Shock index: a simple clinical parameter for quick mortality risk assessment in acute myocardial infarction

Primary percutaneous coronary intervention (PCI) has become the preferred reperfusion strategy in patients with ST-segment elevation myocardial infarction and cardiogenic shock. Early identification of patients at risk for developing cardiogenic shock allows rapid decision making to determine reperfusion and transportation to a PCI centre. The aim of this analysis was to evaluate shock index (SI) as a marker for patients at risk of cardiogenic shock.

A total of 644 consecutive patients (73% male) with acute myocardial infarction with ST elevations were analyzed retrospectively. Primary PCI was performed in 92% of patients, and 7% of patients underwent rescue PCI. The SI parameter was defined as the ratio of heart rate to systolic blood pressure at hospital admission.

SI (odds ratio [OR], 81.26; 95% confidence interval [CI], 9.76-676.51; P<0.001), age (OR, 1.17; 95% CI, 1.08-1.26; P<0.001), and diabetes (OR, 4.94; 95% CI, 1.44-16.97; P<0.011) were independent predictors of mortality. In the group of patients with SI≥0.8, 20% died, whereas in the group with SI<0.8, 4% of patients died (P<0.01).

The proposed clinical parameter SI correlates with patients' prognosis and could therefore be used as a simple indicator of mortality risk of acute myocardial infarction. The simplicity of this proposed index makes its use accessible in large-scale clinical practices for risk stratification during first contact with patients.