Increased Angio-Derived Index of Microcirculatory Resistance Within a Timeframe of 30-60 days After COVID-19 Infection.

BACKGROUND AND OBJECTIVES: Chest pain is a relatively long-term symptom that commonly occurs in patients who have contracted COVID-19. The reasons for these symptoms remain unclear, with coronary microvascular dysfunction (CMD) emerging as a potential factor. This study aimed to assess the presence of CMD in these patients by measuring the angio-derived index of microcirculatory resistance (AMR). METHODS: In this cross-sectional case-control study, patients who had chest pain and a history of COVID-19 infection within the preceding 30 to 60 days were included. The control subjects were patients without COVID-19. Demographic, clinical, and echocardiographic data were recorded. Angiographic images were collected for AMR analysis through an angioplus quantitative flow ratio measurement system. Propensity score matching (PSM) was performed to match the two groups. Multivariate logistic regression was used to examine the association between COVID-19 incidence and the increase in AMR (AMR > 285 mmHg*s/m) after correction for other confounders. RESULTS: After PSM, there were 58 patients in each group (the mean age was 66.3 ± 9.04 years, and 55.2% were men). The average time between the onset of COVID-19 infection and patient presentation at the hospital for coronary angiography was 41 ± 9.5 days. Moreover, there was no significant difference in the quantitative flow ratio between the two groups. Patients with COVID-19 had a greater mean AMR (295 vs. 266, p = 0.002). Multivariate logistic regression analysis revealed that COVID-19 (OR = 3.32, 95% CI = 1.50-7.60, p = 0.004) was significantly associated with an increase in AMR. CONCLUSIONS: Long-term COVID-19 patients who experience chest pain without evidence of myocardial ischemia exhibit an increase in AMR, and CMD may be one of the reasons for this increase. COVID-19 is an independent risk factor for an increase in AMR.

Prognostic impact of coronary microvascular dysfunction in patients with atrial fibrillation.

BACKGROUND: Coronary microvascular dysfunction (CMD) is frequently observed in atrial fibrillation (AF), the most commonly sustained arrhythmia. Nevertheless, an in-depth prognostic significance of CMD in AF is lacking. We aimed to provide insight into the predictive impact of CMD assessed by a novel non-invasive coronary angiography-derived index of microcirculatory resistance (caIMR) for major adverse events (MACE) in AF patients. METHOD: This study included patients with AF who underwent invasive coronary angiography due to suspected cardiac ischemia and did not exhibit obstructive epicardial coronary artery disease (≤50 % stenosis). The caIMR was prospectively evaluated, and the optimal cutoff value for predicting MACE was determined through ROC analysis. RESULT: A total of 463 patients with AF were enrolled. During a median of 33 months of follow-up, 111 (23.97 %) patients had MACE endpoints. The best caIMR cutoff value was 39.28. In patients with MACE, both the mean caIMR and the prevalence of elevated caIMR (caIMR>39.28) were significantly higher compared to those without MACE. An elevated caIMR was linked to a higher risk of MACE (log-rank P < 0.001) and emerged as an independent predictor of clinical outcomes (HR: 4.029; 95 % CI: 2.529-6.418; P < 0.001). In addition, the risk of MACE was higher in high caIMR patients with non-paroxysmal AF (log-rank P < 0.001) and no catheter ablation (log-rank P < 0.001). CONCLUSION: Elevated caIMR is common and showed a vital independent prognostic significance in AF patients. In addition to well-known risk factors, assessment of microvascular function can be a feasible approach for early prevention and a therapeutic target in AF patients.

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 (ß = 0.69 [0.13-1.26]), as well as infarct size (ß = 1.18 [0.24-2.11]) or ejection fraction at 6 months (ß = -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.

Quantitative Flow Ratio-Derived Index of Microcirculatory Resistance as a Novel Tool to Identify Microcirculatory Function in Patients with Ischemia and No Obstructive Coronary Artery Disease.

