Cardiomyopathy is defined as a 'myocardial disorder in which heart muscle is structurally and functionally abnormal without coronary artery disease, hypertension, valvular or congenital heart diseases'.
There are five types, namely hypertrophic, dilated, arrhythmogenic, restrictive and unclassified. Cardiomyopathy is a significant cause of sudden death in the young.
Restrictive cardiomyopathy is a condition characterised by normal left ventricular cavity size and systolic function but with increased myocardial stiffness. This makes the ventricle incompliant and fill predominantly in early diastole. It is often associated with raised left atrial pressure, atrial dilatation and sometimes arrhythmias.
- Relatively uncommon and the least common of the cardiomyopathies.
- Accounts for around 5% of all cardiomyopathies.
- Most patients are elderly.
- Males and females are affected similarly.
- However, idiopathic restrictive cardiomyopathy is more common in older women than in men (although it can also develop in young individuals).
- Restrictive cardiomyopathy is a leading cause of heart transplantation.
- Familial inheritance is not characteristic of restrictive cardiomyopathy.
- Restrictive cardiomyopathy is more prevalent in tropical Africa than in the Western world.
Usually no underlying cause is found.
The most common forms of restrictive cardiomyopathies are:
- Endomyocardial fibrosis associated with Löffler’s syndrome.
- Infiltrative myocardial disease.
- Amyloid heart disease - the most common cause of restrictive cardiomyopathy in the Western World.
- The myocardium may be infiltrated by iron in haemochromatosis, glycogen in Pompe’s and Cori’s disease, or glycolipids in Fabry’s disease.
- Usually presents with heart failure but normal systolic function: dyspnoea, fatigue, loud third heart sound, pulmonary oedema, murmurs due to valve incompetence.
- Heart size is usually normal or slightly enlarged.
- Features of right ventricular failure predominate: raised JVP, with prominent x and y descents, hepatomegaly, oedema, ascites.
- The clinical presentation of restrictive cardiomyopathy and constrictive pericarditis patients may be strikingly similar.
- Up to 75% of patients with idiopathic restrictive cardiomyopathy develop atrial fibrillation.
- Initial investigations are as for heart failure with ECG, CXR, blood tests including renal function, electrolytes, cardiac enzymes and LFTs.
- Echocardiography usually shows thickened ventricular walls, valves and atrial septum with small cavities.
- Cardiac catheterisation.
- Magnetic resonance imaging can be very useful at distinguishing restrictive cardiomyopathy from constrictive pericarditis.
- Advantages of cardiac magnetic resonance are that is provides a three-dimensional visualisation of the heart and its relationship to thoracic structures, it provides quantification of cardiac volumes and function, which can safely be repeated over time and it also provides information regrading tissue characterisation to detect focal scar and fatty infiltration.
- Cardiac CT is sometimes undertaken.
- Newer echocardiographic techniques such as speckle-track imaging, and velocity vector imaging are being introduced.
- Investigations of a possible underlying cause may need to be undertaken.
- The gold-standard diagnostic test is right ventricular biopsy, which demonstrates positivity for Congo red staining.
- Cardiac biopsy may be required to differentiate restrictive cardiomyopathy from constrictive pericarditis and to help identify an underlying cause.
Apart from constrictive pericarditis, which is the main differential diagnosis to consider, other constrictive diseases may mimic restrictive cardiomyopathy, so the following are often considered:
- Cardiac tamponade - constrictive only
- The management of restrictive cardiomyopathy is difficult because the underlying processes usually do not respond to intervention.
- In children, restrictive cardiomyopathy is primarily idiopathic, and transplantation is the treatment of choice.
- Management of heart failure, including diuretics and angiotensin-converting enzyme (ACE) inhibitors.
- Amiodarone can reduce ventricular arrhythmias in high-risk patients.
- All patients with restrictive cardiomyopathy and atrial fibrillation should be anticoagulated unless contra-indicated.
- Beta-blockers and non-dihydropyridine calcium-channel blockers may be used for rate control in those with atrial fibrillation.
- A pacemaker may be required (patients are often not able to tolerate the cardiac dysfunction associated with arrhythmias).
- A implantable cardioverter defibrillator: to prevent sudden death in high-risk patients.
- Transplantation may be indicated for some patients.
- Variable, depending on the underlying cause.
- Restrictive cardiomyopathy due to amyloid has a worse prognosis.
- Cardiac amyloidosis is difficult to treat due to poor tolerance of most cardiovascular medication and poor outcome for transplantation.
- Recent advances in diagnosis and treatment of amyloid are, however, associated with improved prognosis.
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