Catheter-Based Measurements of Absolute Coronary Blood Flow and Microvascular Resistance: Feasibility, Safety, and Reproducibility in Humans

Angiography-Derived Microcirculatory Resistance in Detecting Microvascular Obstruction and Predicting Heart Failure After STEMI

BACKGROUND

Microvascular obstruction (MVO) is associated with heart failure (HF) following ST-segment-elevation myocardial infarction. Angiography-derived microcirculatory resistance (AMR), a wire- and adenosine-free measure, may facilitate early assessment of microvascular function post-primary percutaneous coronary intervention. This study aimed to evaluate the ability of AMR to detect MVO and its prognostic value for predicting HF in patients with ST-segment-elevation myocardial infarction post-primary percutaneous coronary intervention.

METHODS

Patients with consecutive ST-segment-elevation myocardial infarction undergoing primary percutaneous coronary intervention with a cardiac magnetic resonance examination 2 to 7 days post-procedure between April 2016 and February 2023 were retrospectively reviewed. AMR was computed from coronary angiography. MVO was identified and quantified via cardiac magnetic resonance. The end point was new-onset HF during follow-up.

RESULTS

Overall, 475 patients (aged 56.8±11.7 years; 399 men) were included. The area under the curve for AMR to detect MVO was 0.821 (95% CI, 0.782-0.859), with an optimal cutoff value of 2.7 mm Hg*s/cm. During a median follow-up of 37.3 months, 121 (25.5%) patients developed HF. AMR, whether as a continuous (per 0.5-mm Hg*s/cm increase; hazard ratio, 1.29 [95% CI, 1.10-1.52]; P=0.002) or categorical (AMR >2.7 mm Hg*s/cm; hazard ratio, 2.15 [95% CI, 1.43-3.22]; P<0.001) variable, was independently associated with HF after adjusting for traditional risk factors (age, symptom-to-balloon time, left anterior descending coronary artery, and ejection fraction) and late gadolinium enhancement-cardiac magnetic resonance parameters. AMR improved prognostication over traditional risk factors and late gadolinium enhancement-cardiac magnetic resonance parameters (net reclassification improvement, 0.533; P<0.001; integrative discrimination index, 0.023; P=0.005).

CONCLUSIONS

AMR showed good diagnostic performance in detecting MVO and was an independent and incremental predictor of HF in patients with ST-segment-elevation myocardial infarction post-primary percutaneous coronary intervention.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Left Ventricular Unloading in Nonischemic Dilated Cardiomyopathy Improves Coronary Haemodynamic Reserve

BACKGROUND

The Impella CP is a catheter-based ventricular assist device used in the management of cardiogenic shock and to support high-risk percutaneous coronary interventions (PCI). Despite its growing use, the effects of Impella CP on coronary flow dynamics as measured by intracoronary continuous thermodilution have not been fully quantified.

AIMS

This study aimed to evaluate the impact of percutaneous ventricular unloading (PVU) with Impella CP on coronary flow reserve (CFR) and microvascular resistance reserve (MRR) in patients with severe nonischemic dilated cardiomyopathy undergoing intracoronary infusion of autologous bone-marrow derived mononuclear cells (BMMNCs).

METHODS

Coronary flow (Q) was assessed using intracoronary continuous thermodilution both at rest (Qrest) and during hyperemia (Qhyper) before and after PVU with the Impella CP. Measurements were performed in the left anterior descending (LAD) artery using a dedicated pressure/thermistor coronary guidewire. CFR and MRR were calculated post-hoc.

RESULTS

Nine patients underwent investigation with continuous thermodilution. Initiation of LV unloading with Impella CP resulted in a significant increase in CFR (from 2.72 ± 0.76, to 3.9 ± 1.84, p = 0.049) and MRR (from 3.09 ± 0.97, to 4.50 ± 1.93 p = 0.022). A decrease in mean Qrest and an increase in mean Qhyper was also noted.

CONCLUSIONS

PVU with Impella CP led to a significant increase CFR and MRR, suggesting an improvement in coronary haemodynamic reserve. Further studies are needed to validate these findings in a larger patient population.

TRIAL REGISTRATION

Clinicaltrials. org: DCM Support NCT03572660.

Effect of sodium-glucose Co-transporter 2 inhibitors on coronary microcirculation

Coronary microvascular disease (CMVD) has emerged as a new target for the occurrence and development of heart failure treatment. Various indicators such as Index of Microvascular Resistance, Coronary Flow Reserve, Microvascular Resistance Reserve, Hyperemic Microvascular Resistance and Coronary Flow Velocity Reserve can be used to assess CMVD. Coronary microcirculation dysfunction is one of the important pathogenic mechanisms of heart failure. Sodium-Glucose Co-Transporter 2 (SGLT2) Inhibitors have been widely used in the treatment of various types of heart failure, but their specific pharmacological mechanisms are not yet fully understood. Studies have shown that SGLT2 inhibitors may be involved in the pathophysiology of CMVD by regulating cellular pathophysiological processes such as oxidative stress, mitochondrial function, energy metabolism, vascular genesis, and signalling pathways. Therefore, coronary microvascular dysfunction may be one of the treatment targets of using SGLT2 inhibitors in heart failure. Several animal experiments have found that SGLT2 inhibitors can improve microcirculatory dysfunction. However, the results of several clinical trials on the effects of SGLT2 inhibitors on coronary microcirculation have been different. Therefore, it is still lack of conclusive evidence on the effects of SGLT2 inhibitors on microcirculatory dysfunction. This review aims to summarize the completed and ongoing experiments regarding the effects of SGLT2 inhibitors on coronary microcirculation, in order to better elucidate the impact of SGLT2 inhibitors on microcirculation. It seeks to provide valuable information for the pharmacological mechanisms of SGLT2 inhibitors, the study of diseases related to coronary microcirculation disorders, and the treatment of heart failure.

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

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

Diagnosis and Management of Acute Coronary Syndrome Patients Without Obstructive Epicardial Stenosis

PURPOSE OF REVIEW

What is the pathophysiology and clinical findings as well as management of patients presenting with INOCA/MINOCA (Ischemia/Myocardial Infarction with Non-Obstructive Coronary Arteries).

RECENT FINDINGS

INOCA/MINOCA has a complex pathophysiology. In this review article, we aim to summarize the complex pathophysiology and clinical diagnosis, and review the current management options.

Evolution of Coronary Microvascular Dysfunction Prevalence over Time and Across Diagnostic Modalities in Patients with ANOCA: A Systematic Review

Background: A considerable number of patients with angina undergo invasive coronary angiography, which might reveal non-obstructive coronary arteries (ANOCA). In this setting, they might have coronary microvascular disease (CMD). Its prevalence significantly varies in the literature. This systematic review aims to document the prevalence of CMD over time according to the diagnostic modalities. Methods: A systematic literature review was conducted using PubMed, the Cochrane Library, and Embase, covering publications from inception to 1 May 2024. Among 1471 identified articles, 297 full-text articles were assessed for eligibility. All studies reporting the prevalence of CMD in ANOCA patients based on invasive coronary artery (ICA), positron emission tomography-computed tomography (PET-CT), transthoracic echocardiography (TTE), or cardiac magnetic resonance (CMR) were included. Results: The review included 53 studies (published between 1998 and 2024), encompassing a total of 16,602 patients. Of these studies, 23 used ICA, 15 used PET-CT, 8 used TTE, and 7 used CMR. A statistically significant increase in CMD prevalence over time was observed across all diagnostic modalities (p < 0.05), except for PET-CT, which showed a consistent and stable prevalence over time. Notably, the prevalence rates from all of the diagnostic methods converged towards the 50% prevalence detected by PET-CT. Conclusions: The prevalence of CMD in patients with ANOCA is subject to debate. However, the current data suggest that regardless of the diagnostic method used, the most recent studies tend to converge towards a prevalence value of 50%, which has been consistently reported by PET-CT from the beginning.