BACKGROUND: Coronary microvascular disease (CMVD) is associated with adverse cardiovascular outcomes. However, there is no reliable and noninvasive quantitative diagnostic method available for CMVD. The use of a pressure wire to measure the index of microcirculatory resistance (IMR) is possible, but it has inevitable practical restrictions. We hypothesized that computation of the quantitative flow ratio could be used to predict CMVD with symptoms of ischemia and no obstructive coronary artery disease (INOCA). METHODS: We retrospectively assessed the diagnostic efficiency of the quantitative flow ratio-derived index of microcirculatory resistance (QMR) in 103 vessels from 66 patients and compared it with invasive IMR using the thermodilution technique. RESULTS: Patients were divided into the CMVD group (41/66, 62.1%) and non-CMVD group (25/66, 37.9%). Pressure wire IMR measurements were made in 103 coronary vessels, including 44 left descending arteries, 18 left circumflex arteries, and 41 right coronary arteries. ROC curve analysis showed a good diagnostic performance of QMR for all arteries (area under the curve = 0.820, 95% confidence interval 0.736-0.904, p < 0.001) in predicting microcirculatory function. The optimal cut-off for QMR to predict microcirculatory function was 266 (sensitivity: 82.9%, specificity: 72.6%, and diagnostic accuracy: 76.7%). CONCLUSION: QMR is a promising tool for the assessment of coronary microcirculation. The assessment of the IMR without the use of a pressure wire may enable more rapid, convenient, and cost-effective assessment of coronary microvascular function.

[Index of microcirculatory resistance is associated with left ventricular remodeling in patients with acute anterior ST-segment elevation myocardial infarction undergoing emergency primary percutaneous coronary intervention].

OBJECTIVE: To evaluate whether index of microcirculatory resistance (IMR) is associated with left ventricular (LV) remodeling in acute anterior ST elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (PPCI). METHODS: This was a single-center retrospective cohort study. The patients with first anterior STEMI who received PPCI from January 2014 to August 2017 in Peking University Third Hospital was enrolled. After PPCI, IMR was measured immediately by using pressure/temperature guidewire. The success rate of IMR measurement was 100%. Also we collected some related clinical data from the medical records and laboratory results. Infarct size [assessed as creatine kinase (CK) peak], echocardiography at baseline and 1 year follow-up were assessed. LV adverse remodeling (LVAR) was defined as ≥20% increase in LV end-diastolic volume (LVEDV). RESULTS: A total of forty-three patients were enrolled, with an average age of (58.7±12.4) years.The patients were divided into two groups as IMR ≤25 and IMR>25 by normal values recommended by previous literature. Compared with IMR ≤25 group, IMR>25 group had a higher percentage of initial thrombolysis in myocardial infraction (TIMI) grade 0 (95.7% vs. 65.0%, P=0.029), higher serum CK peak value [4 090 (383, 15 833)vs. 1 580 (396, 5 583), P=0.004]. The IMR>25 group suffered higher rates of ventricular aneurysm (30.4% vs. 5.0%, P=0.021). There was no difference in LVEDV [(111.0±18.8) mL vs. (115.0±23.6) mL, P=0.503] between the two groups 1 day after MI, but after 1 year, LVEDV in IMR>25 group was significantly higher than in IMR≤25 group [(141.5±33.7) mL vs. (115.9±27.9) mL, P=0.018]. The incidence of LVAR was more significant in IMR>25 group (47.4% vs. 11.8%, P=0.024). Binary Logistics regression showed that IMR [B=0.079, exp(B) (95%CI)=1.082 (1.018－1.149), P=0.011] and serum triglyceride level [B=1.610, exp(B) (95%CI)=5.005 (1.380－18.152), P=0.014] were the predictors of LVAR 1 year after MI. IMR had a good predictive value for LVAR 1 year after MI [area under the curve (AUC)=0.749, P=0.019], IMR>29 was a good cutoff value with sensitivity 81.8% and specificity 68.0%. CONCLUSION: Our study elaborates that immediate measurement of IMR after PPCI in patients with STEMI can reflect the microvascular function.And IMR could be used as a quantitative biomarker to predict LVAR after STEMI.

Implementation of Microcirculation Examination in Clinical Practice-Insights from the Nationwide POL-MKW Registry.

