Abstract 16047: Quantifying the Cardiovascular Burden of Extreme Heat: A Meta-Analysis of Over 400 Laboratory-Based Heat Exposure Studies

Abstract

Background: Heat waves are associated with increased fatalities from cardiovascular events, which has been attributed to increased cardiac strain secondary to the effects of heat on cardiac function. However, our understanding of these adjustments has come primarily from laboratory research employing insulated/encapsulated heating modalities (hot water perfusion suits). We evaluated whether the cardiac responses seen in this work reflect those experienced in studies exposing participants to high ambient temperatures. Methods: We systematically reviewed studies published up to January 2023 examining cardiac outcomes in adults rendered hyperthermic with water perfusion suits or unencapsulated exposure in a climate chamber. Mixed effects meta-analyses were conducted to evaluate whether changes in each outcome with increasing core temperature were modified by heating modality. We also estimated associations (natural spline) between ambient heat index and thermal and cardiac responses in the climate chamber studies. Results: 584 effect estimates of the heat-induced increase in heart rate (primary outcome) from 406 studies were included (~6800 participant exposures). Heart rate was 7 beats/min [95% CI: 3, 13] greater in the perfusion suit vs. climate chamber studies for similar increases in core temperature (P<0.001). Likewise, there were greater elevations in cardiac output (slope difference: 1.2 L/min/°C [0.1, 2.3]), systolic pressure (14 mm Hg/°C [3, 24]), and rate pressure product (2923 mm Hg·beats/min/°C [1027, 4808]) with rises in core temperature in the perfusion suit compared to climate chambers studies (P≤0.036). In the climate chamber studies, core temperature and heart rate increased as much as 1.0°C [0.8, 1.3] and 31 beats/min [16, 37] (P<0.001) in conditions reflective of deadly North American heat waves (heat index: 50-67°C). Conclusions: Our understanding of the effect of heat on cardiovascular responses primarily comes from encapsulated heating modalities, which we show overestimate heat-induced cardiac burden. To support public health research on extreme heat, we provide the first empirical estimates demonstrating considerable thermal and cardiac strain is experienced in conditions reflective of deadly heat waves.