Invasive Assessment of the Coronary Microvasculature

Prognostic impact of coronary microvascular dysfunction assessed by caIMR in overweight with chronic coronary syndrome patients

OBJECTIVE

Coronary microvascular dysfunction (CMD) may associate with adverse cardiovascular events in obese patients. Coronary angiography-derived index of microcirculatory resistance (caIMR) is proposed as a less-invasive and pressure-wire-free index to assess CMD. We aimed to investigate the impact of coronary microvascular function assessed by caIMR in patients with overweight and chronic coronary syndrome (CCS).

METHODS

CCS patients who underwent coronary angiography between 2015 to 2018 were included. Overweight was defined as BMI≥24.0kg/m². Impaired coronary microvascular function was defined as caIMR≥25U. The patients were classified according to BMI and caIMR. The primary endpoint was major adverse cardiac events (MACE). Kaplan-Meier and Cox regression analyses evaluated the association between caIMR and MACE.

RESULTS

Two hundred and eighty-two CCS patients were enrolled. Among these, 169 (59.93%) were overweight. Impaired coronary microvascular function was higher in overweight patients than in patients with normal weight (49.70% vs. 38.05%; P=0.035). During 35 months of follow-up, 33 MACE had occurred. Among the total CCS population, MACE was higher in patients with high caIMR than in low caIMR (18.11% vs. 6.45%, P=0.003). In subgroups analysis, MACE was higher in overweight patients with high caIMR than low caIMR (20.24% vs. 7.06%, P=0.014), while there were no significant differences in normal-weight patients. Multivariate Cox analysis demonstrated that caIMR≥25 was independently associated with MACE in overweight patients (HR, 2.87; 95% CI, 1.12-7.30; P=0.027) but not in the normal-weight patients. In addition, caIMR showed a significant predictive value for adverse outcomes in overweight patients and provided an incremental prediction when added to a prediction model with BMI.

CONCLUSIONS

Impaired coronary microvascular function assessed by caIMR was common and is an independent predictor of MACE in overweight patients with CCS.

Invasive Assessment of Coronary Microvascular Function

The critical role of the coronary microvascular compartment and its invasive functional assessment has become apparent in light of the significant proportion of patients presenting signs and symptoms of myocardial ischemia, despite the absence of epicardial disease, or after the adequate treatment of it. However, coronary microvascular dysfunction (CMD) represents a diagnostic challenge because of the small dimensions of the coronary microvasculature, which prevents direct angiographic visualization. Several diagnostic tools are now available for the invasive assessment of the coronary microvascular function, which, in association with the physiological indices used to investigate the epicardial department, may provide a comprehensive evaluation of the coronary circulation as a whole. Recent evidence suggests that the physiology-guided management of CMD, although apparently costly and time-consuming, may offer a net clinical benefit in terms of symptom improvement among patients with angina and ischemic heart disease. However, despite the results of several observational studies, the prognostic effect of the physiology-driven management of CMD within this population is currently a matter of debate, and therefore represents an unmet clinical need that urgently deserves further investigation.

Prognostic value of comprehensive intracoronary physiology assessment early after heart transplantation

AIMS

We evaluated the long-term prognostic value of invasively assessing coronary physiology after heart transplantation in a large multicentre registry.

METHODS AND RESULTS

Comprehensive intracoronary physiology assessment measuring fractional flow reserve (FFR), the index of microcirculatory resistance (IMR), and coronary flow reserve (CFR) was performed in 254 patients at baseline (a median of 7.2 weeks) and in 240 patients at 1 year after transplantation (199 patients had both baseline and 1-year measurement). Patients were classified into those with normal physiology, reduced FFR (FFR ≤ 0.80), and microvascular dysfunction (either IMR ≥ 25 or CFR ≤ 2.0 with FFR > 0.80). The primary outcome was the composite of death or re-transplantation at 10 years. At baseline, 5.5% had reduced FFR; 36.6% had microvascular dysfunction. Baseline reduced FFR [adjusted hazard ratio (aHR) 2.33, 95% confidence interval (CI) 0.88-6.15; P = 0.088] and microvascular dysfunction (aHR 0.88, 95% CI 0.44-1.79; P = 0.73) were not predictors of death and re-transplantation at 10 years. At 1 year, 5.0% had reduced FFR; 23.8% had microvascular dysfunction. One-year reduced FFR (aHR 2.98, 95% CI 1.13-7.87; P = 0.028) and microvascular dysfunction (aHR 2.33, 95% CI 1.19-4.59; P = 0.015) were associated with significantly increased risk of death or re-transplantation at 10 years. Invasive measures of coronary physiology improved the prognostic performance of clinical variables (χ2 improvement: 7.41, P = 0.006). However, intravascular ultrasound-derived changes in maximal intimal thickness were not predictive of outcomes.

CONCLUSION

Abnormal coronary physiology 1 year after heart transplantation was common and was a significant predictor of death or re-transplantation at 10 years.

A historical review of experimental imaging of the beating heart coronary microcirculation in vivo

Following a myocardial infarction (MI), the prognosis of patients is highly dependent upon the re-establishment of perfusion not only in the occluded coronary artery, but also within the coronary microcirculation. However, our fundamental understanding of the pathophysiology of the tiniest blood vessels of the heart is limited primarily because no current clinical imaging tools can directly visualise them. Moreover, in vivo experimental studies of the beating heart using intravital imaging have also been hampered due to obvious difficulties related to significant inherent contractile motion, movement of the heart brought about by nearby lungs and its location in an anatomically challenging position for microscopy. However, recent advances in microscopy techniques, and the development of fluorescent reporter mice and fluorescently conjugated antibodies allowing visualisation of vascular structures, thromboinflammatory cells and blood flow, have allowed us to overcome some of these challenges and increase our basic understanding of cardiac microvascular pathophysiology. In this review, the elegant attempts of the pioneers in intravital imaging of the beating heart will be discussed, which focussed on providing new insights into the anatomy and physiology of the healthy heart microvessels. The reviews end with the more recent studies that focussed on disease pathology and increasing our understanding of myocardial thromboinflammatory cell recruitment and flow disturbances, particularly in the setting of diseases such as MI.