Background and Objectives: The assessment of coronary microcirculation may facilitate risk stratification and treatment adjustment. The aim of this study was to evaluate patients' clinical presentation and treatment following coronary microcirculation assessment, as well as factors associated with an abnormal coronary flow reserve (CFR) and index of microcirculatory resistance (IMR) values. Materials and Results: This retrospective analysis included 223 patients gathered from the national registry of invasive coronary microvascular testing collected between 2018 and 2023. Results: The frequency of coronary microcirculatory assessments in Poland has steadily increased since 2018. Patients with impaired IMR (≥25) were less burdened with comorbidities. Patients with normal IMR underwent revascularisation attempts more frequently (11.9% vs. 29.8%, p = 0.003). After microcirculation testing, calcium channel blockers (CCBs) and angiotensin-converting enzyme inhibitors were added more often for patients with IMR and CFR abnormalities, respectively, as compared to control groups. Moreover, patients with coronary microvascular dysfunction (CMD, defined as CFR and/or IMR abnormality), regardless of treatment choice following microcirculation assessment, were provided with trimetazidine (23.2%) and dihydropyridine CCBs (26.4%) more frequently than those without CMD who were treated conservatively (6.8%) and by revascularisation (4.2% with p = 0.002 and 0% with p < 0.001, respectively). Multivariable analysis revealed no association between angina symptoms and IMR or CFR impairment. Conclusions: The frequency of coronary microcirculatory assessments in Poland has steadily increased. Angina symptoms were not associated with either IMR or CFR impairment. After microcirculation assessment, patients with impaired microcirculation, expressed as either low CFR, high IMR or both, received additional pharmacotherapy treatment more often.

Validation of pressure-bounded coronary flow reserve using invasive coronary physiologic assessment.

Coronary flow reserve (CFR) represents entire coronary compensatory capacity. While CFR assessment is recommended to identify patients at an increased risk of cardiovascular events and coronary microvascular dysfunction, invasive CFR measurement is often technically challenging. Although not well validated yet, pressure-bounded CFR (pbCFR) has been proposed as a simple surrogate to estimate impaired CFR. In this study, we evaluated coronary physiological characteristics of low pbCFR using detailed invasive assessment. Invasive physiological assessment including resting ratio of distal coronary pressure to aortic pressure (Pd/Pa), fractional flow reserve (FFR), resting and hyperemic mean transit time, index of microcirculatory resistance (IMR), CFR, resistive reserve ratio, and microvascular resistance reserve (MRR) was performed in 107 patients in the left anterior descending coronary artery. pbCFR was calculated only with resting Pd/Pa and FFR. Patients were divided into low pbCFR and non-low pbCFR groups. Of 107 patients, 50 (46.7%) had low pbCFR. FFR (0.90 ± 0.05 vs. 0.83 ± 0.05, p < 0.001), hyperemic mean transit time (0.27 ± 0.17 vs. 0.21 ± 0.12, p = 0.04), and IMR (20.4 ± 13.2 vs. 15.0 ± 9.1, p = 0.01) were significantly higher in the low pbCFR group than their counterpart. While directly measured CFR did not differ significantly (4.4 ± 2.3 vs. 5.1 ± 2.8, p = 0.18), MRR was lower in the low pbCFR group (5.4 ± 3.0 vs. 6.8 ± 3.8, p = 0.047). The rates of CFR < 2.0 and IMR ≥ 25 were not significantly different between the 2 groups. In conclusion, although CFR did not differ significantly, IMR and MRR were impaired in patients with low pbCFR, suggesting pbCFR as a potential surrogate of coronary microvascular function in clinical practice.

Coronary Microcirculatory Dysfunction and Acute Cellular Rejection After Heart Transplantation.

