Invasive assessment of the coronary microcirculation: superior reproducibility and less hemodynamic dependence of index of microcirculatory resistance compared with coronary flow reserve

The Dynamic Relationship Between Invasive Microvascular Function and Microvascular Injury Indicators, and Their Association With Left Ventricular Function and Infarct Size at 1-Month After Reperfused ST-Segment-Elevation Myocardial Infarction

BACKGROUND

The invasive microvascular function indices, coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR), exhibit a dynamic pattern after ST-segment-elevation myocardial infarction. The effects of microvascular injury on the evolution of the microvascular function and the prognostic significance of the evolution of microvascular function are unknown. We investigated the relationship between the temporal changes of CFR and IMR, and cardiovascular magnetic resonance-derived microvascular injury characteristics in reperfused ST-segment-elevation myocardial infarction patients, and their association with 1-month left ventricular ejection fraction and infarct size (IS).

METHODS

In 109 ST-segment-elevation myocardial infarction patients who underwent angiography for primary percutaneous coronary intervention (PPCI) and at 1-month follow-up, invasive assessment of CFR and IMR were performed in the culprit artery during both procedures. Cardiovascular magnetic resonance was performed 2 to 7 days after PPCI and at 1 month and provided assessment of left ventricular ejection fraction, IS, microvascular obstruction, and intramyocardial hemorrhage.

RESULTS

CFR and IMR significantly changed over 1 month (both, P<0.001). The absolute IMR change over 1 month (ΔIMR) showed association with both microvascular obstruction and intramyocardial hemorrhage presence (both, P=0.01). ΔIMR differed between patients with/without microvascular obstruction (P=0.02) and with/without intramyocardial hemorrhage (P=0.04) but not ΔCFR for both. ΔIMR demonstrated association with both left ventricular ejection fraction and IS at 1 month (P<0.001, P=0.001, respectively), but not ΔCFR for both. Receiver-operating characteristics curve analysis of ΔIMR showed a larger area under the curve than post-PPCI CFR and IMR, and ΔCFR to be associated with both 1-month left ventricular ejection fraction >50% and extensive IS (the highest quartile).

CONCLUSIONS

In reperfused ST-segment-elevation myocardial infarction patients, CFR and IMR significantly improved 1 month after PPCI; the temporal change in IMR is closely related to the presence/absence of microvascular damage and IS. ΔIMR exhibits a stronger association for 1-month functional outcome than post-PPCI CFR, IMR, or ΔCFR.

In Vivo Validation of a Novel Computational Approach to Assess Microcirculatory Resistance Based on a Single Angiographic View

(1) Background: In spite of the undeniable clinical value of the index of microvascular resistance (IMR) in assessing the status of coronary microcirculation, its use globally remains very low. The aim of this study was to validate the novel single-view, pressure-wire- and adenosine-free angiographic microvascular resistance (AMR) index, having the invasive wire-based IMR as a reference standard. (2) Methods: one hundred and sixty-three patients (257 vessels) were investigated with pressure wire-based IMR. Microvascular dysfunction (CMD) was defined by IMR ≥ 25. AMR was independently computed from the diagnostic coronary angiography in a blinded fashion. (3) Results: AMR demonstrated a good correlation (r = 0.83, p < 0.001) and diagnostic performance (AUC 0.94; 95% CI: 0.91 to 0.97) compared with wire-based IMR. The best cutoff value for AMR in determining IMR ≥ 25 was 2.5 mmHg*s/cm. The overall diagnostic accuracy of AMR was 87.2% (95% CI: 83.0% to 91.3%), with a sensitivity of 93.5% (95% CI: 87.0% to 97.3%), a specificity of 82.7% (95% CI: 75.6% to 88.4%), a positive predictive value of 79.4% (95% CI: 71.2% to 86.1%) and a negative predictive value of 94.7% (95% CI: 89.3% to 97.8%). No difference in terms of CMD rate was described among different clinical presentations. (4) Conclusions: AMR derived solely from a single angiographic view is a feasible computational alternative to pressure wire-based IMR, with good diagnostic accuracy in assessing CMD.

Prognostic value of structural and functional coronary microvascular dysfunction in patients with non-obstructive coronary artery disease; from the multicentre international ILIAS registry

BACKGROUND

Coronary microvascular dysfunction (CMD) is an important contributor to angina syndromes. Recently, two distinct endotypes were identified using combined assessment of coronary flow reserve (CFR) and minimal microvascular resistance (MR), termed structural and functional CMD.

AIMS

We aimed to assess the relevance of the combined assessment of CFR and MR in patients with angina and no obstructive coronary arteries.

METHODS

Patients with chronic coronary syndromes (CCS) and non-obstructive coronary artery disease (fractional flow reserve [FFR] ≥0.80) were selected (N=1,102). Functional CMD was defined as abnormal CFR in combination with normal MR and structural CMD as abnormal CFR with abnormal MR. Clinical endpoints were the incidence of major adverse cardiac events (MACE) and target vessel failure (TVF) at 5-year follow-up.

RESULTS

Abnormal CFR was associated with an increased risk of MACE and TVF at 5-year follow-up. Microvascular resistance parameters were not associated with MACE or TVF at 5-year follow-up. The risk of MACE and TVF at 5-year follow-up was similarly increased for patients with structural or functional CMD compared with patients with normal microvascular function. There were no differences between both endotypes (p=0.88 for MACE, and p=0.55 for TVF).

CONCLUSIONS

Coronary microvascular dysfunction, identified by an impaired CFR, was unequivocally associated with increased MACE and TVF rates over a 5-year follow-up period. In contrast, impaired MR was not associated with 5-year adverse clinical events. Moreover, there was no significant difference in the risk of MACE and TVF between a low CFR accompanied by pathologically increased MR (structural CMD) or not (functional CMD).

CLINICALTRIALS

gov: NCT04485234.

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.

MINOCA: One Size Fits All? Probably Not—A Review of Etiology, Investigation, and Treatment

Myocardial infarction with non-obstructive coronary arteries (MINOCA) is a heterogeneous group of conditions that include both atherosclerotic (coronary plaque disruption) and non-atherosclerotic (spontaneous coronary artery dissection, coronary artery spasm, coronary artery embolism, coronary microvascular dysfunction, and supply–demand mismatch) causes resulting in myocardial damage that is not due to obstructive coronary artery disease. Failure to identify the underlying cause may result in inadequate and inappropriate therapy in these patients. The cornerstone of managing MINOCA patients is to identify the underlying mechanism to achieve the target treatment. Intravascular imaging is able to identify different morphologic features of coronary plaques, while cardiac magnetic resonance is the gold standard for detection of myocardial infarction in the setting of MINOCA. In this review, we summarize the relevant clinical issues, contemporary diagnosis, and treatment options of MINOCA.

