Invasive Detection of Coronary Microvascular Dysfunction: How It Began, and Where We Are Now

The landscape of interventional cardiology is ever evolving. Contemporary practice has shifted from a stenosis-centred approach to the total characterisation of both the epicardial and microcirculatory vessels. Microcirculatory dysfunction plays an important role in the pathophysiology of acute and chronic coronary syndromes, and characterisation of the microcirculation has important clinical consequences. Accordingly, the invasive diagnosis of microcirculatory dysfunction is becoming a key feature of the interventional cardiologist's toolkit. This review focuses on the methodology underpinning the invasive diagnosis of microvascular dysfunction and highlights the indices that have arisen from these methodologies.

Coronary Physiology: Delivering Precision Medicine?

Coronary physiological assessment is now widely used to assess epicardial coronary lesions in cath lab. Based on clinical evidence, fractional flow reserve (FFR) is the gold standard method to select whether epicardial coronary lesions need revascularization. While additional epicardial indexes, such as instantaneous wave-free ratio (iFR), are also used for revascularization decision-making, several indexes are now also available to explore the coronary microcirculation. Therefore, coronary physiological assessment now allows to explore the entire coronary tree and offer the potential of precision medicine for patients affected by coronary artery disease (CAD). This paper will provide review of the epicardial and microvascular indexes available for the assessment of coronary physiology. More specifically, the already demonstrated contributions of these indexes in the management of CAD and the role they could play in precision medicine will be reviewed with special emphasis on chronic coronary syndrome.

[Advancement of imaging technology for coronary microcirculation dysfunction assessment]

Coronary microcirculation dysfunction (CMVD) is an important risk factor for the prognosis of re-perfused ischemic heart. Recent studies showed that the evaluation of CMVD has significant impact on both the early diagnosis of heart diseases relevant to blood supply and prognosis after myocardial reperfusion. In this review, the definition of CMVD from the perspective of pathophysiology was clarified, the principles and features of the state-of-the-art imaging technologies for CMVD assessment were reviewed from the perspective of engineering and the further research direction was promoted.

Relationship Between Plasma Total Homocysteine Levels and Mean Corrected TIMI Frame Count in Patients with Acute Myocardial Infarction

Objective

To explore the relationship between the plasma total homocysteine (tHcy) levels and slow coronary flow (SCF) measured by mean corrected TIMI frame count (CTFC) in patients with acute myocardial infarction (AMI).

Methods

Ninety-one patients with primary myocardial infarction were enrolled in this study. The quantitative measurement of coronary blood flow was performed using the mean CTFC method. Plasma tHcy levels were determined using enzymatic assay from venous blood samples. Multivariable linear regression models indicated were used to estimate the effect size (β) of plasma tHcy levels on mean CTFC levels.

Results

Compared with patients with the mean CTFC ≤23.61 frames per second (FPS) group, there were increased plasma tHcy levels in patients of the second, third and highest mean CTFC quartiles (P < 0.001). Linear regression models indicated that plasma tHcy levels were positively associated with mean CTFC levels (adjusted-β per SD increase: 1.96, 95% CI 1.20 to 2.73, P < 0.001). Compared to the tHcy ≤12.30 μmol/L group, the third and highest tHcy-quartile groups had higher mean CTFC levels (adjusted-β: 2.52, 95% CI 0.39 to 4.65, P = 0.023; adjusted-β: 5.07, 95% CI 2.98 to 7.16, P < 0.001, respectively; P for trend <0.001). Moreover, this positive relationship was modified by diabetes mellitus (P-value for interaction was 0.046).

Conclusion

We found a positive relationship between plasma tHcy levels and mean CTFC levels in patients with AMI. Moreover, diabetes mellitus played an interactive role in this positive association between the plasma tHcy levels and mean CTFC levels.

The Role of Coronary Physiology Assessment in the Diagnosis and Treatment of Stable Angina. Dive Inside Recent Findings of Diffuse Coronary Disease Treatment

Coronary physiology is widely used to assess epicardial coronary lesions in patients with stable angina. Based on the available evidence, physiology plays a crucial role in diagnosing and treating patients. There have been invasive methods for determining cardiac physiology, such as fractional flow reserve and instantaneous wave-free ratio. Still, new non-invasive approaches provide extra anatomical information, such as fractional flow reserve computed tomography (FFR-CT) based on computed tomography and physiology based on angiography. Even though FFR-guided percutaneous coronary intervention (PCI) is clinically beneficial, one-third of patients retain suboptimal FFR after the procedure, associated with severe adverse events, rendering PCI in diffuse coronary artery disease questionable. Using the pullback pressure gradient (PPG), we can analyze the magnitude and extent of pressure losses; a lower value may indicate diffuse disease, while a high value with an abrupt curve may indicate focal disease. Since PCI is not the best option for treating diffuse coronary disease, current strategies focus on conservatively using medical therapy or bypass surgery. It has been demonstrated that patients with diffuse disease of the left anterior descending (LAD) are at a greater risk of developing occlusion of the left internal mammary artery graft than those with focal disease and that maximal medical therapy may be the most effective treatment for these patients.