BACKGROUND: Acute cellular rejection is a major determinant of mortality and retransplantation after heart transplantation. We sought to evaluate the prognostic implications of coronary microcirculatory dysfunction assessed by index of microcirculatory resistance (IMR) for the risk of acute cellular rejection after heart transplantation. METHODS: The present study prospectively enrolled 154 heart transplant recipients who underwent scheduled coronary angiography and invasive coronary physiological assessment 1 month after transplantation. IMR is microcirculatory resistance under maximal hyperemia. By measuring hyperemic mean transit time using 3 injections (4 mL each) of room-temperature saline under maximal hyperemia, IMR was calculated as hyperemic distal coronary pressure×hyperemic mean transit time. The primary end point was biopsy-proven acute cellular rejection of grade ≥2R during 2 years of follow-up after transplantation and was compared by using multivariable Cox proportional hazards regression according to IMR. The incremental prognostic value of IMR, in addition to the model with clinical factors, was evaluated by comparison of C-index, net reclassification index, and integrated discrimination index. RESULTS: The mean age of recipients was 51.2±13.1 years (81.2% male), and the cumulative incidence of acute cellular rejection was 19.0% at 2 years. Patients with acute cellular rejection had significantly higher IMR values at 1 month than those without acute cellular rejection (23.1±8.6 versus 16.8±11.1, P=0.002). IMR was significantly associated with the risk of acute cellular rejection (per 5-U increase: adjusted hazard ratio, 1.18 [95% CI, 1.04-1.34], P=0.011) and the optimal cutoff value of IMR to predict acute cellular rejection was 15. Patients with IMR≥15 showed significantly higher risk of acute cellular rejection than those with IMR<15 (34.4% versus 3.8%; adjusted hazard ratio, 15.3 [95% CI 3.6-65.7], P<0.001). Addition of IMR to clinical variables showed significantly higher discriminant and reclassification ability for risk of acute cellular rejection (C-index 0.87 versus 0.74, P<0.001; net reclassification index 1.05, P<0.001; integrated discrimination index 0.20, P<0.001). CONCLUSIONS: Coronary microcirculatory dysfunction assessed by IMR measured early after heart transplantation showed significant association with the risk of acute cellular rejection. In addition to surveillance endomyocardial biopsy, early stratification using IMR could be a clinically useful tool to identify patients at higher risk of future acute cellular rejection after heart transplantation. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02798731.

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.

Effect of thrombus aspiration on microcirculatory resistance and ventricular function in patients with high thrombus burden.

BACKGROUND: Studies have not demonstrated consistent outcomes following thrombus aspiration in Primary Percutaneous Coronary Intervention (PPCI). We investigated the relationship between thrombus aspiration and microvascular obstruction as measured using Index of Microcirculatory Resistance (IMR) immediately following PPCI and Left Ventricle Function Improvement measured using Global Longitudinal Strain (GLS) six months following PPCI. Our aim is to determine microvascular obstruction and left ventricle function improvement six months following thrombus aspiration during PPCI. METHODS: This was a single-center, observational, prospective non-randomized study involving 45 patients with thrombus score 4-5 (defined as high thrombus burden) and Thrombolysis in Myocardial Infarction (TIMI) flow of 0-2 who subsequently underwent PPCI. Thrombus aspiration was conducted based on physician discretion. The IMR was measured immediately following the procedure. All patients underwent echocardiography to measure GLS at 24 h, 3 months and 6 months following PPCI. RESULTS: Thirty-three (73%) patients underwent thrombus aspiration during PPCI and twelve (27%) patients underwent the conventional PPCI. No significant difference in IMR was found between the group that underwent thrombus aspiration and the group that underwent conventional PCI (51.9 ± 41.5 vs 47.1 ± 35.6 p = 0.723). TIMI flow after PPCI was worse in thrombus aspiration group (OR 5.2 [1.2-23.2], p = 0.041). There was no difference in GLS between two groups at 6-month follow-up (- 13.0 ± 3.4 vs - 12.8 ± 4.6, p = 0.912). CONCLUSION: This study indicates no benefit of thrombus aspiration during PPCI in reducing either microvascular obstruction or left ventricular function at 6-month follow-up for patients with high thrombus burden. Nevertheless, further studies are required before definite conclusions can be made.

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

The role of coronary microvascular dysfunction (CMD) in the pathogenesis of ischaemic heart disease and in determining long-term prognosis is increasingly recognised. In selected patients, a comprehensive coronary assessment including an assessment of microvascular function may help refine risk stratification and improve patient outcomes. Various non-invasive and invasive techniques have been developed to assess the coronary microcirculation. Many of these tests utilise the indicator-dilution principle to determine coronary or myocardial blood flow. However, these techniques are often limited by their variability and lack of specificity for the coronary microvasculature. Consequently, there is still paucity of data on targeted therapies for CMD and their implications on long-term clinical outcomes, particularly in the setting of non-ST elevation acute coronary syndromes. Recent technical advancements, such as the index of microcirculatory resistance, have largely overcome these limitations and are able to provide novel insights into the assessment and treatment of CMD. This review summarises the currently available techniques for the assessment of CMD and provides an overview of its clinical implications.

