Restrictive cardiomyopathy is characterized by impaired diastolic filling with reasonably preserved contractile function (VIDEO 10–25). The condition is relatively uncommon, with the most frequent cause being amyloidosis. Cardiac amyloidosis is more common in men than in women and rarely manifests before the age of 40. While light-chain amyloid proteins can be toxic to cardiomyocytes, they may also internalize into many cell types and this may explain some of the cardiac dysfunction observed. The AL (light-chain) type is the most common, with cardiac involvement in 50%. Other forms include mutated transthyretin (ATTR) in familial amyloidosis (usually manifested in the elderly black population) and a wild-type transthyretin amyloidosis. Transthyretin is produced almost entirely in the liver. Secondary (AA) amyloidosis due to fragments of serum amyloid A protein associated with chronic inflammatory disorders is a rare cause of cardiac disease. An isolated atrial amyloid form is also recognized.
The differential diagnosis of a restrictive cardiomyopathy includes infiltrative disorders beside amyloidosis, such as sarcoidosis, Gaucher disease, and Hurler syndrome. Storage diseases such as hemochromatosis, Fabry disease, and glycogen storage diseases can also produce the picture. Noninfiltrative diseases, such as familial cardiomyopathy and pseudoxanthoma elasticum, can be implicated rarely, and other secondary causes include diabetes, scleroderma, radiation, chemotherapy, CAD, and longstanding hypertension.
Concentric LVH usually results in an increase in the LVEF via the law of Laplace where wall thickness is inversely proportional to wall tension. In restrictive cardiomyopathy the walls are thickened, but the LVEF is lower; this is often a clue to the presence of an infiltrative process.