Abstract Body (Do not enter title and authors here): Introduction: The Modified Shock Index (MSI) is easily calculated from a patient’s vital signs on admission. There have been small studies that suggest that MSI can be helpful to risk stratify patients with STEMI.

Methods: We collected retrospective data on 760 patients admitted with STEMI at our quaternary academic medical center from 2018-2022. The MSI was computed as the heart rate divided by the mean arterial pressure collected on initial admission. We defined two cohorts: one with an MSI value of greater than or equal to 0.93 and one with MSI<0.93 based on prior literature on the topic (Abreu et al, 2018). Vasopressors included norepinephrine, neo-synephrine, and vasopressin while inotropes included milrinone and dobutamine. We utilized multivariable logistic regression to compare our two cohorts and adjusted for collinearity.

Results: In a univariate analysis, female sex (OR 1.95, 95% CI 1.32-2.87, p=0.0007), diabetes (OR 1.75, 1.21-2.54, p= 0.003), post-COVID era (OR 1.52, 1.06 to 2.21, p=0.025), and reduced ejection fraction (OR 0.98, 0.96 to 0.99, p= 0.0008) were associated with elevated MSI. In a multivariate analysis, an MSI>= 0.93 was associated with over 6x increased need of vasopressors during admission (OR 6.12, 3.32-11.47, p<0.0001) and almost 6x increased use of inotropes (OR 5.76, 2.54-13.44, p<0.0001). An elevated MSI was also associated with 5.5x increased need for mechanical ventilation (OR 5.45, 2.91-10.41, p<0.0001), 5.7x increased need for temporary mechanical circulatory support (tMCS) (OR 5.68, 3.18-10.30, p<0.0001) and 2x increased risk of LV thrombus development (OR 2.23, 1.1-4.4, p= 0.02). An elevated MSI was also associated with 2.5x increased risk of CICU length of stay (LOS) > 3 days (OR 2.51, 1.37-4.6, p=0.0003) and over 3x increased risk of hospital LOS greater than 1 week (OR 3.1, 1.7-5.7, p=0.0003).

Conclusions: At our center, an MSI greater than or equal to 0.93 was significantly associated with the use of vasoactive agents, mechanical ventilation and tMCS. An elevated MSI was also associated with prolonged CICU and hospital LOS. MSI is a simple yet informative tool to risk stratify STEMI patients and help determine their initial level of care.