Abstract Body (Do not enter title and authors here): Introduction: Thoracic radiotherapy plays a fundamental role in the treatment of various malignancies, including breast cancer, lung cancer, and lymphoma. However, thoracic irradiation has been associated with an elevated risk of cardiovascular complications, particularly coronary artery disease. Despite this known association, limited data exists regarding how prior thoracic irradiation influences clinical outcomes in patients hospitalized with acute myocardial infarction (AMI). This study aims to evaluate the effect of prior thoracic irradiation on clinical outcomes in patients hospitalized with AMI.

Methods: A retrospective analysis was conducted using the National Inpatient Sample database from 2017 to 2022. ICD-10 codes were used to identify patients admitted with a primary diagnosis of “Acute Myocardial Infarction.” Of these patients, further stratification was performed to identify patients with a prior history of radiation therapy to the thorax. Multivariate logistic regression analysis was performed to calculate adjusted odds ratios (aOR) for binary outcomes, accounting for covariates, while linear regression was employed for continuous outcomes. The primary outcome of interest was in-hospital mortality, while secondary outcomes included total cost of hospitalization and length of stay.

Results: A total of 3,705,829 patients admitted for a primary diagnosis of AMI were identified. Of these patients, 4749 were identified as having previous thoracic irradiation. Logistic regression showed a significantly increased risk of in-hospital mortality for patients with prior thoracic irradiation (aOR: 1.30, 95% CI: 1.02-1.66, p=.036) when compared to those without. Linear regression showed lower adjusted total hospitalization costs by $25,270.34 (95% CI: -32,269.37– -18,271.31, p<.001) as well as a decrease in adjusted length of stay by 1.05 nights (95% CI: -1.33 – -0.77, p<.001).

Conclusion: Our findings reveal that patients with a history of thoracic irradiation had a significantly increased risk of in-hospital mortality following AMI. Potential contributors to this increased risk include radiation-induced microvascular dysfunction, accelerated atherosclerosis, and myocardial fibrosis. Further research is needed to better understand these mechanisms and to develop tailored management strategies aimed at improving survival outcomes in this high-risk population.