Relative Contribution of Trends in Myocardial Infarction Event Rates and Case Fatality to Declines in Mortality: An International Comparative Study of 1.95 Million Events in 80.4 Million People in Four Countries

Background: Myocardial infarction (MI) mortality has declined since the 1970s, but contemporary drivers of this trend remain unexplained. The aim was to compare the contribution of trends in event rates and case fatality to declines in MI mortality in four high-income jurisdictions from 2002-2015. Methods: Linked hospitalisation and mortality data were obtained from New South Wales (NSW), Ontario, New Zealand and England. Age-adjusted trends in MI event rates and case fatality were estimated from Poisson and binomial regression models, and their relative contribution to trends in MI mortality calculated.     Findings: A total of 1,947,895 MI events were identified in ≥30 year olds. There were significant declines in MI mortality, event rates and case fatality in all jurisdictions. Age-standardised MI event rates were highest in New Zealand (men: 893/100,000 in 2002, 536/100,000 in 2015; women: 482/100,000 in 2002, 271/100,000 in 2015) and lowest in England (men: 513/100,000 in 2002, 382/100,000 in 2015; women: 238/100,000 in 2002, 173/100,000 in 2015). Annual age-adjusted reductions in event rates ranged from -2·6% (95% CI -2·7, -2·6) in men in England to -4·3% (95% CI -4·4, -4·1) in women in Ontario. Age-standardised case fatality was highest in England in 2002 (48%) but declined at a greater rate than in the other jurisdictions (men: -4·1%/year, (95% CI: -4·2, -4·0%); women: -4·4%/year, (95% CI: -4·5, -4·3%)). Declines in MI mortality rates ranged from -6.1%/year to -7.6%/year. Event rate declines were the greater contributor to MI mortality reductions in Ontario (69·4%), New Zealand (men 68·4%; women 67·5%) and NSW women (60·1%), while reductions in case fatality were the greater contributor in England (60% in men and women). There were greater contributions from case fatality reductions in younger age groups and event rate declines in older age groups. Interpretation: The contribution of trends in MI event rates and case fatality varied between jurisdictions, including by age and sex. Understanding the causes of this variation will enable optimisation of prevention and treatment efforts.   Funding Information: NHMRC (Australia); Health Research Council New Zealand; Canadian Institutes for Health Research; National Institute for Health Research, Oxford. Declaration of Interests: None to declare. Ethics Approval Statement: This study was approved by the University of Toronto Health Sciences Research Ethics Board, NSW Population & Health Services Research Ethics Committee (reference 2016/09/654), the New Zealand Health and Disability Ethics Committees (reference number H13/049) and the Central and South Bristol Multi-Centre Research Ethics Committee (04/Q2006/176).