Microcirculatory Resistance Predicts Allograft Rejection and Cardiac Events After Heart Transplantation

BACKGROUND

Single-center data suggest that the index of microcirculatory resistance (IMR) measured early after heart transplantation predicts subsequent acute rejection.

OBJECTIVES

The goal of this study was to validate whether IMR measured early after transplantation can predict subsequent acute rejection and long-term outcome in a large multicenter cohort.

METHODS

From 5 international cohorts, 237 patients who underwent IMR measurement early after transplantation were enrolled. The primary outcome was acute allograft rejection (AAR) within 1 year after transplantation. A key secondary outcome was major adverse cardiac events (MACE) (the composite of death, re-transplantation, myocardial infarction, stroke, graft dysfunction, and readmission) at 10 years.

RESULTS

IMR was measured at a median of 7 weeks (interquartile range: 3-10 weeks) post-transplantation. At 1 year, the incidence of AAR was 14.4%. IMR was associated proportionally with the risk of AAR (per increase of 1-U IMR; adjusted hazard ratio [aHR]: 1.04; 95% confidence interval [CI]: 1.02-1.06; p < 0.001). The incidence of AAR in patients with an IMR ≥18 was 23.8%, whereas the incidence of AAR in those with an IMR <18 was 6.3% (aHR: 3.93; 95% CI: 1.77-8.73; P = 0.001). At 10 years, MACE occurred in 86 (36.3%) patients. IMR was significantly associated with the risk of MACE (per increase of 1-U IMR; aHR: 1.02; 95% CI: 1.01-1.04; P = 0.005).

CONCLUSIONS

IMR measured early after heart transplantation is associated with subsequent AAR at 1 year and clinical events at 10 years. Early IMR measurement after transplantation identifies patients at higher risk and may guide personalized posttransplantation management.

Vasomotor Dysfunction in Patients with Ischemia and Non-Obstructive Coronary Artery Disease: Current Diagnostic and Therapeutic Strategies

Many patients who present with symptoms or objective evidence of ischemia have no or non-physiologically-significant disease on invasive coronary angiography. The diagnosis of ischemic heart disease is thus often dismissed, and patients receive false reassurance or other diagnoses are pursued. We now know that a significant proportion of these patients have coronary microvascular dysfunction and/or vasospastic disease as the underlying pathophysiology of their clinical presentation. Making the correct diagnosis of such abnormalities is important not only because they impact the quality of life, with recurring symptoms and unnecessary repeated testing, but also because they increase the risk for adverse cardiovascular events. The mainstay of diagnosis remains an invasive comprehensive physiologic assessment, which further allows stratifying these patients into appropriate “endotypes”. It has been shown that tailoring treatment to the patient’s assigned endotype improves symptoms and quality of life. In addition to the conventional drugs used in chronic stable angina, multiple newer agents are being investigated. Moreover, innovative non-pharmacologic and interventional therapies are emerging to provide a bail-out in refractory cases. Many of these novel therapies fail to show consistent benefits, but others show quite promising results.

The Pivotal Role of Invasive Functional Assessment in Patients With Myocardial Infarction With Non-Obstructive Coronary Arteries (MINOCA)

Myocardial infarction with non-obstructive coronary arteries (MINOCA) encompasses several pathophysiological mechanisms not yet fully understood. Among the latter, vasomotion abnormalities and coronary microvascular dysfunction (CMD) play a major role for both epidemiological and prognostic reasons. Despite current guidelines do not recommend routine physiological assessment of both epicardial and microvascular coronary compartments within the context of an acute myocardial infarction, several recent evidence support the critical role of a comprehensive invasive functional assessment in order to identify the underlying pathophysiological mechanism and consequently to select an appropriate therapeutic strategy. Unfortunately, optimal medical therapy for these patients is not currently established due to the lack of dedicated trials evaluating clinical outcomes of commonly used medications for secondary prevention in MINOCA patients. For this reason, additional research is warranted to provide personalized treatments for patients affected by this puzzling clinical entity.

Prognostic impact of coronary microvascular dysfunction in patients with myocardial infarction with non-obstructive coronary arteries

BACKGROUND

Myocardial infarction with non-obstructive coronary arteries (MINOCA) has been and remained a puzzling heterogeneous entity. The index of microcirculatory resistance (IMR) is a quantitative and specific index for the assessment of microvascular function. However, the role of IMR in MINOCA has not yet been studied. This study aimed to evaluate the prognostic value of coronary microvascular function, as assessed by coronary angiography‑derived index of microvascular resistance (caIMR) in MINOCA patients.

METHOD

This study included 109 MINOCA patients. Microvascular function was assessed by caIMR and was analyzed in 280 coronary arteries. The primary endpoint of the study was MACE, defined as cardiovascular death, nonfatal MI, heart failure, stroke and angina rehospitalization. The best cut-off of caIMR was derived from ROC analysis based on MACE prediction.

RESULTS

The patients were classified into high caIMR (caIMR>43U) and low caIMR (caIMR≤43U) based on a caIMR cut-off value of 43U. High caIMR was observed in 55 (50.5%) patients. A total of 27 MACE occurred during the 2 years of follow-up. MACE rate was significantly higher in patients with high caIMR than in patients with low caIMR (36.4% vs 13.0%, P=0.005). The Kaplan-Meier curves showed a significantly increased risk of MACE in patients with high caIMR (log-rank P=0.001). Cox multivariate analysis showed that caIMR>43 was a highly independent predictor of MACE (HR, 3.08; 95% CI, 1.13 - 8.35; P=0.027).

CONCLUSIONS

caIMR is a strong predictor of clinical outcome among MINOCA patients. The evaluation of IMR can provide an objective risk stratification method for patients with MINOCA.