Effect of Kuanxiong Aerosol on Perioperative Coronary Microcirculation in Patients with Unstable Angina Undergoing Elective PCI: A Pilot Randomized Controlled Trial

OBJECTIVE

To evaluate the immediate effect of Kuanxiong Aerosol (KXA) on perioperative coronary microcirculation in patients with unstable angina (UA) suffering from elective percutaneous coronary intervention (PCI).

METHODS

From February 2021 to July 2023, UA inpatients who underwent PCI alone in the left anterior descending (LAD) branch were included. Random numbers were generated to divide patients into the trial group and the control group at a ratio of 1:1. The index of coronary microcirculation resistance (IMR) was measured before PCI, and the trial group was given two sprays of KXA, while the control group was not given. IMR was measured again after PCI, cardiac troponin I (cTnI) and creatine kinase isoenzyme-MB (CK-MB) were detected before and 24 h after surgery, and major cardiovascular adverse events (MACEs) were recorded for 30 days. The data statistics and analysis personnel were blinded.

RESULTS

Totally 859 patients were screened, and 62 of them were involved into this study. Finally, 1 patient in the trial group failed to complete the post-PCI IMR and was excluded, 30 patients were included for data analysis, while 31 patients in the control group were enrolled in data analysis. There was no significant difference in baseline data (age, gender, risk factors, previous history, biochemical index, and drug therapy, etc.) between the two groups. In addition, differences in IMR, cTnI and CK-MB were not statistically significant between the two groups before surgery. After PCI, the IMR level of the trial group was significantly lower than that of the control group (19.56 ± 14.37 vs. 27.15 ± 15.03, P=0.048). Besides, the incidence of perioperative myocardial injury (PMI) was lower in the trial group, but the difference was not statistically significant (6.67% vs. 16.13%, P=0.425). No MACEs were reported in either group.

CONCLUSIONS

KXA has the potential of improving coronary microvascular dysfunction. This study provides reference for the application of KXA in UA patients undergoing elective PCI. (Registration No. ChiCTR2300069831).

Ticagrelor vs. clopidogrel for coronary microvascular dysfunction in patients with STEMI: a meta-analysis of randomized controlled trials

Purpose

Approximately half of ST-segment elevation myocardial infarction (STEMI) patients who undergo revascularization present with coronary microvascular dysfunction. Dual antiplatelet therapy, consisting of aspirin and a P2Y12 inhibitor (e.g., clopidogrel or ticagrelor), is recommended to reduce rates of cardiovascular events after STEMI. The present study performed a pooled analysis of randomized controlled trials (RCTs) to compare effects of ticagrelor and clopidogrel on coronary microcirculation dysfunction in STEMI patients who underwent the primary percutaneous coronary intervention.

Methods

The PubMed, Embase, Cochrane Library, and Web of Science databases were searched for eligible RCTs up to September 2022, with no language restriction. Coronary microcirculation indicators included the corrected thrombolysis in myocardial infarction (TIMI) frame count (cTFC), myocardial blush grade (MBG), TIMI myocardial perfusion grade (TMPG), coronary flow reserve (CFR), and index of microcirculatory resistance (IMR).

Results

Seven RCTs that included a total of 957 patients (476 who were treated with ticagrelor and 481 who were treated with clopidogrel) were included. Compared with clopidogrel, ticagrelor better accelerated microcirculation blood flow [cTFC = -2.40, 95% confidence interval (CI): -3.38 to -1.41, p < 0.001] and improved myocardial perfusion [MBG = 3, odds ratio (OR) = 1.99, 95% CI: 1.35 to 2.93, p < 0.001; MBG ≥ 2, OR = 2.57, 95% CI: 1.61 to 4.12, p < 0.001].

Conclusions

Ticagrelor has more benefits for coronary microcirculation than clopidogrel in STEMI patients who undergo the primary percutaneous coronary intervention. However, recommendations for which P2Y12 receptor inhibitor should be used in STEMI patients should be provided according to results of studies that investigate clinical outcomes.

