Novel index for invasively assessing the coronary microcirculation

Development of myocardial perfusion imaging from coronary angiography for clinical application

This study aimed to generate myocardial perfusion images from coronary angiography (CAG) using Patlak plot analysis and evaluate their effectiveness in detecting ischemia. Data from 29 patients were analyzed. Electrocardiogram-synchronized CAG images of the left coronary artery were registered and processed for pixel-wise Patlak analysis. Image generation succeeded in 18 cases (62%) and failed in 11 due to motion artifacts caused by irregular heartbeats, table panning, or deep breathing. The resulting images clearly distinguished ischemic from normal regions. Perfusion values were significantly lower in ischemic regions compared to normal regions (p < 0.001). Despite technical challenges and variability in patient conditions, this method enabled consistent identification of perfusion deficits. Enhancing image processing increases the success rate. This approach allows ischemia assessment directly from CAG data and supports timely treatment planning, contributing to improved diagnostic precision and clinical decision-making in selected cases.

Index microvascular resistance (IMR) in heart transplant patients (IMR-HT study): Study protocol

BACKGROUND

Acute allograft rejection (AAR) is an important cause of morbi mortality in heart transplant (HT) patients, particularly during the first year. Endomyocardial biopsy (EMB) is the "gold standard" to guide post- heart transplantation treatment. However, it is associated with complications that can be potentially serious. The index of microvascular resistance (IMR) is a specific physiological parameter used to assess microvascular function. Invasive coronary assessment has been shown to be both feasible and safe. Detection of coronary microvascular dysfunction (MCD) by IMR may help to identify high risk HT patients. In fact, an increased IMR measured early after HT has been associated with AAR, higher all-cause mortality and adverse cardiac events. A high IMR value early after HT may identify patients at higher risk who require increased surveillance or adjustments in immunosuppressive therapy. Conversely, a low IMR value may support reducing the number of EMBs. Our aim is to evaluate IMR in heart transplant patients within the first year. Changes in management after knowing IMR values and prognostic implications of IMR in a long term follow up will also be assessed.

STUDY DESIGN

The IMR-HT study (NCT06656065) is a multicenter, prospective study that will include post-HT consecutive stable patients undergoing coronary physiological assessment in the first three months and one year. Cardiac adverse events will be evaluated at one year for up to five years. A clinical management algorithm is proposed: after knowing IMR values the physician will be able to reduce the number of biopsies established in each center protocol or modify immunosuppression therapy.

CONCLUSIONS

IMR values may vary within the first year after heart transplant. IMR assessment will be useful to identify high risk heart transplant patients, leading to possible changes in management and prognosis.

Comparison of Coronary Physiological Indices in Identifying Functionally Significant Myocardial Bridges in ANOCA

BACKGROUND

A functionally significant myocardial bridge (MB) is an important cause of angina with nonobstructive coronary arteries. However, distinguishing a functionally significant versus incidental MB remains challenging. Resting and hyperemic intracoronary functional indices are available, but no studies have compared their diagnostic performance in MBs.

METHODS

We prospectively studied 64 patients with angina and nonobstructive coronary arteries, all of whom had an MB confirmed by intravascular ultrasound. We evaluated the diagnostic performance of instantaneous wave-free ratio (iFR) and resting full-cycle ratio (RFR) under Dobutamine stress, with Dobutamine diastolic fractional flow reserve (dFFR) as a reference standard. Dobutamine iFR and Dobutamine RFR were assessed in the first 18 patients, while only Dobutamine RFR was assessed in the remaining 46. Dobutamine dFFR ≤0.76 was considered indicative of a functionally significant MB.

RESULTS

There was a strong correlation between Dobutamine iFR (R2=0.67, P<0.001) and Dobutamine RFR (R2=0.80, P<0.001) with Dobutamine dFFR. Receiver operating characteristics curve analysis to identify the cutoff for Dobutamine dFFR ≤0.76 was 0.81 for Dobutamine iFR (area under the curve 0.961) and 0.76 for Dobutamine RFR (area under the curve 0.996). The diagnostic accuracy of Dobutamine iFR was 94.4%, with a sensitivity of 100% and specificity of 85.7%. For Dobutamine RFR, the diagnostic accuracy was 96.9%, with a sensitivity of 95.8% and specificity of 100%.

CONCLUSIONS

In patients with angina and nonobstructive coronary arteries and an MB confirmed by intravascular ultrasound, Dobutamine iFR and Dobutamine RFR may serve as alternatives to Dobutamine dFFR in identifying a functionally significant MB, with Dobutamine RFR having superior diagnostic accuracy.

Microcirculatory resistance based on a single angiographic view in ST-segment elevation myocardial infarction patients

BACKGROUND

Angio-based microvascular resistance (AMR) was proposed as a tool to quantitatively assess coronary microvascular based on single angiographic projection. The aims of this study are to assess the diagnostic accuracy and prognostic significance of AMR in ST-segment elevation myocardial infarction (STEMI) patients.

METHODS

AMR was measured (Of these, 22 patients measured index of microvascular resistance (IMR)) in 70 STEMI patients after primary percutaneous coronary intervention (pPCI). ST-segment resolution (STR) was assessed 2 h after pPCI simultaneously. Transthoracic echocardiography was performed within 1 day and approximately 1 year after pPCI. STEMI patients underwent pPCI were followed up for 7.3 years and the primary endpoint was the major adverse cardiac and cerebral events (MACCEs).

RESULTS

AMR showed significant correlations with IMR (R = 0.334, P = 0.005). AMR has good predictive power for STR after pPCI (area under the curve: 0.889, sensitivity: 94.59%, specificity: 75.76%) in receiver operating characteristic (ROC) curve. Low-AMR patients showed markedly improved left ventricular ejection fraction (LVEF) 1 year after pPCI (42(40-49) vs. 41(39-44), P = 0.041). High-AMR patients showed higher risk for MACCEs than those with Low-AMR (HR = 3.90, P = 0.02). In multivariate cox regression analysis, AMR was considered an independent predictor of MACCEs (HR: 1.153, P = 0.020).

CONCLUSIONS

AMR is a reliable tool for the estimation of microvascular resistance and prognosis in the absence of intracoronary pressure-temperature sensor wire and adenosine based on single angiographic projection.

Coronary angiography-derived index of microcirculatory resistance associated with contrast-induced acute kidney injury in patients with STEMI

Background

More than half of ST-segment elevation myocardial infarction (STEMI) patients have coronary microcirculatory dysfunction (CMD) after percutaneous coronary intervention (PCI). This study aimed to explore the role of CMD in the occurrence of contrast-induced acute kidney injury (CI-AKI) in patients with STEMI.

Methods

This was a single-centre retrospective clinical observational study. Coronary angiography-derived index of microcirculatory resistance (caIMR) was measured and used to assess CMD. Regression analysis was used to identify risk factors for CI-AKI. Restricted cubic splines (RCS) was employed to examine the dose-response relationship between caIMR and CI-AKI. The predictive accuracy of the models was assessed with net reclassification index (NRI), and integrated discrimination improvement (IDI).

Results

This study included 745 patients, the incidence of CI-AKI was 10.6% (79/745). Multivariate logistic regression identified caIMR (OR = 1.072, 95% CI: 1.051-1.094) as an independent predictor of CI-AKI. RCS analysis indicated a linear dose-response relationship between caIMR and CI-AKI. Receiver operating characteristic (ROC) analysis demonstrated that the areas under the curve for caIMR was 0.725, the optimal cutoff value was 25.95 U. Integration of caIMR could significantly improve the risk model for CI-AKI in STEMI patients (NRI = 0.721, IDI = 0.102, P < 0.001).

Conclusions

Elevated caIMR is an independent risk factor for the development of CI-AKI after PCI in STEMI patients. Integrating caIMR significantly improves the risk model for CI-AKI.

Invasive Coronary Physiology Assessment in Patients With Arrhythmia-Induced Cardiomyopathy

BACKGROUND

Arrhythmia-induced cardiomyopathy (AIC) is defined as impaired left ventricular function due to cardiac arrhythmias. We sought to investigate the association between coronary microvascular dysfunction (CMD) and AIC in patients with atrial fibrillation (AF).

METHODS

In this multicenter observational study, we enrolled consecutive patients with recent diagnosis of AF (<6 months) who underwent invasive coronary physiology assessment with the bolus thermodilution technique. Patients were divided into two groups according to left ventricular ejection fraction (LVEF): AIC group if LVEF < 50% and preserved LVEF group if LVEF ≥ 50%. A third group of patients with a recent diagnosis of dilated cardiomyopathy (DCM) and without AF was analyzed as control group. CMD was defined as abnormal coronary flow reserve (CFR < 2.5) and/or abnormal index of microcirculatory resistance (IMR ≥ 25).