Effect of direct stenting on microvascular dysfunction during percutaneous coronary intervention in acute myocardial infarction: a randomized pilot study

Objective

Whether direct stenting (DS) without predilatation during primary percutaneous coronary intervention (PPCI) reduces microvascular dysfunction in patients with ST-elevation myocardial infarction is unclear. We performed a randomized study to assess the effect of DS on microvascular reperfusion.

Methods

Seventy-two patients undergoing PPCI were randomly assigned to the DS or conventional stenting (CS) with predilatation groups. The primary endpoint was the post-PPCI index of microcirculatory resistance (IMR). We compared thrombolysis in myocardial infarction myocardial perfusion (TMP) grades, ST-segment resolution, and long-term clinical outcomes between the groups.

Results

Microvascular reperfusion parameters immediately after PPCI (e.g., the IMR, TMP grade, and ST-segment resolution) were not different between the groups. However, significantly fewer patients in the DS group had the IMR measured because of no-reflow or cardiogenic shock during PPCI than those in the CS group. No differences were found in left ventricular functional recovery or clinical outcomes between the groups.

Conclusions

This trial showed no effect of DS on the IMR. However, our finding should be interpreted with caution because the number of patients who could not have the IMR measured was higher in the CS group than in the DS group. A larger randomized trial is required (Research Registry number: 8079).

Prognostic Impact of Coronary Flow Reserve in Patients With Reduced Left Ventricular Ejection Fraction

Background

Intracoronary physiologic indexes such as coronary flow reserve (CFR) and left ventricular ejection fraction (LVEF) have been regarded as prognostic indicators in patients with coronary artery disease. The current study evaluated the association between intracoronary physiologic indexes and LVEF and their differential prognostic implications in patients with coronary artery disease.

Methods and Results

A total of 1889 patients with 2492 vessels with available CFR and LVEF were selected from an international multicenter prospective registry. Baseline physiologic indexes were measured by thermodilution or Doppler methods and LVEF was recorded at the index procedure. The primary outcome was target vessel failure, which was a composite of cardiac death, target vessel myocardial infarction, or clinically driven target vessel revascularization over 5 years of follow‐up. Patients with reduced LVEF <50% (162 patients [8.6%], 202 vessels [8.1%]) showed a similar degree of epicardial coronary artery disease but lower CFR values than those with preserved LVEF (2.4±1.2 versus 2.7±1.2, P<0.001), mainly driven by the increased resting coronary flow. Conversely, hyperemic coronary flow, fractional flow reserve, and the degree of microvascular dysfunction were similar between the 2 groups. Reduced CFR (≤2.0) was seen in 613 patients (32.5%) with 771 vessels (30.9%). Reduced CFR was an independent predictor for target vessel failure (hazard ratio, 2.081 [95% CI, 1.385–3.126], P<0.001), regardless of LVEF.

Conclusions

CFR was lower in patients with reduced LVEF because of increased resting coronary flow. Patients with reduced CFR showed a significantly higher risk of target vessel failure than did those with preserved CFR, regardless of LVEF.

Registration

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04485234.

Mechanisms of Coronary Ischemia in Women

PURPOSE OF REVIEW

Obstructive coronary artery disease is a major cause of ischemia in both men and women; however, women are more likely to present with ischemia in the setting of no obstructive coronary arteries (INOCA) and myocardial infarction with no obstructive coronary arteries (MINOCA), conditions that are associated with adverse cardiovascular prognosis despite absence of coronary stenosis. In this review, we focus on mechanisms of coronary ischemia that should be considered in the differential diagnosis when routine anatomic clinical investigation leads to the finding of non-obstructive coronary artery disease on coronary angiography in the setting of acute myocardial infarction.

RECENT FINDINGS

There are multiple mechanisms that contribute to MINOCA, including atherosclerotic plaque disruption, coronary artery spasm, coronary microvascular dysfunction (CMD), coronary embolism and/or thrombosis, and spontaneous coronary artery dissection. Non-coronary causes such as myocarditis or supply-demand mismatch should also be considered on the differential when there is an unexplained troponin elevation. Use of advanced imaging and diagnostic techniques to determine the underlying etiology of MINOCA is feasible and helpful, as this has the potential to guide management and secondary prevention. Failure to identify the underlying cause(s) may result in inappropriate treatment and inaccurate counseling to patients. MINOCA predominates in young women and is associated with a guarded prognosis. The diagnosis of MINOCA should prompt further investigation to determine the underlying cause of troponin elevation. Patients with INOCA and MINOCA are heterogeneous, and response to treatments can be variable. Large randomized controlled trials to determine longer-term optimal medical therapy for management of these conditions are under investigation.

Prognostic significance of severe coronary microvascular dysfunction post-PCI in patients with STEMI: A systematic review and meta-analysis

Coronary microvascular dysfunction (CMVD) is common and associated with poorer outcomes in patients with ST Segment Elevation Myocardial Infarction (STEMI). The index of microcirculatory resistance (IMR) and the index of hyperemic microvascular resistance (HMR) are both invasive indexes of microvascular resistance proposed for the diagnosis of severe CMVD after primary percutaneous coronary intervention (pPCI). However, these indexes are not routinely assessed in STEMI patients. Our main objective was to clarify the association between IMR or HMR and long-term major adverse cardiovascular events (MACE), through a systematic review and meta-analysis of observational studies. We searched Medline, PubMed, and Google Scholar for studies published in English until December 2020. The primary outcome was a composite of cardiovascular death, non-cardiovascular death, non-fatal myocardial infarction, non-fatal stroke, and rehospitalization for heart failure occurring after at least 6 months following CMVD assessment. We identified 6 studies, reporting outcomes in 1094 patients (mean age 59.7 ± 11.4 years; 18.2% of patients were women) followed-up from 6 months to 7 years. Severe CMVD, defined as IMR > 40 mmHg or HMR > 3mmHg/cm/sec was associated with MACE with a pooled HR of 3.42 [2.45; 4.79]. Severe CMVD is associated with an increased risk of long-term adverse cardiovascular events in patients with STEMI. Our results suggest that IMR and HMR are useful for the early identification of severe CMVD in patients with STEMI after PCI, and represent powerful prognostic assessments as well as new therapeutic targets for clinical intervention.

