Index of microcirculatory resistance as predictor for microvascular functional recovery in patients with anterior myocardial infarction

Impact of Coronary Microvascular Dysfunction on Functional Left Ventricular Remodeling and Diastolic Dysfunction

BACKGROUND

Coronary microvascular dysfunction (CMD) is a common complication of ST-segment-elevation myocardial infarction (STEMI) and can lead to adverse cardiovascular events. Whether CMD after STEMI is associated with functional left ventricular remodeling (FLVR) and diastolic dysfunction, has not been investigated.

METHODS AND RESULTS

This is a nonrandomized, observational, prospective study of patients with STEMI with multivessel disease. Coronary flow reserve and index of microcirculatory resistance of the culprit vessel were measured at 3 months post-STEMI. CMD was defined as index of microcirculatory resistance ≥25 or coronary flow reserve <2.0 with a normal fractional flow reserve. We examined the association between CMD, LV diastolic dysfunction, FLVR, and major adverse cardiac events at 12-month follow-up. A total of 210 patients were enrolled; 59.5% were men, with a median age of 65 (interquartile range, 58-76) years. At 3-month follow-up, 57 patients (27.14%) exhibited CMD. After 12 months, when compared with patients without CMD, patients with CMD had poorer LV systolic function recovery (-10.00% versus 8.00%; P<0.001), higher prevalence of grade 2 LV diastolic dysfunction (73.08% versus 1.32%; P<0.001), higher prevalence of group 3 or 4 FLVR (11.32% versus 7.28% and 22.64% versus 1.99%, respectively; P<0.001), and higher incidence of major adverse cardiac events (50.9% versus 9.8%; P<0.001). Index of microcirculatory resistance was independently associated with LV diastolic dysfunction and adverse FLVR.

CONCLUSIONS

CMD is present in ≈1 of 4 patients with STEMI during follow-up. Patients with CMD have a higher prevalence of LV diastolic dysfunction, adverse FLVR, and major adverse cardiac events at 12 months compared with those without CMD.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique Identifier: NCT05406297.

Ability of the coronary angiography-derived index of microcirculatory resistance to predict microvascular obstruction in patients with ST-segment elevation

Background

The coronary angiography-derived index of microvascular resistance (caIMR) correlates well with the index of microcirculatory resistance (IMR), which predicts microvascular obstruction (MVO). However, the relationship between caIMR and MVO remains unclear.

Aim

To evaluate the predictive ability of caIMR of MVO after ST-segment elevation myocardial infarction (STEMI).

Methods

CaIMR was calculated using computational flow and pressure simulation in patients with STEMI in whom MVO status had been assessed by cardiac magnetic resonance (CMR) after successful primary percutaneous intervention at Peking University First Hospital between December 2016 and August 2019. The clinical, biochemical, echocardiographic, and CMR characteristics were assessed according to MVO status. The predictive value of the clinical parameters and caIMR was evaluated.

Results

Fifty-three eligible patients were divided into an MVO group (n = 32) and a no-MVO group (n = 21). The caIMR tended to be higher in the MVO group (41.6 U vs. 30.1 U; p = 0.136). CaIMR and peak cardiac troponin-I (cTNI) were independent predictors of MVO (per 1-U increment in caIMR: odds ratio [OR] 1.044, 95% confidence interval [CI] 1.004-1.086, p = 0.030; per 1 ng/L increase in peak cTNI: OR 1.018, 95% CI 1.003-1.033, p = 0.022). In receiver-operating characteristic curve analysis, when a cut-off value of 45.17 U was used, caIMR had some ability to predict MVO (area under the curve 0.622, 95% CI 0.478-0.752, p = 0.127).

Conclusions

CaIMR and peak cTNI were independent predictors of short-term MVO in patients with STEMI who had undergone successful primary percutaneous coronary intervention and may help to identify those at high risk of MVO.

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.

Microcirculation function assessment in acute myocardial infarction: A systematic review of microcirculatory resistance indices

BACKGROUND

Up to 50% of acute myocardial infarction (MI) patients present with microvascular dysfunction, after a successful percutaneous coronary intervention (PCI), which leads to worse clinical outcomes. The main purpose of this study is to provide a critical appraisal of the emerging role of invasive microvascular resistance indices in the MI setting, using the index of microcirculatory resistance (IMR), hyperemic microvascular resistance (HMR) and zero-flow pressure (Pzf).

