Weather and Elevated Heart Attack Risk

Freezing outdoor temperatures is associated with an elevated risk for heart attack but weather conditions independent of the cold can also be triggers, suggests a cohort study from across Sweden.

For STEMI and NSTEMI combined, lower daily air temperature, lower atmospheric air pressure, higher wind velocity, and shorter duration of sunshine appeared to be independent triggers among the 274,029 patients in the SWEDEHEART registry cohort.

The strongest association was observed for air temperature, with a higher incidence of MI on days with air temperatures less than 0°C, with rates of MI declining when temperatures rose to greater than 3°C to 4°C,”  (October 24 in JAMA Cardiology)

In the analysis, a one-standard-deviation rise in air temperature that is by 7.4°C, corresponded to a 2.8% reduction in risk for MI.

Pollution and Heart Attack

Every 10 mcg/m3 increase in pollution there is significant increases in the risk of a cardiovascular event,  (hazard ratio 1.24), death from heart disease (HR 1.76), and stroke (HR 1.35). (N Engl J Med 2007; 356:447). PM2.5 concentration is associated with the risk of cardiac death (relative risk 1.2). (N Engl J Med 2009; 360:1085).

CO, NO2, SO2 and PM 2.5 are also linked to an increased risk of acute heart attack with risk ranging from 1 to 5 percent (JAMA 2012; 307:713).

PM < 10 increases the risk by raising the blood pressure through an increase in sympathetic tone (Circulation 2002; 105:1534), transient increases in plasma viscosity and impaired endothelial dysfunction (Circulation 2002; 106:933.) and the initiation of atherosclerosis (Circulation 2010; 121:2755, J Am Coll Cardiol 2010; 56:1803)

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