Classification of the cardiomyopathies

The cardiomyopathies have represented a challenging group of disorders to classify. The diversity of the disorders and the fact that many have only been recognized as clinical entities over the past 25 years continues to impede progress. Classification systems based on morphology, physiology, and etiology have been attempted and most systems are based on a combination of these three organizing principles. Despite these efforts, there are significant limitations with each of these systems, with many ambiguous cases, some newer cardiomyopathies that do not readily fit within the existing nomenclature systems, and a general sense of dissatisfaction with the mixed bases for these classification systems (phenotype and etiology). The continuing and accelerating molecular definition of the causes of many of these disorders has led a number of investigators to suggest that a classification based on the genetic basis for many of these diseases might overcome some of the limitations of prior systems. An American Heart Association Consensus Panel was convened to consider this issue and their scientific statement was published in 2006. This consensus document reviewed the problems associated with the phenotypic-based classification of the cardiomyopathies and proposed a new system that represents a significant departure from current clinical use. The changes recommended by this panel included implementing the presence or absence of a genetic etiology as the first order organizing principle. The panel recommended that use of the term hypertrophic cardiomyopathy be restricted to individuals with sarcomeric gene defects that manifest as a hypertrophic cardiomyopathic phenotype. They also recommended the inclusion of cardiac disorders that manifest primarily as arrhythmias (ion channelopathies) as forms of cardiomyopathies. This article reviews the implications of these recommendations and compares the existing and the proposed systems of classification.