Apnea Hypopnea Index is an Independent Predictor of Coronary Microcirculatory Dysfunction in Stable Angina Pectoris Patients with a Single Borderline Lesion.

BACKGROUND: To investigate the effect and possible mechanism of obstructive sleep apnea hypopnea syndrome on coronary microcirculation in stable angina pectoris (SAP) patients with a single borderline lesion. METHODS: We retrospectively analyzed 102 SAP patients with a single critical lesion [fractional flow reserve > 0.80] who were divided into an abnormal microcirculatory function group [index of microcirculatory resistance (IMR) ≥ 25, n = 52] and normal microcirculatory function (NMF) group (IMR < 25, n = 50). We compared indexes including biochemical indicators, coronary lesion characteristics, apnea hypopnea index (AHI), lowest oxygen saturation (LSaO2), night average heart rate, endothelin-1 (ET-1), nitric oxide (NO) and high-sensitivity C-reactive protein in serum between the two groups. Furthermore, risk factors affecting coronary microcirculation were analyzed. RESULTS: There were no significant differences in biochemical indexes and coronary lesion characteristics between the two groups (p > 0.05). Compared to the NMF group, AHI (23.76 ± 8.41 times/h) and ET-1 (1.96 ± 0.43 ng/L) were obviously increased (p < 0.01), and LSaO2 (77.96 ± 7.26%) and NO (23.63 ± 7.09 µmol/L) was significantly lower in the AMF group (p < 0.01). Moreover, AHI and ET-1 were positively associated with IMR (r1 = 0.887, 0.835, respectively). However, LSaO2 and NO had a negative correlation with IMR (r3 = 0.659, 0.691, respectively). Logistic regression analysis showed that AHI was an independent predictor of coronary microcirculatory dysfunction (odds ratio = 1.260, 95% confidence interval 1.083~1.467, p < 0.01). Receiver operating characteristic (ROC) curve analysis indicated an AHI cut-off value of 13.7 times/h to predict microcirculatory dysfunction (sensitivity 0.942, specificity 0.880). CONCLUSIONS: In SAP patients with a single critical lesion, AHI was associated with coronary microcirculatory dysfunction.

NEUTROPHIL-LYMPHOCYTE RATIO AND PLATELET-LYMPHOCYTE RATIO AS PREDICTORS OF CORONARY MICROCIRCULATORY DISEASE OCCURRENCE AND OUTCOME IN PATIENTS WITH CHRONIC CORONARY SYNDROME AND NO SIGNIFICANT CORONARY ARTERY STENOSIS.

OBJECTIVE: Introduction: Index of microcirculatory resistance assessment is an invasive method of measuring coronary microcirculation function. Association between impaired microcirculatory function and higher rate of cardiovascular events was proven. Neutrophil-lymphocyte ratio and platelet-lymphocyte ratio seem to be a promising parameters to predict coronary microcirculatory disease in patients with chronic coronary syndrome. The aim: To determine neutrophil-lymphocyte ratio and platelet-lymphocyte ratio levels in patients with coronary microcirculatory disease and potential association with clinical outcome. PATIENTS AND METHODS: Material and methods: 82 consecutive patients with mean age of 67 years, 67% male, were tested for presence of coronary microcirculatory disease using index of microcirculatory resistance. Neutrophil-lymphocyte ratio and platelet-lymphocyte ratio were calculated based on admission full blood count. Follow-up with major adverse cardiac and cardiovascular events registration was performed (median 24 months). RESULTS: Results: The study showed significantly higher neutrophil-lymphocyte ratio and platelet-lymphocyte ratio in patients with coronary microcirculatory disease compared to control group (3.58±2.61 vs 2.54±1.09 and 164±87.9 vs 124±36.6 respectively). Higher level of platelet-lymphocyte ratio in patients with coronary microcirculatory disease results in worse MACCE-free survival. Optimal cut-off values of neutrophil-lymphocyte ratio and platelet-lymphocyte ratio to detect coronary microcirculatory disease were 3.2 and 181.3, respectively. CONCLUSION: Conclusions: Higher neutrophil-lymphocyte ratio and platelet-lymphocyte ratio are associated with increased index of microcirculatory resistance value. Platelet-lymphocyte ratio may be used as a predictor of worse outcome in patients with coronary microcirculatory disease.

