Novel index for invasively assessing the coronary microcirculation

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.

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.

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.

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. In this chapter, we review CMD and focus on its endotypes, techniques for microcirculatory assessment, associated tips and tricks and available treatment options.

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.

Chapter 13.0. 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.

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.

Microvascular dysfunction in heart transplantation is associated with altered cardiomyocyte mitochondrial structure and unimpaired excitation-contraction coupling

INTRODUCTION

Microvascular dysfunction (MVD) is a hallmark feature of chronic graft dysfunction in patients that underwent orthotopic heart transplantation (OHT) and is the main contributor to impaired long-term graft survival. The aim of this study was to determine the effect of MVD on functional and structural properties of cardiomyocytes isolated from ventricular biopsies of OHT patients.

METHODS

We included 14 patients post-OHT, who had been transplanted for 8.1 years [5.0; 15.7 years]. Mean age was 49.6 ± 14.3 years; 64% were male. Coronary microvasculature was assessed using guidewire-based coronary flow reserve(CFR)/index of microvascular resistance (IMR) measurements. Ventricular myocardial biopsies were obtained and cardiomyocytes were isolated using enzymatic digestion. Cells were electrically stimulated and subcellular Ca2+ signalling as well as mitochondrial density were measured using confocal imaging.

RESULTS

MVD measured by IMR was present in 6 of 14 patients with a mean IMR of 53±10 vs. 12±2 in MVD vs. controls (CTRL), respectively. CFR did not differ between MVD and CTRL. Ca2+ transients during excitation-contraction coupling in isolated ventricular cardiomyocytes from a subset of patients showed unaltered amplitudes. In addition, Ca2+ release and Ca2+ removal were not significantly different between MVD and CTRL. However, mitochondrial density was significantly increased in MVD vs. CTRL (34±1 vs. 29±2%), indicating subcellular changes associated with MVD.

CONCLUSION

In-vivo ventricular microvascular dysfunction post OHT is associated with preserved excitation-contraction coupling in-vitro, potentially owing to compensatory changes on the mitochondrial level or due to the potentially reversible cause of the disease.

Prognostic Implications of Fractional Flow Reserve and Coronary Flow Reserve After Drug-Eluting Stent Implantation

BACKGROUND

Fractional flow reserve (FFR) after percutaneous coronary intervention (PCI) provides prognostic information, but limited data are available regarding prognostication using post-PCI coronary flow reserve (CFR). In this study we aimed to assess the prognostic value of post-procedural FFR and CFR for target vessel failure (TVF) after PCI.

METHODS AND RESULTS

This lesion-based post-hoc pooled analysis of previously published registry data involved 466 patients with chronic coronary syndrome with single-vessel disease who underwent pre- and post-PCI FFR and CFR measurements, and were followed-up to determine the predictors of TVF. The prognostic value of post-PCI CFR and FFR was compared with that of FFR or CFR alone. Post-PCI FFR/CFR discordant results were observed in 42.5%, and 10.3% of patients had documented TVF. Receiver-operating characteristic curve analysis revealed that the optimal cutoff values of post-PCI FFR and CFR to predict the occurrence of TVF were 0.85 and 2.26, respectively. Significant differences in TVF were detected according to post-PCI FFR (≤0.85 vs. >0.85, P=0.007) and post-PCI CFR (<2.26 vs. ≥2.26, P<0.001). Post-PCI FFR ≤0.85 and post-PCI CFR <2.26 were independent prognostic predictors.

CONCLUSIONS

After PCI completion, discordant results between FFR and CFR were not uncommon. Post-PCI CFR categorization showed incremental prognostic value for predicting TVF independent of post-PCI FFR risk stratification.

Treatment and Care of Patients with ST-Segment Elevation Myocardial Infarction-What Challenges Remain after Three Decades of Primary Percutaneous Coronary Intervention?

