General characteristics and clinical manifestations
Idiopathic cardiomyopathies comprise disorders primarily affecting the heart muscle, while inflammatory, congenital, rheumatic, or ischemic (coronary) factors are excluded.
Despite different pathogenetic mechanisms, all forms share a similar clinical presentation:
- Dyspnea occurring or worsening upon physical exertion.
- Various rhythm disturbances (arrhythmias) and tachycardia.
- Tendency toward dizziness and sudden fainting (syncope).
- In the terminal stage, severe chronic heart failure inevitably develops.
Dilated cardiomyopathy (DCM)
This is the most common form, accounting for about 60% of all idiopathic myocardial lesions. The disease predominantly affects men aged 10 to 30 years.
Etiology and pathogenesis The exact causes are unknown, but the primary hypothesis links DCM development to latent viral myocarditis. The process begins with atrophy and death of cardiomyocytes. Connective tissue proliferates in their place (interstitial fibrosis), while surviving muscle fibers undergo compensatory hypertrophy.
Morphological findings
- Macroscopically: The heart assumes a characteristic globular shape with a blunted apex (transverse dimension equals or exceeds the longitudinal). Organ weight increases to 600–800 g (sometimes up to 1200 g). Marked dilatation of all chambers is observed. Meanwhile, the left ventricular wall thickness is 2–2.5 cm, which is completely disproportionate to the massive heart weight. The valve apparatus and coronary arteries remain intact.
- Microscopically: The picture is nonspecific. There is an alternation of hypertrophic and atrophied fibers, areas of myocytolysis, contracture changes in myofibrils, fine-focal cardiosclerosis, and proliferation of intermuscular adipose tissue. Cellular inflammatory response is weakly expressed.
- Ultrastructurally: Separation of intercalated discs of cardiomyocytes occurs, which is the main cause of myocardial electrical instability.
Clinically, DCM is accompanied by fatigue, cough, hemoptysis, cardiac pain, pallor, and acrocyanosis.
Hypertrophic and restrictive forms
Hypertrophic cardiomyopathy (synonym: hypertrophic obstructive cardiomyopathy) manifests as marked myocardial thickening, most commonly of the left ventricle. Ventricular cavities are significantly reduced. The main functional problem is impaired diastolic relaxation with preserved or even enhanced systole.
Restrictive cardiomyopathy is characterized by marked rigidity of the ventricular walls and severe endocardial fibrosis.
- Pathophysiology: Stiff walls impede normal diastolic chamber filling, and atrioventricular valve function is impaired. Pulmonary hypertension develops, leading to cor pulmonale.
- Etiology: This pathology is extremely rare in Russia. Isolated parietal Löffler's eosinophilic endocarditis is considered a probable cause. There is also a geographic hypothesis: in African populations, endomyocardial fibrosis may develop due to excess cerium against the background of magnesium deficiency.
- Morphogenesis: Severe endocardial fibrosis (more commonly of the left ventricle), foci of hyalinosis, and calcification are observed. The ventricular cavity is reduced, and sclerosis often extends to the posterior leaflet of the mitral valve. Microscopically, cardiomyocyte death and compensatory hypertrophy of the remaining ones are visible.
- Complications and outcome: Reduced contractility leads to mural thrombus formation and thromboembolism. The prognosis is extremely unfavorable: about 70% of patients die within the first 5 years.
Right ventricular cardiomyopathy
A synonym for this pathology is arrhythmogenic right ventricular dysplasia. This is a rare form for which a genetic defect has been definitively proven.
It is of colossal clinical significance as it is the most frequent cause of sudden death syndrome in infants, children, adolescents, and athletes.
Morphogenesis: It is based on thinning of the right ventricular wall due to indolent confluent foci of necrosis. The dead myocardium is replaced by fibrous and adipose tissue, forming the so-called "parchment heart".
Clinic and complications: Patients suffer from severe rhythm disturbances (ventricular tachycardia, extrasystole, sinoatrial block). In rare cases, the thinned right ventricular wall may rupture, leading to fatal cardiac tamponade.
Briefly: answers to topical questions
What macroscopic and microscopic features are characteristic of hypertrophic cardiomyopathy?
Hypertrophic cardiomyopathy is characterized by marked myocardial hypertrophy, reduction of ventricular cavities, disorganized arrangement of muscle fibers, and diffuse fibrosis.
Macroscopic features:
- Heart weight is 500–700 g, apex is pointed.
- Left ventricular wall thickness reaches 2.5–3 cm, cavity size is reduced.
- Valves and coronary arteries are unchanged.
- Asymmetric (thickness of the interventricular septum is 1.5–2 times the left ventricular wall thickness) and symmetric (uniform hypertrophy) forms are distinguished.
Microscopic features:
- The myofiber disarray phenomenon — disorganized arrangement of muscle fibers.
- Global and diffuse myocardial fibrosis.
What genetic mutations underlie the development of hypertrophic cardiomyopathy?
Hypertrophic cardiomyopathy is based on pathogenic variants in genes encoding sarcomeric and non-sarcomeric proteins.
- Sarcomeric protein gene mutations are associated with classical hypertrophic cardiomyopathy; the disease is defined as a sarcomeric disease. It is noted that 11 different mutations have been identified, the most frequent being the $\beta$-myosin heavy chain mutation.
- Multiple mutations — the presence of 2, 3, or more pathogenic variants, most commonly combinations of mutations in sarcomeric protein genes. They occur in 5–7% of cases and are associated with earlier onset, pronounced interventricular septal hypertrophy, and a high risk of sudden cardiac death.
- Non-sarcomeric gene mutations — pathogenic variants in genes encoding cytoskeletal proteins, ion channels, Z-discs, and other intracellular structures; account for 15–20% of HCM causes. Cytoskeletal gene mutations are frequently associated with congenital heart defects and may be accompanied by signs of non-compaction myocardium.
For quick memorization of the main forms, use the mnemonic «DHRM» (or the Russian equivalent «ДГРА»): Dilated (Flabby, globular heart), Hypertrophic (Massive walls), Restrictive (Rigid endocard), Arhythmogenic dysplasia (Atrophy of the right ventricle).
Class and exam questions
Which form of cardiomyopathy is the most common?
Dilated cardiomyopathy — it accounts for about 60% of all idiopathic myocardial lesions.
Why does electrical instability of the heart occur in the dilated form?
At the ultrastructural level, separation of intercalated discs of cardiomyocytes occurs, which disrupts normal electrical impulse propagation.
What are the macroscopic features of dilated cardiomyopathy?
The heart acquires a globular shape with a blunted apex, its weight reaches 600–1200 g due to marked dilatation of all chambers, while the valves and coronary arteries remain unchanged.
Which pathology is a frequent cause of sudden death in young athletes?
Right ventricular cardiomyopathy (arrhythmogenic dysplasia), in which the myocardium thins and is replaced by adipose and fibrous tissue.
What else to study on this topic
- Ultrastructural changes in cardiomyocytes in the dilated form
- Pathogenesis of cor pulmonale in restrictive cardiomyopathy
- Mechanisms of mural thrombus formation and thromboembolism development
- The role of Löffler's eosinophilic endocarditis in the development of fibrosis
- Genetic aspects of arrhythmogenic right ventricular dysplasia
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