Shock index as a predictor of myocardial damage and clinical outcome in ST-elevation myocardial infarction

Background: Data on the prognostic value of the shock index in patients with ST-elevation myocardial infarction (STEMI) are scarce. Furthermore, the relationship of the shock index with myocardial damage is unknown. The aim of this study was to evaluate the association of the shock index with markers of myocardial damage and clinical outcome in patients with STEMI. Methods and Results: This multicenter study analyzed 791 patients. Patients were categorized in 2 groups according to the admission shock index (optimized cut-off=0.62). Infarct severity was determined by cardiac magnetic resonance (CMR) imaging. Patients with cardiogenic shock that were unable to undergo CMR acquisition were excluded. Major adverse cardiac events (MACE) were defined as a composite of death, reinfarction and congestive heart failure within 12 months. Patients with elevated admission shock index (n=321 [40.6%]) had a significantly larger area-at-risk (37.6 [27.8–50.4] % of left ventricular volume [LV] vs. 34.3 [24.5–46.0] % LV, P=0.02), larger infarct size (19.5 [10.7–28.0] % LV vs. 14.9 [7.7–22.3] % LV, P<0.001), lower myocardial salvage index (46.2 [27.9–64.5] vs. 53.5 [36.5–75.2], P<0.001), and a larger extent of microvascular obstruction (0.3 [0.0–2.2] % LV vs. 0.0 [0.0–1.4] % LV, P=0.01). An elevated shock index was associated with reduced MACE-free survival (P<0.001). Furthermore, the admission shock index was identified as an independent predictor of MACE (hazard ratio=2.92 [1.24–4.22], P<0.01). Conclusions: STEMI patients with an elevated admission shock index had more pronounced myocardial and microvascular damage. Moreover, the shock index was independently associated with MACE at 12 months.