Vascular Remodeling in Coronary Microvascular Dysfunction

BACKGROUND

Approximately one-half of the patients with angina and nonobstructive coronary artery disease (ANOCA) have evidence of coronary microvascular dysfunction (CMD).

OBJECTIVES

This study aims to characterize patients with ANOCA by measuring their minimal microvascular resistance and to examine the pattern of vascular remodeling associated with these measurements.

METHODS

The authors prospectively included patients with ANOCA undergoing continuous thermodilution assessment. Lumen volume and vessel-specific myocardial mass were quantified using coronary computed tomography angiography (CTA). CMD was defined as coronary flow reserve <2.5 and high minimal microvascular resistance as >470 WU.

RESULTS

A total of 153 patients were evaluated; 68 had CMD, and 22 of them showed high microvascular resistance. In patients with CMD, coronary flow reserve was 1.9 ± 0.38 vs 3.2 ± 0.81 in controls (P < 0.001). Lumen volume was significantly correlated with minimal microvascular resistance (r = -0.59 [95% CI: -0.45 to -0.71]; P < 0.001). In patients with CMD and high microvascular resistance, lumen volume was 40% smaller than in controls (512.8 ± 130.3 mm3 vs 853.2 ± 341.2 mm3; P < 0.001). Epicardial lumen volume assessed by coronary CTA was independently associated with minimal microvascular resistance (P < 0.001). The predictive capacity of lumen volume from coronary CTA for detecting high microvascular resistance showed an area under the curve of 0.79 (95% CI: 0.69-0.88).

CONCLUSIONS

Patients with CMD and high minimal microvascular resistance have smaller epicardial vessels than those without CMD. Coronary CTA detected high minimal microvascular resistance with very good diagnostic capacity. Coronary CTA could potentially aid in the diagnostic pathway for patients with ANOCA.

Quantifying myocardial perfusion during MR-guided interventions without exogenous contrast agents: intra-arterial spin labeling

PURPOSE

To test intra-arterial spin labeling (iASL) using active guiding catheters for myocardial perfusion measurements during magnetic resonance (MR)-guided interventions in a pig study.

METHODS

In this work, a single-loop radiofrequency (RF) coil at the tip of a 6F active coronary catheter was used as a transmit coil for local spin labeling. The transmit magnetic RF field (B1) of the coil and the labeling efficiency were determined, and iASL was tested in two pigs after the catheter was engaged in the aortic root, the ostium of the left coronary artery (LCA) under MR-guidance. The iASL effect was assessed by the signal difference between spin-labeling On and control (spin-labeling OFF) images, and in a cross-correlation between ON/Off states of spin-labeling a binary labeling paradigm. In addition, quantitative myocardial perfusion was calculated from the iASL experiments.

RESULTS

The maximum B1 in the vicinity of the catheter coil was 2.1 µT. A strong local labeling effect with a labeling efficiency of 0.45 was achieved with iASL both in vitro and in vivo. In both pigs, the proximal myocardial segments supplied by the LCA showed significant labelling effect up to distances of 60 mm from the aortic root with a relative signal difference of (3.14 ± 2.89)% in the first and (3.50 ± 1.25)% in the second animal. The mean correlation coefficients were R = 0.63 ± 0.22 and 0.42 ± 0.16, respectively. The corresponding computed myocardial perfusion values in this region of the myocardium were similar to those obtained with contrast perfusion methods ((1.2 ± 1.1) mL/min/g and (0.8 ± 0.6) mL/min/g).

CONCLUSION

The proposed iASL method demonstrates the feasibility of selective myocardial perfusion measurements during MR-guided coronary interventions, which with further technical improvements may provide an alternative to exogenous contrast-based perfusion. Due to the invasive nature of the iASL method, it can potentially be used in concert with MRI-guided coronary angioplasty.

Development and validation of a novel angiography-derived index of absolute coronary blood flow and resistance

Intracoronary continuous thermodilution has been recently proposed as an invasive method to quantify absolute coronary flow (Qabs) and resistance (Rabs) in vivo. The aim of the present study is to develop and validate of a novel pressure-wire- and microcatheter-free surrogate of coronary flow and resistance derived from a standard coronary angiogram. Angiography derived coronary flow (Qangio) and resistance (Rangio) was prospectively validated in a two-center cohort of patients from Oxford Heart Centre and the Essex Cardiothoracic Centre. Qabs and Rabs were measured during resting and hyperemic conditions with continuous thermodilution using the Rayflow microcatheter. Qangio and Rangio were computed from the diagnostic coronary angiogram in a blinded fashion in resting and hyperemic conditions. A total of 62 patients and 115 vessels were included in the present analysis. The median Qabs at rest was 75 ml/min (53-95) and 151 ml/min (105-203) during hyperemia; Qangio at rest was 84 ml/min (66-108) and 154 ml/min (115-195) during hyperemia. There was a strong correlation between Qabs and Qangio (R = 0,72; p < 0.001, R = 0,86; p < 0.001 respectively) with satisfactory interclass correlation (0.841, 95% CI 0.509-0.957; p = 0.0003). The median Rabs was 1111 mmHg/(L/min) (830-1581.4) at rest and 454 mmHg/(L/min) (348-610) during hyperemia; angiographic resistance (Rangio) was 937.4 mmHg/(L/min) (695.4-1261.9) at rest and 492.4 mmHg/(L/min) (406-697) during hyperemia. There was a strong correlation between Rabs and Rangio in both conditions (R = 0,81; p < 0.001 and R = 0,78; p < 0.001 respectively). The was a good correlation between absolute coronary flow reserve (CFR) and angiography-derived CFR (R = 0,61; p < 0.001) and between absolute microvascular resistance reserve (MRR) and angiography-derived MRR (R = 0,49; p < 0.001).

A recurrent typical angina pectoris without any finding in coronary angiography: Microvascular angina

Key Clinical Message

Microvascular angina (MVA) can present with recurrent chest pain and normal coronary angiography. Recognizing MVA is crucial as it significantly impacts patient morbidity and mortality. Early diagnosis and management with antianginal medications are essential for improving outcomes and quality of life.

Abstract

Cardiovascular diseases are still the main cause of death in many parts of the world. Chest pain and dyspnea are always concerning due to the implications of cardiovascular disease. However, in patients with the involvement of the small coronary vessels (Microvascular Angina), symptoms might be recurrent and persistent despite the presence of normal coronary vessel evaluations. A 45-year-old man with a 25-year smoking history presented with recurrent chest pain, especially during physical activity, and mild shortness of breath. He was admitted, and a coronary angiography the next day appeared normal. However, a cardiac PET scan revealed the involvement of small coronary vessels not visible on angiography. The Patient was a 45-year-old man who presented with recurrent chest pain, more prominent during physical activity. He also had mild shortness of breath. The patient was admitted, and the next day, he underwent normal coronary angiography. The cardiac positron emission tomography (PET scan) showed the involvement of small coronary vessels that were not obvious on angiography.

