3 DECEMBER 2021 ausdoc . com . au
Figure 1 . Air pollution .
Extreme temperature and ischaemic heart disease
Temperature is an important environmental risk factor for IHD with both extremely cold and hot temperatures associated with increased mortality from IHD or CHD . 29-31 A similar U or V shaped relationship to CVD deaths is seen with IHD mortality , with more MI deaths caused by adverse temperatures in winter than in summer . 17
Cold and heat exposure are associated with an increased MI risk , and CHD / MI hospitalisation . 33-38 That said , some studies have shown increased MI hospitalisations with cold but not
39 , 40 high temperatures .
The effect of heat exposure and heatwaves on MI are immediate , whereas the impacts of cold exposure are delayed . 32 The more immediate effects of heat exposure may explain the inconsistent findings in the relationship between heat exposure and MI hospitalisations , as heat exposure might result in an increase in out of hospital deaths with acute MI events . 41
An increase in latitude is associated with a decreased risk of MI hospitalisation due to cold exposure .
32 , 33
An Adelaide study found mortality , morbidity and hospital admissions related to congestive heart failure ( CHF ) were higher in winter relative to summer , with those older than 75 at risk of seasonal variations in morbidity and mortality . 42
Extreme heat and CVD
Climate change negatively impacts CVD , by its association with extreme heat , which is particularly relevant in Australia as our maximum temperatures , heatwave exposure and vulnerability to these extremes is increasing . 7 The frequency , intensity and duration of heatwaves are expected to continue increasing with climate change . 43-45
Heatwaves and high temperatures increase CV morbidity and CV mortality risk . 46-51 The larger the increase in temperature , the higher the risk of CVD death . 52 Heatwaves are associated with increased all-cause and CV mortality , especially among the elderly , and with an increased risk of IHD , stroke and CHF mortality . 49 , 53 Mortality risks are greater for more intense
heatwaves . 49 , 53 With increasing temperatures and intense heatwaves of longer duration , mortality due to CVD ,
54 , 55
MI and CHF is expected to increase . Particularly vulnerable are the elderly , those with pre-existing CVD ( IHD , CHF and stroke ) and those performing
56 , 57 heavy physical labour .
Heatwaves and extremely high temperatures increase hospitalisation for CVD , especially IHD and arrhythmias . 58-62 In the US , hospital admissions for CVD and MI have been shown to increase in synchrony with the average temperature on the same or preceding day . 63 , 64 Some studies have found no or negative associations between increased temperatures / extreme heat and CVD hospitalisations . 65-67 However , others have noted positive associations between high temperature and heatwaves and CV mortality , especially among the elderly . 68 , 69 This suggests individuals may die from CVD during high temperatures before seeking medical attention or being admitted to hospital . 70 An increased risk of out-of-hospital cardiac arrest ( OHCA ) has been reported with elevated temperatures and heatwaves . 71
There is a short lag-effect of extreme heat on increased CVD hospitalisations and mortality of 0-4 days . 52
The ‘ urban heat island ’ is a meteorological phenomenon whereby cities are warmer than surrounding , less-developed regional locations due to human activities , as urbanised areas absorb and re-emit the sun ’ s heat more than ‘ green ’ areas . 72 , 73 Residents of urban regions are more vulnerable to the risk of heat-related mortality than those living rurally . 74 , 75 Almost 90 % of Australians live in urban areas , and this is expected to increase . 76
Pathophysiology
Mechanisms for the effects of temperature / season on CV death and MI have been postulated but are not definitive . Cold may increase cardiac load through raised inflammatory markers and coagulation parameters . 77 Cooling of skin could increase systemic vascular resistance , heart rate and blood pressure ( BP ), decreasing myocardial oxygen supply . 78 , 79 These changes
Table 1 . Air pollution and CVD Condition
Air pollution effect CV mortality Increased CV and all-cause mortality with short-term exposure to PM 2 . 5
, PM 10 and NO 2
132-136
Increased CV mortality with long-term PM 2 . 5 exposure 137-142
Ischaemic heart disease Short- and long-term exposure : Increased IHD death 138-146 Increased ACS / MI , particularly STEMI 147-153 Those with underlying CAD are at particular risk 154
CVD hospital admissions
may lead to ischaemia . 80 , 81 In winter , a rapid decrease in temperatures could then trigger an acute MI / sudden cardiac death . Additionally , cold temperatures may trigger higher HbA1c levels in those with type 2 diabetes . 82
Exposure to heat can increase heart rate , BP , blood viscosity and coagulability , arterial thrombosis and cholesterol levels ; weaken core temperature regulation ; reduce myocardial oxygen supply ; and heighten MI and stroke risk . 83-85 Increased temperatures can cause dehydration ,
Increased admissions for CHF , AMI , cardiac dysrhythmias , and coronary atherosclerosis with short-term exposure , particularly PM 2 . 5
155-162
Elderly are particularly at risk 163-165 Heart failure Increased mortality 166
166 , 167
Increased hospital admissions Increased incidence with long-term PM 2 . 5 exposure 153
Stroke Increased stroke mortality and hospitalisations with short-term PM 2 . 5 and PM 10 exposure 168
Short-term PM 2 . 5 exposure : increased ischaemic ( but not haemorrhagic ) stroke hospital admissions 162 169 , 170
Increased stroke mortality with long-term PM 2 . 5 exposure
170 , 171
Increased stroke incidence with long-term PM 2 . 5 and PM 10 exposure Living close to a roadway is associated with increased stroke risk and severity 172
Blood pressure Increased BP ( acute and chronic , increased prevalence ) 173-179
180 , 181
Traffic-related air pollution poses a particularly high risk
182 , 183
Diabetes Increased insulin resistance
182 , 184-186
Increased diabetes
Arrhythmias Short-term exposure : Increased cardiac arrhythmia hospitalisation or mortality 187 Increased atrial fibrillation ( AF ) 188 Increased ventricular arrhythmias ( VA ), including in those with ICDs 189-191 Increased out-of-hospital cardiac arrest ( OHCA ), especially PM 2 . 5
192,193
Long-term exposure to PM may prolong QT 194
Atherosclerosis Increased atherosclerosis 195 Increased coronary artery calcium ( CAC ) score , odds of detectable CAC and CAC severity 196
197 , 198
Increased carotid intima media thickness ( CIMT ) Increased arterial brachial index Traffic-related air pollution and proximity to traffic is significantly associated with increased coronary atherosclerosis and CAC score 198-200
Other associations Left and right ventricular hypertrophy after long-term exposure to NO 2
201,202
Increased CRP levels in those with metabolic syndrome 203 Obesity in children 182
decrease sodium levels , increase circulation of the surface blood from vasodilation , and can lead to fluid and electrolyte disturbances , a frequent complication in patients with coronary dysfunction . 86 , 87 Under extreme heat stress , the body may lose its ability to thermoregulate , resulting in heat exhaustion , heat syncope and heat stroke . 88 These responses to extreme heat are more significant in the elderly , and in those with underlying CVD including IHD , heart failure and stroke . 89
AIR POLLUTION AND CVD
AIR pollution is composed of particulate matter ( PM ) and gaseous components ( see figure 1 ). Exposure to air pollutants is associated with adverse health outcomes , including CV ( see table 1 ), respiratory and oncologic diseases . 90
The PM fraction is categorised by aerodynamic diameter : less than 0.1μm ultrafine particles , less than 2.5μm fine particles ( PM 2 . 5
), less than 10μm coarse