RESULTS

Among 84 analyzed patients, 33 were in the AIC group, 39 in the preserved LVEF group, and 12 in the DCM group. CMD was more frequently detected in the AIC group compared to the preserved LVEF (79% vs. 38%, p < 0.001) and DCM groups (79% vs. 33%, p = 0.01). In patients with AF, a significant correlation was found between CFR and LVEF (beta coefficient: 3.8; 95% CI: 1.8-5.9; p < 0.001), and IMR and LVEF (beta coefficient: -0.3; 95% CI: -0.4 to -0.1; p = 0.001). At multivariable analysis, CMD was independently associated with AIC (adjusted odds ratio: 6.2; 95% CI: 2.2 to 20.1; p = 0.001).

CONCLUSIONS

CMD is strongly and independently associated with the degree of left ventricular dysfunction and may play a role in the development of AIC in patients with AF.

Myocardial flow reserve derived from D-SPECT for evaluating non-culprit ischemic lesions in STEMI patients: comparison with quantitative flow ratio

OBJECTIVES

This study sought to elucidate the diagnostic performance and concordance between myocardial flow reserve (MFR) derived from dynamic single-photon emission computed tomography (D-SPECT) and quantitative flow ratio (QFR) in evaluating non-culprit ischemic lesions following ST-elevation myocardial infarction (STEMI). Additionally, the study investigated the integration of MFR with angiographic microvascular resistance (AMR) derived from coronary angiography to determine its utility in screening and stratifying non-culprit ischemic lesions.

BACKGROUND

The diagnostic performance and agreement between MFR and QFR in evaluating non-culprit ischemic lesions in STEMI patients with multivessel disease are unknown.

METHODS

This research encompassed a cohort of 106 STEMI patients with at least 1 intermediate non-culprit ischemic lesion, characterized by 40-80% diameter stenosis. After undergoing percutaneous coronary intervention, patients were evaluated using QFR and, approximately five days later, underwent D-SPECT to assess myocardial blood flow (MBF) and MFR. MFR was evaluated against QFR as a reference for diagnostic performance and agreement, including sensitivity analysis in vessels with normal microvascular function. Furthermore, MFR, combined with AMR, effectively screened and stratified non-culprit ischemic lesions. Non-culprit ischemic lesions were defined by QFR ≤ 0.80 and normal microvascular function by AMR < 255 mmHg*s/m.

RESULTS

Among non-culprit lesions, MFR predicted a QFR ≤ 0.80 with a sensitivity of 85%, specificity of 86%, and accuracy of 86%. The positive predictive value was 56%, and the negative predictive value was 96%. The MFR cut-off was 1.93, with an area under the receiver operating characteristic curve of 0.90 (95% CI: 0.84 to 0.94). MFR showed similar diagnostic performance in patients with normal microcirculation. Moreover, low MFR with normal AMR indicated non-culprit ischemic lesions caused solely by epicardial narrowing, while low MFR with abnormal AMR indicated ischemic lesions complicated by microvascular dysfunction.

CONCLUSION

MFR derived from D-SPECT exhibits good diagnostic performance and moderate agreement in identifying non-culprit ischemic lesions in patients with STEMI. Combining AMR with MFR effectively screens and stratifies non-culprit ischemic lesions.

TRIAL REGISTRATION

ChiCTR.org.cn. ChiCTR2200059934. Registered 13 May 2022.

Repeatability and Correlation of Coronary Physiology Indices Measured With Bolus and Continuous Thermodilution

BACKGROUND

Previous studies have shown weak agreement between coronary physiology indices derived from continuous and bolus thermodilution, and suggested greater variability with bolus thermodilution measurements. This study aimed to evaluate the repeatability and correlation of continuous and bolus thermodilution-derived physiology indices in cardiac transplant recipients.

METHODS

Paired fractional flow reserve (FFR), coronary flow reserve (CFR), index of microcirculatory resistance (IMR), absolute hyperemic resistance (RHyp), and microvascular resistance reserve (MRR) using continuous and bolus thermodilution were performed in consecutive cardiac transplant recipients.

RESULTS

In 20 patients, IMR was more repeatable than CFR and MRR derived from either continuous thermodilution (intraclass correlation coefficient, 0.95 versus 0.70 and 0.59; P=0.004 and P=0.002, respectively) or bolus thermodilution (intraclass correlation coefficient, 0.95 versus 0.20 and 0.33; P<0.001 and P=0.002, respectively), and similarly repeatable compared with RHyp (intraclass correlation coefficient, 0.95 versus 0.87; P=0.188). FFR by continuous thermodilution correlated with standard FFR measurements (R=0.89, P<0.001) but were significantly lower in value (0.87±0.05 versus 0.89±0.05; P=0.004). CFR and MRR measurements using continuous thermodilution did not correlate with measurements using bolus thermodilution (R=0.33, P=0.170; R=0.34, P=0.155, respectively) and were significantly lower in value (2.9±1.0 versus 3.7±0.8, P=0.003; 3.4±1.1 versus 4.8±1.3, P<0.001, respectively). IMR and RHyp did not correlate (R=0.28, P=0.226).

CONCLUSIONS

In cardiac transplant recipients, IMR had superior repeatability compared with CFR and MRR derived from either bolus or continuous thermodilution, and was equally repeatable compared with RHyp. FFR, CFR, and MRR values obtained from continuous thermodilution were systematically lower compared with their counterparts obtained from bolus thermodilution.

Physiological Insight Into the Discordance Between Non-Hyperemic Pressure Ratio-Guided and Fractional Flow Reserve-Guided Revascularization

BACKGROUND

Five-year outcomes from the two major trials indicated higher mortality with instantaneous wave-free ratio (iFR)-guided revascularization compared to fractional flow reserve (FFR)-guidance, despite similar outcomes in deferred patients. This discrepancy likely comes from discordant revascularization decisions. To precisely assess the characteristic differences, including microvascular function, between resting full-cycle ratio (RFR)-guided and FFR-guided strategies, we performed virtual randomization, specially targeting discordant lesions, to simulate RFR-guided and FFR-guided groups. Microvascular resistance reserve (MRR) was utilized to assess microvascular function independently of epicardial stenosis.

METHODS AND RESULTS

We retrospectively analyzed 837 intermediate lesions in 620 patients, from our institutional physiological database, with a median follow-up of 6.9 years. Using thresholds of FFR ≤ 0.80 and RFR ≤ 0.89, lesions were categorized into concordant-high (n = 280), high-RFR/low-FFR (n = 105), low-RFR/high-FFR (n = 93), and concordant-low (n = 359) groups. Discordant and concordant lesions were virtually randomized into RFR- and FFR-guided groups. Patients were followed for 6.9 (4.6-9.1) years. Age, sex, percentage diameter stenosis, and MRR differed significantly between the RFR/FFR discordant groups. After randomization, no significant characteristic-based differences were observed between both concordant and discordant virtual RFR/FFR-guided groups. Compared with the patients with FFR-guided would-be-revascularized lesions, those with RFR-guided would-be-revascularized lesions with discordant RFR/FFR results had significantly lower MRR, higher age, and tended to be female. MRR significantly predicted all-cause death in the total and would-be-revascularized cohorts, but not in deferred patients.

CONCLUSIONS

In discordant lesions of virtually randomized RFR- and FFR-guided strategies, RFR-guided would-be-revascularized lesions were associated with impaired microvascular function (low MRR) compared with FFR-guided would-be-revascularized lesions, which may underlie the reported increased mortality in iFR-guided revascularized patients.

A Systematic Approach and Practical Guide to Using Bolus Thermodilution for Invasive Coronary Microvascular Dysfunction Assessment

Angina pectoris with non-obstructive coronary arteries (ANOCA) is a prevalent condition, particularly affecting women, and is often associated with coronary microvascular dysfunction (CMD). CMD, the primary cause of ANOCA, is associated with a diminished quality of life and adverse clinical outcomes. Invasive coronary function testing (CFT) now provides a precise diagnosis of CMD through indices such as coronary flow reserve (CFR) and index of microcirculatory resistance (IMR), assessed using the bolus thermodilution technique. This comprehensive review outlines a systematic approach to evaluating CMD, emphasizing practical steps and troubleshooting strategies to ensure accurate measurements of CFR and IMR. CMD phenotypes, including structural, functional, and compensated CMD, are discussed, along with their distinct pathophysiological mechanisms. Common challenges encountered during CMD testing, such as improper guide or wire positioning, waveform artifacts, and injection errors, are addressed with practical solutions. While continuous thermodilution offers enhanced accuracy, bolus thermodilution remains cost-effective and widely utilized. Proficiency in the intricacies of CMD testing is crucial for accurate diagnosis and management, ultimately enhancing clinical outcomes for this underrecognized patient population.