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.

[Value of index of microcirculatory resistance for early prediction of periprocedural myocardial microcirculatory injury after percutaneous coronary intervention in patients with coronary heart disease].

Objective: To explore the value of index of microcirculatory resistance (IMR) for early prediction of periprocedural myocardial injury (PMI) in patients with stable angina pectoris (SAP) and acute coronary syndrome (ACS) after PCI. Methods: It was a prospective study. One hundred and sixty-four patients who had single coronary lesion were consecutively enrolled from May 2014 to December 2017 at Nanjing Hospital affiliated to Nanjing Medical University. According to clinical manifestation, patients were divided into SAP group (n=81) and ACS group (n=83). IMR was determined by thermal dilution with pressure guide wire. Basic clinical characteristics, coronary angiographic results, PCI procedural details, IMR after PCI, ΔIMR (IMR=post-PCI-IMR pre-PCI), levels of myocardial biomarkers before and after PCI were compared between the two groups. Multivariate logistic regression was used to analyze the relation of PMI with IMR and ΔIMR, and the predictive ability was evaluated by receiver operating characteristic (ROC). Results: The levels of total cholesterol and low density lipoprotein cholesterol were significantly higher in ACS group than in SAP group (P<0.05), other clinical data at baseline were similar between the two groups (P>0.05). Quantitative coronary angiography (QCA) results and PCI related data were also similar between the two groups before PCI (P>0.05). Values of mean transit time (Tmn) of intracoronary injection with room temperature saline, post-PCI IMR and ΔIMR were significantly higher in ACS group than in SAP group after PCI (P<0.05). Plasma creatine kinase isoenzyme-MB difference (ΔCK-MB) (ΔCK-MB=CK-MB post-PCI-CK-MB pre-PCI) and cardiac troponin-I (cTnI) difference (ΔcTnI=cTnI post-PCI-cTnI pre-PCI) were significantly larger in ACS group than in SAP group (P<0.05). Multivariate logistic regression analysis showed that coronary artery disease (CHD) type (SAP and ACS) (OR=1.301, 95%CI 1.083-1.562), age (OR=1.007, 95%CI 1.000-1.013), ΔIMR (OR=1.009, 95%CI 1.000-1.017) and post-PCI IMR (OR=1.008, 95%CI 1.001-1.014) were independent predictors of PMI (P<0.05). The area under the ROC curve (AUC) of ΔIMR was 0.763 to predict PMI (P<0.05), the optimum cut-off value of ΔIMR was 5.485 with 70.0% sensitivity and 77.4% specificity. ΔIMR was positively correlated with ΔcTnI (r=0.592, P<0.05). Conclusions: ΔIMR serves as an early predictor of PMI in CHD patients after PCI. As compared with SAP patients, ACS patients are more likely to develop PMI.

Prognostic value of the index of microcirculatory resistance after percutaneous coronary intervention in patients with non-ST-segment elevation acute coronary syndrome.