A Practical Approach to Invasive Testing in Ischemia with No Obstructive Coronary Arteries (INOCA)

Up to 65% of women and approximately 30% of men have ischemia with no obstructive coronary artery disease (CAD; commonly known as INOCA) on invasive coronary angiography performed for stable angina. INOCA can be due to coronary microvascular dysfunction or coronary vasospasm. Despite the absence of obstructive CAD, those with INOCA have an increased risk of all-cause mortality and adverse outcomes, including recurrent angina and cardiovascular events. These patients often undergo repeat testing, including cardiac catheterization, resulting in lifetime healthcare costs that rival those for obstructive CAD. Patients with INOCA often remain undiagnosed and untreated. This review discusses the symptoms and prognosis of INOCA, offers a systematic approach to the diagnostic evaluation of these patients, and summarizes therapeutic management, including tailored therapy according to underlying pathophysiological mechanisms.

Mechanisms and clinical implications of endothelium-dependent vasomotor dysfunction in coronary microvasculature

Coronary microvascular disease (CMD), which affects the arterioles and capillary endothelium that regulate myocardial perfusion, is an increasingly recognized source of morbidity and mortality, particularly in the setting of metabolic syndrome. The coronary endothelium plays a pivotal role in maintaining homeostasis, though factors such as diabetes, hypertension, hyperlipidemia, and obesity can contribute to endothelial injury and consequently arteriolar vasomotor dysfunction. These disturbances in the coronary microvasculature clinically manifest as diminished coronary flow reserve, which is a known independent risk factor for cardiac death, even in the absence of macrovascular atherosclerotic disease. Therefore, a growing body of literature has examined the molecular mechanisms by which coronary microvascular injury occurs at the level of the endothelium and the consequences on arteriolar vasomotor responses. This review will begin with an overview of normal coronary microvascular physiology, modalities of measuring coronary microvascular function, and clinical implications of CMD. These introductory topics will be followed by a discussion of recent advances in the understanding of the mechanisms by which inflammation, oxidative stress, insulin resistance, hyperlipidemia, hypertension, shear stress, endothelial cell senescence, and tissue ischemia dysregulate coronary endothelial homeostasis and arteriolar vasomotor function.

Coronary Flow Variations Following Percutaneous Coronary Intervention Affect Diastolic Nonhyperemic Pressure Ratios More Than the Whole Cycle Ratios

Background Post-percutaneous coronary intervention (PCI) fractional flow reserve ≥0.90 is an accepted marker of procedural success, and a cutoff of ≥0.95 has recently been proposed for post-PCI instantaneous wave-free ratio. However, stability of nonhyperemic pressure ratios (NHPRs) post-PCI is not well characterized, and transient reactive submaximal hyperemia post-PCI may affect their precision. We performed this study to assess stability and reproducibility of NHPRs post-PCI. Methods and Results Fifty-seven patients (age, 63.77±10.67 years; men, 71%) underwent hemodynamic assessment immediately post-PCI and then after a recovery period of 10, 20, and 30 minutes and repeated at 3 months. Manual offline analysis was performed to derive resting and hyperemic pressure indexes (Pd/Pa resting pressure gradient, mathematically derived instantaneous wave-free ratio, resting full cycle ratio, and fractional flow reserve) and microcirculatory resistances (basal microvascular resistance and index of microvascular resistance). Transient submaximal hyperemia occurring post-PCI was demonstrated by longer thermodilution time at 30 minutes compared with immediately post-PCI; mean difference of thermodilution time was 0.17 seconds (95% CI, 0.07-0.26 seconds; P=0.04). Basal microcirculatory resistance was also higher at 30 minutes than immediately post-PCI; mean difference of basal microvascular resistance was 10.89 mm Hg.s (95% CI, 2.25-19.52 mm Hg.s; P=0.04). Despite this, group analysis confirmed no significant differences in the values of resting whole cycle pressure ratios (Pd/Pa and resting full cycle ratio) as well as diastolic pressure ratios (diastolic pressure ratio and mathematically derived instantaneous wave-free ratio). Whole cardiac cycle NHPRs demonstrated the best overall stability post-PCI, and 1 in 5 repeated diastolic NHPRs crossed the clinical decision threshold. Conclusions Whole cycle NHPRs demonstrate better reproducibility and clinical precision post-PCI than diastolic NHPRs, possibly because of less perturbation from predominantly diastolic reactive hyperemia and left ventricular stunning. Registration URL: https://clinicaltrials.gov/ct2/show/NCT03502083; Unique identifier: NCT03502083 and URL: https://clinicaltrials.gov/ct2/show/NCT03076476; Unique identifier: NCT03076476.

Angiography-derived versus invasively-determined index of microcirculatory resistance in the assessment of coronary microcirculation: A systematic review and meta-analysis

BACKGROUND

The index of microvascular resistance (IMR) is an established tool to assess the status of coronary microcirculation. However, the need for a pressure wire and hyperemic agents have limited its routine use and have led to the development of angiography-derived pressure-wire-free methods (angiography-derived IMR [IMRAngio]). In this review and meta-analysis, we aim to assess the global diagnosis accuracy of IMRAngio versus IMR.

METHODS

A systematic review of the literature was performed. Studies directly evaluating IMRAngio versus IMR were considered eligible. Pooled values of diagnostic test and summary receiver operator curve were calculated.

RESULTS

Seven studies directly comparing IMRAngio versus IMR were included (687 patients; 807 vessels). Pooled sensitivity, specificity, +likelihood ratio (LR), and -LR were 82%, 83%, 4.5, and 0.26 respectively. Pooled accuracy was 83% while pooled positive predictive value and negative predictive value were 76% and 85%, respectively. Comparable results were obtained when analyzing by clinical scenario (acute and nonacute coronary syndromes).

CONCLUSION

IMRAngio shows a good diagnostic performance for the prediction of abnormal IMR.