Coronary microvascular dysfunction: pathophysiology, diagnosis, and therapeutic strategies across cardiovascular diseases

Ischemic heart disease (IHD) is a leading cause of morbidity and mortality worldwide, presenting with acute and chronic coronary syndromes. Although coronary atherosclerosis is a major cause of IHD, many patients with angina or myocardial ischemia do not have obstructive coronary heart disease and impairment of the coronary microcirculation has been increasingly implicated as a relevant cause of IHD. Therefore, coronary microvascular dysfunction (CMD) refers to a term covering a wide spectrum of structural and functional alterations which affect the coronary microcirculation leading to myocardial ischemia and angina. The advent of non-invasive and invasive functional tests has exponentially broadened the ability to recognize CMD and delineate related clinical and biochemical features. Despite major advances in diagnosing and stratifying this condition, therapeutic strategies remain limited and poorly defined. In this review, we will provide an overview of the pathophysiology and the diagnostic evaluation of CMD across the spectrum of cardiovascular diseases. Furthermore, we will discuss the novel therapeutic strategies available for these patients in the perspective of a personalized medicine approach.

Prehospital pulse-dose glucocorticoid on index of microvascular resistance in patients with ST-segment elevation myocardial infarction: a sub-study of the PULSE-MI trial

BACKGROUND

Microvascular injury in patients with ST-segment elevation myocardial infarction (STEMI) occurs in up to 50%, yet no therapeutic target exists. Inflammation contributes directly to myocardial damage in STEMI and may also cause deleteriously effects on the microcirculation. The aim of this prespecified sub-study was to determine the effect of prehospital pulse-dose glucocorticoid on the microcirculation determined by index of microvascular resistance (IMR) and its relation to inflammation. The PULSE-MI trial was a 1:1 randomized, blinded, placebo-controlled clinical trial in patients with STEMI transferred for primary percutaneous coronary intervention (PCI) investigating the cardioprotective effects of prehospital pulse-dose glucocorticoid (methylprednisolone 250 mg) compared with placebo. In this prespecified sub-study, we investigated microvascular function as IMR by thermodilution after primary PCI and inflammation defined by C-reactive protein (CRP) at 24 hours after onset of STEMI.

RESULTS

Of 530 patients included in the PULSE-MI trial, 295 (56%) were assessed with coronary physiology of whom 142 (48%) were treated with glucocorticoid and 153 (52%) with placebo. Baseline characteristics were overall well-balanced in both groups. The median IMR in the glucocorticoid group was 23 (interquartile range (IQR), 11-38) and 18 (IQR, 11-42) in the placebo group (p=0.49). CRP upon arrival did not differ between treatment groups (p=0.81), but CRP at 24 hours was significantly lower in the glucocorticoid group compared to placebo (p<0.001).

CONCLUSIONS

Prehospital glucocorticoid did not impact IMR assessed immediately after primary PCI, albeit this compound, demonstrated significant anti-inflammatory effects as determined by CRP levels at 24 hours.

TRIAL REGISTRATION

http://www.

CLINICALTRIALS

gov ; Unique Identifier: NCT05462730.

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.

Adrenaline has a limited effect on myocardial microvascular blood flow: A randomised experimental study in a porcine cardiac arrest model

Background

Adrenaline (ADR) is a cornerstone of advanced life support (ALS) in cardiac arrest (CA), although its neurologically favourable survival outcomes remain unclear. ADR increases coronary perfusion pressure (CPP), with levels >15 mmHg associated with successful defibrillation. This study aimed to elucidate the relationship between ADR, myocardial microvascular blood flow, and resuscitation outcomes using a porcine CA model simulating refractory ventricular fibrillation (VF).

Methods

This study involved 24 domestic pigs. After instrumentation, intubation, and baseline measurements, the animals were randomised into the ADR or control (saline) groups. VF was induced, and cardiopulmonary resuscitation was initiated using continuous mechanical chest compressions and ventilation. ADR or saline was administered following ALS guidelines. After 21 min of ALS, defibrillation was performed. Continuous measurements of arterial and venous blood pressures using an electrocardiogram and index of myocardial resistance (IMR) and transit mean time (Tmn) 1 min before and after each injection or peak blood pressure were recorded and compared between the groups. CPP-IMR, amplitude spectrum area (AMSA)-IMR, CPP-Tmn, and AMSA-Tmn correlations were assessed.

Results

Compared with six animals in the control group, three in the ADR group achieved a return of spontaneous circulation. No difference was observed in IMR or AMSA; however, significant increases in CPP and arterial end-diastolic blood pressure were observed at several time points. Tmn differed between groups only at two time points.

Conclusion

Repeated ADR doses during prolonged ALS simulating refractory VF did not improve myocardial microvascular blood flow, as measured using IMR, despite leading to an increase in CPP.

Effect of Guiding Catheter Extubation During Physiological Assesment of Stenosis

BACKGROUND

Extubation of the coronary guiding catheter may affect flow and pressure measurements in the coronary vessel during invasive coronary angiography (ICA).

AIM

This study aims to investigate the impact of guiding catheter extubation on fractional flow reserve (FFR), coronary flow reserve (CFR), and the index of microcirculatory resistance (IMR).

METHODS

This predefined subgroup analysis of the Dan-NICAD 2 study included patients with chronic coronary syndrome referred to ICA based on a coronary computed tomography angiography. Thermodilution was performed in all vessels evaluated with 30%-90% diameter stenosis on a visual estimate. The primary endpoints were FFR, CFR, and IMR changes when the guiding catheter was extubated from the coronary ostium. Three-dimensional quantitative coronary angiography analysis was conducted to evaluate whether the proximal flow area, defined as the area of the guiding catheter subtracted from the area of the vessel ostium, correlated with the changes in FFR, CFR, and IMR.

RESULTS

In 84 patients, coronary physiological measurements were performed twice: once with the guiding catheter intubated and once extubated. FFR decreased during guiding catheter extubation (0.82 ± 0.09 vs. 0.80 ± 0.10) with a mean difference of 0.02, 95% CI [0.01-0.03], p < 0.001. Following extubation, eight patients (8.7%) showed FFR values shifting from > 0.80 to ≤ 0.80. IMR increased during guiding catheter extubation (16.8 ± 8.50 vs. 21.4 ± 16.1) with mean difference of 4.67 [95% CI 1.74-7.60], p = 0.002. No significant changes in CFR were observed; intubated 3.09 ± 1.31 vs 2.84 ± 1.30; difference mean 0.25, [95% CI -0.07 to 0.56], p = 0.12. No significant correlations were found between the proximal flow area and the difference in FFR, CFR, and IMR from intubated to extubated: (r -0.14, p = 0.23), (r -0.11, p = 0.34), and (r -0.16, p = 0.17), respectively.

CONCLUSION

Extubating the guiding catheter decreased FFR and increased IMR. This resulted in an FFR decrease from > 0.80 to ≤ 0.80 in 8.7% of patients. CFR remained unchanged. No significant correlation was found between FFR/IMR changes and proximal flow area.

Clinical implications of coronary microvascular dysfunction in patients with non-obstructive coronary artery disease and role of the thermodilution method

More than 60% of patients undergoing coronary angiography present no coronary artery disease (CAD). Angina and myocardial ischemia are classically determined by epicardial vascular obstruction, but coronary microvascular dysfunction (CMD) may also represent a possible cause for these phenomena. Two endotypes of CMD have been recognized, with two different pathophysiological mechanisms: structural CMD, characterized by low coronary flow reserve (CFR) and high microvascular resistance (MVR) values; and functional CMD, characterized by low CFR and normal MVR values. According to the present data, almost half of patients with non-obstructive CAD have shown signs of CMD. For this reason, further investigations for microvascular function assessment should be considered when evaluating no-CAD patients complaining of angina or presenting signs of myocardial ischemia. The thermodilution method is currently becoming a widespread invasive technique due to its feasibility and high reproducibility for coronary physiology evaluation. Furthermore, a recently introduced technique - called continuous thermodilution - allows for direct measurement of absolute coronary flow and resistances. The role of this brand-new technique in the clinical scenario is however still to be fully investigated and its use is at present limited to research purposes only. Among no-CAD patients, both structural and functional CMD are related to a worse prognosis in term of mortality and major adverse cardiovascular events (MACE). In this review, we will discuss the present evidence supporting the definition, prevalence and clinical implication of the different forms of CMD and the technical aspects of its invasive assessment.

Coronary microvascular dysfunction endotypes: IMR tips and tricks

Coronary microvascular dysfunction (CMD) is an important clinical disease spectrum which has gained widespread attention due to chronic anginal symptoms, and worse clinical outcomes, with or without obstructive coronary artery disease (CAD). Coronary microcirculatory dysfunction is due to a wide array of mechanisms such as inflammation, platelet aggregation, vessel wall collagen deposition, imbalance of nitric oxide, free radicals, and sympathetic/parasympathetic simulation. As noted in this supplement, CMD can occur as a primary disease or co-exist with multi-array of diverse cardiac conditions such as CAD (old infarct), hypertrophic cardiomyopathy, Takotsubo cardiomyopathy, hypertension, or infiltrative diseases. CMD, which is often under diagnosed, leads to increase in medical expenses, decrease in quality of life, exacerbation of underlying conditions such as heart failure and even increased mortality. CMD presents a challenge for patients as well as physicians to manage. Here, we review CMD and focus on its endotypes, techniques for microcirculatory assessment, associated tips and tricks and available treatment options.

