Safety and acute effects of Hot water immersion in rehabilitation after Myocardial Infarction (HOT-MI) a randomized controlled study

Background Several studies have investigated thermotherapy, including saunas and warm water baths, as a potential strategy to reduce cardiovascular risk in both healthy individuals and patients with cardiovascular disease. However, a randomized controlled study on thermotherapy has not previously been conducted in patients with recent myocardial infarction (MI). Given the well-documented benefits of exercise training in cardiac rehabilitation after MI and emerging evidence that thermotherapy may enhance cardiovascular function and reduce inflammation, this study aimed to assess the feasibility and safety of hot water immersion (HWI) as a complementary post-MI rehabilitation method. Purpose Our objective was to assess the safety and acute physiological effects of HWI as a complementary method in cardiac rehabilitation for post-MI patients. Future analyses will examine its impact on inflammatory and metabolic status, cardiovascular function, and psychological well-being. Methods This prospective, randomized, controlled study (NCT0572565) included 30 MI patients (STEMI or NSTEMI) enrolled in center-based cardiac rehabilitation at Örebro University Hospital, Sweden. After providing informed consent, participants were randomized 1:1 to an 8-week intervention with pre- and post-testing. Throughout the program, they engaged in supervised progressive aerobic and strength training (60 minutes) two times per week, followed by either 20 minutes of HWI or passive rest (control group). Here, we report safety data on vital parameters. Results HWI resulted in significant changes in heart rate (+4.9 +- 9.8 beats/min; p < 0.001), oxygen saturation (-2.5 +- 2.3 SpO2%; p < 0.001), body temperature (+1.0 +- 0.4 °C; p < 0.001), and diastolic blood pressure (-7.9 +- 8.7 mmHg; p < 0.001) (Fig 1). Self-reported heat stress (+1.7 +- 0.6; p < 0.001) and sweating (+1.2 +- 0.6; p < 0.001) increased. No significant changes in systolic blood pressure were observed. No long-term physiological adaptations to repeated HWI were found, were week 1 (W1) represented baseline (Fig 2). Conclusion HWI led to an acute rise in several vital parameters but was well tolerated, indicating its safety in post-MI patients. The long-term effects of HWI on inflammatory and metabolic status, as well as cardiovascular recovery, will be reported in future analyses. If shown to be effective, HWI could serve as a novel, simple, and safe complementary therapy in cardiac rehabilitation, particularly benefiting patients with limited exercise capacity.Fig 1.Acute physiogical responses to HWIFor image description, please refer to the figure legend and surrounding text. Fig 2.Long-term physiological responsesFor image description, please refer to the figure legend and surrounding text.