Novel diagnostic approaches and management of coronary microvascular dysfunction

The mechanism underlying ischaemic heart disease (IHD) has been primarily attributed to obstructive coronary artery disease (CAD). However, non-obstructive coronary arteries are identified in >50% of patients undergoing elective coronary angiography, recently leading to growing interest in the investigation and management of angina/ischaemia with non-obstructive coronary arteries (ANOCA/INOCA). INOCA is an umbrella term encompassing a multiple spectrum of possible pathogenetic entities, including coronary vasomotor disorders which consist of two major endotypes: coronary microvascular dysfunction (CMD) and vasospastic angina. Both conditions can coexist and be associated with concomitant obstructive CAD. Particularly, CMD refers to myocardial ischaemia due to reduced vasodilatory capacity of coronary microcirculation secondary to structural remodelling or impaired resting microvascular tone (functional) or a combination of both. CMD is not a benign condition and is more prevalent in women presenting with chronic coronary syndrome compared to men. In this setting, an impaired coronary flow reserve has been associated with increased risk of major adverse cardiovascular events. ANOCA/INOCA patients also experience impaired quality of life and associated increased healthcare costs. Therefore, research in this scenario has led to better definition, classification, and prognostic stratification based on the underlying pathophysiological mechanisms. The development and validation of non-invasive imaging modalities, invasive coronary vasomotor function testing and angiography-derived indices provide a comprehensive characterisation of CMD. The present narrative review aims to summarise current data relating to the diagnostic approach to CMD and provides details on the sequence that therapeutic management should follow.

Changes in absolute coronary flow and microvascular resistance during exercise in patients with ANOCA

BACKGROUND

Whether saline-induced hyperaemia captures exercise-induced coronary flow regulation remains unknown.

AIMS

Through this study, we aimed to describe absolute coronary flow (Q) and microvascular resistance (Rμ) adaptation during exercise in participants with angina with non-obstructive coronary artery disease (ANOCA) and to explore the correlations between saline- and exercise-derived coronary flow reserve (CFR) and microvascular resistance reserve (MRR).

METHODS

Rμ, Q, CFR and MRR were assessed in the left anterior descending artery using continuous thermodilution with saline infusion at 10 mL/min (rest), 20 mL/min (hyperaemia) and finally at a 10 mL/min infusion rate during stress testing with a dedicated supine cycling ergometer. An incremental workload of 30 watts every two minutes was applied. A saline-derived CFR (CFRsaline) cutoff <2.5 was used to identify coronary microvascular dysfunction (CMD).

RESULTS

CFRsaline-defined CMD was observed in 53.3% of the participants (16/30). While cycling, these patients less of an ability to increase Q (7 [interquartile range [IQR] 30.5-103.0] vs 21 [IQR 5.8-45.0] mL/min/30 watts; p=0.01) due to a smaller decrease of Rμ (109 {IQR 32-286} vs 202 [IQR 102-379] Wood units [WU]/30 watts; p<0.01) as compared with the group with normal CFRsaline. In the overall population, CFRsaline and exercise-derived CFR (CFRexercise) were 2.70±0.90 and 2.85±1.54, respectively, with an agreement classification of 83.3%. A good correlation between saline and exercise techniques for both CFR (r=0.73; p<0.0001) and MRR (r=0.76; p<0.0001) was observed. Among participants with normal CFRsaline, 28.7% (4/14) had an impaired CFRexercise <2.5 at the peak of exercise due to a moderate and late decrease of Rμ.

CONCLUSIONS

Saline-induced hyperaemia provided a valid surrogate for exercise physiology independently of the absolute level of CFR and MRR, although exercise provided more granularity to evaluate adaptation among participants with exercise-related CMD.

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.

Continuous thermodilution and microvascular resistance reserve during the index procedure in acute coronary syndrome without obstructive coronary artery disease: A pilot study

BACKGROUND

In 5%-25% of non-ST-elevation acute coronary syndrome (NSTE-ACS) patients, coronary angiography reveals no obstructive coronary arteries (MINOCA). Coronary microvascular disease (CMD) is a potential causal pathophysiological mechanism in these patients and can be diagnosed by continuous thermodilution assessment. Recently, the microvascular resistance reserve (MRR) has been introduced as a novel index to assess the vasodilatory capacity of the microcirculation. However, continuous thermodilution and MRR have never been investigated in the acute setting in MINOCA patients and invasive assessment of the microcirculation in these patients are currently lacking.

AIMS

The objectives of the study were to investigate the incidence of CMD (MRR ≤ 2.7) in patients with MINOCA and to evaluate the feasibility and safety of continuous thermodilution-based assessment during index coronary angiography in the acute setting.

METHODS

This study was a prospective, observational, pilot study investigating coronary physiology in the acute setting in MINOCA patients. Patients admitted with a diagnosis of NSTE-ACS were eligible for inclusion.

RESULTS

In total, 19 MINOCA patients were included in this analysis; the mean age was 70 ± 9 years, and 79% were females. CMD was present in 6 patients (32%). Qrest was significantly higher in the MRR ≤ 2.7 group compared to the MRR > 2.7 group (0.076 [0.057-0.100] vs. 0.049 [0.044-0.071] L/min, p = 0.03). Rµ,rest was significantly lower in the MRR ≤ 2.7 group compared to the MRR > 2.7 group (1083 [710-1510] vs. 1563 [1298-1970] WU, p = 0.04). No periprocedural complications or hemodynamic instability have occurred during continuous thermodilution assessment during the index coronary angiography.

CONCLUSION

In patients admitted for MINOCA undergoing immediate coronary angiography, continuous thermodilution assessment and MRR are feasible and safe in the acute setting, and evidence of functional CMD could be observed in one-third of the MINOCA patients.

Microvascular resistance reserve before and after PCI: A serial FFR and [15O] H2O PET study

BACKGROUND AND AIMS

Microvascular Resistance Reserve (MRR) has recently been introduced as a microvasculature-specific index and hypothesized to be independent of coronary stenosis. The aim of this study was to investigate the change of MRR after percutaneous coronary intervention (PCI).

METHODS

In this post-hoc analysis from the PACIFC trials, symptomatic patients underwent [15O]H2O positron emission tomography (PET) and invasive fractional flow reserve (FFR) before and after revascularization. Coronary flow reserve (CFR) from PET and invasive FFR were used to calculate MRR.

RESULTS

Among 52 patients (87 % male, age 59.4 ± 9.4 years), 61 vessels with a median FFR of 0.71 (95 % confidence interval: 0.55 to 0.74) and a mean MRR of 3.80 ± 1.23 were included. Following PCI, FFR, hyperemic myocardial blood flow (hMBF) and CFR increased significantly (all p-values ≤0.001). MRR remained unchanged after PCI (3.80 ± 1.23 before PCI versus 3.60 ± 0.97 after PCI; p=0.23). In vessels with a pre-PCI, FFR ≤0.70 pre- and post-PCI MRR were 3.90 ± 1.30 and 3.73 ± 1.14 (p=0.56), respectively. Similar findings were observed for vessels with a FFR between 0.71 and 0.80 (pre-PCI MRR 3.70 ± 1.17 vs. post PCI MRR 3.48 ± 0.76, p=0.19).

CONCLUSIONS

Our study indicates that MRR, assessed using a hybrid approach of PET and invasive FFR, is independent of the severity of epicardial stenosis. These findings suggest that MRR is a microvasculature-specific parameter.

