Restrictive and Infiltrative Cardiomyopathies

Introduction

Restrictive cardiomyopathy (RCM) refers to either an idiopathic or a systemic myocardial disorder in the absence of underlying atherosclerotic coronary artery disease, valvular disease, congenital heart disease, or systemic hypertension, which is characterized by abnormal left ventricular filling, and is associated with normal or reduced left ventricle (LV) and right ventricle (RV) volumes and function. The term is not precise, but it incorporates infiltrative and fibrotic cardiac pathology, which are dealt with in this chapter. While the majority of patients with infiltrative and fibrotic cardiomyopathies develop a restrictive filling pattern, especially in the later stages of the disease, it is important to differentiate the pathology from a restrictive filling pattern, which can be associated with other types of heart disease, such as dilated cardiomyopathy. In patients with dilated cardiomyopathy the restrictive filling pattern is often a reversible phenomenon, related to worsening heart failure, and morphologically the ventricle is dilated, usually with severe reduction in ejection fraction. Although the clinical presentation of RCM may be similar to dilated cardiomyopathy, the nondilated, stiff ventricles often result in highly sodium-sensitive heart failure symptoms, associated in the late stage of the disease with a low cardiac output due to the small stroke volume. Because of the restriction to diastolic filling and an associated impaired ability to augment cardiac output at higher heart rates, these patients may also present with symptoms of exercise intolerance.

Diastolic dysfunction in the presence of preserved left ventricular ejection fraction (LVEF) is the key component of pathophysiology of RCM. Initial stages of RCM demonstrate preserved LVEF with noncompliant walls that impair the normal diastolic filling of the ventricle. This restriction can be isolated to either ventricle, or show biventricular involvement. Biventricular volumes are either normal or reduced. Over a period of time, the chronically elevated LV diastolic pressure leads to increased atrial size, which may be considerable. Although severe biatrial enlargement without valve disease is a classic finding of RCM, this is a nonspecific feature, as it may occur in other conditions, particularly if associated with long-standing atrial fibrillation. In later stages of the disease, as the compliance of the LV decreases, a small change in LV volume is associated with a steep rise in LV pressure. A reduced ejection fraction may occur in the very late stages of the disease. It is important to recognize that, although the left ventricle may show diastolic dysfunction with a normal ejection fraction, longitudinal systolic function may be significantly impaired, and thus a normal ejection fraction should not be considered synonymous with normal systolic function ( Video 24.1, Video 24.2 ).

Spectrum of Restrictive Cardiomyopathy

RCM can be considered as either “primary” RCM or RCM secondary to other conditions such as infiltrative disorders and storage disorders. Infiltrative disorders primarily affect the interstitial space of the myocardium, whereas storage diseases are associated with deposits within the cardiac myocytes. In addition, endomyocardial involvement, leading to restriction, may occur in a variety of uncommon conditions ( Box 24.1 ).