Prognostic impact of coronary microvascular dysfunction in patients with myocardial infarction evaluated by new angiography-derived index of microvascular resistance

Background

Several methods for measuring IMR derived from angiography have been developed. AngioIMR is a novel method for the assessment of angiography-derived IMR with no requirement for a wire and hyperemia. The prognostic value of AngioIMR is unknown in STEMI patients. We aimed to provide the prognostic value of AngioIMR in patients with ST-elevation myocardial infarction (STEMI).

Methods

This study included patients with STEMI who underwent invasive coronary angiography and primary percutaneous coronary intervention (PPCI). AngioIMR was calculated using computational flow and pressure simulation immediately after PPCI. The presence of significant coronary microvascular dysfunction was defined as AngioIMR > 40. The primary outcome was a composite of all cause death or hospitalization for heart failure (MACE).

Results

A total of 178 patients were included (65.0 ± 12.8 years on average, 74 % male gender). An AngioIMR > 40 was found in 72 patients. During a median follow-up of 2.9 (2.3-6.9) years, a primary endpoint was observed in 56 patients. By Kaplan-Meier analysis, the risk of MACE was significantly higher in patients with AngioIMR > 40 (log-rank P < 0.01). An Angio IMR > 40 was significantly associated with the occurrence of the primary endpoint in univariate (70 % vs 27 %; hazard ratio 4.519; 95 % CI: 2.550-8.009; p < 0.0001) and multivariate analysis (Hazard ratio 4.282; 95 % CI: 2.325-7.886; p < 0.0001). AngioIMR model showed incremental prognostic value compared to a model with clinical and imaging risk predictors (C-index 0.84 vs 0.79; p = 0.04).

Conlusion

Elevated AngioIMR showed a independent prognostic significance in STEMI patients. In addition to well-known risk factors, assessment of coronary microvascular dysfunction can be a feasible approach for early prevention and a therapeutic target in STEMI patients.

FFR, iFR, CFR, and IMR: Results from clinical trials

In this review article, we provide an overview of the definition and application of fractional flow reserve (FFR), instantaneous wave-free ratio (iFR), coronary flow reserve (CFR), and index of microvascular resistance (IMR) in the diagnosis, prognosis, and management of coronary microvascular dysfunction. We discuss their respective limitations as it relates to microvascular dysfunction. In each section, we review the most recent evidence supporting their use in microvascular and epicardial coronary artery disease. We also highlight specific clinical conditions with emerging indications for the use of these indices, including in the setting of microvascular dysfunction due to acute myocardial infarction, heart failure with preserved ejection fraction, and post-cardiac transplant.

Prognostic Value of Coronary Angiography-Derived Index of Microcirculatory Resistance in Patients With Intermediate Coronary Stenosis

BACKGROUND

The association between coronary microcirculation and clinical outcomes in patients with intermediate stenosis remains unclear.

OBJECTIVES

The aim of this study was to assess the prognostic significance of angiography-derived index of microcirculatory resistance (angio-IMR) in patients with intermediate coronary stenosis.

METHODS

This post hoc analysis included 1,658 patients from the FLAVOUR (Fractional Flow Reserve and Intravascular Ultrasound for Clinical Outcomes in Patients with Intermediate Stenosis) trial, with angio-IMR measured in each vessel exhibiting intermediate stenosis. The primary endpoint was a patient-oriented composite outcome (POCO), a composite of all-cause death, myocardial infarction, or revascularization over a 2-year period.

RESULTS

The median follow-up period was 24.8 months (Q1-Q3: 24.4-26.4 months). Over the 2-year follow-up period, patients with angio-IMR >25 exhibited a significantly higher POCO rate in both the percutaneous coronary intervention (PCI) group (35.06% [27 of 77] vs 7.2% [51 of 708]; P < 0.001) and the non-PCI group (17.95% [21 of 117] vs 4.23% [32 of 756]; P < 0.001). After adjusting for potentially related risk factors, angio-IMR >25 remained an independent predictor of the POCO in the PCI group (HR: 6.235; 95% CI: 3.811-10.203; P < 0.001) and the non-PCI group (HR: 5.282; 95% CI: 2.948-9.462; P < 0.001). The addition of angio-IMR demonstrated incremental prognostic value in both an angiographic risk factor model (C-index 0.710 [95% CI: 0.663-0.756] vs 0.615 [95% CI: 0.563-0.664] [P < 0.001]; net reclassification index 0.268 [95% CI: 0.191-0.362; P < 0.001]; integrated discrimination improvement 0.055 [95% CI: 0.030-0.108; P < 0.001]) and a clinical risk factor model (C-index 0.705 [95% CI: 0.658-0.751] vs 0.594 [95% CI: 0.544-0.644] [P < 0.001]; net reclassification index 0.268 [95% CI: 0.171-0.350; P < 0.001]; integrated discrimination improvement 0.057 [95% CI: 0.027-0.102; P < 0.001]).

CONCLUSIONS

In individuals with intermediate coronary stenosis, elevated angio-IMR is linked to an adverse prognosis. Using angio-IMR significantly enhanced the capability to reclassify patients and accurately estimate the risk for the POCO.

Known yet underdiagnosed: Invasive assessment of coronary microvascular disease and its implications

Coronary microvascular disease (CMD) is one of the commonest causes of cardiac chest pain. The condition is more prevalent in women, and incidence is known to increase with age, hypertension, and diabetes. The pathophysiological pathways are heterogenous and related to intrinsic vascular and endothelial dysfunction. Furthermore, this entity is known to be associated with adverse cardiovascular outcomes. Despite this, there is inertia amongst cardiologists to further evaluate patients with non-critical coronary artery disease and suspected CMD. With refinement in technology, we have now better understanding of CMD and invasive testing in the catheterization laboratory is a viable option for confirming the diagnosis of CMD. However, despite advances in diagnosing and stratifying this entity, therapeutic options remain limited and poorly defined. In this editorial, we will briefly focus on the pathophysiology and invasive assessment and therapeutic options available for CMD.

Prediction of microvascular obstruction from angio-based microvascular resistance and available clinical data in percutaneous coronary intervention: an explainable machine learning model

Angio-based microvascular resistance (AMR) as a potential alternative to the index of microcirculatory resistance (IMR) and its relationship with microvascular obstruction (MVO) and other cardiac magnetic resonance (CMR) parameters still lacks comprehensive validation. This study aimed to validate the correlation between AMR and CMR-derived parameters and to construct an interpretable machine learning (ML) model, incorporating AMR and clinical data, to forecast MVO in ST-segment elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (PPCI). We enrolled 452 STEMI patients from Nanjing Drum Tower Hospital between 2018 and 2022, who received both PPCI and CMR. After PPCI, AMR measurements and CMR-derived parameters were recorded, and clinical data were gathered. The ML workflow comprised feature selection using the Boruta algorithm, model construction with seven classifiers, hyperparameter optimization via ten-fold cross-validation, model comparison based on the area under the curve (AUC), and a Shapley additive explanations (SHAP) analysis to analyze the significance of different features. 32.29% of patients showed inconsistency between AMR and MVO, but we successfully constructed a predictive model for MVO. Among the classifiers, Extreme gradient boosting (XGBoost) post hyperparameter optimization displayed superior performance, achieving an AUC of 0.911 and 0.846 in the training and validation sets, respectively. SHAP analysis identified AMR as a pivotal predictor of MVO. Although we observed the inconsistency between AMR and MVO but the ML-based construction of MVO prediction model is feasible, which brings the possibility of timely prediction of patients with MVO and timely imposition of interventions during PPCI.

Acute and Mid-Term Assessment of Microvascular Dysfunction with Index of Microcirculatory Resistance in ST-Segment Elevation Myocardial Infarction Patients

In patients diagnosed with ST-segment elevation myocardial infarction (STEMI), despite exhibiting normal patency in the culprit arteries following percutaneous coronary intervention (PCI), coronary microvessels do not recover adequately, leading to microvascular dysfunction (MVD). Limited data are available regarding microcirculation assessed through invasive measures during the midterm period. This study aimed to investigate the assessment of MVD in STEMI patients using the index of microvascular resistance (IMR) during the midterm period.We prospectively evaluated 41 patients with STEMI who underwent PCI. IMR was measured by placing a coronary pressure wire with intravenous adenosine at 1 week as the acute phase and at 6 months after primary PCI as the midterm period. An improvement in IMR was observed from baseline to follow-up, with values changing from 30.00 (15.00-45.50) to 19.00 (10.50-30.50) (P = 0.020). The degree of MVD significantly decreased during follow-up (from 61.0% to 34.1%, McNemar's test: P = 0.016). Compared to patients with normal microcirculation, those with MVD (IMR > 25) at midterm follow-up exhibited significantly elevated levels of brain natriuretic peptide (180.25 [68.25-370.65] pg/mL versus 75.90 [18.70-169.70] pg/mL, P = 0.043) and prolonged symptom-onset-to-balloon time (727.00 [213.50-1170.00] minutes versus 186.00 [125.00-316.00] minutes, P = 0.002).These findings indicate that the extent of MVD 6 months post-PCI has significantly diminished compared to discharge levels and is associated with symptom-onset-to-balloon time. Therefore, MVD in patients with STEMI can potentially improve in the midterm under specific circumstances.