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.

Optimization of Absolute Coronary Blood Flow Measurements to Assess Microvascular Function: In Vivo Validation of Hyperemia and Higher Infusion Speeds

BACKGROUND

Reliable assessment of coronary microvascular function is essential. Techniques to measure absolute coronary blood flow are promising but need validation. The objectives of this study were: first, to validate the potential of saline infusion to generate maximum hyperemia in vivo. Second, to validate absolute coronary blood flow measured with continuous coronary thermodilution at high (40-50 mL/min) infusion speeds and asses its safety.

METHODS

Fourteen closed-chest sheep underwent absolute coronary blood flow measurements with increasing saline infusion speeds at different dosages under general anesthesia. An additional 7 open-chest sheep underwent these measurements with epicardial Doppler flow probes. Coronary flows were compared with reactive hyperemia after 45 s of coronary occlusion.

RESULTS

Twenty milliliters per minute of saline infusion induced a significantly lower hyperemic coronary flow (140 versus 191 mL/min; P=0.0165), lower coronary flow reserve (1.82 versus 3.21; P≤0.0001), and higher coronary resistance (655 versus 422 woods units; P=0.0053) than coronary occlusion. On the other hand, 30 mL/min of saline infusion resulted in hyperemic coronary flow (196 versus 192 mL/min; P=0.8292), coronary flow reserve (2.77 versus 3.21; P=0.1107), and coronary resistance (415 versus 422 woods units; P=0.9181) that were not different from coronary occlusion. Hyperemic coronary flow was 40.7% with 5 mL/min, 40.8% with 10 mL/min, 73.1% with 20 mL/min, 102.3% with 30 mL/min, 99.0% with 40 mL/min, and 98.0% with 50 mL/min of saline infusion when compared with postocclusive hyperemic flow. There was a significant bias toward flow overestimation (Bland-Altman: bias±SD, -73.09±30.52; 95% limits of agreement, -132.9 to -13.27) with 40 to 50 mL/min of saline. Occasionally, ischemic changes resulted in ventricular fibrillation (9.5% with 50 mL/min) at higher infusion rates.

CONCLUSIONS

Continuous saline infusion of 30 mL/min but not 20 mL/min induced maximal hyperemia. Absolute coronary blood flow measured with saline infusion speeds of 40 to 50 mL/min was not accurate and not safe.

Mixing properties of coronary infusion catheters assessed by in vitro experiments and computational fluid dynamics

Aims

Continuous infusion thermodilution is an established technique for the assessment of absolute coronary blood flow and microvascular resistance due to its proven accuracy and reproducibility. However, for this technique to yield reliable measurements, direct and homogenous mixing of injected saline and blood is mandatory. This study aimed to assess and compare the mixing properties of two different microcatheters, namely the Rayflow® (with sideholes for infusion) and the Finecross® catheter (single end-hole for infusion), which are commonly used in the catheterization laboratory.

Methods and results

The study employed three different methods to evaluate the mixing properties of the catheters. Firstly, a qualitative assessment of mixing was performed using ink injections in an in vitro bench model of a coronary artery. Secondly, in analogy to the human catheterization laboratory, mixing properties over the length of the coronary artery were assessed semi-quantitatively by temperature measurements in the bench model. Lastly, a quantitative assessment was performed by 3D computational fluid dynamics, where the standard deviation and entropy ratio of the temperature over the cross-section in the coronary artery model were calculated for both catheters.

Conclusion

All three evaluation methods demonstrated that the Rayflow catheter's specific design leads to a more optimal, homogeneous mixture of blood and saline over both the cross-section and length of a coronary vessel, as compared with the standard end-hole catheter.

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.

Comparison of bolus versus continuous thermodilution derived indices of microvascular dysfunction in revascularized coronary syndromes

Background

The assessment of coronary microvascular dysfunction (CMD) using invasive methods is a field of growing interest, however the preferred method remains debated. Bolus and continuous thermodilution are commonly used methods, but weak agreement has been observed in patients with angina with non-obstructive coronary arteries (ANOCA). This study examined their agreement in revascularized acute coronary syndromes (ACS) and chronic coronary syndromes (CCS) patients.

Objective

To compare bolus thermodilution and continuous thermodilution indices of CMD in revascularized ACS and CCS patients and assess their diagnostic agreement at pre-defined cut-off points.

Methods

Patients from two centers underwent paired bolus and continuous thermodilution assessments after revascularization. CMD indices were compared between the two methods and their agreements at binary cut-off points were assessed.

Results

Ninety-six patients and 116 vessels were included. The mean age was 64 ± 11 years, and 20 (21 %) were female. Overall, weak correlations were observed between the Index of Microcirculatory Resistance (IMR) and continuous thermodilution microvascular resistance (Rµ) (rho = 0.30p = 0.001). The median coronary flow reserve (CFR) from continuous thermodilution (CFRcont) and bolus thermodilution (CFRbolus) were 2.19 (1.76-2.67) and 2.55 (1.50-3.58), respectively (p < 0.001). Weak correlation and agreement were observed between CFRcont and CFRbolus (rho = 0.37, p < 0.001, ICC 0.228 [0.055-0.389]). When assessed at CFR cut-off values of 2.0 and 2.5, the methods disagreed in 41 (35 %) and 45 (39 %) of cases, respectively.

Conclusions

There is a significant difference and weak agreement between bolus and continuous thermodilution-derived indices, which must be considered when diagnosing CMD in ACS and CCS patients.

Measuring Absolute Coronary Flow and Microvascular Resistance by Thermodilution: JACC Review Topic of the Week

Diagnosing coronary microvascular dysfunction remains challenging, primarily due to the lack of direct measurements of absolute coronary blood flow (Q) and microvascular resistance (Rμ). However, there has been recent progress with the development and validation of continuous intracoronary thermodilution, which offers a simplified and validated approach for clinical use. This technique enables direct quantification of Q and Rμ, leading to precise and accurate evaluation of the coronary microcirculation. To ensure consistent and reliable results, it is crucial to follow a standardized protocol when performing continuous intracoronary thermodilution measurements. This document aims to summarize the principles of thermodilution-derived absolute coronary flow measurements and propose a standardized method for conducting these assessments. The proposed standardization serves as a guide to ensure the best practice of the method, enhancing the clinical assessment of the coronary microcirculation.

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.

Assessing the Impact of Prolonged Averaging of Coronary Continuous Thermodilution Traces

Continuous Thermodilution is a novel method of quantifying coronary flow (Q) in mL/min. To account for variability of Q within the cardiac cycle, the trace is smoothened with a 2 s moving average filter. This can sometimes be ineffective due to significant heart rate variability, ventricular extrasystoles, and deep inspiration, resulting in a fluctuating temperature trace and ambiguity in the location of the "steady state". This study aims to assess whether a longer moving average filter would smoothen any fluctuations within the continuous thermodilution traces resulting in improved interpretability and reproducibility on a test-retest basis. Patients with ANOCA underwent repeat continuous thermodilution measurements. Analysis of traces were performed at averages of 10, 15, and 20 s to determine the maximum acceptable average. The maximum acceptable average was subsequently applied as a moving average filter and the traces were re-analysed to assess the practical consequences of a longer moving average. Reproducibility was then assessed and compared to a 2 s moving average. Of the averages tested, only 10 s met the criteria for acceptance. When the data was reanalysed with a 10 s moving average filter, there was no significant improvement in reproducibility, however, it resulted in a 12% diagnostic mismatch. Applying a longer moving average filter to continuous thermodilution data does not improve reproducibility. Furthermore, it results in a loss of fidelity on the traces, and a 12% diagnostic mismatch. Overall, current practice should be maintained.