Primary percutaneous coronary intervention (pPCI) has revolutionized the prognosis of ST-segment elevation myocardial infarction (STEMI) and is the gold standard treatment. As a result of its success, the number of pPCI centres has expanded worldwide. Despite decades of advancements, clinical outcomes in STEMI patients have plateaued. Out-of-hospital cardiac arrest and cardiogenic shock remain a major cause of high in-hospital mortality, whilst the growing burden of heart failure in long-term STEMI survivors presents a growing problem. Many elements aiming to optimize STEMI treatment are still subject to debate or lack sufficient evidence. This review provides an overview of the most contentious current issues in pPCI in STEMI patients, with an emphasis on unresolved questions and persistent challenges.

Angiographic microvascular resistance in patients with obstructive hypertrophic cardiomyopathy

BACKGROUND

Coronary microvascular dysfunction (CMD) is an important feature of obstructive hypertrophic cardiomyopathy (oHCM). Angiographic microvascular resistance (AMR) offers a potent means for assessing CMD. This study sought to evaluate the prognostic value of CMD burden calculated by AMR among oHCM patients.

METHODS

We retrospectively screened all patients diagnosed with oHCM from Fuwai Hospital between January 2017 and November 2021. Off-line AMR assessments were performed for all 3 major coronary vessels by the independent imaging core laboratory. Patients were followed every 6 months post discharge via office visit or telephone contacts. The primary outcome was major adverse cardiovascular events (MACE), including all-cause death, and unplanned rehospitalization for heart failure.

RESULTS

A total of 342 patients presented with oHCM diseases enrolled in the present analyses. Mean age was 49.7, 57.6 % were men, mean 3-vessel AMR was 6.9. At a median follow-up of 18 months, high capability of 3-vessel AMR in predicting MACE was identified (AUC: 0.70) with the best cut-off value of 7.04. The primary endpoint of MACE was significantly higher in high microvascular resistance group (3-vessel AMR ≥ 7.04) as compared with low microvascular resistance group (56.5 % vs. 16.5 %; HR: 5.13; 95 % CI: 2.46-10.7; p < 0.001), which was mainly driven by the significantly higher risk of heart failure events in high microvascular resistance group. Additionally, 3-vessel AMR (HR: 4.37; 95 % CI: 1.99-9.58; p < 0.001), and age (per 1 year increase, HR: 1.03; 95 % CI: 1.01-1.06; p = 0.02) were independently associated with MACE.

CONCLUSION

The present retrospective study demonstrated that the novel angiography-based AMR was a useful tool for CMD evaluation among patients with oHCM. High microvascular resistance as identified by 3-vessel AMR (≥7.04) was associated with worse prognosis.

Correlation of Non-Invasive Transthoracic Doppler Echocardiography with Invasive Doppler Wire-Derived Coronary Flow Reserve and Their Impact on Infarct Size in Patients with ST-Segment Elevation Myocardial Infarction Treated with Primary Percutaneous Coronary Intervention

Background: Coronary microvascular dysfunction is associated with adverse prognosis after ST-segment elevation myocardial infarction (STEMI). We aimed to compare the invasive, Doppler wire-based coronary flow reserve (CFR) with the non-invasive transthoracic Doppler echocardiography (TTDE)-derived CFR, and their ability to predict infarct size. Methods: We included 36 patients with invasive Doppler wire assessment on days 3-7 after STEMI treated with primary percutaneous coronary intervention (PCI), of which TTDE-derived CFR was measured in 47 vessels (29 patients) within 6 h of the invasive Doppler. Infarct size was assessed by cardiac magnetic resonance at a median of 8 months. Results: The correlation between invasive and non-invasive CFR was modest in the overall cohort (rho 0.400, p = 0.005). It improved when only measurements in the LAD artery were considered (rho 0.554, p = 0.002), with no significant correlation in the RCA artery (rho -0.190, p = 0.435). Both invasive (AUC 0.888) and non-invasive (AUC 0.868) CFR, measured in the recanalized culprit artery, showed a good ability to predict infarct sizes ≥18% of the left ventricular mass, with the optimal cut off values of 1.85 and 1.80, respectively. Conclusions: In patients with STEMI, TTDE- and Doppler wire-derived CFR exhibit significant correlation, when measured in the LAD artery, and both have a similarly strong association with the final infarct size.