Challenges in Diagnosis and Functional Assessment of Coronary Artery Disease in Patients With Severe Aortic Stenosis

More than half of patients with severe aortic stenosis (AS) over 70 years old have coronary artery disease (CAD). Exertional angina is often present in AS-patients, even in the absence of significant CAD, as a result of oxygen supply/demand mismatch and exercise-induced myocardial ischemia. Moreover, persistent myocardial ischemia leads to extensive myocardial fibrosis and subsequent coronary microvascular dysfunction (CMD) which is defined as reduced coronary vasodilatory capacity below ischemic threshold. Therefore, angina, as well as noninvasive stress tests, have a low specificity and positive predictive value (PPV) for the assessment of epicardial coronary stenosis severity in AS-patients. Moreover, in symptomatic patients with severe AS exercise testing is even contraindicated. Given the limitations of noninvasive stress tests, coronary angiography remains the standard examination for determining the presence and severity of CAD in AS-patients, although angiography alone has poor accuracy in the evaluation of its functional severity. To overcome this limitation, the well-established invasive indices for the assessment of coronary stenosis severity, such as fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR), are now in focus, especially in the contemporary era with the rapid increment of transcatheter aortic valve replacement (TAVR) for the treatment of AS-patients. TAVR induces an immediate decrease in hyperemic microcirculatory resistance and a concomitant increase in hyperemic flow velocity, whereas resting coronary hemodynamics remain unaltered. These findings suggest that FFR may underestimate coronary stenosis severity in AS-patients, whereas iFR as the non-hyperemic index is independent of the AS severity. However, because resting coronary hemodynamics do not improve immediately after TAVR, the coronary vasodilatory capacity in AS-patients treated by TAVR remain impaired, and thus the iFR may overestimate coronary stenosis severity in these patients. The optimal method for evaluating myocardial ischemia in patients with AS and co-existing CAD has not yet been fully established, and this important issue is under further investigation. This review is focused on challenges, limitations, and future perspectives in the functional assessment of coronary stenosis severity in these patients, bearing in mind the complexity of coronary physiology in the presence of this valvular heart disease.

Concurrently Low Coronary Flow Reserve and Low Index of Microvascular Resistance Are Associated With Elevated Resting Coronary Flow in Patients With Chest Pain and Nonobstructive Coronary Arteries

BACKGROUND

Coronary microvascular function can be distinctly quantified using the coronary flow reserve (CFR) and index of microvascular resistance (IMR). Patients with low CFR can present with low or high IMR, although the prevalence and clinical characteristics of these patient groups remain unclear.

METHODS

One hundred ninety-nine patients underwent coronary microvascular assessments using coronary thermodilution techniques. A pressure-temperature sensor-tipped guidewire measured proximal and distal coronary pressure, whereas the inverse of the mean transit time to room temperature saline was used to measure coronary blood flow. The CFR and IMR were quantified during adenosine and acetylcholine hyperemia.

RESULTS

Low adenosine and acetylcholine CFR was observed in 70 and 49 patients, respectively, whereas low CFR/low IMR to adenosine and acetylcholine was observed in 39(56%) and 19(39%) patients, respectively. Despite similar adenosine CFR, patients with low CFR/low IMR had increased resting (2.8±1.2 versus 1.3±0.4s^-1) and hyperemic coronary blood flow (4.8±1.5 versus 2.1±0.5s^-1) compared with patients with low CFR/high IMR (both P<0.01). The same pattern was observed in response to acetylcholine. Patients with low CFR/low IMR to adenosine were younger (56±12 versus 63±10 years), women (84% versus 66%), had fewer coronary risk factors (1.1±1.0 versus 1.6±1.1), lower hemoglobin A1c (5.8±0.7 versus 6.1±0.9 mmol/L), and thinner septal thickness (8.5±2.5 versus 9.9±1.6 mm) compared with patients with low CFR/high IMR to adenosine (all P<0.05).

CONCLUSIONS

Low CFR/low IMR to adenosine and acetylcholine are associated with elevated resting coronary blood flow and preserved hyperemic coronary blood flow. These patients present with distinct phenotypic characteristics. Simultaneous CFR and IMR measures appear necessary to differentiate these endotypes.

Index of microcirculatory resistance: state-of-the-art and potential applications in computational simulation of coronary artery disease

The dysfunction of coronary microcirculation is an important cause of coronary artery disease (CAD). The index of microcirculatory resistance (IMR) is a quantitative evaluation of coronary microcirculatory function, which provides a significant reference for the prediction, diagnosis, treatment, and prognosis of CAD. IMR also plays a key role in investigating the interaction between epicardial and microcirculatory dysfunctions, and is closely associated with coronary hemodynamic parameters such as flow rate, distal coronary pressure, and aortic pressure, which have been widely applied in computational studies of CAD. However, there is currently a lack of consensus across studies on the normal and pathological ranges of IMR. The relationships between IMR and coronary hemodynamic parameters have not been accurately quantified, which limits the application of IMR in computational CAD studies. In this paper, we discuss the research gaps between IMR and its potential applications in the computational simulation of CAD. Computational simulation based on the combination of IMR and other hemodynamic parameters is a promising technology to improve the diagnosis and guide clinical trials of CAD.

Evaluate the Correlation between the TIMI Frame Count, IMR, and CFR in Coronary Microvascular Disease

Objective

To evaluate the correlation between the TIMI frame count, IMR, and CFR in coronary microvascular disease (slow flow phenomenon).

Methods

TFC and IMR were recorded in the nitroglycerin and ATP administration states, and the relationship between TFC, IMR, and CFR in specific states was analyzed.

Results

A total of 41 patients with baseline TFC >25 frames on coronary angiography were enrolled, and nitroglycerin reduced TFC by 50% from baseline in 24 (58.54%) patients; 16 of the remaining 17 patients were able to achieve a 50% reduction in TFC by further intracoronary ATP injection. 10 patients were further tested for IMR, and the results showed significant correlations between baseline TFC and IMR (r = 0.775, P=0.008), TFC and IMR after nitroglycerin (r = 0.875, P=0.001), and the minimal TFC and IMR that could be obtained with nitroglycerin or ATP administration (r = 0.890, P=0.001). There was also a significant correlation between the proportional improvement in TFC and CFR before and after nitroglycerin injection (r = 0.685, P=0.029). In addition, we observed a lower IMR measured after nitroglycerin than after ATP in three patients, suggesting that CMD may be dominated by NO-sensitive vascular such as prearterioles and that an extensive analysis of the target site of CMD may be achieved by stepwise drug administration.

Conclusion

Induction of TFC in different states by a stepwise drug approach may serve as a potential primary screening method for coronary microcirculatory dysfunction, thereby reducing the need for further IMR or CFR testing.

Ischemia and no obstructive coronary arteries in patients with stable ischemic heart disease

A large proportion of patients with suspected obstructive coronary artery disease (CAD) is found to have ischemia with no obstructive coronary artery disease (INOCA). Based on current evidence, these patients are at increased risk of adverse cardiovascular events, even though they have no obstructive CAD. Importantly, INOCA is associated with recurrent clinical presentations with chest pain, impaired functional capacity, reduced health-related quality of life, and high healthcare costs. Underlying coronary microvascular dysfunction (CMD), through endothelium-dependent and independent mechanisms contribute to these adverse outcomes in INOCA. While non-invasive and invasive diagnostic testing has typically focused on identification of obstructive CAD in symptomatic patients, functional testing to detect coronary epicardial and microvascular dysfunction should be considered in those with INOCA who have persistent angina. Current diagnostic methods to clarify functional abnormalities and treatment strategies for epicardial and/or microvascular dysfunction in INOCA are reviewed.