Coronary Microvascular Dysfunction in Takotsubo Syndrome Assessed by Angiography-Derived Index of Microcirculatory Resistance: A Pressure-Wire-Free Tool

Background: Coronary microvascular dysfunction (CMD) has been proposed as a key mechanism in Takotsubo syndrome (TTS). The non-hyperaemic angiography-derived index of microcirculatory resistance (NH-IMRangio) has been validated as a pressure-wire-free tool for the assessment of coronary microvasculature. We aimed to study the presence of CMD in TTS patients and its association with levels of cardiac biomarkers and systolic dysfunction patterns. Methods: We recruited 181 consecutive patients admitted for TTS who underwent cardiac angiography at a tertiary center from January 2014 to January 2021. CMD was defined as an NH-IMRangio ≥ 25. Plasma levels of NT-proBNP, high-sensitive cardiac troponin T (hs-cTnT) and the left ventricular ejection fraction (LVEF) by echocardiography were measured at admission. Results: Mean age was 75.3 years, 83% were women and median LVEF was 45%. All patients presented CMD (NH-IMRangio ≥ 25) in at least one epicardial coronary artery. The left anterior descending artery (LAD) showed higher median NH-IMRangio values than left circumflex (LCx) and right coronary arteries (RCA) (44.6 vs. 31.3 vs. 36.1, respectively; p < 0.001). NH-IMRangio values differed among ventricular contractility patterns in the LAD and RCA (p = 0.0152 and 0.0189, respectively) with the highest values in the mid-ventricular + apical and mid-ventricular + basal patterns. NT-proBNP levels, but not high-sensitive cardiac troponin T (hs-cTnT), were correlated with both the degree and the extent of CMD in patients with TTS. Lower LVEF was also associated with higher NH-IMRangio values. Conclusions: CMD is highly prevalent in patients admitted for TTS and is associated with both a higher degree of systolic dysfunction and higher BNP levels, but not troponin.

Diagnostic approach for coronary microvascular dysfunction in patients with chest pain and no obstructive coronary artery disease

A large number of studies has demonstrated that abnormalities of coronary microcirculation may be responsible for both acute and chronic cardiac ischemic syndromes. In clinical practice the microvascular origin of myocardial ischemia and angina is usually considered in patients who are found to have normal or near-normal coronary arteries at angiography. In this article, we review the diagnostic approach to patients with suspected coronary microvascular dysfunction as a cause of ischemic syndromes and also suggest a classification of chronic and acute microvascular coronary ischemic syndrome, including myocardial infarction with normal coronary arteries.

Coronary Microvascular Dysfunction: A Practical Approach to Diagnosis and Management

PURPOSE OF REVIEW

The purpose of this review is to provide an overview of diagnostic and treatment considerations in patients with coronary microvascular dysfunction (CMD) in the absence of obstructive coronary artery disease (CAD).

RECENT FINDINGS

The prevalence of obstructive CAD in unselected patient populations referred for evaluation of angina is less than 10%. A significant proportion of patients with angina and no obstructive CAD have CMD, a condition associated with impaired cardiovascular prognosis. Non-invasive and invasive evaluation of coronary microvascular function is feasible and widely available, yet CMD is underdiagnosed and undertreated. A patient-tailored treatment approach guided by coronary microvascular testing shows promising results for patient-reported outcomes of symptom burden and quality of life. Coronary microvascular testing should be considered in angina patients with no obstructive CAD, before other causes of chest pain are explored. A patient-tailored treatment approach guided by a complete evaluation of epicardial anatomy and macro-and microvascular function may help optimize treatment strategy and prevent unnecessary medical interventions. More research is needed to establish the long-term effect of patient-tailored therapies on risk reduction in CMD.

Diagnostic pathways in myocardial infarction with non-obstructive coronary artery disease (MINOCA)

When acute myocardial injury is found in a clinical setting suggestive of myocardial ischaemia, the event is labelled as acute myocardial infarction (AMI), and the absence of coronary stenosis angiographically 50% or greater leads to the working diagnosis of myocardial infarction with non-obstructive coronary arteries (MINOCA). The initial diagnosis of MINOCA can be confirmed or ruled out based on the results of subsequent investigations. This narrative review discusses the downstream diagnostic approaches to MINOCA, and appraises strengths and limitations of invasive and non-invasive investigations for this condition. The aim of this article is to increase the awareness that establishing the underlying cause of a MINOCA is possible in the vast majority cases. Determining the cause of MINOCA and excluding other possible causes for cardiac troponin elevation has notable implications for tailoring secondary prevention measures aimed at improving the overall prognosis of AMI.

Results of bicycle exercise stress test in patients with stable coronary heart disease depending on the angiographic signs of atherosclerotic lesions of coronary arteries

The aim. To identify features of exercise response in coronary heart disease (CHD) patients depending on coronary artery condition and to identify factors associated with a positive test in patients with no obstructive coronary artery disease (INOCA). Materials and methods. The study included 105 patients diagnosed with stable coronary artery disease (CAD) who were hospitalized at the City Clinical Hospital No. 8 of the Kharkiv City Council. The criteria for diagnosis of ischemia with no obstructive coronary artery disease (INOCA) were met by 53 patients who formed group I. Group II included 52 patients who were consistently hospitalized in the period from June to December 2020, and had obstructive CAD for more than 50 % according to their coronary angiography (CAG). Results. According to the results of bicycle exercise stress test, a positive test was significantly more often registered in group II – n=30 (57.7 %) patients compared to group I – n=19 (35.8 %) patients (p=0.0249). The duration of the test in patients of group I was significantly longer than 420 seconds [290–540], compared with group II – 300.0 [210.0–540.0] (р=0.0352). Also, in patients in group II, the maximum volume of the test performed was probably lower than in group I (p=0.0324). When calculating the double product, it was also found that in group I its value was significantly higher compared to group II (p=0.0292). In group I there was a significantly higher rate of chronotropic reserve (44.0 [26.0–60.0]), compared with group II (p=0.0168). Elevated total cholesterol (above 5 mmol/l) is a statistically significant and independent factor of a positive exercise test in patients with INOCA (OR, 1.98 [0.9992-3.926], p=0.05). A correlation was found between the level of exercise tolerance and smoking in INOCA-patients (r =-0.388975, p=0.010899). Patients who underwent MINOCA also showed reduced tolerance to exercise (r=-0.3104, p=0.042721) Conclusions. The sensitivity of bicycle exercise stress test in patients with CAD depends on the presence and severity of atherosclerotic lesions of the coronary arteries (63 % in stenotic atherosclerosis, 36 % in no obstructive coronary arteries. It was found that exercise test duration, double product, chronotropic and inotropic reserve of the heart in patients with a positive exercise test with INOCA were significantly higher compared with patients with obstructive CAD. Independent factors associated with a positive exercise test in patients with no obstructive CAD are an increase in total cholesterol (multivariate regression logistic analysis).

