Response to Letter Regarding Article, “Prognostic Value of the Index of Microcirculatory Resistance Measured After Primary Percutaneous Coronary Intervention”

We thank Dr Poullis for his interest in our article. The index of microcirculatory resistance (IMR) is not a ratio like coronary flow reserve but is defined as pressure divided by flow during maximal hyperemia and therefore is a measure of the minimal achievable microvascular resistance. We and others have published articles on the clear relationship between IMR and cardiac biomarker elevation in the setting of ST-segment–elevation myocardial infarction.1–3 These studies have demonstrated that patients with higher IMR values immediately after primary percutaneous intervention for ST-segment–elevation myocardial infarction have higher levels of cardiac biomarkers, greater degrees of microvascular dysfunction on noninvasive imaging, and less recovery of left ventricular function over time. Measuring IMR in the nonculprit vessels …