Coronary Microvascular Dysfunction in Patients With Heart Failure: Characterization of Patterns in HFrEF Versus HFpEF

BACKGROUND

Coronary microvascular dysfunction (CMD) is involved in heart failure (HF) onset and progression, independently of HF phenotype and obstructive coronary artery disease. Invasive assessment of CMD might provide insights into phenotyping and prognosis of patients with HF. We aimed to assess absolute coronary flow, absolute microvascular resistance, myocardial perfusion, coronary flow reserve, and microvascular resistance reserve in patients with HF with preserved ejection fraction and HF with reduced ejection fraction (HFrEF).

METHODS

Single-center, prospective study of 56 consecutive patients with de novo HF with nonobstructive coronary artery disease divided into HF with preserved ejection fraction (n=21) and HFrEF (n=35). CMD was invasively assessed by continuous intracoronary thermodilution and defined as coronary flow reserve <2.5. Left ventricular and left anterior descending artery-related myocardial mass was quantified by echocardiography and coronary computed tomography angiography. Myocardial perfusion (mL/min per g) was calculated as the ratio between absolute coronary flow and left anterior descending artery-related mass.

RESULTS

Patients with HFrEF showed a higher left ventricular and left anterior descending artery-related myocardial mass compared with HF with preserved ejection fraction (P<0.010). Overall, 52% of the study population had CMD, with a similar prevalence between the 2 groups. In HFrEF, CMD was characterized by lower absolute microvascular resistance and higher absolute coronary flow at rest (functional CMD; P=0.002). CMD was an independent predictor of a lower rate of left ventricular reverse remodeling at follow-up. In patients with HF with preserved ejection fraction, CMD was mainly due to higher absolute microvascular resistance and lower absolute coronary flow during hyperemia (structural CMD; P≤0.030).

CONCLUSIONS

Continuous intracoronary thermodilution allows the definition and characterization of patterns with distinct CMD in patients with HF and could identify patients with HFrEF with a higher rate of left ventricular reverse remodeling at follow-up.

Invasive Assessment of Coronary Microcirculation: A State-of-the-Art Review

A significant proportion of patients presenting with signs and symptoms of myocardial ischemia have no "significant" epicardial disease; thereby, the assessment of coronary microcirculation gained an important role in improving diagnosis and guiding therapy. In fact, coronary microvascular dysfunction (CMD) could be found in a large proportion of these patients, supporting both symptoms and signs of myocardial ischemia. However, CMD represents a diagnostic challenge for two main reasons: (1) the small dimension of the coronary microvasculature prevents direct angiographic visualization, and (2) despite the availability of specific diagnostic tools, they remain invasive and underused in the current clinical practice. For these reasons, CMD remains underdiagnosed, and most of the patients remain with no specific treatment and quality-of-life-limiting symptoms. Of note, recent evidence suggests that a "full physiology" approach for the assessment of the whole coronary vasculature may offer a significant benefit in terms of symptom improvement among patients presenting with ischemia and non-obstructive coronary artery disease. We analyze the pathophysiology of coronary microvascular dysfunction, providing the readers with a guide for the invasive assessment of coronary microcirculation, together with the available evidence supporting its use in clinical practice.

Effects of ticagrelor and prasugrel on coronary microcirculation in elective percutaneous coronary intervention

OBJECTIVE

To compare the effects of ticagrelor and prasugrel on absolute coronary blood flow (Q) and microvascular resistance (R) in patients with stable coronary artery disease (CAD) treated with elective percutaneous coronary intervention (PCI) (NCT05643586). Besides being at least as effective as prasugrel in inhibiting platelet aggregation, ticagrelor has been shown to have additional properties potentially affecting coronary microcirculation.

METHODS

We randomly assigned 50 patients to ticagrelor (180 mg) or prasugrel (60 mg) at least 12 hours before intervention. Continuous thermodilution was used to measure Q and R before and after PCI. Platelet reactivity was measured before PCI. Troponin I was measured before, 8 and 24 hours after PCI.

RESULTS

At baseline, fractional flow reserve, Q and R were similar in two study groups. Patients in the ticagrelor group showed higher post-PCI Q (242±49 vs 205±53 mL/min, p=0.015) and lower R values (311 (263, 366) vs 362 (319, 382) mm Hg/L/min, p=0.032). Platelet reactivity showed a negative correlation with periprocedural variation of Q values (r=-0.582, p<0.001) and a positive correlation with periprocedural variation of R values (r=0.645, p<0.001). The periprocedural increase in high-sensitivity troponin I was significantly lower in the ticagrelor compared with the prasugrel group (5 (4, 9) ng/mL vs 14 (10, 24) ng/mL, p<0.001).

CONCLUSIONS

In patients with stable CAD undergoing PCI, pretreatment with a loading dose of ticagrelor compared with prasugrel improves post-procedural coronary flow and microvascular function and seems to reduce the related myocardial injury.

Chinese expert consensus on the diagnosis and treatment of coronary microvascular diseases (2023 Edition)

Since the four working groups of the Chinese Society of Cardiology issued first expert consensus on coronary microvascular diseases (CMVD) in 2017, international consensus documents on CMVD have increased rapidly. Although some of these documents made preliminary recommendations for the diagnosis and treatment of CMVD, they did not provide classification of recommendations and levels of evidence. In order to summarize recent progress in the field of CMVD, standardize the methods and procedures of diagnosis and treatment, and identify the scientific questions for future research, the four working groups of the Chinese Society of Cardiology updated the 2017 version of the Chinese expert consensus on CMVD and adopted a series of measures to ensure the quality of this document. The current consensus has raised a new classification of CMVD, summarized new epidemiological findings for different types of CMVD, analyzed key pathological and molecular mechanisms, evaluated classical and novel diagnostic technologies, recommended diagnostic pathways and criteria, and therapeutic strategies and medications, for patients with CMVD. In view of the current progress and knowledge gaps of CMVD, future directions were proposed. It is hoped that this expert consensus will further expedite the research progress of CMVD in both basic and clinical scenarios.

Continuous Versus Bolus Thermodilution-Derived Coronary Flow Reserve and Microvascular Resistance Reserve and Their Association With Angina and Quality of Life in Patients With Angina and Nonobstructive Coronaries: A Head-to-Head Comparison

Background Coronary flow reserve (CFR) and microvascular resistance reserve (MRR) are physiological parameters to assess coronary microvascular dysfunction. CFR and MRR can be assessed using bolus or continuous thermodilution, and the correlation between these methods has not been clarified. Furthermore, their association with angina and quality of life is unknown. Methods and Results In total, 246 consecutive patients with angina and nonobstructive coronary arteries from the multicenter Netherlands Registry of Invasive Coronary Vasomotor Function Testing (NL-CFT) were investigated. The 36-item Short Form Health Survey Quality of Life and Seattle Angina questionnaires were completed by 153 patients before the invasive measurements. CFR and MRR were measured consecutively with bolus and continuous thermodilution. Mean continuous thermodilution-derived coronary flow reserve (CFRabs) was significantly lower than mean bolus thermodilution-derived coronary flow reserve (CFRbolus) (2.6±1.0 versus 3.5±1.8; P<0.001), with a modest correlation (ρ=0.305; P<0.001). Mean continuous thermodilution-derived microvascular resistance reserve (MRRabs) was also significantly lower than mean bolus thermodilution-derived MRR (MRRbolus) (3.1±1.1 versus 4.2±2.5; P<0.001), with a weak correlation (ρ=0.280; P<0.001). CFRbolus and MRRbolus showed no correlation with any of the angina and quality of life domains, whereas CFRabs and MRRabs showed a significant correlation with physical limitation (P=0.005, P=0.009, respectively) and health (P=0.026, P=0.012). In a subanalysis in patients in whom spasm was excluded, the correlation further improved (MRRabs versus physical limitation: ρ=0.363; P=0.041, MRRabs versus physical health: ρ=0.482; P=0.004). No association with angina frequency and stability was found. Conclusions Absolute flow measurements using continuous thermodilution to calculate CFRabs and MRRabs weakly correlate with, and are lower than, the surrogates CFRbolus and MRRbolus. Absolute flow parameters showed a relationship with physical complaints. No relationship with angina frequency and stability was found.