Presence of Microvascular Dysfunction and CHA2DS2-VASc Score in Patients with ST-Segment Myocardial Infarction after Primary Percutaneous Coronary Intervention

Objective

We aimed to investigate the relation between CHA₂DS₂-VASc score and microvascular dysfunction (MVD) assessed by the index of microvascular resistance (IMR) immediately after primary percutaneous intervention (PPCI) for patients with ST-segment elevation myocardial infarction (STEMI).

Subjects and Methods

The study included 115 consecutive patients with STEMI who underwent successful PPCI. Angiographic results of reperfusion were inspected to evaluate the association of high CHA₂DS₂-VASc score and IMR. Also, we assessed echocardiographic changes with respect to CHA₂DS₂-VASc score.

Results

Subjects were stratified into 2 groups based on IMR </≥ 40 U; 72 patients (62.6) with IMR <40 U and 43 patients (37.4) with IMR ≥40 U. Patients with IMR ≥40 U had higher CHA₂DS₂-VASc score (p < 0.001). CHA₂DS₂-VASc score was significantly correlated with increased left atrial volume index, diastolic dysfunction, wall motion score index, and inversely correlated left ventricular ejection. Moreover, CHA₂DS₂-VASc score was strongly correlated with IMR (p < 0.001). At multivariate analysis, low systolic blood pressure, stent diameter, and CHA₂DS₂-VASc score were associated with MVD. Besides, CHA₂DS₂-VASc score ≥4 was the optimal value in predicting MVD (IMR ≥40) in STEMI patients.

Conclusions

The data of the current study point out that increased CHA₂DS₂-VASc score, lower systolic blood pressure <90 mm Hg, and stent diameter are associated with increased incidence of MVD (increased IMR) after PPCI of STEMI. We suggest that the CHA₂DS₂-VASc score may be a simple, inexpensive useful risk score for the prediction of MVD risk after PPCI for STEMI patients.

The Role of Coronary Physiology in Contemporary Percutaneous Coronary Interventions

Invasive assessment of coronary physiology has radically changed the paradigm of myocardial revascularization in patients with coronary artery disease. Despite the prognostic improvement associated with ischemia-driven revascularization strategy, functional assessment of angiographic intermediate epicardial stenosis remains largely underused in clinical practice. Multiple tools have been developed or are under development in order to reduce the invasiveness, cost, and extra procedural time associated with the invasive assessment of coronary physiology. Besides epicardial stenosis, a growing body of evidence highlights the role of coronary microcirculation in regulating coronary flow with consequent pathophysiological and clinical and prognostic implications. Adequate assessment of coronary microcirculation function and integrity has then become another component of the decision-making algorithm for optimal diagnosis and treatment of coronary syndromes. This review aims at providing a comprehensive description of tools and techniques currently available in the catheterization laboratory to obtain a thorough and complete functional assessment of the entire coronary tree (both for the epicardial and microvascular compartments).

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.

Effects of Shexiang Baoxin Pill for Coronary Microvascular Function: A Systematic Review and Meta-Analysis

Background: The coronary microvascular dysfunction has attracted more and more attention in recent years, but there is still a lack of effective treatment. Shexiang Baoxin Pill is one of the commonly used drugs for the treatment of coronary artery disease in China. More recently, some studies found that it has the effect of improving coronary microvascular function. Objective: To evaluate the effects of Shexiang Baoxin Pill for coronary microvascular function. Methods: Databases including MEDLINE, Web of Science, CNKI, Wanfang, The Cochrane Library, EMbase, VIP and CBM were searched from inception to June 2021 to screen out relevant clinical studies. The 2019 version 2 of the Cochrane risk of bias tool (RoB2) were used to assess the methodological quality of the included studies. RevMan 5.3 software was used for meta-analysis. Results: Eleven studies meeting the criteria were included, with a total of 1,075 patients. The results of meta-analysis showed that compared with conventional treatment alone, combination of Shexiang Baoxin Pill and conventional treatment can further increase the coronary flow reserve (CFR) [mean difference (MD) = 0.43, 95%CI (0.28, 0.58), p < 0.000 01], decrease the index of microvascular resistance (IMR) [MD = -4.23, 95%CI (-5.49, -2.97), p < 0.000 01], increase serum nitric oxide (NO) [MD = 11.96, 95%CI (2.74, 21.18), p = 0.001] and decrease serum hypersensitive C-reactive protein (hs-CRP) [MD = -2.49, 95%CI (-3.08, -1.90), p < 0.000 01], but did not increase the time of duration on the exercise testing (TET) [MD = 3.64, 95%CI (-1.17, 8.45), p = 0.14]. In terms of safety, a total of 10 patients developed adverse reactions in the intervention group and 17 patients developed adverse reactions in the control group. Conclusion: Current evidence suggests that Shexiang Baoxin Pill may be effective in the improvement of coronary microvascular function when used in combination with conventional treatment. However, due to the low quality of the included studies, lack of placebo control and high heterogeneity among different studies, we should take a cautious attitude towards this conclusion. Moreover, the safety of Shexiang Baoxin Pill remains uncertain, more high-quality clinical studies are needed to verify the efficacy and safety of this drug in the future. Systematic Review Registration: [website], identifier [registration number: CRD42021265113].

The Index of Microcirculatory Resistance after Primary Percutaneous Coronary Intervention Predicts Long-Term Clinical Outcomes in Patients with ST-Segment Elevation Myocardial Infarction

The index of microcirculatory resistance (IMR) is a simple method that can measure microvascular function after primary percutaneous coronary intervention (PCI) in patients with ST-segment Elevation Myocardial Infarction (STEMI). This study is to find out whether IMR predicts clinical long-term outcomes in STEMI patients. A total of 316 patients with STEMI who underwent primary PCI from 2005 to 2015 were enrolled. The IMR was measured using pressure sensor/thermistor-tipped guidewire after primary PCI. The primary endpoint was the rate of death or hospitalization for heart failure (HF) over a mean follow-up period of 65 months. The mean corrected IMR was 29.4 ± 20.0. Patients with an IMR > 29 had a higher rate of the primary endpoint compared to patients with an IMR ≤ 29 (10.3% vs. 2.1%, p = 0.001). During the follow-up period, 13 patients (4.1%) died and 6 patients (1.9%) were hospitalized for HF. An IMR > 29 was associated with an increased risk of death or hospitalization for HF (OR 5.378, p = 0.004). On multivariable analysis, IMR > 29 (OR 3.962, p = 0.022) remained an independent predictor of death or hospitalization for HF with age (OR 1.048, p = 0.049) and symptom-to-balloon time (OR 1.002, p = 0.049). High IMR was an independent predictor for poor long-term clinical outcomes in STEMI patients after primary PCI.

