Potential Effects of Global Warming on Heart Failure Decompensation

According to international data, in direct correlation with increased industrialization and greenhouse gas emissions since 1880, the global mean temperature already has increased by greater than 1.5 degrees Celsius and is expected only to continue to rise.1 Ongoing industrialization and changes in climate are projected to generate several untoward health effects—such as the direct consequences of increased air pollution and natural disasters, illnesses from impaired access to, and contamination of, food and drinking water, redistribution of infectious diseases given the variable hospitable climates of vectors such as mosquitoes and ticks, and several mental health problems as a result of these traumas.2 Additionally, it is anticipated that several pre-existent health problems will be exacerbated by global warming.3  Elderly and those who suffer from respiratory conditions are most at risk of increased mortality associated with heat waves in several cities across Europe.5 Minimum all-cause mortality occurs when ambient temperatures most resemble those of the mean of the region,4 which suggests that fluctuations in climate are what may be most detrimental to patients. As the current trend in global climate change is associated with augmented extremes of hot and cold6, it is logical to expect that these health ramifications will only be heightened as changes in climate continue to trend in their current direction. Previous studies have shown associations between the effects of waves of temperature change on morbidity associated with categories of disease (cardiac, respiratory, etc.). However, few have examined the effects of daily, ambient conditions on the outcomes connected to any particular condition and none has evaluated the effects of ambient pressure on health outcomes.

Miró and colleagues examined the probability of hospitalization and of all-cause mortality associated with the temperature and atmospheric pressure of the day preceding presentation among patients presenting to the emergency department for evaluation of acute decompensated heart failure.7 They retrospectively assessed the Epidemiology of Acute Heart Failure Emergency (EAHFE) registry and identified the maximum temperature, in degrees Celsius, and the anomaly of the maximum atmospheric pressure (calculated by subtracting the maximum atmospheric pressure on the day of interest from the average atmospheric pressure, over the course of the study, in the city of interest), in hectopascals, on the day prior to presentation. The hospitalization for HF was associated with a maximum temperature greater than 25 degrees or less than 5.4 degrees and with an anomaly of the daily maximum pressure that was greater than 7 hectopascals. Additionally, all-cause, in-hospital mortality correlated with a daily maximum temperature greater than 24.3 degrees Celsius and with an anomaly of the daily maximum pressure that was greater than 3.4 hectopascals. Lastly, the contour plots demonstrated that hospitalization was most common when the ambient temperature was greater than 30 degrees (regardless of the corresponding atmospheric pressure) and that in-hospital, all-cause mortality was greatest when temperature was greater than 35 degrees and when the anomaly of the atmospheric pressure was less than 5 hectopascals.

Unique to this study is an examination of the effect of ambient conditions on acute decompensated heart failure. It is conceivable that examination of ambient temperatures over a short duration of time, just one day preceding admission, may serve to emphasize physiologic changes that occur in the context of variations in ambient conditions as opposed to behavioral effects. Whereas one day may not be enough time to influence the ability of a patient to access medications, or other necessary resources, it may be significant enough that it alters his or her physiology in the context of illness. The study postulates that mortality in heart failure may be associated with changes in environmental conditions because they may, in conjunction with the medications the patient takes, influence blood viscosity, which could impair an already ailing heart. Future work may evaluate this hypothesis by comparing disease-associated outcomes among those patients taking variable doses of diuretics or by measuring blood viscosity at the time of presentation.

The study has several limitations. It examines only patients who are clinically diagnosed on hospital presentation with acute decompensated heart failure, but assesses all-cause mortality in hospitalized patients as opposed to disease-associated mortality. Such a broad inclusion of data makes it challenging to draw a direct conclusion about the effects of ambient conditions on heart failure as opposed to those imposed upon any other acute or chronic disease. Similarly, although the authors conclude that extremes of climate are most associated with hospitalization and mortality in this population, due to staffing issues, the authors note that they were unable to include any measurements from Summer months—when the effects of ambient temperature and pressure may have been most drastic—possibly dampening any measurement of association between environmental conditions and the outcome of interest.

The study presents a valuable analysis of the effects of day-to-day changes in climate on disease-associated outcomes in patients who suffer from acute decompensated heart failure. Uniquely, it is the first study to examine the direct effects of ambient pressure, in conjunction with temperature, on health outcomes. As environmental pressure, unlike temperature, cannot easily be adjusted through household modifications, such as air conditioning or heating, this research highlights dangerous health trends that may occur as a result of climate change but may not be easy to fix. In addition to showing that increased daily temperature and pressure are associated with increased hospitalizations, and in-hospital mortality, for patients with acute decompensated heart failure, the study provides a useful concept for studying the effects of environmental changes on outcomes for patients with any particular disease. As climate change progresses, studies such as this one will become more and more valuable. In addition to highlighting the importance of international action to abate climate change, if they ultimately elucidate mechanisms of disease, they could provide another avenue for tackling climate-associated morbidity and mortality.

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