An EAPCI Expert Consensus Document on Ischaemia with Non-Obstructive Coronary Arteries in Collaboration with European Society of Cardiology Working Group on Coronary Pathophysiology & Microcirculation Endorsed by Coronary Vasomotor Disorders International Study Group

This consensus document, a summary of the views of an expert panel organized by the European Association of Percutaneous Cardiovascular Interventions (EAPCI), appraises the importance of ischaemia with non-obstructive coronary arteries (INOCA). Angina pectoris affects approximately 112 million people globally. Up to 70% of patients undergoing invasive angiography do not have obstructive coronary artery disease, more common in women than in men, and a large proportion have INOCA as a cause of their symptoms. INOCA patients present with a wide spectrum of symptoms and signs that are often misdiagnosed as non-cardiac leading to under-diagnosis/investigation and under-treatment. INOCA can result from heterogeneous mechanism including coronary vasospasm and microvascular dysfunction and is not a benign condition. Compared to asymptomatic individuals, INOCA is associated with increased incidence of cardiovascular events, repeated hospital admissions, as well as impaired quality of life and associated increased health care costs. This consensus document provides a definition of INOCA and guidance to the community on the diagnostic approach and management of INOCA based on existing evidence from research and best available clinical practice; noting gaps in knowledge and potential areas for further investigation.

Angiogenic CD34 Stem Cell Therapy in Coronary Microvascular Repair-A Systematic Review

Ischemia with non-obstructive coronary arteries (INOCA) is an increasingly recognized disease, with a prevalence of 3 to 4 million individuals, and is associated with a higher risk of morbidity, mortality, and a worse quality of life. Persistent angina in many patients with INOCA is due to coronary microvascular dysfunction (CMD), which can be difficult to diagnose and treat. A coronary flow reserve <2.5 is used to diagnose endothelial-independent CMD. Antianginal treatments are often ineffective in endothelial-independent CMD and thus novel treatment modalities are currently being studied for safety and efficacy. CD34+ cell therapy is a promising treatment option for these patients, as it has been shown to promote vascular repair and enhance angiogenesis in the microvasculature. The resulting restoration of the microcirculation improves myocardial tissue perfusion, resulting in the recovery of coronary microvascular function, as evidenced by an improvement in coronary flow reserve. A pilot study in INOCA patients with endothelial-independent CMD and persistent angina, treated with autologous intracoronary CD34+ stem cells, demonstrated a significant improvement in coronary flow reserve, angina frequency, Canadian Cardiovascular Society class, and quality of life (ESCaPE-CMD, NCT03508609). This work is being further evaluated in the ongoing FREEDOM (NCT04614467) placebo-controlled trial.

Coronary microvascular adaptations distal to epicardial artery stenosis

Until recently, epicardial coronary stenosis has been considered the primary outcome of coronary heart disease, and clinical interventions have been dedicated primarily to the identification and removal of flow-limiting stenoses. However, a growing body of literature indicates that both epicardial stenosis and microvascular dysfunction contribute to damaging myocardial ischemia. In this review, we discuss the coexistence of macro- and microvascular disease, and how the structure and function of the distal microcirculation is impacted by the hemodynamic consequences of an epicardial, flow-limiting stenosis. Mechanisms of endothelial dysfunction as well as alterations of smooth muscle function in the coronary microcirculation distal to stenosis are discussed. Risk factors including diabetes, metabolic syndrome, and aging exacerbate microvascular dysfunction in the myocardium distal to a stenosis, and our current understanding of the role of these factors in limiting collateralization and angiogenesis of the ischemic myocardium is presented. Importantly, exercise training has been shown to promote collateral growth and improve microvascular function distal to stenosis; thus, the current literature reporting the mechanisms that underlie the beneficial effects of exercise training in the microcirculation distal to epicardial stenosis is reviewed. We also discuss recent studies of therapeutic interventions designed to improve microvascular function and stimulate angiogenesis in clinically relevant animal models of epicardial stenosis and microvascular disease. Finally, microvascular adaptation to removal of epicardial stenosis is considered.

Coronary Flow Reserve and Glycemic Variability in Patients with Coronary Artery Disease

Objective Glycemic variability is being increasingly recognized as an early indicator of glucose metabolic disorder and may contribute to the development of diabetic vascular complications, such as coronary microvascular dysfunction. The present study sought to investigate the relationship between coronary microvascular function assessed by intracoronary thermodilution method and glycemic variability on a continuous glucose monitoring system (CGMS). Methods We prospectively enrolled 40 patients with or without known diabetes mellitus who had epicardial coronary artery disease referred for coronary angiography and were not treated with diabetic medications. Of these, two had a significant stenosis in the left main coronary artery and were therefore excluded from the analyses. In the end, 38 patients were equipped with a CGMS and underwent intracoronary physiological assessments in the unobstructed left anterior descending artery. The mean amplitude of glycemic excursion (MAGE) and standard deviation were calculated from the obtained CGMS data as indicators of glucose variability. Results Coronary flow reserve (CFR) was negatively correlated with MAGE (r=-0.328, p=0.044) and standard deviation (r=-0.339, p=0.037) on CGMS, while the index of microcirculatory resistance showed no such correlation. Multivariable linear regression analyses showed that MAGE on CGMS was significantly associated with CFR after adjusting for age, sex, fractional flow reserve and hemoglobin A1c. Conclusion Higher MAGE on CGMS was associated with reduced CFR in stable patients with coronary artery disease, suggesting a potential effect of glycemic variability on coronary microvascular flow regulation. A further study with a larger sample size needs to be conducted to confirm our findings.

