Assessment of Restrictive Cardiomyopathy

1. Introduction

1.1 The BSE Education Committee has published a minimum dataset for a standard adult transthoracic echocardiogram, available on-line at www.bsecho.org. This document specifically states that the minimum dataset is usually only sufficient when the echocardiographic study is entirely normal. The aim of the Education Committee is to publish a series of appendices to cover specific pathologies to support this minimum dataset.

1.2 The intended benefits of such supplementary recommendations are to:

• Support cardiologists and echocardiographers to develop local protocols and quality control programs for adult transthoracic study;

• Promote quality by defining a set of descriptive terms and measurements, in conjunction with a systematic approach to performing and reporting a study in specific disease-states;

• Facilitate the accurate comparison of serial echocardiograms performed in patients at the same or different sites.

1.3 Understanding restrictive cardiomyopathy (RCM).

This document gives recommendations for the image and analysis dataset required in patients being assessed for restrictive cardiomyopathy (RCM). RCM is a functional classification that is made on the basis of adverse filling of the left ventricle and is therefore different from the structural changes that describe other forms of cardiomyopathy (such as hypertrophic or dilated). RCM can either be primary or more commonly secondary to various conditions (see table) adversely affecting the filling pattern of the left ventricle. The natural histories of conditions causing myocardial restriction exhibit a spectrum of cardiac pathophysiology from subclinical (including the early stages of diastolic dysfunction) through to severely restrictive diastolic filling patterns. Thus the operator should take care to interpret more subtle findings that may be the only manifestations of disease development, with novel deformation imaging assisting in the identification of early disease states.

The morphological and anatomical features of causative pathologies in RCM can be indicative but not specific of an underlying disease state. The majority of RCMs are secondary to systemic aetiologies, the commonest of which is amyloidosis. In contrast, idiopathic (primary) RCM is rare. The term amyloidosis describes a group of disorders caused by abnormal folding, aggregation and accumulation of certain proteins in the tissues, in an abnormal form known as amyloid deposits. This document gives recommendations for the image and analysis dataset required in patients being assessed for RCM with a particular reference to cardiac amyloidosis and the transthoracic echocardiography protocol performed at The UK National Amyloidosis Centre (NAC), with whom this guideline has been co-authored (http://www.ucl.ac.uk/medicine/amyloidosis).

While echocardiography allows a comprehensive assessment in RCM, it is important to remember the complementary role of other imaging modalities, including cardiac MRI.

Adapted from Nihoyannopoulos & Dawson, European Journal of Echocardiography (2009) 10, iii23-iii33

1.4 The distinction between concentric remodeling versus concentric hypertrophy (see figure) is an important concept that is poorly understood, but is of prognostic significance in patients with preserved left ventricular ejection fraction.

The distinction requires the calculation of relative wall thickness (RWT) and LV mass using the following formulae:

RWT = (2 x LVPWd) ÷ LVIDd

LV mass = 0.8 x {1.04 x [(LVIDd + LVPWd + IVSd)³ - (LVIDd)³]} + 0.6 g

Where LVIDd = left ventricular internal dimension in diastole, LVPWd = left ventricular posterior wall width in diastole, IVSd = interventricular septal width in diastole.

RWT is increased (= 0.42) in both concentric remodeling and hypertrophy, but in infiltrative cardiomyopathy the important distinction is the increased left ventricular mass (>95 g/m² in females, >115 g/m² in males). Conversely, the measurement of RWT in cases of increased LV mass allows the distinction between concentric (relative wall thickness = 0.42) and eccentric (< 0.42) hypertrophy.

1.5 The views and measurements are focused upon RCM and are supplementary to those outlined in the minimum dataset. These are given assuming a full study will be performed in all patients.

1.6 When the condition or acoustic windows of the patient prevent the acquisition of one or more components of the supplementary Dataset, or when measurements result in misleading information (e.g. off-axis measurements) this should be stated.

1.7 This document is a guideline for echocardiography in the assessment of RCM and will be up-dated in accordance with changes directed by publications or changes in practice.

Abbreviations

References and Further Reading

A '*' indicates that these findings, particularly when found together within an individual echo study, are strongly suggestive of cardiac amyloidosis