Coronary Vascular (DYS) Function and Invasive Physiology Assessment: Insights into Bolus and Continuous Thermodilution Methods

A considerable number of patients with angina or myocardial ischemia have no significant coronary artery disease on invasive angiography. In recent years, several steps towards a better comprehension of the pathophysiology of these conditions, angina or ischemia with non-obstructive coronary arteries (ANOCA/INOCA), have been made. Nevertheless, several gaps in knowledge still remain. This review is intended to provide a comprehensive overview of ANOCA and INOCA, with a particular focus on pathophysiology, recent diagnostic innovations, gaps in knowledge and treatment modalities.

Changes in absolute flow, myocardial resistance and FFR after chronic total occlusion percutaneous coronary intervention

BACKGROUND

Randomised studies of percutaneous coronary intervention (PCI) in patients with chronic total occlusion (CTO) have shown inconsistent outcomes, suggesting incomplete understanding of this cohort and their coronary physiology. To address this shortcoming, we designed a prospective observational study to measure the recovery of absolute coronary blood flow following successful CTO PCI Aims: We sought to identify patient and procedural characteristics associated with a favourable physiological outcome after CTO PCI.

METHODS

Consecutive patients with a CTO subtending viable myocardium underwent PCI utilising contemporary techniques and the hybrid algorithm. Immediately after PCI, and at 3-month follow-up, physiological measurements were performed utilising continuous thermodilution.

RESULTS

A total of 81 patients were included with a mean age of 63.6±8.9 years, and 66 (81.5%) were male. Physiological measurements of absolute coronary blood flow in the CTO vessel increased by 30% (p<0.001) and microvascular resistance reduced by 16% (p<0.001) from immediately post-CTO PCI to follow-up assessment. Fractional flow reserve increased by 0.02 (p=0.015) in the same period. Prior coronary artery bypass graft (CABG) and a higher estimated glomerular filtration rate (eGFR) were associated with a larger change in absolute flow. An extraplaque strategy was associated with a smaller change in absolute flow.

CONCLUSIONS

Post-CTO PCI, there is a continued augmentation in absolute coronary blood flow and reduction in microvascular resistance from baseline to follow-up at 3 months. Prior CABG and a higher baseline eGFR were predictors of a larger change in absolute coronary flow, whilst an extraplaque final wire path strategy predicted a smaller change. Lastly, the patient characteristics and comorbidities had a larger influence than procedural factors on the observed change in absolute flow.

Angiography-Derived and Sensor-Wire Methods to Assess Coronary Microvascular Dysfunction in Patients With Acute Myocardial Infarction

ST-segment elevation myocardial infarction (STEMI) treatment with primary percutaneous coronary intervention has dramatically impacted prognosis. However, despite satisfactory angiographic result, occurrence or persistence of coronary microvascular dysfunction after revascularization still affects long-term outcomes. The diagnostic and therapeutic value of understanding the status of coronary microcirculation is gaining attention in the cardiology community. However, current methods to assess microvascular function (namely, cardiac magnetic resonance and invasive wire-based coronary physiology) remain, at least in part, limited by technical and logistic aspects. On the other hand, angiography-based indices of microcirculatory resistance are emerging as valid and user-friendly tools with potential impact on prognostic stratification of patients with STEMI. This review provides an overview about conventional and novel methods to assess coronary microvascular dysfunction in patients with STEMI. The authors also provide a proposed procedural algorithm to facilitate optimal use of wire-based and angiography-based indices in the acute setting of STEMI.

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

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

Microvascular Resistance Reserve to Assess Microvascular Dysfunction in ANOCA Patients

BACKGROUND

Microvascular resistance reserve (MRR) is a new index to assess coronary microvascular (dys)function, which can be easily measured invasively using continuous thermodilution. In contrast to coronary flow reserve (CFR), MRR is independent of epicardial coronary disease and hemodynamic variations. Its measurement is accurate, reproducible, and operator independent.

OBJECTIVES

The aim of this study was to establish the range of normal values for MRR and to determine an optimal cutoff point.

METHODS

In this exploratory study in 214 patients with angina and no obstructive coronary artery disease, after excluding significant epicardial disease, all physiological parameters, such as fractional flow reserve, index of microvascular resistance, CFR, absolute blood flow, absolute microvascular resistance, and MRR, were measured. On the basis of concordant positive or concordant negative results of index of microvascular resistance and CFR, subgroups of patients were defined with high probability of either normal (n = 122) or abnormal (n = 24) microcirculatory function, and MRR was studied in these groups.

RESULTS

Mean MRR in the "normal" group was 3.4 compared with a mean MRR of 1.9 in the "abnormal" group; these values were significantly different between the groups. MRR >2.7 ruled out coronary microvascular dysfunction (CMD) with a certainty of 96%, whereas MRR <2.1 indicated the presence of CMD with a similar high certainty of 96%.

CONCLUSIONS

MRR is a suitable index to distinguish the presence or absence of CMD in patients with angina and no obstructive coronary artery disease. The present data indicate that an MRR of 2.7 virtually excludes the presence of CMD, while an MRR value <2.1 confirms its presence.

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.

Invasive coronary physiology in patients with angina and non-obstructive coronary artery disease: a consensus document from the coronary microvascular dysfunction workstream of the British Heart Foundation/National Institute for Health Research Partnership

Nearly half of all patients with angina have non-obstructive coronary artery disease (ANOCA); this is an umbrella term comprising heterogeneous vascular disorders, each with disparate pathophysiology and prognosis. Approximately two-thirds of patients with ANOCA have coronary microvascular disease (CMD). CMD can be secondary to architectural changes within the microcirculation or secondary to vasomotor dysfunction. An inability of the coronary vasculature to augment blood flow in response to heightened myocardial demand is defined as an impaired coronary flow reserve (CFR), which can be measured non-invasively, using imaging, or invasively during cardiac catheterisation. Impaired CFR is associated with myocardial ischaemia and adverse cardiovascular outcomes.The CMD workstream is part of the cardiovascular partnership between the British Heart Foundation and The National Institute for Health Research in the UK and comprises specialist cardiac centres with expertise in coronary physiology assessment. This document outlines the two main modalities (thermodilution and Doppler techniques) for estimation of coronary flow, vasomotor testing using acetylcholine, and outlines a standard operating procedure that could be considered for adoption by national networks. Accurate and timely disease characterisation of patients with ANOCA will enable clinicians to tailor therapy according to their patients' coronary physiology. This has been shown to improve patients' quality of life and may lead to improved cardiovascular outcomes in the long term.