BACKGROUND: The prognostic value of physiological indices in non-ST-segment elevation acute coronary syndrome (NSTE-ACS) patients undergoing percutaneous coronary intervention (PCI) is unknown. We investigated the prognostic efficacy of physiological indices obtained after PCI in patients with NSTE-ACS. METHODS: Eighty-three patients (men: n = 70, age: 63.7 ± 9.7 years) undergoing PCI for NSTE-ACS within 48 hr postadmission were investigated. Fractional flow reserve (FFR), coronary flow reserve (CFR), and the index of microcirculatory resistance (IMR) of the culprit vessels were measured after the completion of PCI. The patients were clinically followed up to determine major cardiac adverse events (MACE), including death, congestive heart failure requiring hospitalization, and remote coronary revascularization. RESULTS: The median FFR, CFR, and IMR values were 0.90 (interquartile range [IQR] 0.86-0.95), 2.38 (IQR 1.75-4.17), and 22.9 (IQR 11.2-31.5), respectively. During a median follow-up of 20.7 months, 19 MACEs (22.9%) were documented. No significant difference in baseline patient characteristics, except for age, was detected between patients with and without MACE. Patients with MACE showed higher IMR and lower CFR than those without (IMR: 27.2 vs. 16.3; P = 0.001, CFR: 1.82 vs. 2.55; P = 0.04), whereas FFR was not significantly different (0.92 vs. 0.89; P = 0.72), irrespective of the MACE occurrence. Post-PCI IMR was the only independent predictor of MACE (hazard ratio 1.033, 95% confidence interval 1.013-1.052, P = 0.001). The MACE-free survival was significantly worse in patients with high post-PCI IMR (χ2 7.12; P = 0.008). CONCLUSION: Post-PCI IMR may help identify patients at high risk for subsequent adverse coronary events who require adjunctive therapeutic strategies.

[Coronary microvascular resistance and its relevant factors in patients with moderate coronary stenosis and chest pain].

Objective: To evaluate the impact of cardiovascular risk factors on index of microvascular resistance (IMR) and coronary flow reserve (CFR) and to explore the characteristics of IMR and CFR and the relationship between IMR and angiographic features in patients with intermediate coronary stenosis and chest pain. Methods: Fractional flow reserve (FFR), CFR, and IMR were measured in patients who underwent invasive coronary angiography with 40%-70% stenosis by visual assessment. All patients with FFR>0.75 were enrolled and grouped with the cut-off points of IMR≥25 and CFR≤2.0. Patients with IMR≥25 were group H, including two sub-groups (high IMR-low CFR, group H1 and high IMR-high CFR, group H2), while those with IMR<25 were group N. The thrombolysis in myocardial infarction (TIMI) frame were counted. Results: A total of 34 patients with FFR>0.75 were enrolled with 61.8%(21 cases) of males and 38.2% (13 cases) of females. The mean age was (57.3±8.1) years old. High IMR accounted for 47.1% of all cases. There was significant difference between group H and N in TIMI frame (33.0 vs. 20.8, P=0.031). There were significant differences between group H1 and H2 in homocysteine (17.8 µmol/L vs. 12.0 µmol/L, P=0.005) and IMRcorr (58.0 vs. 36.1, P=0.002). IMRcorr was correlated to TIMI frame (r=0.40, P=0.012) for all cases. The sensitivity and specificity of inferring IMR≥35.3 by TIMI frame were 0.75 and 0.65 (P=0.049) with TIMI frame over 40.5. Conclusions: High IMR may be one of the reasons for chest pain in patients with intermediate coronary stenosis. There is no correlation between vascular risk factors and IMR or CFR, while there is positive correlation between TIMI frame and IMR. The specificity is 65% for inferring IMR rise with TIMI frame over 40.5.

The influence of elective percutaneous coronary intervention on microvascular resistance: a serial assessment using the index of microcirculatory resistance.

This study investigates whether hyperemic microvascular resistance (MR) is influenced by elective percutaneous coronary intervention (PCI) by using the index of microcirculatory resistance (IMR). Seventy-one consecutive patients with stable angina pectoris undergoing elective PCI were prospectively studied. The IMR was measured before and after PCI and at the 10-mo follow-up. The IMR significantly decreased until follow-up; the pre-PCI, post-PCI, and follow-up IMRs had a median of 19.8 (interquartile range, 14.6-28.9), 16.2 (11.8-22.1), and 14.8 (11.8-18.7), respectively (P < 0.001). The pre-PCI IMR was significantly correlated with the change in IMR between pre- and post-PCI (r = 0.84, P < 0.001) and between pre-PCI and follow-up (r = 0.93, P < 0.001). Pre-PCI IMR values were significantly higher in territories with decreases in IMR than in those with increases in IMR [pre-PCI IMR: 25.4 (18.4-35.5) vs. 12.5 (9.4-16.8), P < 0.001]. At follow-up, IMR values in territories showing decreases in IMR were significantly lower than those with increases in IMR [IMR at follow-up: 13.9 (10.9-17.6) vs. 16.6 (14.0-21.4), P = 0.013]. The IMR decrease was significantly associated with a greater shortening of mean transit time, indicating increases in coronary flow (P < 0.001). The optimal cut-off values of pre-PCI IMR to predict a decrease in IMR after PCI and at follow-up were 16.8 and 17.0, respectively. In conclusion, elective PCI affected hyperemic MR and its change was associated with pre-PCI MR, resulting in showing a wide distribution. Overall hyperemic MR significantly decreased until follow-up. The modified hyperemic MR introduced by PCI may affect post-PCI coronary flow.

