Cardiovascular Disease and Stroke
Impacts on Risk
Cardiovascular mortality associated with heat has been declining over time, presumably the result of increased air conditioning use; mortality associated with extreme cold has remained constant. Cardiovascular hospital admissions increase with heat. Dysrhythmias are primarily associated with extreme cold, though associations with dysrhythmias and heat illness have been reported. Stroke incidence increases with increasing temperature, as well. For all direct associations between temperature and cardiovascular disease and stroke, elderly and isolated individuals are at greatest risk.
Indirect impacts of weather, weather variability, and climate changes on cardiovascular disease are many and varied. Associations between air quality, especially ozone and particulate burdens, and cardiovascular disease appear to be modified by weather and climate. Ozone, whose formation increases with temperature, increases cardiac effort and impairs pulmonary gas exchange. Ozone concentrations modify the association between temperature and cardiovascular mortality, and are also associated with acute myocardial infarction (as discussed in the chapter on Asthma, Respiratory Allergies, and Airway Diseases). Particulate matter is associated with a variety of pathophysiological changes including systemic inflammation, deranged coagulation and thrombosis, blood vessel dysfunction and atherosclerotic disease, compromised heart function, deep venous thromboses,95 and pulmonary embolism.Increased burden of PM2.5 is associated with increased hospital admissions and mortality from cardiovascular disease, as well as ischemic heart disease. Other climate-related exposures are indirectly associated with incidence of cardiovascular disease and disease exacerbations. Extreme weather events affect cardiovascular health through several pathways. Directly, the stress of the event and anxiety over event recurrence are associated with myocardial infarction, sudden cardiac death, and development of stress-related cardiomyopathy. Indirectly, displacement related to disasters is frequently associated with interruptions of medical care for chronic medical conditions, putting populations with chronic cardiovascular conditions at risk for disease exacerbations. Climate is also implicated in another indirect risk for cardiovascular disease: the incidence of certain vectorborne and zoonotic diseases (VBZD) with cardiovascular manifestations. One estimate holds that approximately 10% of strokes in the developing world are related to exposure to certain VBZD, many of which are climate sensitive. In particular, Chagas disease is an important cause of stroke worldwide (although not in the United States); 20 million people globally have chronic Chagas, which is an independent risk factor for stroke in Latin America and a leading cause of heart failure in South America. There is some evidence of climate sensitivity for Chagas disease, though the topic is little studied. In the United States, Lyme disease is a prevalent vectorborne disease that has cardiovascular manifestations, though the incidence of such manifestations is much lower than that associated with Chagas disease.
There is little published literature on the projected direct and indirect impacts of climate change on cardiovascular disease incidence. Many of the studies coupling down-scaled climate projections with health outcomes have examined a particular exposure, such as heat or ozone, and projected mortality based on known associations, but do not make specific projections as to the incidence of cardiovascular morbidity and mortality. Insofar as climate change will bring increased ambient temperatures, increasingly variable weather, and increased extreme events, we can infer that climate change will likely have an overall adverse impact on the incidence of cardiovascular disease. Similarly, the impact of climate change on the incidence of cardiovascular complications from extreme weather events and certain VBZD is also likely to increase. However, the magnitude of these effects and the degree to which they can be lessened with adaptation efforts is unclear and warrants much further study.