METHODS

We systematically explored relevant studies in the context of MI that correlated microcirculation resistance indices with microvascular dysfunction on cardiac magnetic resonance (CMR), microvascular dysfunction occurring in infarct related arteries (IRA) and non-IRA and its relation to clinical outcomes.

RESULTS

The microcirculation resistance indices correlated significantly with microvascular obstruction (MVO) and infarct size (IS) on CMR. Although HMR and Pzf seem to have better diagnostic accuracy for MVO and IS, IMR has more validation data. Although, both IMR and HMR were independent predictors of adverse cardiovascular events, HMR has no validated cut-off value and data is limited to small observational studies. The presence of microvascular dysfunction in non-IRA does not impact prognosis.

CONCLUSION

Microvascular resistance indices are valuable means to evaluate microcirculation function following MI. Microvascular dysfunction relates to the extent of myocardial damage and clinical outcomes after MI.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021228432], identifier [CRD42021228432].

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

Background

To evaluate the predictive value of the index of microcirculatory resistance (IMR) for long-term cardiac systolic function after primary percutaneous coronary intervention (pPCI) in patients with acute anterior wall ST-segment elevation myocardial infarction (STEMI).

Methods

A total of 53 acute anterior wall STEMI patients were included and followed up within 1-year. IMR was measured to evaluate the immediate intraoperative reperfusion. IMR > 40 U was defined as the high IMR group and ≤ 40 U was defined as the low IMR group. Left ventricular ejection fraction (LVEF) was measured by echocardiography at 24 h, 1 month, 3 months, and 1 year after PCI to analyze the correlation between IMR and cardiac systolic function. Heart failure was estimated according to classification within one year.

Results

The ratio of TMPG (TIMI myocardial perfusion grade) 3 (85.7% vs. 52%, p = 0.015) and STR (ST-segment resolution) > 70% (82.1% vs. 48%, p = 0.019) were significantly higher in the low IMR group. The LVEF in the low IMR group was significantly higher than that in the high IMR group at 3 months (43.06 ± 2.63% vs. 40.20 ± 2.67%, p < 0.001) and 1 year (44.16 ± 2.40% vs. 40.13 ± 3.48%, p < 0.001). IMR was negatively correlated with LVEF at 3 months (r = − 0.1014, p = 0.0040) and 1 year (r = − 0.1754, p < 0.0001).

Conclusions

The IMR showed significant negative correlation with the LVEF value after primary PCI. The high IMR is a strong predictor of heart failure within 1 year after anterior myocardial infarction.

The Potential Use of the Index of Microcirculatory Resistance to Guide Stratification of Patients for Adjunctive Therapy in Acute Myocardial Infarction

The goal of reperfusion therapies in ST-segment elevation myocardial infarction has evolved to include effective reperfusion of the microcirculation subtended by the culprit epicardial coronary artery. The index of microcirculatory resistance is measured using a pressure- and temperature-sensing coronary guidewire and quantifies microvascular dysfunction. The index of microcirculatory resistance is an independent predictor of microvascular obstruction, infarct size, and adverse clinical outcomes. It has the advantage of being immediately measurable in the catheterization laboratory, before the results of blood biomarkers or noninvasive imaging become available. This provides an opportunity for additional intervention that may alter outcomes. In this review, the authors provide a critical appraisal of the published research on the emerging role of the index of microcirculatory resistance as a tool to guide the stratification of patients for adjunctive therapeutic strategies in acute ST-segment elevation myocardial infarction.

Lancaster G, W. Zarich S. Invasive Evaluation of the Microvasculature in Acute Myocardial Infarction: Coronary Flow Reserve versus the Index of Microcirculatory Resistance

Acute myocardial infarction (AMI) is one of the most common causes of death in both the developed and developing world. It has high associated morbidity despite prompt institution of recommended therapy. The focus over the last few decades in ST-segment elevation AMI has been on timely reperfusion of the epicardial vessel. However, microvascular consequences after reperfusion, such as microvascular obstruction (MVO), are equally reliable predictors of outcome. The attention on the microcirculation has meant that traditional angiographic/anatomic methods are insufficient. We searched PubMed and the Cochrane database for English-language studies published between January 2000 and November 2019 that investigated the use of invasive physiologic tools in AMI. Based on these results, we provide a comprehensive review regarding the role for the invasive evaluation of the microcirculation in AMI, with specific emphasis on coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR).

