Shock Index as a Predictor of Myocardial Injury in ST-segment Elevation Myocardial Infarction

Background: Little is known about the association between shock index and myocardial injury in patients with ST-segment elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PCI). Methods: We analyzed cardiac magnetic resonance imaging from 306 consecutive patients treated with primary PCI for STEMI. The patients were divided into the following 2 groups: initial shock index >0.7 (n = 88) and <= 0.7 (n = 218). Shock index was calculated as the ratio of heart rate to systolic blood pressure based on the first recorded vital signs upon arrival. The primary end point was myocardial infarct size. Results: The shock index >0.7 group, exhibited a lower baseline left ventricular ejection fraction (P = 0.01), higher N-terminal prohormone of brain natriuretic peptide level (P = 0.01), higher Killip class (P < 0.01) and higher prevalence of diabetes (P = 0.02) than the shock index <= 0.7 group. There were no significant differences in the angiographic or procedural characteristics between the 2 groups. In cardiac magnetic resonance imaging analysis, the shock index >0.7 group had a larger infarct size than did the shock index <= 0.7 group (22.9 +/- 11.2% versus 19.2 +/- 11.5%, P < 0.01). According to multivariate analysis, shock index >0.7 was associated with large myocardial infarctions (odds ratio = 3.02; 95% CI: 1.62-5.65; P < 0.01). Conclusions: Initial shock index is a potentially reliable predictor of myocardial injury in patients with STEMI undergoing primary PCI.