Acute Coronary Syndromes (ACS)-Unravelling Biology to Identify New Therapies-The Microcirculation as a Frontier for New Therapies in ACS

In acute coronary syndrome (ACS) patients, restoring epicardial culprit vessel patency and flow with percutaneous coronary intervention or coronary artery bypass grafting has been the mainstay of treatment for decades. However, there is an emerging understanding of the crucial role of coronary microcirculation in predicting infarct burden and subsequent left ventricular remodelling, and the prognostic significance of coronary microvascular obstruction (MVO) in mortality and morbidity. This review will elucidate the multifaceted and interconnected pathophysiological processes which underpin MVO in ACS, and the various diagnostic modalities as well as challenges, with a particular focus on the invasive but specific and reproducible index of microcirculatory resistance (IMR). Unfortunately, a multitude of purported therapeutic strategies to address this unmet need in cardiovascular care, outlined in this review, have so far been disappointing with conflicting results and a lack of hard clinical end-point benefit. There are however a number of exciting and novel future prospects in this field that will be evaluated over the coming years in large adequately powered clinical trials, and this review will briefly appraise these.

Basics of Coronary Thermodilution

Coronary microvascular dysfunction is a highly prevalent condition in both obstructive and nonobstructive coronary artery disease. Intracoronary thermodilution is a promising technique to investigate coronary microvascular (dys)function in vivo and to assess its most important metric: microvascular resistance. Here, the authors provide a practical review of bolus and continuous thermodilution for the measurement of coronary flow and microvascular resistance. The authors describe the basic principles of indicator-dilution theory and of coronary thermodilution and detail the practicalities of their application in the catheterization laboratory. Finally, the authors discuss contemporary clinical applications of coronary thermodilution-based microvascular assessment in humans and future perspectives.

Functional Coronary Angiography-Derived Index of Microcirculatory Resistance in Patients With ST-Segment Elevation Myocardial Infarction

OBJECTIVES

The aim of this study was to evaluate the diagnostic accuracy and prognostic implications of angiography-derived index of microcirculatory resistance (angio-IMR) in patients with ST-segment elevation myocardial infarction (STEMI).

BACKGROUND

The index of microcirculatory resistance (IMR) is a reliable invasive measure of coronary microvascular dysfunction in patients with STEMI. A functional coronary angiography-derived method to estimate IMR is a wire- and hyperemic agent-free alternative to IMR.

METHODS

The study population consisted of 2 independent cohorts. The diagnostic cohort comprised patients with IMR from the culprit vessel immediately after successful primary percutaneous coronary intervention (n = 31). The prognostic cohort was patients with STEMI who were successfully treated with primary percutaneous coronary intervention and followed for 10 years from the index procedure (n = 309). Angio-IMR was calculated using computational flow and pressure simulation. The primary outcome was a composite of cardiac death and readmission for heart failure over 10 years of follow-up.

RESULTS

In the diagnostic cohort, angio-IMR correlated well with IMR (R = 0.778; P < 0.001). Sensitivity, specificity, accuracy, and area under the curve of angio-IMR to predict IMR >40 U were 75.0%, 84.2%, 80.6%, and 0.899 (95% confidence interval: 0.786-0.949), respectively. In the prognostic cohort, patients with angio-IMR >40 U showed significantly higher risk for cardiac death or readmission for heart failure than did those with angio-IMR ≤40 U (46.7% vs 16.6%; adjusted hazard ratio: 2.909; 95% CI: 1.670-5.067; P < 0.001). Angio-IMR >40 U was an independent predictor of cardiac death or readmission for heart failure (hazard ratio: 2.173; 95% CI: 1.157-4.079; P = 0.016) and showed incremental prognostic value compared with a model with clinical risk factors only (C index = 0.726 vs 0.666 [P < 0.001], net reclassification index = 0.704 [P < 0.001]).

CONCLUSIONS

Angio-IMR showed high correlation and diagnostic accuracy to predict IMR. Patients with STEMI with angio-IMR >40 U showed a significantly higher risk for cardiac death or readmission for heart failure than those with preserved angio-IMR values. (Prognostic Implication of Angiography-Derived IMR in STEMI Patients; NCT04628377).

Invasive Assessment of Microvascular Resistance in Hypertrophic Cardiomyopathy With Echocardiographic Correlates

INTRODUCTION

Hypertrophic cardiomyopathy (HCM) is often associated with ischaemia despite lack of focal epicardial coronary stenosis. Our aim was to assess invasive coronary microvascular circulation and correlate findings with echocardiography.

METHODS

We prospectively enrolled patients with HCM and controls who were referred for diagnostic coronary angiography. A pressure-temperature sensor coronary guidewire was used with intracoronary injections of room-temperature saline to measure mean coronary transit time during rest and hyperaemia induced with intravenous adenosine. The index of microvascular resistance (IMR) was calculated. Left ventricular mass was calculated during echocardiographic studies.

RESULTS

Patients with HCM (n=12) and controls (n=7), had similar demographics. Left ventricular ejection fraction was higher in HCM (76.7%±11.0% vs 55.0%±15.9%, p=0.003). IMR was non-significantly higher in HCM (21.7±10.2 vs 15.3±4.8, p=0.16). Only patients with HCM had abnormal IMR (>25). Coronary flow reserve was non-significantly higher in HCM (2.7±1.6 vs 2.1±1.2, p=0.34). IMR correlated with left ventricular mass in hypertrophic cardiomyopathy subjects (Pearson r=0.68, p=0.02).

CONCLUSIONS

Microvascular dysfunction as assessed by IMR may be abnormal in HCM and is correlated with left ventricular mass.

Thermodilution-derived temperature recovery time: a novel predictor of microvascular reperfusion and prognosis after myocardial infarction

BACKGROUND

Novel parameters that detect failed microvascular reperfusion might identify better the patients likely to benefit from adjunctive treatments during primary percutaneous coronary intervention (PCI).

