Ischaemic heart disease and sudden death, 1901-61.

Abstract

Several distinguished authorities have recently questioned the widely held belief that death rates from ischaemic heart disease (IHD) have increased during the present century. Robb-Smith (1967) has devoted a monograph to the subject and con cludes that the evidence in favour of any real in crease is very insubstantial. He believes that the apparent increase in IHD mortality in England and Wales can be entirely explained by the ageing of the population and by the changes in medical termino logy which have taken place during the past few decades. Similar conclusions have been reached by Campbell (1963a, b) and Bedford (1968) in Britain, and by Moriyama and Woolsey (1951) and Lew (1957) in the United States. The resolution of this controversy is of more than academic interest, since a substantial part of the current large-scale effort to control IHD through public health education and aetiological research is based on the belief that some modern factors in our way of life are responsible for the present 'epidemic'. We have therefore re-examined the evidence provided by death certificates, taking care to avoid the pitfalls documented by Robb-Smith and the other critics. Our study has been restricted to deaths occurring among men aged 45 to 64 in the Province of Ontario between 1901 and 1961, and we have based our conclusions on information obtained from original death certificates, on the records of the Toronto chief coroner's office, and on the official mortality tabulations of the Registrar General of Ontario. Mortality records based on death certificates have often in the past proved to be an unsatisfactory method of studying trends in IHD mortality, because of the uncertainty surrounding the diagnosis of this condition (particularly in the early years of the century) and because of the frequent changes which have taken place in the international classification of causes of death, on which most official mortality tabulations are based. Blockage of a coronary artery by a thrombosis or an embolus was well recognized as a cause of sudden death by the end of the nine teenth century (Osier, 1895), but it was not until after the reports of Herrick (1912, 1919) that non-fatal coronary thrombosis came to be recognized as the underlying lesion in many cases of 'myocarditis' or 'fatty degeneration of the heart'. In any retrospective study it is therefore necessary to take account of these changes in medical terminology if misleading conclusions are to be avoided (Stewart, 1950; Piatt, 1951). In addition to errors resulting from a lack of knowledge of ischaemic heart disease in the past, errors may also have occurred in the diagnoses appearing on death certificates as a result of the physican's misinterpretation of symptoms and physical signs. Thus dyspnoea of cardiac origin may sometimes have been ascribed to bronchial asthma, ankle oedema to Bright's disease (chronic nephritis), substernal pain to indigestion, and sudden death to apoplexy or cerebral haemorrhage. Rheu matic and syphilitic heart disease may also have been overdiagnosed in the past at the expense of ischaemic heart disease (Campbell, 1963a, b). We have attempted to circumvent some of these problems by using three definitions of ischaemic heart disease. First, a narrow definition of 'pure' IHD in which only terms such as angina pectoris, arteriosclerotic heart disease, and coronary throm bosis were accepted. Second, a somewhat broader definition in which, in addition to the preceding terms, certain non-specific diagnoses were accepted su h as heart failure, myocarditis, cardiac dropsy, and organic heart disease. Third, a very broad definition in which rheumatic heart disease, chronic nephritis, cardio-renal disease, asthma, indigestion, hypertension, and apoplexy were included. It was hoped that the first and third of these definitions would provide a form of lower and upper probability limit for the true rate of IHD mortality, and that over the years there might be common trends in all three definitions which would enable valid con clusions to be drawn. To ensure that the death rates calculated for each of these definitions were undistorted by the periodic variations in the international classification of causes of death, we have worked with original death 1