Quantitative flow ratio as a new tool for angiography-based physiological evaluation of coronary artery disease: a review

The functional evaluation of coronary stenoses has obtained important clinical results in recent years, resulting in strong guideline recommendations. Nonetheless, the use of coronary wire-based functional evaluation has not yet become part of the routine in catheterization laboratories for several reasons, including the need to advance a wire into the coronary vessel to interrogate the stenosis. Angiography-derived indexes have been introduced to expand the current use of physiology to estimate the functional meaning of a stenosis on the basis of angiographic data only. The most studied and validated angiography-derived index is certainly the quantitative flow ratio. This article will summarize the basics of the quantitative flow ratio, the related validation studies and its current and future applications.

Coronary microvascular dysfunction assessed by continuous intracoronary thermodilution: A comparative study with index of microvascular resistance

BACKGROUND

This study aimed to assess the correlation between the standard of care, the index of microvascular resistance (IMR) versus the novel microvascular resistance (R_micro) and to determine the pathologic cut-off value in a selected population with suspected coronary microvascular dysfunction (CMD).

METHODS

One-hundred and twenty patients with high clinical suspicion of CMD due to ischemic symptoms in the absence of significant epicardial coronary lesions were prospectively included. Following a standardized systematic protocol, coronary flow reserve, IMR, fractional flow reserve, Q and R_micro were measured in the left anterior descending coronary artery using a temperature/pressure sensor-tipped guidewire and a dedicated infusion catheter.

RESULTS

There was a high prevalence of CMD with 50 (42%) patients showing an IMR ≥ 25. Median IMR was 23 [IQR: 14-34] and median R_micro was 464 Woods Units (WU) [IQR: 354-636WU]. ROC analyses identified 500 WU as the optimal R_micro cut-off to identify patients with an IMR ≥ 25, with an area under the ROC curve (C statistic) of 0.83 (95% CI: 0.74 to 0.89, p < 0.0001).

CONCLUSIONS

R_micro derived from continuous intracoronary thermodilution is an accurate index to measure microvascular resistances enabling the invasive diagnostic of CMD.

Relationship between peripheral arterial reactive hyperemia and the index of myocardial resistance in patients undergoing invasive coronary angiography

BACKGROUND

Coronary microvascular dysfunction is a powerful prognostic factor in patients with coronary artery disease. We investigated the role of reactive digital hyperemia peripheral arterial tonometry (RH-PAT) as a non-invasive tool to identify patients with impaired coronary microvasculature.

METHODS

Patients undergoing elective coronary angiography were consecutively assessed for peripheral microvascular endothelial function before coronary angiography: both the Reactive Hyperemic Index (RHI) and the Framingham reactive hyperemic index (Endoscore) were measured. During coronary angiography, the Index of microvascular resistance (IMR) was measured in all patients, and an IMR value > 25 identified patients with coronary microvascular impairment.

RESULTS

A total of 47 patients with chronic coronary syndromes candidate to coronary angiography were included. Those with coronary microvascular impairment (n = 18 [38%]) presented with significantly lower RHI (1.68 ± 0.38 vs. 1.94 ± 0.93, p = 0.04) and Endoscore 0.50 ± 0.23 vs. 0.64 ± 0.23, p = 0.04) values as compared with patients with preserved coronary microvasculature. A significant relationship was observed between IMR with both RHI (r = 0.35, p = 0.02) and Endoscore (r = 0.34, p = 0.02). At the multivariable analysis, RHI and Endoscore were the only independent predictors of an IMR > 25.

CONCLUSIONS

Our study demonstrates that digital reactive hyperemia indexes are lower in patients with high IMR values, suggesting a role for RH-PAT as non-invasive tool for identifying patients with coronary microvascular impairment.

The effect of antiplatelet drug on coronary endothelial and microvascular function: comparison with ticagrelor and clopidogrel

BACKGROUND/AIMS

Coronary endothelial and microvascular function play important roles in cardiovascular disease. We aimed to evaluate the effect of ticagrelor on coronary artery function and tested the antiplatelet effect of low dose ticagrelor in East-Asian patients.

METHODS

Sixty-one consecutive patients with non-significant coronary disease were included in the study. Initially, patients were randomized in 1:1:1 ratio to receive drugs: ticagrelor 90 mg twice a day (bid; n = 22), ticagrelor 45 mg bid (n = 19) or clopidogrel 75 mg once a day (qd; n = 20) and then divided into two groups (ticagrelor vs clopidogrel) for evaluation of coronary artery function, and three groups for evaluation of antiplatelet function. Endothelial dysfunction was measured by coronary flow reserve (CFR), and changes in the levels of asymmetric dimethylarginine (ADMA), cluster of differentiation (CD) 40 ligand, and P-selectin. Microvascular function was evaluated as index of microvascular resistance (IMR). Platelet reactivity was assessed by VerifyNow P2Y12 assay.

RESULTS

The levels of CFR, ADMA, and CD 40 ligand were not different between the two groups. However, P-selectin was lower in the ticagrelor group compared with clopidogrel group. IMR was significantly lower in the ticagrelor group compared with clopidogrel group (median, 15.0 [interquartile range, 12.0 to 21.0] vs. 47.5 [23.0 to 67.5], p = 0.014). There was significant difference in platelet inhibition among the three groups (ticagrelor 90 mg bid vs. ticagrelor 45 mg bid vs. clopidogrel 75 mg qd; 85.57 ± 47.63 vs. 120.33 ± 51.09 vs. 256.42 ± 55.10, p < 0.001).

CONCLUSION

It is hypothesized that ticagrelor might ameliorate the coronary microvascular function. When compared with clopidogrel, low dose ticagrelor exhibited satisfactory antiplatelet effect in the present study.

