title: Heat and risk of myocardial infarction: hourly level case-crossover analysis of MINAP database.
abstract: OBJECTIVE
  To quantify the association between exposure to higher temperatures and the risk of myocardial infarction at an hourly temporal resolution.
  
  
  METHODS
  Case-crossover study.
  
  
  METHODS
  England and Wales Myocardial Ischaemia National Audit Project (MINAP) database.
  
  
  METHODS
  24,861 hospital admissions for myocardial infarction occurring in 11 conurbations during the warmest months (June to August) of the years 2003-09.
  
  
  METHODS
  Odds ratio of myocardial infarction for a 1 °C increase in temperature.
  
  
  RESULTS
  Strong evidence was found for an effect of heat acting 1-6 hours after exposure to temperatures above an estimated threshold of 20 °C (95% confidence interval 16 °C to 25 °C). For each 1 °C increase in temperature above this threshold, the risk of myocardial infarction increased by 1.9% (0.5% to 3.3%, P=0.009). Later reductions in risk seemed to offset early increases in risk: the cumulative effect of a 1 °C rise in temperature above the threshold was 0.2% (-2.1% to 2.5%) by the end of the third day after exposure.
  
  
  CONCLUSIONS
  Higher ambient temperatures above a threshold of 20 °C seem to be associated with a transiently increased risk of myocardial infarction 1-6 hours after exposure. Reductions in risk at longer lags are consistent with heat triggering myocardial infarctions early in highly vulnerable people who would otherwise have had a myocardial infarction some time later ("short term displacement"). Policies aimed at reducing the health effects of hot weather should include consideration of effects operating at sub-daily timescales.
authors.affiliation: Department of Non-communicable Diseases Epidemiology, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK.
authors.forename: Krishnan
authors.initials: K
authors.lastname: Bhaskaran
authors.forename: Ben
authors.initials: B
authors.lastname: Armstrong
authors.forename: Shakoor
authors.initials: S
authors.lastname: Hajat
authors.forename: Andy
authors.initials: A
authors.lastname: Haines
authors.forename: Paul
authors.initials: P
authors.lastname: Wilkinson
authors.forename: Liam
authors.initials: L
authors.lastname: Smeeth
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D016001:Confidence Intervals; D018592:Cross-Over Studies; D004562:Electrocardiography; D004739:England / Q000453:epidemiology; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000453:epidemiology* / Q000209:etiology; D016017:Odds Ratio; D012042:Registries; D012307:Risk Factors; D013997:Time Factors; D014852:Wales / Q000453:epidemiology; D055815:Young Adult