Modified shock index: A bedside clinical index for risk assessment of ST-segment elevation myocardial infarction at presentation.

Introduction: Prompt identification of higher-risk patients presenting with ST-segment elevation myocardial infarction (STEMI) is crucial to pursue a more aggressive approach.

Objective: We aimed to assess whether the modified shock index (MSI), the ratio of heart rate to mean arterial pressure, could predict six-month mortality among patients admitted with STEMI.

Methods: A retrospective observational cohort study was performed in a single center including 1158 patients diagnosed with STEMI, without cardiogenic shock on admission, between July 2009 and December 2014. They were divided into two groups: group 1 - patients with MSI<0.93 (72%); group 2 - patients with MSI≥0.93 (28%). The primary endpoint was six-month all-cause mortality.

Results: MSI≥0.93 identified patients who were more likely to have signs of heart failure (p=0.002), anemia (p<0.001), renal insufficiency (p=0.014) and left ventricular systolic dysfunction (p=0.045). They more often required inotropic support (p<0.001), intra-aortic balloon pump (p<0.001) and mechanical ventilation (p<0.001). Regarding in-hospital adverse events, they had a higher prevalence of malignant arrhythmias (p=0.01) and mechanical complications (p=0.027). MSI≥0.93 was an independent predictor of overall six-month mortality (adjusted HR 2.00, 95% CI 1.20-3.34, p=0.008).

Conclusion: MSI was shown to be a valuable bedside tool which can rapidly identify high-risk STEMI patients at presentation.