Risk Stratification Guided by the Index of Microcirculatory Resistance and Left Ventricular End-Diastolic Pressure in Acute Myocardial Infarction

Index of Microcirculatory Resistance to predict microvascular obstruction in STEMI: A systematic review and meta-analysis

BACKGROUND

Microvascular obstruction (MVO) is an independent predictor of adverse cardiac events after ST-elevation myocardial infarction (STEMI). The Index of Microcirculatory Resistance (IMR) may be a useful marker of MVO, which could simplify the care pathway without the need for Cardiac Magnetic Resonance (CMR). We assessed whether the IMR can predict MVO in STEMI patients.

METHODS AND RESULTS

We conducted a systematic review and meta-analysis, including articles where invasive IMR was performed post primary percutaneous coronary intervention (PCI) in addition to MVO assessment with cardiac MRI. We searched PubMed, Scopus, Embase, and Cochrane databases from inception until January 2023. Baseline characteristics, coronary physiology and cardiac MRI data were extracted by two independent reviewers. The random-effects model was used to pool the data. Among 15 articles identified, nine articles (n = 728, mean age 61, 81% male) contained IMR data stratified by MVO. Patients with MVO had a mean IMR of 41.2 [95% CI 32.4-50.4], compared to 25.3 [18.3-32.2] for those without. The difference in IMR between those with and without MVO was 15.1 [9.7-20.6]. Meta-regression analyses demonstrated a linear relationship between IMR and TIMI grade (β = 0.69 [0.13-1.26]), as well as infarct size (β = 1.18 [0.24-2.11]) or ejection fraction at 6 months (β = -0.18 [-0.35 to -0.01]).

CONCLUSION

In STEMI, patients with MVO had 15-unit higher IMR than those without. IMR also predicts key prognostic endpoints such as infarct size, MVO, and long-term systolic function.

Coronary physiology thresholds associated with microvascular obstruction in myocardial infarction

OBJECTIVES

To ascertain whether invasive assessment of coronary physiology soon after recanalisation of the culprit artery by primary percutaneous coronary intervention is associated with the development of microvascular obstruction by cardiac magnetic resonance in patients with ST-segment elevation myocardial infarction (STEMI).

METHODS

Between November 2020 and December 2021, 102 consecutive patients were prospectively enrolled in five tertiary centres in Italy. Coronary flow reserve (CFR) and index of microvascular resistance (IMR) were measured in the culprit vessel soon after successful primary percutaneous coronary intervention. Optimal cut-off points of IMR and CFR to predict the presence of microvascular obstruction were estimated, stratifying the population accordingly in four groups. A comparison with previously proposed stratification models was carried out.

RESULTS

IMR>31 units and CFR≤1.25 yielded the best accuracy. Patients with IMR>31 and CFR≤1.25 exhibited higher microvascular obstruction prevalence (83% vs 38%, p<0.001) and lower left ventricular ejection fraction (45±9% vs 52±9%, p=0.043) compared with those with IMR≤31 and CFR>1.25, and lower left ventricular ejection fraction compared with patients with CFR≤1.25 and IMR≤31 (45±9% vs 54±7%, p=0.025). Infarct size and area at risk were larger in the former, compared with other groups.

CONCLUSIONS

IMR and CFR are associated with the presence of microvascular obstruction in STEMI. Patients with an IMR>31 units and a CFR≤1.25 have higher prevalence of microvascular obstruction, lower left ventricular ejection fraction, larger infarct size and area at risk.

TRIAL REGISTRATION NUMBER

NCT04677257.

Storax Attenuates Cardiac Fibrosis following Acute Myocardial Infarction in Rats via Suppression of AT1R-Ankrd1-P53 Signaling Pathway

Myocardial fibrosis following acute myocardial infarction (AMI) seriously affects the prognosis and survival rate of patients. This study explores the role and regulation mechanism of storax, a commonly used traditional Chinese medicine for treatment of cardiovascular diseases, on myocardial fibrosis and cardiac function. The AMI rat model was established by subcutaneous injection of Isoproterenol hydrochloride (ISO). Storax (0.1, 0.2, 0.4 g/kg) was administered by gavage once/d for 7 days. Electrocardiogram, echocardiography, hemodynamic and cardiac enzyme in AMI rats were measured. HE, Masson, immunofluorescence and TUNEL staining were used to observe the degree of pathological damage, fibrosis and cardiomyocyte apoptosis in myocardial tissue, respectively. Expression of AT1R, CARP and their downstream related apoptotic proteins were detected by WB. The results demonstrated that storax could significantly improve cardiac electrophysiology and function, decrease serum cardiac enzyme activity, reduce type I and III collagen contents to improve fibrosis and alleviate myocardial pathological damage and cardiomyocyte apoptosis. It also found that storax can significantly down-regulate expression of AT1R, Ankrd1, P53, P-p53 (ser 15), Bax and cleaved Caspase-3 and up-regulate expression of Mdm2 and Bcl-2. Taken together, these findings indicated that storax effectively protected cardiomyocytes against myocardial fibrosis and cardiac dysfunction by inhibiting the AT1R-Ankrd1-P53 signaling pathway.