AIMS

The aim of this study was to test the hypothesis that a novel invasive parameter, the thermodilution-derived temperature recovery time (TRT), would be associated with microvascular obstruction (MVO) and prognosis.

METHODS

TRT was derived and validated in two independent ST-elevation myocardial infarction populations and was measured immediately post PCI. TRT was defined as the duration (seconds) from the nadir of the hyperaemic thermodilution curve to 20% from baseline body temperature. MVO extent (% left ventricular mass) was assessed by cardiovascular magnetic resonance imaging at 2-7 days.

RESULTS

In the retrospective derivation cohort (n=271, mean age 60±12 years, 72% male), higher TRT was associated with more MVO (coefficient: 4.09 [95% CI: 2.70-5.48], p<0.001), independently of IMR >32, CFR ≤2, hyperaemic Tmn >median, thermodilution waveform, age and ischaemic time. At five years, higher TRT was multivariably associated with all-cause death/heart failure hospitalisation (OR 4.14 [95% CI: 2.08-8.25], p<0.001) and major adverse cardiac events (OR 4.05 [95% CI: 2.00-8.21], p<0.001). In the validation population (n=144, mean age 59±11 years, 80% male), the findings were confirmed prospectively.

CONCLUSIONS

TRT represents a novel diagnostic advance for predicting MVO and prognosis. ClinicalTrials.gov Identifiers: NCT02072850 & NCT02257294 Visual summary. Thermodilution-derived temperature recovery time (TRT): a novel predictor of microvascular reperfusion & prognosis after STEMI. CMR: cardiovascular magnetic resonance; MACE: major adverse cardiac events; MVO: microvascular obstruction; PCI: percutaneous coronary intervention; STEMI: ST-segment elevation myocardial infarction.

Simplified Assessment of the Index of Microvascular Resistance

Background

To validate a simplified invasive method for the calculation of the index of microvascular resistance (IMR).

Methods

This is a prospective, single-center study of patients with chronic coronary syndromes presenting with nonobstructive coronary artery disease. IMR was obtained using both intravenous (IV) adenosine and intracoronary (IC) papaverine. Each IMR measurement was obtained in duplicate. The primary objective was the agreement between IMR acquired using adenosine and papaverine. Secondary objectives include reproducibility of IMR and time required for the IMR measurement.

Results

One hundred and sixteen IMR measurements were performed in 29 patients. The mean age was 68.8 ± 7.24 years, and 27.6% was diabetics. IMR values were similar between papaverine and adenosine (17.7 ± 7.26 and 20.1 ± 8.6, p=0.25; Passing-Bablok coefficient A 0.58, 95% CI −2.42 to 3.53; coefficient B 0.90, 95% CI −0.74 to 1.07). The reproducibility of IMR was excellent with both adenosine and papaverine (ICC 0.78, 95% CI 0.63 to 0.88 and ICC 0.93, 95% CI 0.87 to 0.97). The time needed for microvascular assessment was significantly shortened by the use of IC papaverine (3.23 (2.84, 3.78) mins vs. 5.48 (4.94, 7.09) mins, p < 0.0001).

Conclusion

IMR can be reliably measured using IC papaverine with similar results compared to intravenous infusion of adenosine with increased reproducibility and reduced procedural time. This approach simplifies the invasive assessment of the coronary microcirculation in the catheterization laboratory.

Impact of a micro-net mesh technology covering stent on coronary microvascular dysfunction in patients with high thrombus burden

BACKGROUND

Highly thrombotic coronary lesions continue to be a serious and clinically significant problem that is not effectively and completely addressed by current technology.

OBJECTIVES

We aimed to investigate whether a micro-net mesh (MNM) technology covering stent could preserve the index of microcirculatory resistance (IMR) after percutaneous coronary intervention (PCI) in patients with high thrombus burden.

METHODS AND RESULTS

Fifty-two patients with non-ST elevation myocardial infarction or ST Elevation Myocardial Infarction and high thrombus burden (TIMI thrombus grade ≥ 3) were randomized into two groups, PCI with a MNM covering stent (MNM group, n = 25) and PCI with any commercially available stent (DES group, n = 27). As the primary endpoint, IMR was measured immediately after PCI using a pressure-temperature sensor-tipped coronary wire. The secondary endpoint was left ventricular ejection fraction (LVEF) at 6 months of follow-up. The IMR in the MNM group was significantly lower in comparison to the DES group (33.2 [21.3, 48.9] vs. 57.2 [39.9, 98.0], p = 0.005). No significant differences were observed in baseline LVEF (54.5 ± 10.2% vs. 53.1 ± 6.87%, p = .57), while LVEF was significantly improved at follow-up in the MNM group (61.1 ± 7.1% vs. 53.9 ± 6.35%, p = .0001).

CONCLUSION

MNM technology significantly improved coronary microvascular dysfunction after PCI in patient with acute coronary syndrome and appears as a useful technological option for thrombus management.

Sweat the small stuff: The human microvasculature and heart disease

Traditionally thought of primarily as the predominant regulator of myocardial perfusion, it is becoming more accepted that the human coronary microvasculature also exerts a more direct influence on the surrounding myocardium. Coronary microvascular dysfunction (CMD) not only precedes large artery atherosclerosis, but is associated with other cardiovascular diseases such as heart failure with preserved ejection fraction and hypertrophic cardiomyopathy. It is also highly predictive of cardiovascular events in patients with or without atherosclerotic cardiovascular disease. This review focuses on this recent paradigm shift and delves into the clinical consequences of CMD. Concepts of how resistance arterioles contribute to disease will be discussed, highlighting how the microvasculature may serve as a potential target for novel therapies and interventions. Finally, both invasive and non-invasive methods with which to assess the coronary microvasculature both for diagnostic and risk stratification purposes will be reviewed.

Effects of salvianolate on microcirculatory disturbance in patients with stable coronary heart disease: study protocol for a randomized controlled trial

BACKGROUND

Obstruction of coronary microcirculation can lead to myocardial ischemia and poor prognosis. Salvianolate exerts cardiovascular protection at cellular levels. However, no studies have confirmed the effect of salvianolate on stable coronary heart disease (CHD) with high fractional flow reserve (FFR) and myocardial microcirculatory disturbances.

METHODS/DESIGN

This study will enroll 78 patients who have stable coronary disease with 50 to 70% stenosis in major coronary arteries and whose FFR > 0.80 and index of microcirculatory resistance (IMR) > 25. Patients will be randomly divided into the salvianolate group or the placebo group. After above evaluations, salvianolate 200 mg will be intravenously dripped immediately for the next 30 min and subsequent 7 days in the salvianolate group, and matching 0.9% normal saline will be arranged in the placebo group. IMR will be reevaluated in immediate phase after first 30 min of salvianolate or placebo treatment. The primary end point will be the IMR change in this phase, and the secondary end points will be the total ischemic burden assessed by the Seattle angina scale, quality of life scale, Holter electrocardiography, and 6-min walk test after 7 days before discharge.