The Use of Thrombectomy during Primary Percutaneous Coronary Intervention: Resurrecting an Old Concept in Contemporary Practice

Optimal myocardial reperfusion during primary percutaneous coronary intervention (pPCI) is increasingly recognized to be beyond restoring epicardial coronary flow. Both invasive and non-invasive tools have highlighted the limitation of using this metric, and more efforts are focused towards achieving optimal reperfusion at the level of the microcirculation. Recent data highlighted the close relationship between thrombus burden and impaired microcirculation in patients presenting with ST-segment elevation myocardial infarction (STEMI). Moreover, distal embolization was an independent predictor of mortality in patients with STEMI. Likewise, the development of no-reflow phenomenon has been directly linked with worse clinical outcomes. Adjunctive thrombus aspiration during pPCI is intuitively intended to remove atherothrombotic material to mitigate the risk of distal embolization and the no-reflow phenomenon (NRP). However, prior trials on the use of thrombectomy during pPCI did not support its routine use, with comparable clinical endpoints to patients who underwent PCI alone. This article aims to review the existing literature highlighting the limitation on the use of thrombectomy and provide future insights into trials investigating the role of thrombectomy in contemporary pPCI.

Impact of vessel volume on thermodilution measurements in patients with coronary microvascular dysfunction

BACKGROUND

Two invasive methods are available to estimate microvascular resistance: bolus and continuous thermodilution. Comparative studies have revealed a lack of concordance between measurements of microvascular resistance obtained through these techniques.

AIMS

This study aimed to examine the influence of vessel volume on bolus thermodilution measurements.

METHODS

We prospectively included patients with angina with non-obstructive coronary arteries (ANOCA) undergoing bolus and continuous thermodilution assessments. All patients underwent coronary CT angiography to extract vessel volume. Coronary microvascular dysfunction was defined as coronary flow reserve (CFR) < 2.0. Measurements of absolute microvascular resistance (in Woods units) and index of microvascular resistance (IMR) were compared before and after volumetric adjustment.

RESULTS

Overall, 94 patients with ANOCA were included in this study. The mean age was 64.7 ± 10.8 years, 48% were female, and 19% had diabetes. The prevalence of CMD was 16% based on bolus thermodilution, while continuous thermodilution yielded a prevalence of 27% (Cohen's Kappa 0.44, 95% CI 0.23-0.65). There was no correlation in microvascular resistance between techniques (r = 0.17, 95% CI -0.04 to 0.36, p = 0.104). The adjustment of IMR by vessel volume significantly increased the agreement with absolute microvascular resistance derived from continuous thermodilution (r = 0.48, 95% CI 0.31-0.63, p < 0.001).

CONCLUSIONS

In patients with ANOCA, invasive methods based on coronary thermodilution yielded conflicting results for the assessment of CMD. Adjusting IMR with vessel volume improved the agreement with continuous thermodilution for the assessment of microvascular resistance. These findings strongly suggest the importance of considering vessel volume when interpreting bolus thermodilution assessment.

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

BACKGROUND

This study aims to investigate prognostic implications of coronary slow flow (CSF) and angiography-derived index of microcirculatory resistance (caIMR) in patients with angina and normal coronary arteries.

METHODS

A total of 582 patients were enrolled with angiographically normal coronary arteries. caIMR was calculated using a commercial software. Patients were followed up for a median of 45 months. The primary endpoint was defined as major adverse cardiovascular events (MACEs) comprising death, myocardial infarction and readmission for angina or heart failure.

RESULTS

CSF was diagnosed when TIMI grade 2 flow presented in at least one coronary artery. Multivariate analysis indicated TIMI-flow-based determination of CSF was not significantly associated with MACEs [hazard ratio (HR): 2.14; 95% confidence interval (CI): 0.87-5.31; p = 0.099), while caIMR >42 (HR: 2.53; 95% CI: 1.02-6.32; p = 0.047) were independent predictors of MACEs. Incorporation of caIMR improved the area under the curve from 0.587 to 0.642.

CONCLUSIONS

caIMR was an independent prognostic factor of long-term cardiovascular events in patients with CSF. Evaluation of caIMR improved the risk stratification of patients with angiographically-normal coronary arteries.