Restrictive Cardiomyopathy
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Direct answer
Restrictive cardiomyopathy is a myocardial disorder in which stiff ventricles impair diastolic filling, while systolic function is usually preserved or only mildly reduced. Its hallmarks are a restrictive filling pattern on echocardiography, a dip-and-plateau pattern on pressure tracings and biatrial enlargement, with cardiac amyloidosis and sarcoidosis among the common causes. Distinguishing it from constrictive pericarditis matters, because pericardiectomy cures constriction but does nothing for restriction.
What you must remember
- Core defect: a stiff myocardium that fills poorly in early diastole, with near-normal systolic ejection fraction in the early stages.
- Haemodynamics: raised filling pressures with a small ventricular cavity and biatrial enlargement.
- Echo: restrictive filling with a high E/A ratio, a short deceleration time and low annular tissue velocities.
- Square-root sign: a dip-and-plateau pattern on the ventricular pressure tracing, which can also occur in constrictive pericarditis.
- Causes: cardiac amyloidosis, sarcoidosis, haemochromatosis, endomyocardial fibrosis and radiation-induced fibrosis.
- Amyloid clue: low ECG voltage out of proportion to the thickness of the ventricular wall.
- Diagnosis: cardiac MRI with late gadolinium enhancement, and endomyocardial biopsy when the cause is unclear.
- Management: cause-specific therapy, careful diuresis, and avoidance of digoxin in amyloid.
Where the exam tries to catch you
Restrictive cardiomyopathy questions test the distinction from constriction.
- Trap: Recommending pericardiectomy for restrictive cardiomyopathy. Correct: Surgery treats constriction, but restrictive cardiomyopathy needs treatment of its underlying cause.
- Trap: Calling restrictive cardiomyopathy systolic heart failure. Correct: Systolic function is usually preserved early, and the defect lies in diastolic filling.
- Trap: Dismissing amyloid when the voltage looks normal. Correct: Low voltage with a thick ventricular wall is a red flag, though some amyloid cases have normal voltage.
- Trap: Using digoxin for atrial fibrillation or failure in amyloid. Correct: Amyloid fibrils bind digoxin, which raises the risk of toxicity, so caution is needed.
Frequently asked questions
What is the square-root sign in restrictive cardiomyopathy?
The square-root sign is a rapid early diastolic descent followed by a plateau on the ventricular pressure tracing, seen in restrictive cardiomyopathy. A similar dip-and-plateau pattern can appear in constrictive pericarditis, so the sign alone does not separate the two.
How does restrictive cardiomyopathy differ from constrictive pericarditis on imaging?
Constrictive pericarditis shows a thickened or calcified pericardium on CT or MRI and marked respiratory variation in mitral inflow. Restrictive cardiomyopathy shows a normal pericardium with an infiltrated or stiff myocardium, which is the key distinction.
Which ECG clue suggests cardiac amyloidosis?
Low limb-lead voltage out of proportion to ventricular wall thickness is a key ECG clue to cardiac amyloidosis. Conduction disease and atrial arrhythmias may accompany the diagnosis.
Why is pericardiectomy not used for restrictive cardiomyopathy?
Pericardiectomy removes a constricting pericardium, which is not the problem in restrictive cardiomyopathy. The stiffness lies within the myocardium, so treatment targets the underlying cause such as amyloidosis or sarcoidosis.