General overview and etiology
Cardiomyopathies are divided into three main forms: dilated (DCM), hypertrophic (HCM), and restrictive (RCM).
The causes of the disease are diverse. Genetic factors play a huge role, especially in the hypertrophic form, where mutations in genes encoding cardiomyocyte structural proteins have been proven. Acquired forms can result from infections, systemic metabolic disorders, or toxic exposure. For example, there is a proven direct link between chronic alcohol consumption and the development of dilated cardiomyopathy.
Dilated cardiomyopathy (DCM)
This is a heterogeneous group of disorders accounting for more than half of all cases. The underlying pathology is a marked dilation of the heart chambers and a drop in contractility.
The disease develops in stages: signs of left ventricular failure appear first, followed by rhythm disturbances, and finally right ventricular failure.
Clinical picture:
- Low cardiac output syndrome and pulmonary congestion: dyspnea, cough, hemoptysis, fatigue.
- Systemic venous congestion: peripheral edema, hepatomegaly, ascites, jugular venous distension.
- Physical examination: pallor, acrocyanosis, possible cardiac cachexia. Cardiac borders are uniformly enlarged, and the apex beat is displaced to the left.
- Auscultation: muffled heart sounds, gallop rhythm (additional S3 and S4 sounds), accentuation of the second sound over the pulmonary artery. Systolic murmurs are frequently heard due to fibrous ring stretching and relative mitral and tricuspid regurgitation.
Echocardiography reveals an increase in left ventricular (LV) end-systolic and end-diastolic dimensions, dilation of other chambers, and a reduced ejection fraction. Treatment is aimed at managing heart failure and controlling heart rate in atrial fibrillation.
Hypertrophic cardiomyopathy (HCM)
HCM is characterized by massive myocardial hypertrophy leading to a reduced ventricular cavity. Systolic function remains normal or enhanced for a long time, but relaxation (diastole) is impaired.
The most common form is asymmetric with thickening of the interventricular septum (IVS). During contraction, the anterior leaflet of the mitral valve moves toward the septum, creating dynamic outflow tract obstruction.
Symptoms and diagnostics:
- Symptoms: dyspnea, chest pain (resembling angina due to insufficient blood supply to the hypertrophied muscle), as well as dizziness and syncope upon physical exertion (due to increased obstruction).
- Auscultation: muffled first sound and a harsh, rasping midsystolic ejection murmur along the left sternal border. Important: the intensity of the murmur changes with body position and does not radiate to the neck.
- ECG: signs of hypertrophy, deep Q waves (in I, aVL, V5-6), left bundle branch block, ischemia-like changes.
- Echocardiography: IVS thickening (1.8–2.2 cm or more), asymmetry, SAM syndrome (systolic anterior motion of the mitral valve leaflet).
The leading threat in HCM is sudden cardiac death (SCD) due to fatal arrhythmias. Beta-blockers (to improve diastole) and amiodarone are used for treatment, while high-risk patients have an indication for implantable cardioverter-defibrillator (ICD) placement.
Restrictive cardiomyopathy (RCM)
This form is characterized by impaired diastolic function with preserved systole, but, unlike DCM, without dilation of the left ventricle.
The heart walls become rigid due to endocardial thickening, cardiomyocyte death and replacement by fibrous tissue, or myocardial infiltration (amyloidosis, hemochromatosis, Löffler syndrome). Rigidity leads to a sharp increase in filling pressures.
Clinically, symptoms of biventricular heart failure predominate (dyspnea, orthopnea, edema, hepatomegaly) along with severe arrhythmias (paroxysmal and permanent atrial fibrillation). Echocardiography shows no cardiomegaly, but reveals significant left atrial enlargement against the background of moderately thickened ventricular walls. Treatment is limited to symptomatic management of heart failure.
Mnemonic for forms: DHR. Dilated (Flabby dilated heart), Hypertrophic (Mountain of muscle, tight cavity), Restrictive (Rigid shell).
Class and exam questions
Why do patients with hypertrophic cardiomyopathy experience syncope during physical exertion?
Exertion increases myocardial contractility, which paradoxically worsens dynamic obstruction. The anterior mitral leaflet is pulled closer to the septum, obstructing blood ejection into the aorta and reducing cerebral blood flow.
How to differentiate the murmur in obstructive HCM from that of aortic stenosis?
Unlike aortic stenosis, the systolic murmur in HCM does not radiate to the great vessels of the neck and tends to change in intensity when the patient changes body position.
Do heart dimensions change in restrictive cardiomyopathy?
Left ventricular dimensions remain normal (no dilation), but due to its stiffness, pressure in the left atrium rises, leading to its significant enlargement (atrial dilation).
What else to study on this topic
- Mechanisms of SAM syndrome formation on echocardiography in HCM
- Differential diagnosis of DCM and coronary artery disease
- Features of Holter monitoring for assessing SCD risk
- Specific causes of restrictive cardiomyopathies (amyloidosis, hemochromatosis)
- Pharmacological approaches to the treatment of diastolic heart failure
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