Angiography derived assessment of the coronary microcirculation: is it ready for prime time?

INTRODUCTION

Non-obstructive coronary arteries (NOCA) are present in 39.7% to 62.4% of patients who undergo elective angiography. Coronary microcirculation (<400 µm) is not visible on angiography therefore functional assessment, invasive or non-invasive plays a prior role to help provide a more personalized diagnosis of angina.

AREA COVERED

In this review, we revise the pathophysiology, clinical importance and invasive assessment of the coronary microcirculation, and discuss angiography-derived indices of microvascular resistance. A comprehensive literature review over four decades is also undertaken.

EXPERT OPINION

The coronary microvasculature plays an important role in flow autoregulation and metabolic regulation. Invasive assessment of microvascular resistance is a validated modality with independent prognostic value, nevertheless, its routine application is hampered by the requirement of intravascular instrumentation and hyperaemic agents. The angiography-derived index of microvascular resistance has emerged as a promising surrogate in pilot studies, however, more data are needed to validate and compare the diagnostic and prognostic accuracy of different equations as well as to illustrate the relationship between angiography-derived parameters for epicardial coronary arteries and those for the microvasculature.

Multiple Blood Biomarkers and Stroke Risk in Atrial Fibrillation: The REGARDS Study

Background

Atrial fibrillation is associated with increased stroke risk; available risk prediction tools have modest accuracy. We hypothesized that circulating stroke risk biomarkers may improve stroke risk prediction in atrial fibrillation.

Methods and Results

The REGARDS (Reasons for Geographic and Racial Differences in Stroke) study is a prospective cohort study of 30 239 Black and White adults age ≥45 years. A nested study of stroke cases and a random sample of the cohort included 175 participants (63% women, 37% Black adults) with baseline atrial fibrillation and available blood biomarker data. There were 81 ischemic strokes over 5.2 years in these participants. Adjusted for demographics, stroke risk factors, and warfarin use, the following biomarkers were associated with stroke risk (hazard ratio [HR]; 95% CI for upper versus lower tertile): cystatin C (3.16; 1.04–9.58), factor VIII antigen (2.77; 1.03–7.48), interleukin‐6 (9.35; 1.95–44.78), and NT‐proBNP (N‐terminal B‐type natriuretic peptide) (4.21; 1.24–14.29). A multimarker risk score based on the number of blood biomarkers in the highest tertile was developed; adjusted HRs of stroke for 1, 2, and 3+ elevated blood biomarkers, compared with none, were 1.75 (0.57–5.40), 4.97 (1.20–20.5), and 9.51 (2.22–40.8), respectively. Incorporating the multimarker risk score to the CHA₂DS₂VASc score resulted in a net reclassification improvement of 0.34 (95% CI, 0.04–0.65).

Conclusions

Findings in this biracial cohort suggested the possibility of substantial improvement in stroke risk prediction in atrial fibrillation using blood biomarkers or a multimarker risk score.

What an Interventionalist Needs to Know About MI with Non-obstructive Coronary Arteries

MI with non-obstructive coronary arteries (MINOCA) is caused by a heterogeneous group of vascular or myocardial disorders. MINOCA occurs in 5.15% of patients presenting with acute ST-segment elevation MI or non-ST segment elevation MI and prognosis is impaired. The diagnosis of MINOCA is made during coronary angiography following acute MI, where there is no stenosis ≥50% present in an infarct-related epicardial artery and no overt systemic aetiology for the presentation. Accurate diagnosis and subsequent management require the appropriate utilisation of intravascular imaging, coronary function testing and subsequent imaging to assess for myocardial disorders without coronary involvement. Although plaque-related MINOCA is currently managed with empirical secondary prevention strategies, there remains an unmet therapeutic need for targeted and evidence-based therapy for MINOCA patients and increased awareness of the recommended diagnostic pathway.