The role of coronary microcirculation in heart failure with preserved ejection fraction: An unceasing odyssey

Heart failure with preserved ejection fraction (HFpEF) represents an entity with complex pathophysiologic pathways, among which coronary microvascular dysfunction (CMD) is believed to be an important orchestrator. Research in the field of CMD has highlighted impaired vasoreactivity, capillary rarefaction, and inflammation as potential mediators of its development. CMD can be diagnosed via several noninvasive methods including transthoracic echocardiography, cardiac magnetic resonance, and positron emission tomography. Moreover, invasive methods such as coronary flow reserve and index of microcirculatory resistance are commonly employed in the assessment of CMD. As far as the association between CMD and HFpEF is concerned, numerous studies have highlighted the coexistence of CMD in the majority of HFpEF patients. Additionally, patients affected by both conditions may be facing an adverse prognosis. Finally, there is limited evidence suggesting a beneficial effect of renin-angiotensin-aldosterone system blockers, ranolazine, and sodium-glucose cotransporter-2 inhibitors in CMD, with further evidence being awaited regarding the impact of other pharmacotherapies such as anti-inflammatory agents.

Coronary microvascular dysfunction in Takotsubo syndrome: an analysis using angiography-derived index of microcirculatory resistance

BACKGROUND

Coronary microvascular dysfunction (CMD) has been proposed as a crucial factor in the pathophysiology of Takotsubo syndrome (TTS). The angiography-derived index of microcirculatory resistance (caIMR) offers an alternative to conventional hyperemic wire-based IMR to assess CMD. We aimed to evaluate CMD's prevalence, transience, and impact on in-hospital outcomes in TTS.

METHODS

All three coronary arteries of 96 patients with TTS were assessed for their coronary angiography derived Index of microcirculatory Resistance (caIMR) and compared to non-obstructed vessels of matched patients with ST-elevation myocardial infarction. Further, the association between caIMR and the TTS-specific combined in-hospital endpoint of death, cardiac arrest, ventricular arrhythmogenic events and cardiogenic shock was investigated.

RESULTS

Elevated IMR was present in all TTS patients, with significantly elevated caIMR values in all coronary arteries compared to controls. CaIMR did not differ between apical and midventricular TTS types. CaIMR normalized in TTS patients with follow-up angiographies performed at a median of 28 months (median caIMR at event vs follow-up: LAD 34.8 [29.9-41.1] vs 20.3 [16.0-25.3], p < 0.001; LCX: 38.7 [32.9-50.1] vs 23.7 [19.4-30.5], p < 0.001; RCA: 31.7 [25.0-39.1] vs 19.6 [17.1-24.0], p < 0.001). The extent of caIMR elevation significantly correlated with the combined in-hospital endpoint (p = 0.036).

CONCLUSION

TTS patients had evidence of elevated caIMR in at least one coronary artery with a trend towards higher LAD caIMR in apical type TTS and normalization after recovery. Furthermore, extent of caIMR elevation was associated with increased risk of in-hospital MACE of TTS patients.

Angiography-based coronary microvascular assessment with and without intracoronary pressure measurements: a systematic review

BACKGROUND

In recent years, several indices have been proposed for quantifying coronary microvascular resistance. We intended to conduct a comprehensive review that systematically evaluates indices of microvascular resistance derived from angiography.

OBJECTIVE

The objective of this study was to identify and analyze angiography-derived indices of microvascular resistance that have been validated against an invasive reference method. We aimed to compare their limits of agreement with their reference methods and explore their advantages and inherent limitations.

METHODS AND RESULTS

We searched PubMed from inception until 2022 for studies on different techniques for quantifying microvascular resistance. Seven studies met the inclusion criteria. Five studies included techniques that applied calculations based solely on invasive angiography, and were validated against invasively measured thermodilution-derived index of microvascular resistance. The remaining two studies combined angiography with invasively measured intracoronary pressure data, and were validated against invasive Doppler measurements. We converted the ± 1.96 standard deviation limits of agreement with the reference method from the seven studies into percentages relative to the cut-off value of the reference method. The lower limits of agreement for angiography-based methods ranged from - 122 to - 60%, while the upper limits ranged from 74 to 135%. The range of the limits of agreement was considerably lower for the two combined angiography- and pressure-based methods, standing at - 52 to 60% and - 25 to 27%.

CONCLUSION

Our findings suggest that combined angiography- and pressure-based methods provide a more reliable assessment of microvascular resistance compared to methods relying solely on angiography.

Feasibility and Improved Diagnostic Yield of Intracoronary Adenosine to Assess Microvascular Dysfunction With Bolus Thermodilution

BACKGROUND

Bolus thermodilution and intravenous adenosine are established methods for coronary microcirculatory assessment. Yet, its adoption remains low, partly due to procedural time and patient discomfort associated with intravenous adenosine. We investigated differences between intracoronary and intravenous adenosine using bolus thermodilution in terms of microcirculatory indices, procedural time, and side effects associated with adenosine in patients with myocardial ischemia and nonobstructive coronary arteries.

METHODS AND RESULTS

In this prospective, observational study, 102 patients with suspected myocardial ischemia and nonobstructive coronary arteries underwent measurements of mean transit time, coronary flow reserve, index of microcirculatory resistance, procedure time and patient tolerability with low-dose intracoronary adenosine, high-dose intracoronary adenosine (HDIC), and intravenous adenosine. HDIC induced greater hyperemia compared with low-dose intracoronary IC adenosine and intravenous adenosine with a shorter hyperemic mean transit time, P<0.0001. Coronary flow reserve was higher and index of microcirculatory resistance lowest with HDIC, compared with low-dose intracoronary IC adenosine and intravenous adenosine, P<0.05. Low coronary flow reserve was downgraded from 21% with intravenous adenosine to 10% with HDIC adenosine (P=0.031); high index of microcirculatory resistance was downgraded from 23% with intravenous adenosine to 14% with HDIC (P=0.098). Intracoronary adenosine was associated with lower procedural times (P<0.0001). More patients experienced chest pain with intravenous adenosine (P<0.01) and the chest pain intensity was higher compared with intracoronary adenosine (P<0.0001).

CONCLUSIONS

In patients with suspected myocardial ischemia and nonobstructive coronary arteries undergoing coronary microcirculatory assessment with bolus thermodilution, the use of HDIC compared with intravenous adenosine was associated with enhanced induction of hyperemia. The use of intracoronary adenosine allowed for a shorter procedure time and was better tolerated.

REGISTRATION+

URL: clinicaltrials.gov; Unique Identifier: NCT04827498.

The Belgian Registry on Coronary Function Testing (BELmicro Registry): Study Population, Prevalence of Coronary Vascular Dysfunction, and Procedural Safety

Coronary function testing (CFT) plays a pivotal role in the diagnosis of coronary vascular dysfunction and providing patients with tailored therapy. The Belgian registry on CFT (BELmicro registry) is a prospective, observational, multicenter registry including 14 centers in Belgium. All patients who underwent clinically indicated CFT were included in the registry. Baseline characteristics, CFT data, and clinical outcomes were collected. This analysis aimed to describe the baseline characteristics of a real-world population of patients who underwent CFT, evaluate the prevalence of coronary vascular dysfunction, and assess the safety of CFT in daily clinical practice. Between October 2021 and September 2023, 449 patients were enrolled. The mean age was 65 ± 10 years, and 47.4% of patients were men. A total of 59% of patients had hypertension, 18.7% had diabetes, 69.5% had hypercholesterolemia, and 40.1% had a smoking habit. Angina and nonobstructive coronary arteries (ANOCAs) were identified in 85.1% of the patients. Microvascular physiology assessment was performed in 95.5% of patients, vasoreactivity test in 28.5%, and both in 24.0%. coronary microvascular dysfunction was diagnosed in 23.4% of patients with ANOCA, epicardial vasospasm in 26.3%, and microvascular spasm in 14.9%. Rates of major complications were 0.7% for microvascular physiology assessment and 0% for vasoreactivity test. In conclusion, participants in the BELmicro registry represented a real-world population of patients, characterized by a high burden of cardiovascular risk factors. Coronary microvascular dysfunction and coronary vasospasm were frequent in patients with ANOCA. Performing CFT in daily clinical practice was feasible, with a low rate of complications.