Absolute coronary flow and microvascular resistance reserve in patients with severe aortic stenosis

BACKGROUND

Development of left ventricle (LV) hypertrophy in aortic stenosis (AS) is accompanied by adaptive coronary flow regulation. We aimed to assess absolute coronary flow, microvascular resistance, coronary flow reverse (CFR) and microvascular resistance reserve (MRR) in patients with and without AS.

METHODS

Absolute coronary flow and microvascular resistance were measured by continuous thermodilution in 29 patients with AS and 29 controls, without AS, matched for age, gender, diabetes and functional severity of epicardial coronary lesions. Myocardial work, total myocardial mass and left anterior descending artery (LAD)-specific mass were quantified by echocardiography and cardiac-CT.

RESULTS

Patients with AS presented a significantly positive LV remodelling with lower global longitudinal strain and global work efficacy compared with controls. Total LV myocardial mass and LAD-specific myocardial mass were significantly higher in patients with AS (p=0.001). Compared with matched controls, absolute resting flow in the LAD was significantly higher in the AS cohort (p=0.009), resulting into lower CFR and MRR in the AS cohort compared with controls (p<0.005 for both). No differences were found in hyperaemic flow and resting and hyperaemic resistances. Hyperaemic myocardial perfusion (calculated as the ratio between the absolute coronary flow subtended to the LAD, expressed in mL/min/g), but not resting, was significantly lower in the AS group (p=0.035).

CONCLUSIONS

In patients with severe AS and non-obstructive coronary artery disease, with the progression of LV hypertrophy, the compensatory mechanism of increased resting flow maintains adequate perfusion at rest, but not during hyperaemia. As a consequence, both CFR and MRR are significantly impaired.

Contemporary and future invasive coronary vasomotor function testing and treatment in patients with ischaemia with no obstructive coronary arteries

In the current review, we emphasize the importance of diagnostics and therapy in patients with ischaemia with no obstructive coronary arteries (INOCA). The importance of the diagnostic coronary function test (CFT) procedure is described, including future components including angiography-derived physiology and invasive continuous thermodilution. Furthermore, the main components of treatment are discussed. Future directions include the national registration ensuring a high quality of INOCA care, besides a potential source to improve our understanding of pathophysiology in the various phenotypes of coronary vascular dysfunction, the diagnostic CFT procedure, and treatment.

Invasive evaluation of coronary microvascular dysfunction

Coronary microvascular dysfunction (CMD) is a prevalent cause of ischemic heart disease and is associated with poorer quality of life and worse patient outcomes. Both functional and structural abnormalities of the microcirculation can generate ischemia in the absence of epicardial stenosis or worsen concomitant obstructive coronary artery disease (CAD). The invasive assessment of CMD allows for the evaluation of the entirety of the coronary vascular tree, from the large epicardial vessels to the microcirculation, and enables the study of vasomotor function through vasoreactivity testing. The standard evaluation of CMD includes vasomotor assessment with acetylcholine, as well as flow- and resistance-derived indices calculated with either thermodilution or Doppler guidewires. Tailored treatment based upon the information gathered from the invasive evaluation of CMD has been demonstrated to reduce the burden of angina; therefore, a thorough understanding of these procedures is warranted with the aim of improving the quality of life of the patient. This review summarizes the most widespread approaches for the invasive evaluation of CMD, with a focus on patients with ischemia and non-obstructive CAD.

Impact of Serial Coronary Stenoses on Various Coronary Physiologic Indices

BACKGROUND

Determining the functional significance of each individual coronary lesion in patients with serial coronary stenoses is challenging. It has been proposed that nonhyperemic pressure ratios, such as the instantaneous wave free ratio (iFR) and the ratio of resting distal to proximal coronary pressure (Pd/Pa) are more accurate than fractional flow reserve (FFR) because autoregulation should maintain stable resting coronary flow and avoid hemodynamic interdependence (cross-talk) that occurs during hyperemia. This study aimed to measure the degree of hemodynamic interdependence of iFR, resting Pd/Pa, and FFR in a porcine model of serial coronary stenosis.

METHODS

In 6 anesthetized female swine, 381 serial coronary stenoses were created in the left anterior descending artery using 2 balloon catheters. The degree of hemodynamic interdependence was calculated by measuring the absolute changes in iFR, resting Pd/Pa, and FFR across the fixed stenosis as the severity of the other stenosis varied.

RESULTS

The hemodynamic interdependence of iFR, resting Pd/Pa, and FFR was 0.039±0.048, 0.021±0.026, and 0.034±0.034, respectively (all P<0.001). When the functional significance of serial stenoses was less severe (0.70-0.90 for each index), the hemodynamic interdependence was 0.009±0.020, 0.007±0.013, and 0.017±0.022 for iFR, resting Pd/Pa, and FFR, respectively (all P<0.001). However, in more severe serial coronary stenoses (<0.60 for each index), hemodynamic interdependence was 0.060±0.050, 0.037±0.030, and 0.051±0.037 for iFR, resting Pd/Pa, and FFR, respectively (all P<0.001).

CONCLUSIONS

When assessing serial coronary stenoses, nonhyperemic pressure ratios are affected by hemodynamic interdependence. When the functional significance of serial coronary stenoses is severe, the effect is similar to that which is seen with FFR.

Human coronary microvascular contractile dysfunction associates with viable synthetic smooth muscle cells

AIMS

Coronary microvascular smooth muscle cells (SMCs) respond to luminal pressure by developing myogenic tone (MT), a process integral to the regulation of microvascular perfusion. The cellular mechanisms underlying poor myogenic reactivity in patients with heart valve disease are unknown and form the focus of this study.

METHODS AND RESULTS

Intramyocardial coronary micro-arteries (IMCAs) isolated from human and pig right atrial (RA) appendage and left ventricular (LV) biopsies were studied using pressure myography combined with confocal microscopy. All RA- and LV-IMCAs from organ donors and pigs developed circa 25% MT. In contrast, 44% of human RA-IMCAs from 88 patients with heart valve disease had poor (<10%) MT yet retained cell viability and an ability to raise cytoplasmic Ca2+ in response to vasoconstrictor agents. Comparing across human heart chambers and species, we found that based on patient medical history and six tests, the strongest predictor of poor MT in IMCAs was increased expression of the synthetic marker caldesmon relative to the contractile marker SM-myosin heavy chain. In addition, high resolution imaging revealed a distinct layer of longitudinally aligned SMCs between ECs and radial SMCs, and we show poor MT was associated with disruptions in these cellular alignments.

CONCLUSION

These data demonstrate the first use of atrial and ventricular biopsies from patients and pigs to reveal that impaired coronary MT reflects a switch of viable SMCs towards a synthetic phenotype, rather than a loss of SMC viability. These arteries represent a model for further studies of coronary microvascular contractile dysfunction.

Automation of intracoronary continuous thermodilution for absolute coronary flow and microvascular resistance measurements

AIM

Microvascular resistance reserve (MRR) as derived from continuous intracoronary thermodilution specifically quantifies microvasculature function. As originally described, the technique necessitates reinstrumentation of the artery and manual reprogramming of the infusion pump when performing resting and hyperemic measurements. To simplify and to render this procedure operator-independent, we developed a fully automated method. The aim of the present study is to validate the automated procedure against the originally described one.