Microvascular obstruction in acute myocardial infarction: an old and unsolved mystery

In the setting of acute myocardial infarction, flow restoration in the culprit epicardial coronary artery is not synonymous with efficient reperfusion. Microvascular obstruction occurs in 50% of cases and represents a predictor of a long-term unfavorable outcome. Its prevalence has remained constant in recent years despite various treatment attempts. However, the success of targeted therapies could be mainly a problem of timing. Recent data bring evidence with regard to the role of pre-procedural distal embolization and highlight the relation between distal embolism, microvascular obstruction and intramyocardial inflammation. As a result, early detection of microvascular injury represents the first step in the development of targeted, individualized therapeutic approaches. In this context, the identification of new invasive surrogate parameters for the timely assessment and quantification of microvascular obstruction in the catheterization laboratory has become an important subject of current research. Among these, coronary wedge pressure is the most practical and revealing in the setting of primary percutaneous coronary intervention. It may offer comprehensive details on the mechanisms of microvascular injury and may therefore offer guidance for appropriate treatment selection.

Combined Primary PCI with Multiple Thrombus Burden Reduction Therapy Improved Cardiac Function in Patients with Acute Anterior Myocardial Infarction

High thrombus burden induced slow-flow and no-reflow during primary percutaneous coronary intervention (PCI) and is associated with a poor prognosis. We aimed to investigate whether a combined thrombus burden reduction therapy during primary PCI, could improve microcirculation and enhance cardiac function in the long-term.Anterior wall STEMI patients with high thrombus burden were randomly assigned to receive a combined thrombus burden reduction therapy or thrombus aspiration alone. The primary end points included the percentage of patients with TMPG (TIMI myocardial perfusion grade) 3, STR (ST-segment resolution) above 70%, the index of microcirculatory resistance (IMR) and left ventricular ejection fraction (LVEF) difference.Twenty-two patients in the combined interventional group and 24 in the control group completed 1-year follow-up. The percentages of patients with TMPG 3 (68.2% versus 33.3%, P = 0.006) and STR above 70% (63.6% versus 25%, P = 0.016) were significantly higher in the combined group. IMR was significantly lower in the combined interventional group (31.50 ± 13.39 U versus 62.72 ± 22.80 U, P = 0.002). At 3 months and 1 year, the overall LVEF value was better in the combined interventional group (42.1% versus 40.0%, P = 0.049; 41.9% versus 39.8%, P = 0.042), respectively. The IMR value was negatively correlated with the EF value at 3 months (r = -0.145, P = 0.013) and 1 year (r = -0.333, P = 0.031).A combined thrombus burden reduction therapy during primary PCI can safely reduce thrombus burden, improve myocardial tissue perfusion, and improve cardiac function among STEMI patients with high thrombus burden. IMR might be a good predictor for post-myocardial infarction cardiac function.

Invasive Assessment of the Coronary Microvasculature

Traditionally, invasive coronary physiological assessment has focused on the epicardial coronary artery. More recently, appreciation of the importance of the coronary microvasculature in determining patient outcomes has grown. Several invasive modalities for interrogating microvascular function have been proposed. Angiographic techniques have been limited by their qualitative and subjective nature. Doppler wire-derived coronary flow reserve has been applied in research studies, but its clinical role has been limited by its lack of reproducibility, its lack of a clear normal value, and the fact that it is not specific for the microvasculature but interrogates the entire coronary circulation. The index of microcirculatory resistance—a thermodilution-derived measure of the minimum achievable microvascular resistance—is relatively easy to measure, more reproducible, has a clearer normal value, and is independent of epicardial coronary artery stenosis. The index of microcirculatory resistance has been shown to have prognostic value in patients with ST-segment–elevation myocardial infarction and cardiac allograft vasculopathy after heart transplantation. Emerging data demonstrate its role in evaluating patients with chest pain and nonobstructive coronary artery disease. Increasingly, the index of microcirculatory resistance is used as a reference standard for invasively assessing the microvasculature in clinical trials.