An EAPCI Expert Consensus Document on Ischaemia with Non-Obstructive Coronary Arteries in Collaboration with European Society of Cardiology Working Group on Coronary Pathophysiology & Microcirculation Endorsed by Coronary Vasomotor Disorders International Study Group

This consensus document, a summary of the views of an expert panel organized by the European Association of Percutaneous Cardiovascular Interventions (EAPCI), appraises the importance of ischaemia with non-obstructive coronary arteries (INOCA). Angina pectoris affects approximately 112 million people globally. Up to 70% of patients undergoing invasive angiography do not have obstructive coronary artery disease, more common in women than in men, and a large proportion have INOCA as a cause of their symptoms. INOCA patients present with a wide spectrum of symptoms and signs that are often misdiagnosed as non-cardiac leading to under-diagnosis/investigation and under-treatment. INOCA can result from heterogeneous mechanism including coronary vasospasm and microvascular dysfunction and is not a benign condition. Compared to asymptomatic individuals, INOCA is associated with increased incidence of cardiovascular events, repeated hospital admissions, as well as impaired quality of life and associated increased health care costs. This consensus document provides a definition of INOCA and guidance to the community on the diagnostic approach and management of INOCA based on existing evidence from research and best available clinical practice; noting gaps in knowledge and potential areas for further investigation.

Assessment of Vascular Dysfunction in Patients Without Obstructive Coronary Artery Disease: Why, How, and When

Ischemic heart disease secondary to coronary vascular dysfunction causes angina and impairs quality of life and prognosis. About one-half of patients with symptoms and signs of ischemia turn out not to have obstructive coronary artery disease, and coronary vascular dysfunction may be relevant. Adjunctive tests of coronary vasomotion include guidewire-based techniques with adenosine and reactivity testing, typically by intracoronary infusion of acetylcholine. The CorMicA (Coronary Microvascular Angina) trial provided evidence that routine management guided by an interventional diagnostic procedure and stratified therapy improves angina and quality of life in patients with angina but no obstructive coronary artery disease. In this paper, the COVADIS study group provide a comprehensive review of why, how, and when coronary vascular dysfunction should be assessed invasively. They discuss the rationale through a shared understanding of vascular pathophysiology and clinical evidence. They propose a consensus approach to how an interventional diagnostic procedure is performed with focus on practical aspects. Finally, the authors discuss the clinical scenarios in patients with stable and acute coronary syndromes in which measurement of coronary vascular function may be helpful for patient care.

Effects of different strategies on high thrombus burden in patients with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary catheterization

OBJECTIVE

This study aimed at evaluating efficacy and safety of thrombus aspiration and intracoronary-targeted thrombolysis on coronary thrombus burden in ST-elevation myocardial infarction (STEMI) patients undergoing primary percutaneous catheterization, comparing their effects on myocardial perfusion through index of microcirculatory resistance (IMR) and single-photon emission computed tomography (SPECT).

PARTICIPANTS AND METHODS

From January 2017 to January 2018, STEMI patients with high thrombus burden undergoing primary catheterization were enrolled and randomly assigned to receiving thrombus aspiration (TA group) or intracoronary thrombolysis (IT group). IMR, SPECT, and other conventional measurements were adopted to assess myocardial perfusion. Major adverse cardiovascular events (MACEs) and complications were recorded over a 90-day follow-up and a 12-month follow-up after the procedure.

RESULTS

The study consisted of 38 patients in the IT group and 33 in the TA group. After recanalization, thrombus burden score, corrected thrombolysis in myocardial infarction (TIMI) frame count, the proportion of TIMI myocardial perfusion 3 grade, and IMR in the IT group were significantly better than those of the TA group (P<0.05). During the 90-day follow-up, no difference was observed in cardiac function and MACEs. During the 12-month follow-up, there were significant differences in infarct size of SPECT (18.56±8.56 vs. 22.67±7.66, P=0.046), left ventricular ejection fraction of echocardiography (58.13±5.92 vs. 55.17±5.68, P=0.043), and the composite MACEs between the two groups (P=0.034).

CONCLUSION

Thrombus aspiration and intracoronary-targeted thrombolysis are effective and safe strategies in managing high coronary thrombus burden in STEMI patients. Compared with aspiration, intracoronary-targeted thrombolysis is more beneficial in improving myocardial microcirculation perfusion.

Cardiac Rehabilitation and Endothelial Function

Endothelial dysfunction is an early abnormality in the process of atherosclerosis and cardiovascular disease and has been associated with worse clinical outcome. Cardiac rehabilitation (CR) has been reported to be helpful to reduce cardiovascular events in various types of cardiac disease, but the mechanisms of its beneficial effects remain only partially known. In this article, we review the studies that assessed the effect of CR on endothelial function in patients with various cardiac conditions. Available data show that CR significantly improves impaired endothelial function in these patients, which may contribute to the beneficial effects of CR on clinical outcome.

Prognostic implications of coronary physiological indices in patients with diabetes mellitus

INTRODUCTION AND OBJECTIVES

Has been performed of the prognostic value of coronary physiological indices in patients with diabetes mellitus (DM) after coronary revascularization deferral.

METHODS

We analyzed 714 patients (235 with DM) with deferred revascularization according to fractional flow reserve (> 0.80). A comprehensive physiological evaluation including coronary flow reserve (CFR), index of microcirculatory resistance, and fractional flow reserve was performed at the time of revascularization deferral. The median values of the CFR (2.88), fractional flow reserve (0.88), and index of microcirculatory resistance (17.85) were used to classify patients into high- or low-index groups. The primary outcome was the patient-oriented composite outcome (POCO) at 5 years, comprising all-cause death, any myocardial infarction, and any revascularization.

RESULTS

Compared with the non-DM population, the DM population showed higher risk of POCO (HR, 2.49; 95%CI, 1.64-3.78; P<.001). In the DM population, the low-CFR group had a higher risk of POCO than the high-CFR group (HR, 3.22; 95%CI, 1.74-5.97; P <.001). In contrast, CFR values could not differentiate the risk of POCO in the non-DM population. There was a significant interaction between CFR and the presence of DM regarding the risk of POCO (P for interaction=.025). Independent predictors of POCO were a low CFR and family history of coronary artery disease in the DM population and percent diameter stenosis and multivessel disease in the non-DM population.

