Restrictive Cardiomyopathy

A 60-year-old man presents with progressive shortness of breath and fatigue. He has also noticed swelling in his legs and abdomen. Echocardiography shows normal left ventricular size and systolic function with evidence of diastolic dysfunction.

Pathophysiology

Restrictive cardiomyopathy is characterised by reduced ventricular compliance, resulting in impaired diastolic filling. The myocardium itself may be normal, but infiltration or fibrosis of the ventricular walls prevents them from relaxing properly during diastole. This leads to increased filling pressures in the atria and elevated systemic venous pressures, while stroke volume and cardiac output remain low.

Aetiology

The causes of restrictive cardiomyopathy can be classified by the underlying pathology:

Myocardial causes:

• Infiltrative:
  • Amyloidosis
  • Sarcoidosis
  • Primary Hyperoxaluria (oxalate deposition within the heart)
• Storage Disease:
  • Metabolic Enzyme Deficiencies:
    • Lysosomal Storage Diseases (Gaucher’s, Hurler’s, Fabry)
    • Glycogen Storage Disease
  • Haemochromatosis and Iron Overload
• Non-infiltrative:
  • Idiopathic
  • Scleroderma

Endomyocardial causes:

• Endomyocardial fibrosis: most common form, mostly affecting younger patient
  • Possibly initiated by: viral/parasitic infections, chronic eosinophilia, magnesium deficiency, elemental cerium
• Hypereosinophilic syndrome (Löffler endocarditis)
• Endocardial Fibroelastosis: proliferation of fibrous and elastic tissue causing diffuse thickening of LV endocardium
• Metastatic malignancies
• Carcinoid
• Iatrogenic (radiation, anthracyclines)

The most common cause of restrictive cardiomyopathy in the UK is amyloidosis, often secondary to multiple myeloma. Cardiac amyloidosis is characterised by the extracellular deposition of insoluble amyloid fibril proteins in the myocardium, leading to impaired ventricular function.

Epidemiology & Risk Factors

Restrictive cardiomyopathy is a relatively rare condition compared to other types of cardiomyopathy. The incidence and prevalence vary depending on the specific underlying cause. For example, the prevalence of cardiac amyloidosis is higher in older adults, and it is also more common in certain racial and ethnic groups. Risk factors for restrictive cardiomyopathy are essentially the same as those for the underlying conditions, such as multiple myeloma in the case of amyloidosis.

Clinical Features

The clinical presentation of restrictive cardiomyopathy often overlaps with that of constrictive pericarditis, making it challenging to distinguish the two conditions based on symptoms alone.  

Clinical features of restrictive cardiomyopathy typically resemble right-sided heart failure:

• Exertional dyspnoea
• Fatigue
• Peripheral oedema
• Ascites
• Elevated JVP with prominent x and y descents
• Hepatomegaly
• S4 heart sound

Investigations

Investigations for restrictive cardiomyopathy aim to establish the diagnosis and identify the underlying cause. They also help differentiate it from conditions like constrictive pericarditis:

• ECG: A characteristic finding in restrictive cardiomyopathy is diffusely diminished QRS voltages in infiltrative disease. Other non-specific ECG abnormalities may also be present.
• CXR: The CXR may show an enlarged cardiac silhouette, similar to that seen in pericardial effusion. However, the absence of significant cardiomegaly does not rule out restrictive cardiomyopathy.
• Echocardiography: Assess ventricular size, wall thickness and diastolic function. It may reveal thickened ventricular walls with normal or near-normal systolic function. However, echocardiography alone may not be sufficient to differentiate restrictive cardiomyopathy from constrictive pericarditis.
• Cardiac MRI: Increasingly used to diagnose restrictive cardiomyopathy and identify specific causes such as amyloidosis. It provides detailed images of the myocardium and can detect characteristic patterns of amyloid deposition.
• Cardiac catheterisation: Can help distinguish restrictive cardiomyopathy from constrictive pericarditis based on haemodynamic findings. While both conditions show elevated filling pressures, there is no "square root" sign in the right ventricular pressure tracing with restrictive cardiomyopathy. The left ventricular end-diastolic pressure (LVEDP) and right ventricular end-diastolic pressure (RVEDP) are approximately equal in both conditions.
• Endomyocardial biopsy: Considered the gold standard for diagnosing restrictive cardiomyopathy and identifying the underlying cause in cases where non-invasive tests are inconclusive. Biopsy findings can reveal specific features of amyloid deposition, sarcoidosis or other infiltrative diseases.

Management

Treatment of restrictive cardiomyopathy focuses on managing symptoms, treating the underlying cause, and preventing complications:

Lifestyle modifications:

• Fluid restriction: Restricting fluid intake can help manage fluid overload and symptoms of heart failure.
• Salt restriction: Reducing dietary sodium can also help control fluid retention and blood pressure.

Medical management:

• Diuretics: Diuretics are used to reduce fluid retention and relieve symptoms of congestion, but their effectiveness may be limited in advanced cases.
• Antiarrhythmic drugs: Medications like beta-blockers and amiodarone may be used to control heart rhythm abnormalities, such as atrial fibrillation and ventricular tachycardia.

Specific treatment for underlying causes:

• Amyloidosis: Treatment for amyloidosis is complex and depends on the type of amyloid protein involved. Chemotherapy and stem cell transplantation may be used in some cases.
• Sarcoidosis: Corticosteroids are the mainstay of treatment for sarcoidosis, though other immunosuppressive agents may be used in severe cases.
• Haemochromatosis: Treatment for haemochromatosis involves regular phlebotomy to remove excess iron from the body.

Surgical management:

Unlike constrictive pericarditis, there is no definitive surgical treatment for restrictive cardiomyopathy. Heart transplantation may be considered in end-stage disease.

Complications & Prognosis

Complications of restrictive cardiomyopathy include:

• Heart failure
• Atrial fibrillation
• Stroke
• Sudden cardiac death

Prognosis for restrictive cardiomyopathy is generally poor, and it often depends on the underlying cause and the severity of the disease. Cardiac amyloidosis, in particular, carries a poor prognosis, with a median survival of less than one year in untreated cases.