Association of Coronary Computed Tomography-Defined Myocardial Bridge With Pre- and Post-Procedural Fractional Flow Reserve in Patients Undergoing Elective Percutaneous Coronary Intervention

BACKGROUND

Myocardial bridge (MB) is a common coronary anomaly characterized by a tunneled course through the myocardium. Coronary computed tomography angiography (CCTA) can identify MB. The impact of MB detected by CCTA on coronary physiological parameters before and after percutaneous coronary intervention (PCI) is unknown.

METHODS AND RESULTS

We investigated 141 consecutive patients who underwent pre-PCI CCTA and fractional flow reserve (FFR)-guided elective PCI for de novo single proximal lesions in the left anterior descending artery (LAD). We compared clinical demographics and physiological parameters between patients with and without CCTA-defined MB. MB was identified in 46 (32.6%) patients using pre-PCI CCTA. The prevalence of diabetes was higher among patients with MB. Median post-PCI FFR values were significantly lower among patients with than without MB (0.82 [interquartile range 0.79-0.85] vs. 0.85 [interquartile range 0.82-0.89]; P=0.003), whereas pre-PCI FFR values were similar between the 2 groups. Multivariable linear regression analysis revealed that the presence of MB and greater left ventricular mass volume in the LAD territory were independently associated with lower post-PCI FFR values. Multivariable logistic regression analysis also revealed that the presence of MB and lower pre-PCI FFR values were independent predictors of post-PCI FFR values ≤0.80.

CONCLUSIONS

CCTA-defined MB independently predicted both lower post-PCI FFR as a continuous variable and ischemic FFR as a categorical variable in patients undergoing elective PCI for LAD.

Basal Coronary Microvascular Resistance Predicting Death and Heart Failure in Patients Without Functional Coronary Stenosis

BACKGROUND

Abnormal coronary microcirculation is linked to poor patient prognosis, so the aim of the present study was to assess the prognostic relevance of basal microvascular resistance (b-IMR) in patients without functional coronary stenosis.

METHODS AND RESULTS

Analyses of 226 patients who underwent intracoronary physiological assessment of the left anterior descending artery included primary endpoints of all-cause death and heart failure, as well as secondary endpoints of cardiovascular death and atherosclerotic vascular events. During a median follow-up of 2 years, there were 12 (5.3%) primary and 21 (9.3 %) secondary endpoints. The optimal b-IMR cutoff for the primary endpoints was 47.1 U. Kaplan-Meier curve analysis demonstrated worse event-free survival of the primary endpoints in patients with a b-IMR below the cutoff (χ2=21.178, P<0.001). b-IMR was not significantly associated with the secondary endpoints (P=0.35). A low coronary flow reserve (CFR; <2.5) had prognostic value for both endpoints (primary endpoints: χ2=11.401, P=0.001; secondary endpoints: (χ2=6.015; P=0.014), and high hyperemic microvascular resistance (≥25) was associated only with the secondary endpoints (χ2=4.420; P=0.036). Incorporating b-IMR into a clinical model that included CFR improved the Net Reclassification Index and Integrated Discrimination Improvement for predicting the primary endpoints (P<0.001 and P=0.034, respectively).

CONCLUSIONS

b-IMR may be a specific marker of the risk of death and heart failure in patients without functional coronary stenosis.

Contemporary Functional Coronary Angiography: An Update

Functional coronary angiography (FCA) is a novel modality for assessing the physiology of coronary lesions, going beyond anatomical visualization by traditional coronary angiography. FCA incorporates indices like fractional flow reserve (FFR) and instantaneous wave-free ratio (IFR), which utilize pressure measurements across coronary stenoses to evaluate hemodynamic impacts and to guide revascularization strategies. In this review, we present traditional and evolving modalities and uses of FCA. We will also evaluate the existing evidence and discuss the applicability of FCA in various clinical scenarios. Finally, we provide insight into emerging evidence, current challenges, and future directions in FCA.

Absolute coronary blood flow across different endotypes of ANOCA

BACKGROUND

Intracoronary continuous thermodilution is a novel technique to quantify absolute true coronary flow and microvascular resistance. However, few data are available in patients with angina with non-obstructive coronary arteries (ANOCA).

AIMS

This study aimed to investigate the diagnostic potential of hyperaemic absolute coronary flow (Qmax) and absolute microvascular resistance (Rμ,hyper) among different ANOCA endotypes, and to determine the correlation between continuous - and bolus - thermodilution indexes.

METHODS

A total of 222 patients were scheduled for clinically indicated coronary function testing (CFT), of whom 120 patients were included in this analysis. These patients underwent CFT including acetylcholine (ACh) provocation testing and microvascular function assessment using both bolus and continuous thermodilution.

RESULTS

CFT was negative (CFT-) in 32 (26.7%) patients. Endothelium-dependent dysfunction (ACh+) was present in 63 (52.5%) patients, and coronary microvascular dysfunction (CMD) identified at bolus thermodilution (CMD+) was present in 62 (51.7%) patients. Patients with a positive CFT (CFT+) showed significantly lower Qmax and higher Rμ,hyper values as compared to CFT-. Qmax was significantly lower in CMD+ versus CMD- patients (0.174 vs 0.222 L/min; p=0.04) but did not differ in patients with or without a positive ACh test (0.198 vs 0.219 L/min; p=0.86).

CONCLUSIONS

The prevalence of a CFT+ is high in a selected ANOCA population. In our study, Qmax and Rμ,hyper were associated with a positive CFT. Qmax was associated with the presence of microvascular dysfunction but not with a positive acetylcholine test. The novel continuous thermodilution method can provide further insights into ANOCA endotypes.

Advances in the Computational Assessment of Disturbed Coronary Flow and Wall Shear Stress: A Contemporary Review

Coronary artery blood flow is influenced by various factors including vessel geometry, hemodynamic conditions, timing in the cardiac cycle, and rheological conditions. Multiple patterns of disturbed coronary flow may occur when blood flow separates from the laminar plane, associated with inefficient blood transit, and pathological processes modulated by the vascular endothelium in response to abnormal wall shear stress. Current simulation techniques, including computational fluid dynamics and fluid-structure interaction, can provide substantial detail on disturbed coronary flow and have advanced the contemporary understanding of the natural history of coronary disease. However, the clinical application of these techniques has been limited to hemodynamic assessment of coronary disease severity, with the potential to refine the assessment and management of coronary disease. Improved computational efficiency and large clinical trials are required to provide an incremental clinical benefit of these techniques beyond existing tools. This contemporary review is a clinically relevant overview of the disturbed coronary flow and its associated pathological consequences. The contemporary methods to assess disturbed flow are reviewed, including clinical applications of these techniques. Current limitations and future opportunities in the field are also discussed.

Pathogenesis, Assessment, and Treatment of Coronary Microcirculation Dysfunction

Cardiovascular disease is the predominant cause of mortality on a global scale. Research indicates that women exhibit a greater likelihood of presenting with non-obstructive coronary artery disease (CAD) when experiencing symptoms of myocardial ischemia in comparison to men. Additionally, women tend to experience a higher burden of symptoms relative to men, and despite the presence of ischemic heart disease, they are frequently reassured erroneously due to the absence of obstructive CAD. In cases of ischemic heart disease accompanied by symptoms of myocardial ischemia but lacking obstructive CAD, it is imperative to consider coronary microvascular dysfunction as a potential underlying cause. Coronary microvascular dysfunction, characterized by impaired coronary flow reserve resulting from functional and/or structural abnormalities in the microcirculation, is linked to adverse cardiovascular outcomes. Lifestyle modifications and the use of anti-atherosclerotic and anti-anginal medications may offer potential benefits, although further clinical trials are necessary to inform treatment strategies. This review aims to explore the prevalence, underlying mechanisms, diagnostic approaches, and therapeutic interventions for coronary microvascular dysfunction.

Ischemia with non-obstructive coronary artery (INOCA): Non-invasive versus invasive techniques for diagnosis and the role of #FullPhysiology

Ischemia with non-obstructive coronary arteries (INOCA) is an increasingly recognized entity. It encompasses different pathophysiological subtypes (i.e., endotypes), including coronary microvascular dysfunction (CMD), vasospastic angina (VSA) and mixed entities resulting from the variable combination of both. Diagnosing INOCA and precisely characterizing the endotype allows for accurate medical treatment and has proven prognostic implications. A breadth of diagnostic technique is available, ranging from non-invasive approaches to invasive coronary angiography adjuvated by functional assessment and provocative tests. This review summarizes the strength and limitations of these methodologies and provides the rationale for the routine referral for invasive angiography and functional assessment in this subset of patients.