METHODS AND RESULTS

For the automated procedure, an infusion pump was preprogrammed to allow paired resting-hyperemic thermodilution assessment without interruption. To validate the accuracy of this new approach, 20 automated measurements were compared to those obtained in the same vessels with conventional paired resting-hyperemic thermodilution measurements (i.e., with a sensor pullback at each infusion rate and manual reprogramming of the infusion pump).  A close correlation between the conventional and the automated measuring technique was found for resting flow (Q_rest : r = 0.89, mean bias = 2.52; SD = 15.47), hyperemic flow (Q_hyper : r = 0.88, mean bias = -2.65; SD = 27.96), resting microvascular resistance (R_μ-rest : r = 0.90, mean bias = 52.14; SD = 228.29), hyperemic microvascular resistance R_μ-hyper : r = 0.92, mean bias = 12.95; SD = 57.80), and MRR (MRR: r = 0.89, mean bias = 0.04, SD = 0.59).  Procedural time was significantly shorter with the automated method (5'25″ ± 1'23″ vs. 4'36″​​​​​​​ ± 0'33″​​​​​​​, p = 0.013).

CONCLUSION

Continuous intracoronary thermodilution-derived measurements of absolute flow, absolute resistance, and MRR can be fully automated. This further shortens and simplifies the procedure when performing paired resting-hyperemic measurements.

Methods to evaluate vascular function: a crucial approach towards predictive, preventive, and personalised medicine

Endothelium, the gatekeeper of our blood vessels, is highly heterogeneous and a crucial physical barrier with the ability to produce vasoactive and protective mediators under physiological conditions. It regulates vascular tone, haemostasis, vascular inflammation, remodelling, and angiogenesis. Several cardio-, reno-, and cerebrovascular diseases begin with the dysfunction of endothelial cells, and more recently, COVID-19 was also associated with endothelial disease highlighting the need to monitor its function towards prevention and reduction of vascular dysfunction. Endothelial cells are an important therapeutic target in predictive, preventive, and personalised (3P) medicine with upmost importance in vascular diseases. The development of novel non-invasive techniques to access endothelial dysfunction for use in combination with existing clinical imaging modalities provides a feasible opportunity to reduce the burden of vascular disease. This review summarises recent advances in the principles of endothelial function measurements. This article presents an overview of invasive and non-invasive techniques to determine vascular function and their major advantages and disadvantages. In addition, the article describes mechanisms underlying the regulation of vascular function and dysfunction and potential new biomarkers of endothelial damage. Recognising these biomarkers is fundamental towards a shift from reactive to 3P medicine in the vascular field. Identifying vascular dysfunction earlier with non-invasive or minimally invasive techniques adds value to predictive diagnostics and targeted prevention (primary, secondary, tertiary care). In addition, vascular dysfunction is a potential target for treatments tailored to the person.

Modelling coronary flows: impact of differently measured inflow boundary conditions on vessel-specific computational hemodynamic profiles

BACKGROUND AND OBJECTIVES

The translation of hemodynamic quantities based on wall shear stress (WSS) or intravascular helical flow into clinical biomarkers of coronary atherosclerotic disease is still hampered by the assumptions/idealizations required by the computational fluid dynamics (CFD) simulations of the coronary hemodynamics. In the resulting budget of uncertainty, inflow boundary conditions (BCs) play a primary role. Accordingly, in this study we investigated the impact of the approach adopted for in vivo coronary artery blood flow rate assessment on personalized CFD simulations where blood flow rate is used as inflow BC.

METHODS

CFD simulations were carried out on coronary angiograms by applying personalized inflow BCs derived from four different techniques assessing in vivo surrogates of flow rate: continuous thermodilution, intravascular Doppler, frame count-based 3D contrast velocity, and diameter-based scaling law. The impact of inflow BCs on coronary hemodynamics was evaluated in terms of WSS- and helicity-based quantities.

RESULTS

As main findings, we report that: (i) coronary flow rate values may differ based on the applied flow derivation technique, as continuous thermodilution provided higher flow rate values than intravascular Doppler and diameter-based scaling law (p = 0.0014 and p = 0.0023, respectively); (ii) such intrasubject differences in flow rate values lead to different surface-averaged values of WSS magnitude and helical blood flow intensity (p<0.0020); (iii) luminal surface areas exposed to low WSS and helical flow topological features showed robustness to the flow rate values.

CONCLUSIONS

Although the absence of a clinically applicable gold standard approach prevents a general recommendation for one coronary blood flow rate derivation technique, our findings indicate that the inflow BC may impact computational hemodynamic results, suggesting that a standardization would be desirable to provide comparable results among personalized CFD simulations of the coronary hemodynamics.

Coronary microvascular disease: The "Meeting Point" of Cardiology, Rheumatology and Endocrinology

BACKGROUND

Exertional chest pain/dyspnea or chest pain at rest are the main symptoms of coronary artery disease (CAD), which are traditionally attributed to insufficiency of the epicardial coronary arteries. However, 2/3 of women and 1/3 of men with angina and 10% of patients with acute myocardial infarction have no evidence of epicardial coronary artery stenosis in X-ray coronary angiography. In these cases, coronary microvascular disease (CMD) is the main causative factor.

AIMS

To present the pathophysiology of CMD in Cardiology, Rheumatology and Endocrinology.

MATERIALS-METHODS

The pathophysiology of CMD in Cardiology, Rheumatology and Endocrinology was evaluated. It includes impaired microvascular vasodilatation, which leads to inability of the organism to deal with myocardial oxygen needs and, hence, development of ischemic pain. CMD, observed in inflammatory autoimmune rheumatic and endocrine/metabolic disorders, brings together Cardiology, Rheumatology and Endocrinology. Causative factors include persistent systemic inflammation and endocrine/metabolic abnormalities influencing directly the coronary microvasculature. In the past, the evaluation of microcirculation was feasible only with the use of invasive techniques, such as coronary flow reserve assessment. Currently, the application of advanced imaging modalities, such as cardiovascular magnetic resonance (CMR), can evaluate CMD non-invasively and without ionizing radiation.

RESULTS

CMD may present with a variety of symptoms with 1/3 to 2/3 of them expressed as typical chest pain in effort, more commonly found in women during menopause than in men. Atypical presentation includes chest pain at rest or exertional dyspnea,but post exercise symptoms are not uncommon. The treatment with nitrates is less effective in CMD, because their vasodilator action in coronary micro-circulation is less pronounced than in the epicardial coronary arteries.

DISCUSSION

Although both classic and new medications have been used in the treatment of CMD, there are still many questions regarding both the pathophysiology and the treatment of this disorder. The potential effects of anti-rheumatic and endocrine medications on the evolution of CMD need further evaluation.

CONCLUSION

CMD is a multifactorial disease leading to myocardial ischemia/fibrosis alone or in combination with epicardial coronary artery disease. Endothelial dysfunction/vasospasm, systemic inflammation, and/or neuroendocrine activation may act as causative factors and bring Cardiology, Rheumatology and Endocrinology together. Currently, the application of advanced imaging modalities, and specifically CMR, allows reliable assessment of the extent and severity of CMD. These measurements should not be limited to "pure cardiac patients", as it is known that CMD affects the majority of patients with autoimmune rheumatic and endocrine/metabolic disorders.

Angina with coronary microvascular dysfunction and its physiological assessment: a review with cases

Imagine that it is possible to know, the actual coronary blood flow. Would this not remove any doubt, if a chest pain is the heart's fault?