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Restrictive cardiomyopathy (RCM) is characterized by noncompliant ventricular walls that resist diastolic filling; one, most commonly the left, or both ventricles may be affected. Symptoms include fatigue and exertional dyspnea. Diagnosis is by echocardiography and cardiac catheterization. Treatment is often unsatisfactory and is best directed at the cause. Surgery is sometimes useful.
RCM is the least prevalent form of cardiomyopathy. It is classified as
Either type may be diffuse or nondiffuse (when the disorder affects only one ventricle or part of one ventricle unevenly).
The cause is usually unknown; identified causes are listed in Causes of Restrictive Cardiomyopathy. Some disorders that cause RCM also affect other tissues (eg, amyloidosis, hemochromatosis). Some myocardial infiltrative disorders also affect other cardiac tissue. Rarely, amyloidosis affects coronary arteries. Sarcoidosis and Fabry disease may also affect nodal conduction tissue. Löffler syndrome (a subcategory of hypereosinophilic syndrome with primary cardiac involvement), which occurs in the tropics, begins as an acute arteritis with eosinophilia, followed by thrombus formation on the endocardium, chordae, and atrioventricular (AV) valves, progressing to fibrosis. Endocardial fibroelastosis, which occurs in temperate zones, affects only the left ventricle.
Causes of Restrictive Cardiomyopathy
Endocardial thickening or myocardial infiltration (sometimes with death of myocytes, papillary muscle infiltration, compensatory myocardial hypertrophy, and fibrosis) may occur in one, typically the left, or both ventricles. As a result, the mitral or tricuspid valves may malfunction, leading to regurgitation. Functional AV valve regurgitation may result from myocardial infiltration or endocardial thickening. If nodal and conduction tissues are affected, the sinoatrial node malfunctions, sometimes causing various grades of AV block.
The main hemodynamic consequence is diastolic dysfunction (see Heart Failure:Diastolic dysfunction) with a rigid, noncompliant ventricle, impaired diastolic filling, and high filling pressure, leading to pulmonary venous hypertension. Systolic function may deteriorate if compensatory hypertrophy of infiltrated or fibrosed ventricles is inadequate. Mural thrombi can form, resulting in systemic emboli.
Symptoms are exertional dyspnea, orthopnea, and, when the right ventricle is affected, peripheral edema. Fatigue results from a fixed cardiac output due to resistance to ventricular filling. Atrial and ventricular arrhythmias and AV block are common; angina and syncope are uncommon. Symptoms and signs closely mimic those of constrictive pericarditis (see Constrictive pericarditis).
Physical examination detects a quiet precordium, a low-volume and rapid carotid pulse, pulmonary crackles, and pronounced neck vein distention with a rapid y descent (see Figure: Normal jugular vein waves.). A 4th heart sound (S 4 ) is almost always present; a 3rd heart sound (S 3 ) may occur and must be differentiated from the precordial knock of constrictive pericarditis. In some cases, a murmur of functional mitral or tricuspid regurgitation results because myocardial or endocardial infiltration or fibrosis changes chordae or ventricular geometry. Pulsus paradoxus does not occur.
ECG, chest x-ray, and echocardiography are required. The ECG is usually nonspecifically abnormal, showing ST-segment and T-wave abnormalities and sometimes low voltage. Pathologic Q waves, not due to previous MI, sometimes occur. Left ventricular hypertrophy due to compensatory myocardial hypertrophy sometimes occurs. On chest x-ray, the heart size is often normal or small but can be enlarged in late-stage amyloidosis or hemochromatosis.
Echocardiography shows normal systolic function. Common findings include dilated atria and myocardial hypertrophy. RCM due to amyloidosis has an unusually bright echo pattern from the myocardium. Echocardiography helps differentiate constrictive pericarditis with its thickened pericardium, but paradoxical septal motion can occur in either disorder. If the diagnosis is still in doubt, CT may be more sensitive in showing whether the pericardium is normal, and MRI can show abnormal myocardial texture in disorders with myocardial infiltration (eg, by amyloid or iron).
Cardiac catheterization and myocardial biopsy are not often necessary. If done, catheterization detects high atrial pressure in RCM, with a prominent y descent and an early diastolic dip followed by a high diastolic plateau in the ventricular pressure curve. In contrast to constrictive pericarditis findings, diastolic pressure is usually a few mm Hg higher in the left ventricle than in the right. Angiography detects normal-sized ventricular cavities with normal or decreased systolic shortening. AV valve regurgitation may be present. Biopsy can detect endocardial fibrosis and thickening, myocardial infiltration by iron or amyloid, and chronic myocardial fibrosis. Coronary angiography is normal, except when amyloidosis affects epicardial coronary arteries. Occasionally, cardiac catheterization is not diagnostic, and rarely, thoracotomy is required to explore the pericardium.
Tests for the most common causes of RCM (eg, rectal biopsy for amyloidosis, iron tests or liver biopsy for hemochromatosis) should be done.
Prognosis is poor (see Diagnosis and Treatment of Cardiomyopathies) because the diagnosis is often made at a late stage. No treatment is available for most patients; symptomatic, supportive care can be provided.
Diuretics may be used for patients with edema or pulmonary vascular congestion but must be given cautiously because they can lower preload; the noncompliant ventricles depend on preload to maintain cardiac output. Digoxin does little to alter hemodynamic abnormalities and may cause serious arrhythmias in cardiomyopathy due to amyloidosis, in which extreme digitalis sensitivity is common. If heart rate is elevated, β-blockers or rate-limiting Ca channel blockers may be used cautiously in low doses. Afterload reducers (eg, nitrates) may cause profound hypotension and usually are not useful.
Septal myectomy/ablation may ameliorate some symptoms. Pacemaker implantation may help older patients who want to avoid more invasive procedures. Implantable cardioverter-defibrillators may help younger patients at higher risk of sudden cardiac death.
If the diagnosis is made at an early stage, specific treatment of hemochromatosis, sarcoidosis, and Löffler syndrome may help.
Transplantation is not recommended because the disorder may recur in the transplanted heart.
In restrictive cardiomyopathy, endocardial thickening or myocardial infiltration leads to a rigid, noncompliant ventricle and thus diastolic dysfunction; systolic function is normal until late in the disease.
Sometimes, valvular tissue or the conduction system is involved, causing valvular regurgitation or heart block and arrhythmias.
Etiology is usually unknown, but some cases are caused by amyloidosis, hemochromatosis or sarcoidosis.
Diagnosis is by echocardiography plus testing for cause.
Treatment is often unsatisfactory unless the cause can be addressed; diuretics may benefit patients with edema or pulmonary vascular congestion but must be used cautiously to avoid lowering preload.
Implantable devices may prolong life for certain patients.
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