Assessing Coronary Blood Flow Physiology in the Cardiac Catheterisation Laboratory

Background:

Contemporary management of coronary disease focuses on the treatment of stenoses in the major epicardial vessels. However, myocardial blood flow is known to be contingent on a range of factors in addition to the patency of the epicardial vessels. These include anatomical and physiological factors such as the extent of myocardium supplied by the vessel, systemic blood pres-sure, the natural variation in vascular tone in response to physiological needs which allows for coro-nary autoregulation and pathological factors such as the presence of downstream obstruction to flow due to disease of the small coronary vessels or myocardium. The assessment of clinical effectiveness and adequacy of coronary revascularisation requires the ability to comprehensively and accurately as-sess and measure myocardial perfusion.

Conclusion:

In this article, we review the current methods of evaluating coronary blood flow and my-ocardial perfusion in the cardiac catheterisation laboratory.

Invasive Assessment of the Coronary Microcirculation in Reperfused ST-Segment-Elevation Myocardial Infarction Patients: Where Do We Stand?

For patients presenting with an acute ST-segment-elevation myocardial infarction, the most effective therapy for reducing myocardial infarct size and preserving left ventricular systolic function is primary percutaneous coronary intervention (PPCI). However, mortality and morbidity remain significant. This is partly attributed to the development of microvascular obstruction, which occurs in around 50% of ST-segment-elevation myocardial infarction patients post-PPCI, and it is associated with adverse left ventricular remodeling and worse clinical outcomes. Although microvascular obstruction can be detected by cardiac imaging techniques several hours post-PPCI, it may be too late to intervene at that time. Therefore, being able to predict the development of microvascular obstruction at the time of PPCI may identify high-risk patients who might benefit from further adjuvant intracoronary therapies, such as thrombolysis, vasodilators, glycoprotein IIb/IIIa inhibitors, and anti-inflammatory agents that may reduce microvascular obstruction. Recent studies have shown that invasive coronary physiology measurements performed during PPCI can be used to assess the coronary microcirculation. In this article, we provide an overview of the various invasive methods currently available to assess the coronary microcirculation in the setting of ST-segment-elevation myocardial infarction, and how they could potentially be used in the future for tailoring therapies to those most at risk.

Comprehensive assessment of microcirculation after primary percutaneous intervention in ST-segment elevation myocardial infarction: insight from thermodilution-derived index of microcirculatory resistance and coronary flow reserve

Objectives

A pathophysiological mechanism of microvascular dysfunction in ST-segment elevation myocardial infarction (STEMI) is multifactorial; thus, multiple modalities were needed to precisely evaluate a microcirculation.

Methods

We complementarily assessed microcirculation in STEMI by the index of microcirculatory resistance (IMR) and coronary flow reserve (CFR) immediately after a primary percutaneous intervention in 89 STEMI patients. Cardiovascular and cerebrovascular events (MACCE) including cardiovascular death, target vessel failure, heart failure, and stroke were assessed during a mean follow-up period of 3.0 years.

Results

The microcirculation of enrolled patients was classified into four groups using cutoff CFR and IMR values (CFR>2 and mean IMR): group-1 (n=23, CFR>2 and IMR≤27); group-2 (n=31, CFR≤2 and IMR≤27); group-3 (n=9, CFR>2 and IMR>27); and group-4 (n=26, CFR<2 and IMR>27). On echocardiography 3 months later, improvement in the wall motion score index was shown in group-1 (P<0.01), group-2 (P<0.01), and group-3 (P=0.04), whereas group-4 did not show improvement in wall motion score index (P=0.06). During clinical follow-up, there were no MACCE in group-1 and the patients in group-2 and group-3 showed significantly lower MACCE compared with group-4 (group-1=0%, group-2, and group-3=10%, group-4=23.1%, P=0.04).

Conclusion

Complimentary assessment of microcirculation by the IMR and CFR may be useful to evaluate myocardial viability and the long-term prognosis of STEMI patients.

Intracoronary injection of tirofiban prevents microcirculation dysfunction during delayed percutaneous coronary intervention in patients with acute myocardial infarction

OBJECTIVE

To determine whether tirofiban can prevent microcirculation dysfunction during delayed percutaneous coronary intervention (PCI) of spontaneously recanalized and severe narrowing coronary artery in patients with acute myocardial infarction.

