Predicting Poor Outcomes in Myocardial Infarction

In life-threatening situations, clinicians treasure the ability to accurately predict outcomes. In patients with acute coronary syndrome (ACS) that progresses to acute myocardial infarction (AMI), the ability to predict the likely course of disease could help clinicians plan for aggressive treatment or frequent monitoring. Counseling patients that they are at high risk for future complications may also increase adherence to lifestyle changes and medication.

A multinational team of researchers has identified a potential marker of poor prognosis after AMI: pro-substance P (ProSP). The results of their study were published in the October 21, 2014, issue of the Journal of the American College of Cardiology.

Substance P is a neuropeptide that has proinflammatory effects, increases platelet aggregation and clot strength, and reduces fibrinolysis. A potent vasodilator, substance P is dependent on nitric oxide release. Its levels are low in myocardium tissue, but its multiple roles in inflammation have tangential effects on the heart. It is also labile, with a half-life of 12 minutes in humans, and, consequently, difficult to measure. ProSP is a stable surrogate marker for substance P that can be measured in the clinical laboratory.

The authors of this study assessed ProSP levels to identify potential association with poor prognosis after AMI. They hoped to identify novel pathophysiologic mechanisms that can become treatment targets.

They enrolled 1148 AMI patients and measured ProSP. They followed patients for 2 years, monitoring for major adverse cardiac events (MACE), death/reinfarction, and death. They compared patients’ GRACE (Global Registry of Acute Coronary Events) scores with ProSP for death and/or reinfarction at 6 months.

Among the study population, 140 patients died, 112 were hospitalized for heart failure (HF), and 149 suffered another AMI.

ProSP levels were highest on the first 2 days after admission for chest pain, and elevated levels predicted all major cardiac events. Elevations were related to renal function; age; sex; history of diabetes, ischemic heart disease, or hypertension; Killip class; and left ventricular wall motion index score.

When the researchers augmented ProSP with the patient’s GRACE score, they were able to predict patients with low risk, which is also a useful tool in clinical settings.

The authors indicate, “Existing biomarkers such as NT-proBNP [N-terminal pro-B-type natriuretic peptide] mainly predicted mortality and HF, with poorer detection of death and/or reinfarction. In contrast, ProSP provided independent prognostic information for the composite of MACE, death and/or reinfarction, and also death and/or HF.”