Background and aims: Heart failure (HF) is a common health problem worldwide. Despite its importance, the epidemiology of HF is incompletely understood. Frequent references to an epidemic of HF are at odds with recent reports of a decline in mortality from heart failure. In addition, reports based on admissions to hospital with a diagnosis of HF show that an earlier upward trend levelled off in the late 1990s in most developed countries. However, HF is a heterogeneous condition with multiple underlying causes. A decline in the severity of acute myocardial infarction (AMI), one of the major underlying causes of HF, and improvement in the treatment of patients with AMI as well as of hypertension are factors that might produce contradictory effects on the epidemiology of HF. Recent claims of a major contribution of improved survival after AMI to the reported epidemic of HF in the United States of America need to be examined in other populations. This thesis aims to define more precisely the epidemiological features of heart failure in Australia, and how these have evolved over the last decade. It examines secular trends in mortality, hospital admissions, incidence and survival related to HF. Methods: Trends in mortality from HF and admission to hospital with a diagnosis of HF are examined using computerized records of all deaths occurring in Australia for calendar years 1997-2003 and National Hospital Morbidity Data for financial years 1996-1997 to 2003-2004, obtained from the Australian Institute of Health and Welfare. A death or admission to hospital was defined as involving HF if at least one of the causes of death or one of the diagnoses of each separation was coded to any of the relevant rubrics within the International Classification of Disease, 9th Revision, Clinical Modification (ICD-9-CM) or 10th Revision, Australian Modification (ICD-10-AM). The analyses are based on age- and sex-specific death and hospital separation rates for HF either as underlying cause (or principal diagnosis) or mentioned anywhere on the death certificate (or recorded in any diagnostic position in the hospital electronic file) for each calendar or financial year. The investigation of trends in incidence and outcome of early-onset HF (HF complicating an index AMI within 28 days) and late-onset HF after AMI (HF developing 28 days after an index AMI) was based on the World Health Organization MONItoring trends and determinants of CArdiovascular disease (MONICA) register in Western Australia. The study included all residents aged 25-64 years of Perth, the capital city of Western Australia, who were admitted to hospital between 1988 and 1993 with non-fatal definite AMI and who had no history of AMI or HF in the hospital record. Trends in incidence and outcome of early- and late-onset HF were investigated using appropriate statistical methods. Results: From a total of 907,242 deaths occurring in Australia between 1997 and 2003, heart failure was coded as the underlying cause of death (UCD) for 29,341 (3.2%) and was mentioned anywhere on the death certificate in 135,268 (14.9%). Over this period, in both sexes, there were decreases in the absolute numbers of deaths and in the age-specific and age-standardized mortality rates for HF either as UCD or mentioned anywhere on the death certificate. HF was mentioned in 24.6% and 17.8% of deaths attributed to ischaemic heart disease and circulatory disease respectively, and these proportions remained unchanged over the period of study. In addition, HF as UCD accounted for 8.3% of deaths due to circulatory disease and this did not change from 1997 to 2003. From a total of 48,562,285 separations from hospital between 1996-7 and 2003-4, HF was coded as the principal diagnosis for 344,081 (0.8%) and was mentioned anywhere on the hospital record in 1,212,109 (2.5%). While the number of separations with HF remained stable, the age- and sex-standardized separation rate for HF recorded as principal diagnosis decreased from 2.0 per 1000 population in 1996-1997 to 1.7 per 1000 population in 2003- 2004. The corresponding values for HF recorded in any diagnostic position were 7.8 and 5.0 per 1000 population. From all patients (N = 4006) who met the criteria for first-ever, non fatal definite AMI in the Perth MONICA Register, 897 (22.4%) had early-onset HF complicating the index event. After adjustment for age and sex, the odds of developing HF declined by 13% (odds ratio for the period 1989-1993 relative to 1984-1988 = 0.87, 95% confidence interval (95%CI): 0.75 to 1.01). After adjustment for age and history of diabetes and hypertension, the hazard of death in patients with early-onset HF (i.e. case fatality) declined by 26% (HR for the period 1989-1993 relative to 1984-1988 = 0.74, 95%CI: 0.57 to 0.96). Of 3109 patients who did not develop early-onset HF, 406 (13.1%) had at least one subsequent hospital admission with a diagnosis of HF (defined as late-onset HF). Following adjustment for age and sex, the hazard ratio for late-onset HF for the period 1989-1993 relative to 1984-1988 was 0.85 (95% confidence interval (95%CI): 0.69-1.04). History of diabetes and hypertension, current smoking, length of initial admission for AMI, recurrent acute coronary syndrome and coronary artery revascularization procedures were predictors of late-onset HF. After a median follow-up of 3.2 years and adjustment for age (≥70 years) and history of diabetes, the hazard of death in patients with late-onset HF did not change over the period of study (HR for year = 1.02, 95%CI: 0.98 to 1.06). Conclusion: For reasons discussed in the body of the thesis, the observed decline in mortality from HF measured as either number of deaths or rate probably reflects a real change in the epidemiology of HF. In addition, there was no increase in the number of hospital admissions involving HF and standardized rates of hospital separations fell in Australia between 1996 and 2004. These results do not support a major increase in the caseload of HF over recent years. In addition, a decline in the risk of early- and late-onset HF after AMI as well as all the evidence on decline in incidence and severity of coronary artery disease and hypertension argue against an increase in inflow from these two important risk factors of HF. However, taking all of the influences on the epidemiology of HF together, it is likely that because of the increasing number of older people, the number of new cases of HF will rise over the next few years, even if the incidence rate falls.
| Identifer | oai:union.ndltd.org:ADTP/253139 |
| Creators | Najafi, Farid |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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