The implications of increasingly extreme fluctuations in Australia’s (and the rest of the world’s) climate, on the risk of acute coronary events and the resulting demand for acute cardiac services, require urgent exploration.
Special attention should be paid to extreme weather events in summer, when high temperatures can be combined with increased air pollution and, all too often, the occurrence of forest fires. Australians are no strangers to this combination, but the summer of 2019-20 was particularly problematic, with record temperatures complicated by widespread bushfires in Australia’s eastern and southern states. Not surprisingly, there have been isolated reports of collapse, and sometimes death, among people fighting fires.
Previous publications suggest that chronically high temperatures and persistently increased air pollution represent coronary risk factors and that increased environmental pollution by fine particles (on the order of 2.5 µm or less) . [PM2.5]) is particularly dangerous. However, much less information is available on the impact of rapid changes in these circumstances, particularly in relation to bushfires.
My colleagues and I therefore chose to use hospital admission data from Adelaide to assess the individual and combined impacts of elevated temperature, atmospheric PM2.5 density and the presence of active bushfires at 200 km on the frequency of hospital presentation with acute coronary syndromes (ACS; for example, acute myocardial infarctions [AMI] or unstable angina pectoris [UAP]) over a 120-day period from November 2019 to the end of February 2020. Data on hospital admissions from all adult public tertiary hospitals in the Adelaide metropolitan area were classified as follows .
Since Takotsubo syndrome (TTS; i.e., stress cardiomyopathy or “broken heart syndrome”) can theoretically be precipitated by acute stressful events, especially in older women, we also evaluated possible associations between these environmental factors and the incidence of TTS. Previously thought to be rare, the methodology for differentiating TSS from AMI has improved substantially over the past 10 years and is now known to account for approximately 10% of suspected cases of ACS in women.
Data were available on 539 patients: 402 had AMI and 92 had UAP. Most patients were older (median age 69 years) and most patients with AMI or PAU were male. Ten other patients had presumed AMI without hemodynamically significant coronary artery stenoses. On the other hand, only 35 patients were diagnosed with TTS, 89% of these were women. A total of 25 patients died in hospital.
Wildfires were present within 200 km of Adelaide on 47 of the 120 days assessed. Atmospheric concentrations of PM2.5 were generally low, exceeding “safe” limits (25 µg/m3) in just 14 days.
Analyzes of data from patients with AMI or UAP showed that elevated temperatures were strongly predictive of the number of daily presentations, as were elevated PM2.5 concentrations beyond “safe” limits. As a univariate parameter, the presence of forest fires was associated only with a non-significant trend towards increased incidence of AMI and UAP.
On days when these three risk factors occurred together, there was an incremental impact on the risk of AMI and UAP. Thus, when all three risk factors were present, there was an approximate doubling of the incidence of AMI and UAP (Figure 1).
Figure 1: The impact of the 3 factors individually and in combination on the number of daily presentations. Reproduced with permission.
Regarding TTS, we found no significant variability in incidence according to the presence or absence of any of the risk factors for AMI and PAU. This may reflect the relatively small number of TTS patients studied.
Our study had a number of limitations beyond the small number of TTS patients. For example, we did not have individual data on how far the assessed patients had actually come to wildfires, or what the concentration of PM2.5 particles was in the atmosphere in the precise region where they lived. We did not have data available on which of the patients studied had pre-existing coronary artery disease. We were unable to determine whether “hysteresis” (a lag phase between risk factor exposure and symptom onset) might apply because none of the factors assessed fluctuated substantially from day to day.
Finally, our results might have been different if we had considered a region where year-round air pollution levels are higher than in Adelaide.
Despite these limitations, it can be concluded from our results that the rise in ambient temperature, the presence of increased atmospheric concentrations of PM2.5, and the proximity of wildfires should be considered, especially cumulatively, as to predictors of increased frequency of presentation to hospital emergency departments with AMI. and UAP Although not yet studied in the same way, similar considerations may apply to respiratory emergencies.
The potential public health implications of these findings are that efforts should be made to maximize bed availability in emergency departments on what might now be considered “high ACS risk” days. . In addition, the public, especially the elderly, must be made aware of this incremental risk.
John Horowitz is Emeritus Professor of Cardiology at the Basil Hetzel Institute at the University of Adelaide.
Gao Jing Ong, Cardiology Research Laboratory, Basil Hetzel Institute for Translational Health Research, Queen Elizabeth Hospital.
Alexander Sellers, Department of Cardiology, Central Adelaide Local Health Network, Adelaide.
Gnanadevan Mahadavan, Department of Cardiology, Central Adelaide Local Health Network, Adelaide.
Thanh H Nguyen, Cardiology Research Laboratory, Basil Hetzel Institute for Translational Health Research, Queen Elizabeth Hospital, Adelaide.
Matthew I Worthley, University of Adelaide.
Derek P Chew, South Australian Health and Medical Research Institute, Adelaide.
Statements or opinions expressed in this article reflect the views of the authors and do not necessarily represent the official policy of the AMA, the MJA, or InSight+ unless otherwise stated.
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