Index of Microcirculatory Resistance at the Time of Primary Percutaneous Coronary Intervention Predicts Early Cardiac Complications: Insights From the OxAMI (Oxford Study in Acute Myocardial Infarction) Cohort

Abstract

BackgroundEarly risk stratification after primary percutaneous coronary intervention (PPCI) for ST‐segment–elevation myocardial infarction is currently challenging. Identification of a low‐risk group may improve triage of patients to alternative clinical pathways and support early hospital discharge. Our aim was to assess whether the index of microcirculatory resistance (IMR) at the time of PPCI can identify patients at low risk of early major cardiac complications and to compare its performance against guideline‐recommended risk scores.Methods and Results IMR was measured using a pressure–temperature sensor wire. Cardiac complications were defined as the composite of cardiac death, cardiogenic shock, pulmonary edema, malignant arrhythmias, cardiac rupture, and presence of left ventricular thrombus either before hospital discharge or within 30‐day follow‐up. In total, 261 patients undergoing PPCI who were eligible for coronary physiology assessment were prospectively enrolled. Twenty‐two major cardiac complications were reported. Receiver operating characteristic curve analysis confirmed the utility of IMR in predicting complications and showed significantly better performance than coronary flow reserve, the Primary Angioplasty in Myocardial Infarction II (PAMI‐II), and Zwolle score (P≤0.006). Low microvascular resistance (IMR ≤40) was measured in 159 patients (61%) of the study population and identified all patients who were free of major cardiac complications (sensitivity: 100%; 95% CI, 80.5–100%).Conclusions IMR immediately at the end of PPCI for ST‐segment–elevation myocardial infarction reliably predicts early major cardiac complications and performed significantly better than recommended risk scores. These novel data have implications for early risk stratification after PPCI.

Long-Term Clinical Outcomes in Patients With an Acute ST-Segment-Elevation Myocardial Infarction Stratified by Angiography-Derived Index of Microcirculatory Resistance

“…Kaplan-Meier survival curves separate early on, suggesting a prognostic role of NH IMR angio for early cardiac complications; a finding corroborated by previous IMR based work ( 6 ). Since this early separation could influence our analysis, we conducted a landmark analysis from 30 day onwards.…”

“…The prognostic equivalence is also maintained when analysing a stricter cardiac endpoint excluding non-cardiac mortality. These findings are consistent with the results and effect (6). Since this early separation could influence our analysis, we conducted a landmark analysis from 30 day onwards.…”

“…Our group and others have previously shown the good diagnostic performance of IMR in predicting microvascular injury diagnosed by cardiac magnetic resonance (CMR) imaging ( 1 , 5 ). Contemporary studies highlight the early- and long-term prognostic implications of an IMR > 40U in patients with STEMI ( 6 , 7 ). Recently, IMR has also been proposed as a tool to triage novel or additional therapies in STEMI, with promising clinical and research implications ( 8 , 9 ).…”

Assessing Coronary Microvascular Dysfunction in Ischaemic Heart Disease: Little Things Can Make a Big Difference

“…Notably, other invasive measures of CMD including TIMI flow grade and CFR were not predictive in this study. Similarly, in a more recent study of 261 STEMI patients, IMR > 40 immediately after primary PCI was better than CFR at predicting major cardiac complications at 30-day follow-up [49].…”

Index of microcirculatory resistance predicts long term cardiac systolic function in patients with STEMI undergoing primary PCI

“…In this regard, the index of microcirculatory resistance (IMR), an invasive physiological index and readily available method with extensive clinical evidence, might be used in the evaluation of microvascular function during pPCI [6]. An IMR > 40 U measured after STEMI has been shown to predict cardiac complications, HF readmission, and mortality [7][8][9]. The aim of this retrospective study with prospectively enrolled patients with acute anterior wall STEMI was to evaluate the predictive value of IMR for long-term cardiac systolic function after pPCI.…”