventricular emptying.
The heart's pumping function is therefore influenced not only by the myocardium's intrinsic capabilities, but also by volume and pressure. Cardiac muscle tissue has a limited capacity to proliferate and can adapt to chronic volume and pressure overloads through the hypertrophy mechanism.
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, concentric hypertrophy develops, characterized by the addition of sarcomeres in parallel and a thickening of the ventricular wall, with a reduction in cavity volume.
The myocardium is involved in all major cardiac diseases. Cardiac conditions that significantly alter heart function always, to varying degrees, result in increased volume and/or pressure, to which the myocardium responds with hypertrophy. In addition, there is ischemic disease, which leads to necrosis of muscle tissue with replacement by fibrous tissue, and myocardial involvement in endocardial or pericardial processes.
Diseases of the myocardium, characterized by primary alterations of the muscle tissue, are distinguished as myocarditis and cardiomyopathies, depending on whether they are sustained by inflammatory processes or not.
Myocarditis: inflammation of the myocardium, mainly due to viral, bacterial, fungal or parasitic infections, but also to autoimmune, toxic, or reactive causes.
Cardiomyopathies: primary diseases of the myocardium that are not a direct consequence of other cardiovascular diseases (e.g. valvular diseases, arterial hypertension).
- These are classified as primary, of idiopathic or genetic origin, and secondary, when associated with systemic diseases such as endocrine, metabolic, or neuromuscular disorders.
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 that usually present with ventricular hypertrophy or dilation and 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: consequent to systemic, metabolic, toxic, or infectious diseases.
Based on morphology and pathophysiology, cardiomyopathies are subdivided 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): fibrofatty replacement of the myocardium with a predisposition to arrhythmias.
Unclassified cardiomyopathies: including Takotsubo cardiomyopathy and other rare forms.
Conclusions
Cardiomyopathies are one of the main causes of heart failure and sudden death. Early recognition and adequate 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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