What is the clinical evidence from this study?

Study design: Cohort. Population: ST-segment-elevation myocardial infarction (n=261). Intervention: Index of microcirculatory resistance (IMR) vs. Guideline-recommended risk scores. Primary outcome: Early major cardiac complications (Sensitivity 100%, 95% CI 80.5-100%, p=≤0.006).

November 1, 2017Open Access

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

Key Result

Low microvascular resistance (IMR ≤40) measured immediately after primary PCI identified all patients free of major cardiac complications with 100% sensitivity (95% CI, 80.5-100%).

Study Design

Type

Cohort (n=261)

Structured PICO

Does the index of microcirculatory resistance (IMR) measured at the end of primary percutaneous coronary intervention predict early major cardiac complications in patients with STEMI better than guideline-recommended risk scores?

Population

261 patients presenting with acute ST-segment-elevation myocardial infarction (STEMI) and referred for primary percutaneous coronary intervention (PPCI), mean age 61.4 years, 80.0% male, UK-based (Oxford Heart Centre). Key inclusion: ongoing chest pain and ST-segment elevation on ECG. Exclusion: safety or clinical concerns based on operator's judgment.

Intervention

Measurement of the index of microcirculatory resistance (IMR) using a combined pressure- and temperature-sensitive guidewire immediately at the end of emergency primary percutaneous coronary intervention (PPCI), with hyperemia induced by intravenous adenosine 140 µg/kg per minute.

Comparator

Guideline-recommended risk scores (PAMI-II and Zwolle scores) and coronary flow reserve (CFR) for diagnostic performance comparison.

Outcome

Composite of early major cardiac complications within 30 days (cardiac death, cardiogenic shock, documented pulmonary edema, malignant ventricular tachycardia, malignant bradyarrhythmia, cardiac wall rupture, and intraventricular thrombus).composite

The index of microcirculatory resistance (IMR) measured immediately after primary PCI for STEMI reliably identifies patients at low risk for early major cardiac complications, outperforming current guideline-recommended risk scores.

Main Result

Effect estimate: Sensitivity 100% (95% CI 80.5-100%)

p-value: p=≤0.006

Abstract

BACKGROUND: Early 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: ≤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.

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