For many years, paediatric cardiologists and paediatric cardiac surgeons have felt the need for a common diagnostic and therapeutic coding system with which to classify patients of all ages with congenital and acquired heart disease. This desire has been highlighted by the recent, and ongoing, enquiry into the outcome of paediatric cardiac surgery at the unit in Bristol, in the United Kingdom, and the resulting obligation to provide national and international comparisons of surgical results between centres caring for these patients. In order to incorporate effective clinical governance and best practice into our speciality, a method is required to gather accurate and validated data on the diagnosis, therapy and outcome of patients with heart disease from prenatal life through to adulthood. This would facilitate comparisons between individual units which fully take into account the mix of cases involved, and thus attempt to focus on the relevant and genuine factors underlying the differing outcomes in terms of both mortality and morbidity. For this to be achieved, it is essential to have a comprehensive system of coding and classification, using mutually exclusive and unambivalent terms. The system must be both easy to use, and fulfil the needs and expectations of widely different cultures of practice. Although many centres have developed their own system of internal audit, with their own coding system, and some co-operation has taken place between centres nationally and across international boundaries within Europe by the European Congenital Heart Surgeons Federation (see below), a cohesive, and comprehensive system suitable for setting standards has yet to emerge. Historically, this has partly been due to the lack of recognition by governments of the importance of such a process, with underfunding of initiatives aimed at addressing these issues, both technologically and in terms of human resources.

The Long List is a comprehensive hierarchical system of coding and classification for the diagnosis and treatment of heart disease. Although originally aimed at the clinician or surgeon treating heart disease first appearing in infancy or childhood, it has now been enlarged to encompass abnormalities first diagnosed in fetal life, as well as heart disease first acquired during adult life. There are a total of 3,876 individual terms. For the most part, these are mutually exclusive and unambivalent, given the constraints of clinical ambiguities and differing cultures of practice. In addition, there are 564 qualifier terms. These provide additional detail to individual or multiple items, such as fine anatomical detail, the severity of a lesion, the size of an interposition shunt or conduit, or the material used to close a septal defect. Finally, there are a further 341 duplicate diagnostic or procedural terms included in the List to aid its use, as some terms may have relevance in multiple areas. For example, Hypoplastic left heart syndrome is found under congenital anomalies of the left ventricle as well as in the section dealing with the aortic valve. Thus, altogether the listing consists of 4,781 items. The System is hierarchically arranged, with a major division between diagnostic and therapeutic subhierarchies. The developmental history of the Long List has been published previously, and is detailed earlier in this supplement.