CONCLUSIONS

The association between coronary physiological indices and clinical outcomes differs according to the presence of DM. In deferred patients, CFR is the most important prognostic factor in patients with DM, but not in those without DM.

Moderate Hypothermia Modifies Coronary Hemodynamics and Endothelium-Dependent Vasodilation in a Porcine Model of Temperature Management

Background Hypothermia has been associated with therapeutic benefits including reduced mortality and better neurologic outcomes in survivors of cardiac arrest. However, undesirable side effects have been reported in patients undergoing coronary interventions. Using a large animal model of temperature management, we aimed to describe how temperature interferes with the coronary vasculature. Methods and Results Coronary hemodynamics and endothelial function were studied in 12 pigs at various core temperatures. Left circumflex coronary artery was challenged with intracoronary nitroglycerin, bradykinin, and adenosine at normothermia (38°C) and mild hypothermia (34°C), followed by either rewarming (38°C; n=6) or moderate hypothermia (MoHT; 32°C, n=6). Invasive coronary hemodynamics by Doppler wire revealed a slower coronary blood velocity at 32°C in the MoHT protocol (normothermia 20.2±11.2 cm/s versus mild hypothermia 18.7±4.3 cm/s versus MoHT 11.3±5.3 cm/s, P=0.007). MoHT time point was also associated with high values of hyperemic microvascular resistance (>3 mm Hg/cm per second) (normothermia 2.0±0.6 mm Hg/cm per second versus mild hypothermia 2.0±0.8 mm Hg/cm per second versus MoHT 3.4±1.6 mm Hg/cm per second, P=0.273). Assessment of coronary vasodilation by quantitative coronary analysis showed increased endothelium-dependent (bradykinin) vasodilation at 32°C when compared with normothermia (normothermia 6.96% change versus mild hypothermia 9.01% change versus MoHT 25.42% change, P=0.044). Results from coronary reactivity in vitro were in agreement with angiography data and established that endothelium-dependent relaxation in MoHT completely relies on NO production. Conclusions In this porcine model of temperature management, 34°C hypothermia and rewarming (38°C) did not affect coronary hemodynamics or endothelial function. However, 32°C hypothermia altered coronary vasculature physiology by slowing coronary blood flow, increasing microvascular resistance, and exacerbating endothelium-dependent vasodilatory response.

Noninvasive Microvascular Indices Reveal Peripheral Vascular Abnormalities in Patients With Suspected Coronary Microvascular Dysfunction

BACKGROUND

Reactive hyperemia peripheral arterial tonometry and flow-mediated dilation are common noninvasive measures of peripheral vascular function. However, their relationship with the coronary circulation, particularly in coronary microvascular dysfunction (CMD), is unclear. Therefore, the purpose of this study is to compare these noninvasive measurements with coronary microvascular function after endothelial-independent, endothelial-dependent, and sympathetically mediated pharmacologic hyperemia.

METHODS

Forty-seven patients with suspected CMD completed peripheral and coronary assessments. The reactive hyperemia index was collected using the EndoPAT2000 device, whereas a subset of patients (n = 28) completed brachial artery flow-mediated dilation using duplex ultrasound. Coronary microvascular function was quantified using the resistance and flow responses to intravenous adenosine (140 μg/kg/min), dobutamine (40 μg/kg/min), and intracoronary acetylcholine (100 μg). Abnormal coronary microvascular responses to adenosine and/or acetylcholine were used to define CMD.

RESULTS

The reactive hyperemia index (No CMD: 0.85 ± 0.23 vs CMD: 0.61 ± 0.26, P < 0.05) and flow-mediated dilation (No CMD: 7.2 ± 2.3 vs CMD: 4.8 ± 3.1; P < 0.05) were attenuated in patients with CMD. Whereas the reactive hyperemia index was correlated with the resistance and flow responses to dobutamine (ρ = -0.44 and ρ = 0.39, respectively; P < 0.05), flow-mediated dilation was correlated with the resistance responses to both adenosine (ρ = -0.48; P < 0.05) and acetylcholine (ρ = -0.66; P < 0.05). Lastly, the reactive hyperemia index and flow-mediated dilation had sensitivities of 80% and 69% and specificities of 71% and 93%, respectively, for identifying patients with CMD.

CONCLUSIONS

Peripheral vascular function is attenuated in CMD, and noninvasive measurements are associated with coronary responses to pharmaceutical stimulation.

Ischemia and No Obstructive Coronary Artery Disease: Prevalence and Correlates of Coronary Vasomotion Disorders

BACKGROUND

Determine the prevalence and correlates of microvascular and vasospastic angina in patients with symptoms and signs of ischemia but no obstructive coronary artery disease (INOCA).

METHODS

Three hundred ninety-one patients with angina were enrolled at 2 regional centers over 12 months from November 2016 (NCT03193294). INOCA subjects (n=185; 47%) had more limiting dyspnea (New York Heart Association classification III/IV 54% versus 37%; odds ratio [OR], 2.0 [1.3-3.0]; P=0.001) and were more likely to be female (68% INOCA versus 38% in coronary artery disease; OR, 1.9 [1.5 to 2.5]; P<0.001) but with lower cardiovascular risk scores (ASSIGN score median 20% versus 24%; P=0.003). INOCA subjects had similar burden of angina (Seattle Angina Questionnaire) but reduced quality of life compared with coronary artery disease; subjects (EQ5D-5 L index 0.60 versus 0.65 units; P=0.041).

RESULTS

An interventional diagnostic procedure with reference invasive tests including coronary flow reserve, microvascular resistance, and vasomotor responses to intracoronary acetylcholine (vasospasm provocation) was performed in 151 INOCA subjects. Overall, 78 (52%) had isolated microvascular angina, 25 (17%) had isolated vasospastic angina, 31 (20%) had both, and 17 (11%) had noncardiac chest pain. Regression analysis showed inducible ischemia on treadmill testing (OR, 7.5 [95% CI, 1.7-33.0]; P=0.008) and typical angina (OR, 2.7 [1.1-6.6]; P=0.032) were independently associated with microvascular angina. Female sex tended to associate with a diagnosis of microvascular angina although this was not significant (OR, 2.7 [0.9-7.9]; P=0.063). Vasospastic angina was associated with smoking (OR, 9.5 [2.8-32.7]; P<0.001) and age (OR, 1.1 per year, [1.0-1.2]; P=0.032].