Single-Center Analysis of Soluble TREM2 as a Biomarker in Coronary Microvascular Dysfunction: A Cross-Sectional Study

Background: The soluble triggering receptor expressed on myeloid cells 2 (sTREM2) is linked to the progression of cardiovascular conditions, but its role in coronary microcirculation dysfunction (CMD) is not yet clear. Methods: A cross-sectional observational study from July 2023 to May 2024 was conducted in the China-Japan Friendship Hospital, after registration in the ClinicalTrials database (Registry Name: Coronary Microvascular Dysfunction in Angina Patients With Non-obstructive Coronary Artery Disease (ANOCA-CMD); Registry Number: NCT06503640; Registry Date: 23 September 2022). This cross-sectional study involved 76 subjects, including 55 patients with CMD and 21 without CMD, admitted to the China-Japan Friendship Hospital. CMD was defined by a coronary flow reserve (CFR) < 2.5 or index of microvascular resistance (IMR) ≥ 25. sTREM2 levels were measured using an enzyme-linked immunosorbent assay. Linear correlation analysis assessed the relationship between sTREM2 levels and CFR, IMR, microvascular resistance reserve (MRR), and the resistive reserve ratio (RRR). Univariate and multivariate regression analyses further examined the association between sTREM2 and CMD. Additionally, receiver operating characteristic (ROC) analysis was used to evaluate the diagnostic accuracy of plasma sTREM2 for identifying CMD patients. Results: Elevated sTREM2 levels were found in the CMD group. Correlation analysis showed a significant positive relationship with IMR and an inverse correlation with CFR, MRR, and RRR. After adjusting for confounders, sTREM2 was found to be an independent risk factor for CMD [OR = 1.003, 95% CI 1.001-1.007, p = 0.008]. ROC analysis revealed a sensitivity of 59.46%, specificity of 90.48%, and an AUC of 0.7677 (95% CI: 0.6481-0.8872, p = 0.008) for CMD diagnosis at a threshold of 595.5 pg/mL, indicating good diagnostic performance. Conclusions: Elevated sTREM2 levels in CMD patients indicate its potential as a biomarker.

Trimetazidine: Activating AMPK Signal to Ameliorate Coronary Microcirculation Dysfunction after Myocardial Infarction

BACKGROUND

Myocardial ischemia-reperfusion (I/R) injury and coronary microcirculation dysfunction (CMD) are observed in patients with myocardial infarction after vascular recanalization. The antianginal drug trimetazidine has been demonstrated to exert a protective effect in myocardial ischemia-reperfusion injury.

OBJECTIVES

This study aimed to investigate the role of trimetazidine in endothelial cell dysfunction caused by myocardial I/R injury and thus improve coronary microcirculation.

METHODS

The myocardial I/R mouse model was established, and trimetazidine was administered for 7 days before myocardial I/R model establishment. Echocardiography, 2,3,5-triphenyltetrazolium chloride (TTC) staining, hematoxylin-eosin (H&E) staining, and thioflavin S staining were applied to assess myocardial injury and microvascular function. Additionally, the oxygen-glucose deprivation/reperfusion (OGD/R) model was developed in endothelial cells to simulate myocardial I/R injury in vitro. Griess reaction method, immunofluorescence, and western blotting (WB) were employed to detect the expressions of nitric oxide (NO), platelet endothelial cell adhesion molecule-1 (CD31) and vascular endothelial (VE)-cadherin, zonula occludens protein 1 (ZO-1), occludin, vascular endothelial growth factor (VEGF) and adenosine monophosphate (AMP)-activated protein kinase (AMPK) signaling-related proteins in endothelial cells and mouse cardiomyocytes. AMPK pathway inhibitor compound C was used for further mechanism validation.

RESULTS

Our research demonstrated that trimetazidine can alleviate myocardial pathological injury and cardiac function injury during myocardial I/R. Trimetazidine was observed to improve microvascular reflux phenomenon and microvascular function and barrier injury in myocardial I/R and OGD/R models. Additionally, the expressions of AMPK signal-related proteins were found to be inhibited in myocardial I/R and OGD/R models, which were then activated in mice administered trimetazidine. However, the effects of trimetazidine on endothelial cell function and barrier damage were attenuated after co-treatment with compound C and trimetazidine.

CONCLUSION

Trimetazidine ameliorated myocardial I/R-induced CMD by activating AMPK signaling.