Insulin in Acute Coronary Syndrome: a Narrative Review with Contemporary Perspectives

The role of insulin in the treatment of acute coronary syndrome (ACS) has been widely studied over the past 100 years. The current indication for its use in this context is the treatment of hyperglycemia, irrespective of diabetes, which is associated with adverse outcome. Initial theories proposed that glucose was beneficial in the context of myocardial ischemia and insulin was required to enable glucose cell uptake. However, studies testing this hypothesis with routine insulin administration during ACS have produced disappointing results and research interest has therefore declined. We propose that the less well known but important vasodilator effect of insulin has been overlooked by some of these studies and warrants further consideration. Previous reports have shown that hyperinsulinemic euglycaemia improves myocardial blood flow reserve. With this in mind, this review considers the role of insulin in the context of ACS from the perspective of a vasodilator rather than a metabolic modulator. We discuss the importance of time to treatment, dosage of insulin administered, problems with hypoglycaemia and insulin resistance, and how they may have affected the outcomes of the major trials. Finally, we propose new study designs that allow determination of the optimal vasodilator conditions for the use of insulin as adjunctive pharmacotherapy during myocardial ischaemia.