METHODS

62 patients who have a single angiographically confirmed narrowing culprit coronary artery for more than 75% between 7 and 14 days after the onset of acute myocardial infarction were randomly divided into the tirofiban group (32 cases) and the placebo group (30 cases). All the patients received measurement of the index of microcirculatory resistance (IMR) before tirofiban/placebo administration and PCI. After PCI, IMR value was measured again.

RESULTS

There was no significant variation between the two groups before PCI (11.67 ± 6.45 of placebo group vs. 14.65 ± 12.45 of tirofiban group, P=0.158). After PCI, the IMR value of the tirofiban group is significantly lower than that of the placebo group (23.63 ± 9.91 of placebo group vs. 16.75 ± 9.98 of tirofiban group, P=0.008).

CONCLUSIONS

Intracoronary injection of tirofiban can significantly prevent the abnormal increase of IMR value during delayed PCI in patients with acute myocardial infarction.

Clinical and Angiographic Predictors of Microvascular Dysfunction in ST-Segment Elevation Myocardial Infarction

PURPOSE

We aimed to discover clinical and angiographic predictors of microvascular dysfunction using the index of microcirculatory resistance (IMR) in patients with ST-segment elevation myocardial infarction (STEMI).

MATERIALS AND METHODS

We enrolled 113 patients with STEMI (age, 56±11 years; 95 men) who underwent primary percutaneous coronary intervention (PCI). The IMR was measured with a pressure sensor/thermistor-tipped guidewire after primary PCI. The patients were divided into three groups based on IMR values: Low IMR [<18 U (12.9±2.6 U), n=38], Mid IMR [18-31 U (23.9±4.0 U), n=38], and High IMR [>31 U (48.1±17.1 U), n=37].

RESULTS

The age of the Low IMR group was significantly lower than that of the Mid and High IMR groups. The door-to-balloon time was <90 minutes in all patients, and it was not significantly different between groups. Meanwhile, the symptom-onset-to-balloon time was significantly longer in the High IMR group, compared to the Mid and Low IMR groups (p<0.001). In the high IMR group, the culprit lesion was found in a proximal location significantly more often than in a non-proximal location (p=0.008). In multivariate regression analysis, age and symptom-onset-to-balloon time were independent determinants of a high IMR (p=0.013 and p=0.003, respectively).

CONCLUSION

Our data suggest that age and symptom-onset-to-balloon time might be the major predictors of microvascular dysfunction in STEMI patients with a door-to-balloon time of <90 minutes.

Impact of microvascular obstruction on the assessment of coronary flow reserve, index of microcirculatory resistance, and fractional flow reserve after ST-segment elevation myocardial infarction

BACKGROUND

Invasive assessment of coronary physiology (IACP) offers important prognostic insights in ST-segment elevation myocardial infarction (STEMI) but the dynamics of coronary recovery are poorly understood.

OBJECTIVES

This study sought to examine the evolution of coronary flow reserve (CFR), index of microcirculatory resistance (IMR), ratio of distal coronary pressure (Pd) to mean aortic pressure (Pa), and fractional flow reserve (FFR) in patients undergoing primary percutaneous coronary intervention (PPCI).

METHODS

82 patients with STEMI underwent IACP at PPCI. Repeat IACP was performed in 61 patients (74%) at day 1 and in 46 patients (56%) at 6 months. Contrast-enhanced cardiac magnetic resonance imaging (CMR) was performed in 45 patients (55%) at day 1 and in 41 patients (50%) at 6 months. Changes in IACP were compared between patients with and without microvascular obstruction (MVO) on CMR.

RESULTS

MVO was present in 21 of 45 patients (47%). Patients with MVO had lower CFR at PPCI and day 1 (p < 0.05) and a trend toward higher IMR values (p = 0.07). At 6 months, CFR and IMR were not significantly different between the groups. Baseline flow and Pd/Pa remained stable over time but FFR reduced significantly between PPCI and 6 months (p = 0.008); this reduction was mainly observed in patients with MVO (p = 0.006) but not in those without MVO (p = 0.21).

CONCLUSIONS

In PPCI-treated patients with STEMI, coronary microcirculation begins to recover within 24 h and recovery progresses further by 6 months. FFR significantly reduces from baseline to 6 months. The presence of MVO indicates a highly dysfunctional microcirculation.