CONCLUSIONS

Over three quarters of patients with INOCA have identifiable disorders of coronary vasomotion including microvascular and vasospastic angina. These patients have comparable angina burden but reduced quality of life compared to patients with obstructive coronary artery disease. Microvascular angina and vasospastic angina are distinct disorders that may coexist but differ in associated clinical characteristics, symptoms, and angina severity.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT03193294.

Reappraisal of Ischemic Heart Disease

In recent years, it has become apparent that coronary microvascular dysfunction plays a pivotal pathogenic role in angina pectoris. Functional and structural mechanisms can affect the physiological function of the coronary microvasculature and lead to myocardial ischemia in people without coronary atheromatous disease and also in individuals with obstructive coronary artery disease. Abnormal dilatory responses of the coronary microvessels, coronary microvascular spasm, and extravascular compressive forces have been identified as pathogenic mechanisms in both chronic and acute forms of ischemic heart disease. The condition characterized by anginal symptoms and evidence of myocardial ischemia triggered by coronary microvascular dysfunction, in the absence of obstructive coronary disease, is known as microvascular angina. The concept of microvascular angina, however, may extend further to include patients with obstructive coronary artery disease and individuals with angina after coronary revascularization or heart transplantation because coronary microvascular dysfunction contributes to myocardial ischemia in many such patients. Patients with microvascular angina constitute a sizeable proportion of all cases of stable angina undergoing diagnostic coronary angiography and of those with persisting angina after successful coronary revascularization. Coronary microvascular dysfunction is also often responsible for angina in individuals with cardiomyopathy and heart valve disease as well as acute coronary syndrome cases such as Takotsubo syndrome and myocardial infarction with no obstructive coronary artery disease. Patients with stable microvascular angina present typically with effort or rest chest pain and a reduced coronary flow reserve or microvascular spasm. This condition, which affects women and men, can markedly impair quality of life and prognosis and represents a substantial cost burden to healthcare systems and individuals alike. In recent years, progress in the diagnosis of myocardial ischemia and the use of tests to investigate functional and structural causes for a reduced coronary flow reserve and microvascular spasm have allowed the identification of an increased number of cases of microvascular angina in everyday clinical practice. Although some of the available anti-anginal drugs may be helpful, treatment of coronary microvascular dysfunction remains a major challenge. The present article discusses the fundamental role that coronary microvascular dysfunction plays in the pathogenesis of ischemic heart disease, the clinical characteristics of patients presenting with microvascular angina, and possible diagnostic and therapeutic strategies.

Diagnostic Approach to Patients with Stable Angina and No Obstructive Coronary Arteries

The diagnosis of microvascular angina (MVA) is usually considered in patients presenting with angina symptoms and evidence of MI on non-invasive stress tests but normal coronary arteries at angiography. A definitive diagnosis of MVA, however, would require the presence of coronary microvascular dysfunction. Several invasive (e.g. intracoronary Doppler wire recording and thermodilution) and non-invasive (e.g. PET, cardiac MRI, transthoracic Doppler echocardiography) methods can be applied to obtain a diagnosis. Both endothelium-dependent and -independent coronary microvascular dilator function, as well as increased microvascular constrictor activity, should be investigated. The main issues in the assessment of clinical and diagnostic findings in patients with suspected MVA are discussed and a diagnostic approach is suggested.

Automated Pixel-Wise Quantitative Myocardial Perfusion Mapping by CMR to Detect Obstructive Coronary Artery Disease and Coronary Microvascular Dysfunction: Validation Against Invasive Coronary Physiology

OBJECTIVES

This study sought to assess the performance of cardiovascular magnetic resonance (CMR) myocardial perfusion mapping against invasive coronary physiology reference standards for detecting coronary artery disease (CAD, defined by fractional flow reserve [FFR] ≤0.80), microvascular dysfunction (MVD) (defined by index of microcirculatory resistance [IMR] ≥25) and the ability to differentiate between the two.

BACKGROUND

Differentiation of epicardial (CAD) and MVD in patients with stable angina remains challenging. Automated in-line CMR perfusion mapping enables quantification of myocardial blood flow (MBF) to be performed rapidly within a clinical workflow.

METHODS

Fifty patients with stable angina and 15 healthy volunteers underwent adenosine stress CMR at 1.5T with quantification of MBF and myocardial perfusion reserve (MPR). FFR and IMR were measured in 101 coronary arteries during subsequent angiography.

RESULTS

Twenty-seven patients had obstructive CAD and 23 had nonobstructed arteries (7 normal IMR, 16 abnormal IMR). FFR positive (epicardial stenosis) areas had significantly lower stress MBF (1.47 ± 0.48 ml/g/min) and MPR (1.75 ± 0.60) than FFR-negative IMR-positive (MVD) areas (stress MBF: 2.10 ± 0.35 ml/g/min; MPR: 2.41 ± 0.79) and normal areas (stress MBF: 2.47 ± 0.50 ml/g/min; MPR: 2.94 ± 0.81). Stress MBF ≤1.94 ml/g/min accurately detected obstructive CAD on a regional basis (area under the curve: 0.90; p < 0.001). In patients without regional perfusion defects, global stress MBF <1.82 ml/g/min accurately discriminated between obstructive 3-vessel disease and MVD (area under the curve: 0.94; p < 0.001).

CONCLUSIONS

This novel automated pixel-wise perfusion mapping technique can be used to detect physiologically significant CAD defined by FFR, MVD defined by IMR, and to differentiate MVD from multivessel coronary disease. A CMR-based diagnostic algorithm using perfusion mapping for detection of epicardial disease and MVD warrants further clinical validation.