Chapter 31

Cardiomyopathies are an important and heterogeneous group of diseases for which an understanding in both the public and medical community has historically been impaired by confusion surrounding definitions and nomenclature. Classification schemes, of which there have been many,1-8 are useful in defining and drawing relationships or distinctions between these complex diseases for the purpose of promoting greater clarity. Indeed, the precise language of these diseases is profoundly important.

However, many classifications in the literature are to some degree contradictory in design, and indeed none of the proposed schemes can be regarded as ideal (including the most recent and contemporary one presented here). The dilemma is caused by the heterogeneity in the presentation of this diverse group of diseases. A previous prominent classification of cardiomyopathies (1995) was represented in a very brief document under the auspices of the World Health Organization (WHO).1 However, with the identification of new diseases over the past decade, and dramatic advances in cardiovascular diagnosis and knowledge regarding etiology, some disease definitions have become outdated and the WHO classification rendered essentially obsolete. Indeed, the past several years has witnessed a rapid evolution in the molecular genetics of cardiology.9-14 In particular, ion-channelopathies have emerged as conditions predisposing to potentially lethal ventricular tachyarrhythmias, caused by mutations in proteins leading to dysfunctional sodium, potassium, calcium, and other ion channels.

Recently, under the auspices of the American Heart Association, a contemporary classification of cardiomyopathies has been presented,15 relying substantially on recent advances in the characterization of diseases affecting the myocardium.16-18 The new classification scheme affords a large measure of clarity to this area of investigation and facilitates interaction among the clinical and research communities in assessing the diagnosis, prognosis, and management of these complex diseases. This classification takes the place of the WHO document, but as new data emerge it also will undoubtedly require further review and revision.

The contemporary definitions of cardiomyopathies presented here are in concert with the molecular era of cardiovascular disease7 and have direct clinical applications and implications for cardiac diagnosis. However, the classification is a scientific presentation which does not provide methodologies or strategies for clinical diagnosis, nor is it directly applicable to management decisions for patients.

### Historical Context

The definition and classification of heart muscle diseases has seen a notable and evolving history. For example, chronic myocarditis was the only recognized cause of heart muscle disease in the 1850s.2 In 1900, the designation of primary myocardial disease was first introduced. However, it was not until 1957 that the term cardiomyopathy was used for the first time. Over the next 25 years, a number of definitions for cardiomyopathies were advanced in concert with an increasing awareness of the nature of these diseases. Indeed, in the original WHO classification,3 cardiomyopathies were defined only as, "heart muscle diseases of unknown cause," seemingly primitive by today's standards, and reflecting the paucity of ...

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