Restrictive Cardiomyopathy

Restrictive cardiomyopathy (RCM) is a form of cardiomyopathy where the walls of the heart become rigid but not thickened, restricting the heart's ability to stretch and fill with blood properly. It is the least common of the three primary subtypes of cardiomyopathy: hypertrophic, dilated, and restrictive. It should not be confused with constrictive pericarditis, a condition with similar presentation but different treatment and prognosis.

Signs and Symptoms

Untreated RCM often leads to several characteristic features including biatrial enlargement, thickened left ventricular (LV) walls with normal chamber size, and thickened right ventricular (RV) free wall with normal chamber size. Hemodynamic changes include elevated right atrial pressure (>12mmHg), moderate pulmonary hypertension, normal systolic function, and poor diastolic function, typically leading to Grade III - IV diastolic heart failure. Patients with RCM generally experience decreased exercise tolerance, fatigue, jugular venous distention, peripheral oedema, and ascites. Arrhythmias and conduction blocks are also common.

Causes

RCM can be triggered by genetic or non-genetic factors. The causes are often divided into primary and secondary, with a modern classification into infiltrative, storage diseases, non-infiltrative, and endomyocardial etiologies.

Genetic Causes

• DES (desmin)
• CRYAB (alpha B Crystallin, HSPB5)
• FLNC (filamin C)

Infiltrative Causes

• Amyloidosis
• Sarcoidosis
• Primary hyperoxaluria

Storage Diseases

• Fabry disease
• Gaucher disease
• Hereditary hemochromatosis
• Glycogen storage diseases
• Mucopolysaccharidosis type I (Hurler syndrome)
• Mucopolysaccharidosis type II (Hunter syndrome)
• Niemann-Pick disease

Non-infiltrative Causes

• Idiopathic
• Diabetic cardiomyopathy
• Scleroderma
• Myofibrillar myopathies
• Pseudoxanthoma elasticum
• Sarcomeric protein disorders
• Werner's syndrome

Endomyocardial Causes

• Carcinoid heart disease
• Endomyocardial fibrosis
• Idiopathic
• Hypereosinophilic syndrome
• Chronic eosinophilic leukaemia
• Drugs (e.g., serotonin, methysergide, ergotamine, mercurial agents, busulfan)
• Endocardial fibroelastosis
• Consequence of cancer or cancer therapy
• Metastatic cancer
• Drugs (e.g., anthracyclines)
• Radiation

The most common cause of restrictive cardiomyopathy is amyloidosis.

Mechanism

In RCM, the heart's rhythmicity and contractility may remain normal, but the stiff walls of the heart chambers (atria and ventricles) prevent adequate filling, thus reducing preload and end-diastolic volume. This results in reduced blood flow and backup of blood in the circulatory system, ultimately leading to diastolic dysfunction and heart failure.

Diagnosis

Diagnosis is typically made via echocardiography, which shows normal systolic function, diastolic dysfunction, and a restrictive filling pattern. Two-dimensional and Doppler studies are necessary to differentiate RCM from constrictive pericarditis. Cardiac MRI and transvenous endomyocardial biopsy may also be required in some cases. Reduced QRS voltage on ECG may indicate amyloidosis-induced RCM.

Treatment

Treatment focuses on managing causative conditions, such as using corticosteroids for sarcoidosis, and slowing the progression of the disease. Salt restriction, diuretics, angiotensin-converting enzyme inhibitors, and anticoagulation may be used. Care must be taken with diuretics to avoid inadequate blood perfusion and tissue hypoperfusion due to reduced blood volume.

Calcium channel blockers are generally contraindicated due to their negative inotropic effect, especially in amyloidosis-related RCM. Digoxin, calcium channel blockers, and beta-adrenergic blockers provide little benefit, except in cases with atrial fibrillation. Vasodilators are typically ineffective because systolic function is usually preserved.

Heart failure resulting from RCM often necessitates cardiac transplantation or a left ventricular assist device.

Epidemiology

Endomyocardial fibrosis is more common in the tropics and sub-Saharan Africa, while the highest incidence of death due to cardiac sarcoidosis is found in Japan.

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Self-assessment MCQs (single best answer)

What is the least common subtype of cardiomyopathy?

Which symptom is NOT typically associated with restrictive cardiomyopathy?

What is a genetic cause of restrictive cardiomyopathy?

Which of the following is an infiltrative cause of restrictive cardiomyopathy?

Which diagnostic tool is primarily used to diagnose restrictive cardiomyopathy?

Which treatment is generally contraindicated in amyloidosis-related restrictive cardiomyopathy?

Which condition is NOT a storage disease that can cause restrictive cardiomyopathy?

Which of the following statements about restrictive cardiomyopathy is true?

What is the most common cause of restrictive cardiomyopathy?

Which geographic region has the highest incidence of death due to cardiac sarcoidosis?