Background:Extreme-heat events are increasing as a result of climate change. Prior studies, typically limited to urban settings, suggest an association between extreme heat and cardiovascular mortality. However, the extent of the burden of cardiovascular deaths associated with extreme heat across the United States and in different age, sex, or race and ethnicity subgroups is unclear.Methods:County-level daily maximum heat index levels for all counties in the contiguous United States in summer months (May–September) and monthly cardiovascular mortality rates for adults ≥20 years of age were obtained. For each county, an extreme-heat day was identified if the maximum heat index was ≥90 °F (32.2 °C) and in the 99th percentile of the maximum heat index in the baseline period (1979–2007) for that day. Spatial empirical Bayes smoothed monthly cardiovascular mortality rates from 2008 to 2017 were the primary outcome. A Poisson fixed-effects regression model was estimated with the monthly number of extreme-heat days as the independent variable of interest. The model included time-fixed effects and time-varying environmental, economic, demographic, and health care–related variables.Results:Across 3108 counties, from 2008 to 2017, each additional extreme-heat day was associated with a 0.12% (95% CI, 0.04%–0.21%; P=0.004) higher monthly cardiovascular mortality rate. Extreme heat was associated with an estimated 5958 (95% CI, 1847–10 069) additional deaths resulting from cardiovascular disease over the study period. In subgroup analyses, extreme heat was associated with a greater relative increase in mortality rates among men compared with women (0.20% [95% CI, 0.07%–0.33%]) and non-Hispanic Black compared with non-Hispanic White adults (0.19% [95% CI, 0.01%–0.37%]). There was a greater absolute increase among elderly adults compared with nonelderly adults (16.6 [95% CI, 14.6–31.8] additional deaths per 10 million individuals per month).Conclusions:Extreme-heat days were associated with higher adult cardiovascular mortality rates in the contiguous United States between 2008 and 2017. This association was heterogeneous among age, sex, race, and ethnicity subgroups. As extreme-heat events increase, the burden of cardiovascular mortality may continue to increase, and the disparities between demographic subgroups may widen.

中文翻译：

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美国极端高温与心血管死亡率的关联：2008年至2017年县级纵向分析

背景：由于气候变化，极端高温事件正在增加。先前的研究通常仅限于城市环境，表明极端高温与心血管死亡率之间存在关联。然而，美国境内不同年龄、性别或种族和族裔亚组中与极端高温相关的心血管死亡负担的程度尚不清楚。方法：美国本土所有县的县级每日最高高温指数水平获得了夏季月份（5 月至 9 月）的状态以及 20 岁以上成年人的每月心血管死亡率。对于每个县，如果最高炎热指数≥90°F（32.2°C）并且位于该天基准期（1979-2007）最高炎热指数的第99个百分位，则确定为极端高温日。主要结果是 2008 年至 2017 年空间经验贝叶斯平滑每月心血管死亡率。以每月极端高温天数作为感兴趣的自变量来估计泊松固定效应回归模型。该模型包括时间固定效应和随时间变化的环境、经济、人口和医疗保健相关变量。结果：从 2008 年到 2017 年，在 3108 个县中，每增加一个极端高温日，就会导致 0.12%（95% CI，0.04%–0.21%；P =0.004) 每月心血管死亡率较高。在研究期间，极端高温与估计 5958 例（95% CI，1847-10 069）额外因心血管疾病死亡有关。在亚组分析中，与女性相比，极端高温与男性死亡率的相对增加有关（0.20% [95% CI，0.07%–0.33%]），与非西班牙裔白人成人相比，非西班牙裔黑人死亡率相对增加更大（0.19 % [95% CI，0.01%–0.37%]）。与非老年人相比，老年人的绝对增加幅度更大（每月每 1000 万人中额外死亡 16.6 [95% CI，14.6–31.8]）。结论：极端炎热的日子与老年人较高的成人心血管死亡率相关。 2008 年至 2017 年间，美国本土存在这种关联。这种关联在年龄、性别、种族和族裔亚组之间存在异质性。随着极端高温事件的增加，心血管死亡的负担可能会继续增加，人口亚组之间的差异可能会扩大。