How does coronary stent implantation impact on the status of the microcirculation during primary percutaneous coronary intervention in patients with ST-elevation myocardial infarction?

AIMS: Primary percutaneous coronary intervention (PPCI) is the optimal treatment for patients presenting with ST-elevation myocardial infarction (STEMI). An elevated index of microcirculatory resistance (IMR) reflects microvascular function and when measured after PPCI, it can predict an adverse clinical outcome. We measured coronary microvascular function in STEMI patients and compared sequential changes before and after stent implantation. METHODS AND RESULTS: In 85 STEMI patients, fractional flow reserve, coronary flow reserve, and IMR were measured using a pressure wire (Certus, St Jude Medical, St Paul, MN, USA) immediately before and after stent implantation. Stenting significantly improved all of the measured parameters of coronary physiology including IMR from 67.7 [interquartile range (IQR): 56.2-95.8] to 36.7 (IQR: 22.7-59.5), P < 0.001. However, after stenting, IMR remained elevated (>40) in 28 (32.9%) patients. In 15 of these patients (17.6% of the cohort), only a partial reduction in IMR occurred and these patients were more likely to be late presenters (pain to wire time >6 h). The extent of jeopardized myocardium [standardized beta: -0.26 (IMR unit/Bypass Angioplasty Revascularization Investigation score unit), P: 0.009] and pre-stenting IMR [standardized beta: -0.34 (IMR unit), P: 0.001] predicted a reduction in IMR after stenting (ΔIMR = post-stenting IMR - pre-stenting IMR), whereas thrombotic burden [standardized beta: 0.24 (IMR unit/thrombus score unit), P: 0.01] and deployed stent volume [standardized beta: 0.26 (IMR unit/mm(3) of stent), P: 0.01] were associated with a potentially deleterious increase in IMR. CONCLUSION: Improved perfusion of the myocardium by stent deployment during PPCI is not universal. The causes of impaired microvascular function at the completion of PPCI treatment are heterogeneous, but can reflect a later clinical presentation and/or the location and extent of the thrombotic burden.

Coronary slow flow and angiography-derived index of microcirculatory resistance as prognostic predictors in patients with angina and normal coronary arteries: a retrospective cohort study.

BACKGROUND: This study aims to investigate prognostic implications of coronary slow flow (CSF) and angiography-derived index of microcirculatory resistance (caIMR) in patients with angina and normal coronary arteries. METHODS: A total of 582 patients were enrolled with angiographically normal coronary arteries. caIMR was calculated using a commercial software. Patients were followed up for a median of 45 months. The primary endpoint was defined as major adverse cardiovascular events (MACEs) comprising death, myocardial infarction and readmission for angina or heart failure. RESULTS: CSF was diagnosed when TIMI grade 2 flow presented in at least one coronary artery. Multivariate analysis indicated TIMI-flow-based determination of CSF was not significantly associated with MACEs [hazard ratio (HR): 2.14; 95% confidence interval (CI): 0.87-5.31; p = 0.099), while caIMR >42 (HR: 2.53; 95% CI: 1.02-6.32; p = 0.047) were independent predictors of MACEs. Incorporation of caIMR improved the area under the curve from 0.587 to 0.642. CONCLUSIONS: caIMR was an independent prognostic factor of long-term cardiovascular events in patients with CSF. Evaluation of caIMR improved the risk stratification of patients with angiographically-normal coronary arteries.