An Automatic Coronary Microvascular Dysfunction Classification Method Based on Hybrid ECG Features and Expert Features

OBJECTIVE

In recent years, the early diagnosis and treatment of coronary microvascular dysfunction (CMD) have become crucial for preventing coronary heart disease. This paper aims to develop a computer-assisted autonomous diagnosis method for CMD by using ECG features and expert features.

APPROACH

Clinical electrocardiogram (ECG), myocardial contrast echocardiography (MCE), and coronary angiography (CAG) are used in our method. Firstly, morphological features, temporal features, and T-wave features of ECG are extracted by multi-channel residual network with BiLSTM (MCResnet-BiLSTM) model and the multi-source T-wave features (MTF) extraction model, respectively. And these features are fused to form ECG features. In addition, the CFR[Formula: see text] is calculated based on the parameters related to the MCE at rest and stress state, and the Angio-IMR is calculated based on CAG. The combination of CFR[Formula: see text] and Angio-IMR is termed as expert features. Furthermore, the hybrid features, fused from the ECG features and the expert features, are input into the multilayer perceptron to implement the identification of CMD. And the weighted sum of the softmax loss and center loss is used as the total loss function for training the classification model, which optimizes the classification ability of the model.

RESULT

The proposed method achieved 93.36% accuracy, 94.46% specificity, 92.10% sensitivity, 95.89% precision, and 93.95% F1 score on the clinical dataset of the Second Affiliated Hospital of Zhejiang University.

CONCLUSION

The proposed method accurately extracts global ECG features, combines them with expert features to obtain hybrid features, and uses weighted loss to significantly improve diagnostic accuracy. It provides a novel and practical method for the clinical diagnosis of CMD.

Developments and Controversies in Invasive Diagnosis of Coronary Microvascular Dysfunction in Angina With Nonobstructive Coronary Arteries

Approximately half of all coronary angiograms performed for angina do not show obstructive coronary artery disease, and many of these patients have coronary microvascular dysfunction (CMD). Invasive testing for CMD has increased with the advent and wider availability of thermodilution systems. We review CMD pathophysiology and invasive diagnostic testing using the Doppler and thermodilution systems. We report the results of a PubMed search of invasive microvascular testing and discuss limitations of current diagnostic algorithms in the diagnosis of CMD, including controversies regarding the optimal cutoff value for abnormal coronary flow reserve, use of microvascular resistance indices, and options for increasing sensitivity of testing.

Evaluation of microcirculatory protection in percutaneous revascularisation: A stent implantation technique and device comparison

BACKGROUND

Coronary microvascular dysfunction (CMD) after percutaneous coronary intervention (PCI) is prognostically important and may also be a cause of persistent angina. The stent balloon inflation technique or material properties may influence the degree of CMD post-PCI.

METHODS

Thirty-six patients with stable angina attending for elective PCI were randomized to either slow drug eluting stent (DES) implantation technique (DES slow group): +2 atm. every 5 s., maintained for a further 30 s or a standard stent implantation technique (DES std group): rapid inflation and deflation. PressureWire X with thermodilution at rest and hyperemia and optical coherence tomography (OCT) were performed pre- and post-PCI. Combined primary endpoints were changes in index of microvascular resistance (delta IMR) and coronary flow reserve (delta CFR) following PCI. The secondary endpoints included differences in cardiac troponin I (delta cTnI) at 6 h post-PCI, Seattle angina questionnaire (SAQ) at 1, 3, 6, and 12 months and OCT measures of stent results immediately post-PCI and at 3 months.

RESULTS

Both groups were well matched, with similar baseline characteristics and OCT-defined plaque characteristics. Delta IMR was significantly better in the DES slow PCI arm with a median difference of -4.14 (95% CI -10.49, -0.39, p = 0.04). Delta CFR was also numerically higher with a median difference of 0.47 (95% CI -0.52, 1.31, p = 0.46). This did not translate to improved delta median cTnI (1.5 (34.8) vs. 0 (27.5) ng/L, p = 0.75) or median SAQ score at 3 months, (85 (20) vs. 95 (17.5), p = 0.47).

CONCLUSION

Slow stent implantation is associated with less CMD after elective PCI in patients with stable angina.

Coronary Microvascular Dysfunction: A Guide for Clinicians

Dysfunction of the coronary microvasculature has become increasingly recognized as an important mechanism of myocardial ischemia in patients without obstructive coronary artery disease. The causes and management of coronary microvascular dysfunction remain poorly understood and are still largely based on extrapolation of epicardial coronary artery disease data. Quantification of myocardial blood flow and flow reserve have improved diagnosis, though important questions remain. In this review, we explain current understanding of the spectrum of pathophysiology of coronary microvascular dysfunction, summarize current diagnostic techniques to assess for coronary microvascular dysfunction, and appraise the limited data on management options specifically for patients with coronary microvascular dysfunction.

Prognostic Value of Coronary Angiography-Derived Index of Microcirculatory Resistance in Non-ST-Segment Elevation Myocardial Infarction Patients

BACKGROUND

The index of microcirculatory resistance is a reliable measure for evaluating coronary microvasculature, but its prognostic value in patients with non-ST-segment elevation myocardial infarction (NSTEMI) remains unclear.

OBJECTIVES

This study aimed to evaluate the prognostic impact of postpercutaneous coronary intervention (PCI) angiography-derived index of microcirculatory resistance (angio-IMR) in patients with NSTEMI.

METHODS

The culprit vessel's angio-IMR was measured after PCI in 2,212 NSTEMI patients at 3 sites. The primary endpoint was 2-year major adverse cardiac events (MACEs), defined as a composite of cardiac death, readmission for heart failure, myocardial reinfarction, and target vessel revascularization.

RESULTS

The mean post-PCI angio-IMR was 20.63 ± 4.17 in NSTEMI patients. A total of 206 patients were categorized as the high post-PCI angio-IMR group according to maximally selected log-rank statistics. Patients with angio-IMR >25 showed a higher rate of MACEs than those with angio-IMR ≤25 (32.52% vs 9.37%; P < 0.001). Post-PCI angio-IMR >25 was an independent predictor of MACEs (HR: 4.230; 95% CI: 3.151-5.679; P < 0.001) and showed incremental prognostic value compared with conventional risk factors (AUC: 0.774 vs 0.716; P < 0.001; net reclassification index: 0.317; P < 0.001; integrated discrimination improvement: 0.075; P < 0.001).

CONCLUSIONS

In patients undergoing PCI for NSTEMI, an increased post-PCI angio-IMR is associated with a higher risk of MACEs. The addition of post-PCI angio-IMR into conventional risk factors significantly improves the ability to reclassify patients and estimate the risk of MACEs. (Angiograph-Derived Index of Microcirculatory Resistance in Patients With Acute Myocardial Infarction; NCT05696379).

Growth differentiation factor-15 as a biomarker of coronary microvascular dysfunction in ST-segment elevation myocardial infarction

Background

The predictive value of growth differentiation factor-15 (GDF-15) in coronary microvascular dysfunction (CMD) following primary percutaneous coronary intervention (PPCI) in ST-segment elevation myocardial infarction (STEMI) patients is unclear.

Methods

This study continuously recruited STEMI patients treated with PPCI at the Chest Pain Center of Qilu Hospital of Shandong University from April 2023 to December 2023. Blood samples were taken before PPCI and the level of circulating GDF-15 was measured by enzyme-linked immunosorbent assay (ELISA), and the patients were divided into CMD and Control group according to angiographic microvascular resistance (AMR) (cut-off value 2.50 mmHg*s/cm). The differences in GDF-15 expression levels between the two groups were compared, and the predictive value of GDF-15 for CMD was systematically evaluated.

Results

A total of 134 patients, with an average age of 59.78 ± 12.69 years and 75.37 % being male, were included in this study. Multivariable logistic regression revealed a significant association between GDF-15 and CMD (adjusted OR = 2.505, 95 % CI: 1.661-3.779, P < 0.001). The area under the curve (AUC) of GDF-15 for CMD was 0.782 (95 % CI: 0.704-0.861), with a sensitivity of 0.795 and specificity of 0.643 in predicting CMD in PPCI. The AUC of the GDF-15 model (Model With GDF-15) was 0.867 (95 % CI: 0.806-0.928), significantly outperforming the clinical baseline model (Model Without GDF-15) (Δ AUC = 0.079, 95 % CI: 0.020-0.138, P = 0.009). Furthermore, the net reclassification improvement (NRI) was 0.854 (95 % CI: 0.543-1.166, P < 0.001), and the integrated discrimination improvement (IDI) was 0.151 (95 % CI: 0.089-0.213, P < 0.001).

Conclusions

GDF-15 can serve as a biomarker for predicting the development of CMD in STEMI patients undergoing PPCI.

