Exploring changes in electrocardiography during passive heat strain in healthy adults

Introduction: Heat stress places significant strain on the cardiovascular system. Hyperthermia elevates heart rate through direct temperature effects on pacemaker cells, sympathetic activation, and vagal withdrawal. To support heat loss, skin blood flow increases, requiring higher cardiac output driven by rising heart rate. The heart’s electrical conduction system maintains rhythmic pumping and can be assessed non-invasively via electrocardiography (ECG), an over century old clinical tool for detecting cardiovascular disease and arrhythmias. Since cardiovascular problems are a major reason for medical visits during extreme heat events, ECG monitoring may offer a simple biomarker of heat-related cardiovascular strain, particularly as ECG abnormalities are present in heat stroke patients. However, limited work has explored how the typical ECG waveform is modified during heat stress in healthy adults. This preliminary study sought to examine changes in ECG components during common laboratory heat-stress protocols in healthy adults which increase heart rate but with different core temperature responses. Methods: Two passive heat stress protocols were conducted: i) a water perfusion suit (WPS) model, and ii) ambient heat exposure (AH). In the WPS model, 10 participants (5 females; 23±2yrs, 1.7±0.1m, 73.6±10.8kg) were passively heated by circulating 49°C water through the suit until core temperature increased ~1.0°C above baseline. ECG traces were captured pre-heating, and following a 0.5°C and 1.0°C rise in core temperature. In the AH model, 29 participants (14 females, 38±19yrs; 1.7±0.1m; 80.0±17.2kg) remained seated in a climate-controlled room (40°C and with T-wave amplitude reduction (R 2 =0.28, p=0.003). With respect to AH, no differences in ECG components or relationships with heart rate were observed. Across all trials, ECG components remained within normal clinically defined thresholds. Conclusion: Preliminary results suggest that changes in ECG components can be observed during passive heat exposure, and are more pronounced with greater hyperthermia and rises in heart rate. Funding: This research was supported by Dr. Ravanelli’s Lakehead University Research Funding and the Natural Sciences and Engineering Research Council of Canada Discovery Grant (PIN#2022-05096). This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.