The coronary angiography-derived index of microcirculatory resistance predicts perioperative myocardial injury in stable coronary artery disease patients undergoing PCI

Background

Coronary microvascular dysfunction (CMD) assessed by the index of microcirculatory resistance (IMR) is associated with perioperative myocardial injury (PMI).The angiographically derived index of microcirculatory resistance (caIMR) represents a novel and accurate alternative to IMR.

Objective

This study aims to evaluate the predictive ability of caIMR for PMI in patients with stable coronary artery disease (CAD) undergoing percutaneous coronary intervention (PCI).

Methods

Consecutive patients with stable CAD undergoing elective PCI of a single lesion were recruited. caIMR was measured before and after revascularisation, and total creatine kinase-MB (CK-MB) and high-sensitivity troponin T (hsTnT) levels were measured before and within 24 h after PCI.

Results

A total of 65 patients were enrolled and 26 patients fulfilled the diagnostic criteria for PMI. Post-PCI caIMR values were significantly higher in the PMI group than in the control group (27.02 ± 3.70 vs. 15.91 ± 3.43U, P < 0.001). Pearson correlation analysis showed that increased post-PCI caIMR values had a significant positive correlation with peak hsTnT (r = 0.803, P < 0.001) and peak CK-MB (r = 0.512, P = 0.001). Multivariate logistic regression analysis showed that post-PCI caIMR was an independent predictor of PMI (OR,1.731; 95 % CI:1.348-2.023; P < 0.001).ROC analysis suggested that the best cut-off value of post-PCI caIMR was 25.17U to diagnose PMI (AUC = 0.951, sensitivity 88.5 %, specificity 97.1 %). During a median follow-up 16 months, patients with PMI had a higher incidence of major adverse cardiovascular events (MACE) (42.31 % vs 5.13 %, P = 0.04).

Conclusions

Post-PCI caIMR can accurately predict PMI and clinical outcomes in stable CAD patients undergoing elective PCI, which supports the use of caIMR in clinical practice.

The Influence of Epicardial Resistance on Microvascular Resistance Reserve

BACKGROUND

The optimal index of microvascular function should be specific for the microvascular compartment. Yet, coronary flow reserve (CFR), despite being widely used to diagnose coronary microvascular dysfunction (CMD), is influenced by both epicardial and microvascular resistance. Conversely, microvascular resistance reserve (MRR) adjusts for fractional flow reserve (FFR), and thus is theoretically independent of epicardial resistance.

OBJECTIVES

The authors tested the hypothesis that MRR, unlike CFR, is not influenced by increasing epicardial resistance, and thus is a more specific index of microvascular function.

METHODS

In a cohort of 16 patients who had undergone proximal left anterior descending artery stenting, we created 4 grades of artificial stenosis (no stenosis, mild, moderate, and severe) using a coronary angioplasty balloon inflated to different degrees within the stent. For each stenosis grade, we calculated CFR and MRR using continuous thermodilution (64 measurements of each) to assess their response to changing epicardial resistance.

RESULTS

Graded balloon inflation resulted in a significant sequential decrease in mean FFR (no stenosis: 0.82 ± 0.05; mild: 0.72 ± 0.04; moderate: 0.61 ± 0.05; severe: 0.48 ± 0.09; P < 0.001). This translated into a linear decrease in mean hyperemic coronary flow (no stenosis: 170.5 ± 66.8 mL/min; mild: 149.8 ± 58.8 mL/min; moderate: 124.4 ± 53.0 mL/min; severe: 94.0 ± 45.2 mL/min; P < 0.001). CFR exhibited a marked linear decrease with increasing stenosis (no stenosis: 2.5 ± 0.9; mild: 2.2 ± 0.8; moderate: 1.8 ± 0.7; severe: 1.4 ± 0.6), corresponding to a decrease of 0.3 for a decrease in FFR of 0.1 (P < 0.001). In contrast, MRR exhibited a negligible decrease across all stenosis grades (no stenosis: 3.0 ± 1.0; mild: 3.0 ± 1.0; moderate: 2.9 ± 1.0; severe: 2.8 ± 1.0), corresponding to a decrease of just 0.05 for a decrease in FFR of 0.1 (P < 0.001).

CONCLUSIONS

MRR, unlike CFR, is minimally influenced by epicardial resistance, and thus should be considered the more specific index of microvascular function. This suggests that MRR can also reliably evaluate microvascular function in patients with significant epicardial disease.

Future of invasive and non-invasive hemodynamic assessment for coronary artery disease management

Coronary artery disease represents a global health challenge. Accurate diagnosis and evaluation of hemodynamic parameters are crucial for optimizing patient management and outcomes. Nowadays a wide range of both non-invasive and invasive methods are available to assess the hemodynamic impact of both epicardial coronary stenosis and vasomotor disorders. In fact, over the years, important developments have reshaped the nature of both invasive and non-invasive diagnostic techniques, and the future holds promises for further innovation and integration. Non-invasive techniques have progressively evolved and currently a broad spectrum of methods are available, from cardiac magnetic resonance imaging with pharmacological stress and coronary computed tomography (CT) to the newer application of FFR-CT and perfusion CT. Invasive methods, on the contrary, have developed to a full-physiology approach, able not only to identify functionally significant lesions but also to evaluate microcirculation and vasospastic disease. The aim of this review is to summarize the current state-of-the-art of invasive and non-invasive hemodynamic assessment for CAD management.

Interventions for renal artery stenosis: Appraisal of novel physiological insights and procedural techniques to improve clinical outcome

Randomized clinical trials failed to show additional benefit of renal artery stenting on top of medical therapy. Instead of writing an obituary on renal artery stenting, we try to explain these disappointing results. A transstenotic pressure gradient is needed to reduce renal perfusion and to activate the renin-angiotensin-aldosterone system. In only a minority of patients included in trials, a transstenotic pressure gradient is measured and reported. Like the coronary circulation, integration of physiological lesion assessment will allow to avoid stenting of non-significant lesions and select those patients that are most likely to benefit from renal artery stenting. Renal artery interventions are associated with peri-procedural complications. Contemporary techniques, including radial artery access, no-touch technique to engage the renal ostium and the use of embolic protection devices, will minimize procedural risk. Combining optimal patient selection and meticulous technique might lead to a netto clinical benefit when renal artery stenting is added to optimal medical therapy.

Beyond Coronary Artery Disease: Assessing the Microcirculation

Ischemic heart disease (IHD) affects more than 20 million adults in the United States. Although classically attributed to atherosclerosis of the epicardial coronary arteries, nearly half of patients with stable angina and IHD who undergo invasive coronary angiography do not have obstructive epicardial coronary artery disease. Ischemia with nonobstructive coronary arteries is frequently caused by microvascular angina with underlying coronary microvascular dysfunction (CMD). Greater understanding the pathophysiology, diagnosis, and treatment of CMD holds promise to improve clinical outcomes of patients with ischemic heart disease.

A Systematic Approach to the Evaluation of the Coronary Microcirculation Using Bolus Thermodilution: CATH CMD

Coronary microvascular dysfunction (CMD) can cause myocardial ischemia in patients presenting with angina without obstructive coronary artery disease (ANOCA). Evaluating for CMD by using the thermodilution technique offers a widely accessible means of assessing microvascular resistance. Through this technique, 2 validated indices, namely coronary flow reserve and the index of microcirculatory resistance, can be computed, facilitating investigation of the coronary microcirculation. The index of microcirculatory resistance specifically estimates minimum achievable microvascular resistance within the coronary microcirculation. We aim to review the bolus thermodilution method, outlining the fundamental steps for conducting measurements and introducing an algorithmic approach (CATH CMD) to systematically evaluate the coronary microcirculation. Embracing a standardized approach, exemplified by the CATH CMD algorithm, will facilitate adoption of this technique and streamline the diagnosis of CMD.

Links Between Obstructive Sleep Apnea and Myocardial Blood Flow Changes Impacting Adverse Cardiovascular Disease-related Outcomes

PURPOSE OF REVIEW

Recent studies have demonstrated an association between obstructive sleep apnea (OSA) and abnormal myocardial blood flow (MBF), myocardial flow reserve (MFR), and coronary microvascular dysfunction (CMD). Here, we review the evidence and describe the potential underlying mechanisms linking OSA to abnormal MBF. Examining relevant studies, we assess the impact of OSA-specific therapy, such as continuous positive airway pressure (CPAP), on MBF.

RECENT FINDINGS

Recent studies suggest an association between moderate to severe OSA and abnormal MBF/MFR. OSA promotes functional and structural abnormalities of the coronary microcirculation. OSA also promotes the uncoupling of MBF to cardiac work. In a handful of studies with small sample sizes, CPAP therapy improved MBF/MFR. Moderate to severe OSA is associated with abnormal MFR, suggesting an association with CMD. Evidence suggests that CPAP therapy improves MBF. Future studies must determine the clinical impact of improved MBF with CPAP.