DISCUSSION

This study will firstly clarify the improvement effect of salvianolate on coronary microcirculation and provide an effective treatment method for stable CHD patients with high FFR and myocardial microcirculatory disturbance.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR1800018772 . Registered on 9 October 2018 and updated on 2 March 2020.

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.

Characterization of the Human Coronary Microvascular Response to Multiple Hyperaemic Agents

Background

It is unclear whether the coronary microvascular responses to multiple, mechanistically distinct hyperaemic agents exert similar dilatory responses or share common clinical predictors. This study therefore sought to characterize the index of microvascular resistance (IMR) response to multiple hyperaemic agents in the human coronary circulation.

Methods

Thermodilution-derived IMR was determined during intravenous adenosine, intracoronary acetylcholine, and intravenous dobutamine in patients with ischemic symptoms and nonobstructive coronary angiograms. A total of 128 patients were studied (44 with adenosine and acetylcholine, and 84 with all agents). Adenosine IMR >25, acetylcholine IMR >31, and dobutamine IMR >29 were used to define elevated responses.

Results

IMR responses demonstrated weak-to-moderate association (adenosine vs acetylcholine IMR: ρ = 0.33; adenosine vs dobutamine IMR: ρ = 0.51; acetylcholine vs dobutamine IMR: ρ = 0.28; all P < 0.01). Logistic regression analyses revealed that: (1) elevated adenosine IMR was associated with increasing age and left ventricle hypertrophy (odds ratio [OR] = 1.27 and 1.58; both P < 0.05, respectively), (2) elevated acetylcholine IMR was associated with increasing plasma uric acid (OR = 1.09; P < 0.05), and (3) elevated dobutamine IMR was associated with hypertension and left atrial volume index (OR = 3.99 and 1.07; both P < 0.05, respectively). Subset analyses to evaluate clinical utility of the acetylcholine and dobutamine IMR, independent of abnormal adenosine IMR, revealed that elevated acetylcholine and/or dobutamine IMR were associated with higher risk exercise stress tests, left atrial volumes, and burden of exertional chest pain.

Conclusions

Microvascular-specific IMR responses to different hyperaemic agents are only moderately associated, whereas the predictors for agent-specific IMR responses varied, suggesting that multiple pharmacologic agents interrogate different microvascular control mechanisms.

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.

Predictors of Microvascular Reperfusion After Myocardial Infarction

Purpose of Review

In acute ST-segment elevation myocardial infarction (STEMI), successful restoration of blood flow in the infarct-related coronary artery may not secure effective myocardial reperfusion. The mortality and morbidity associated with acute MI remain significant. Microvascular obstruction (MVO) represents failed microvascular reperfusion. MVO is under-recognized, independently associated with adverse cardiac prognosis and represents an unmet therapeutic need.

Recent Findings

Multiple factors including clinical presentation, patient characteristics, biochemical markers, and imaging parameters are associated with MVO after MI.

Summary

Impaired microvascular reperfusion is common following percutaneous coronary intervention (PCI). New knowledge about disease mechanisms underpins precision medicine with individualized risk assessment, investigation, and stratified therapy. To date, there are no evidence-based therapies to prevent or treat MVO post-MI. Identifying novel therapy for MVO is the next frontier.

Invasive Diagnosis of Coronary Functional Disorders Causing Angina Pectoris

Coronary vasomotion disorders represent a frequent cause of angina and/or dyspnoea in patients with non-obstructed coronary arteries. The highly sophisticated interplay of vasodilatation and vasoconstriction can be assessed in an interventional diagnostic procedure. Established parameters characterising adequate vasodilatation are coronary blood flow at rest, and, after drug-induced vasodilation, coronary flow reserve, and microvascular resistance (hyperaemic microvascular resistance, index of microcirculatory resistance). An increased vasoconstrictive potential is diagnosed by provocation testing with acetylcholine or ergonovine. This enables a diagnosis of coronary epicardial and/or microvascular spasm. Ischaemia associated with microvascular spasm can be confirmed by ischaemic ECG changes and the measurement of lactate concentrations in the coronary sinus. Although interventional diagnostic procedures are helpful for determining the mechanism of the angina, which may be the key to successful medical treatment, they are still neither widely accepted nor applied in many medical centres. This article summarises currently well-established invasive methods for the diagnosis of coronary functional disorders causing angina pectoris.

Invasive assessment of myocardial bridging in patients with angina and no obstructive coronary artery disease

AIMS

Angina and no obstructive coronary artery disease (ANOCA) is common. A potential cause of angina in this patient population is a myocardial bridge (MB). We aimed to study the anatomical and haemodynamic characteristics of an MB in patients with ANOCA.

METHODS AND RESULTS

Using intravascular ultrasound (IVUS), we identified 184 MBs in 154 patients. We evaluated MB length, arterial compression, and halo thickness. MB muscle index (MMI) was defined as MB length×halo thickness. Haemodynamic testing of the MB was performed using an intracoronary pressure/Doppler flow wire at rest and during dobutamine stress. We defined an abnormal diastolic fractional flow reserve (dFFR) as ≤0.76 during stress. The median MB length was 22.9 mm, arterial compression 30.9%, and halo thickness 0.5 mm. The median MMI was 12.1. Endothelial and microvascular dysfunction were present in 85.4% and 22.1%, respectively. At peak dobutamine stress, 94.2% of patients had a dFFR ≤0.76 within and/or distal to the MB. MMI was associated with an abnormal dFFR.

CONCLUSIONS

In select patients with ANOCA who have an MB by IVUS, the majority have evidence of a haemodynamically significant dFFR during dobutamine stress, suggesting the MB as being a cause of their angina. A comprehensive invasive assessment of such patients during coronary angiography provides important diagnostic information that can guide management.

Sex differences in non-obstructive coronary artery disease

Ischaemic heart disease is a leading cause of morbidity and mortality in both women and men. Compared with men, symptomatic women who are suspected of having myocardial ischaemia are more likely to have no obstructive coronary artery disease (CAD) on coronary angiography. Coronary vasomotor disorders and coronary microvascular dysfunction (CMD) have been increasingly recognized as important contributors to angina and adverse outcomes in patients with no obstructive CAD. CMD from functional and structural abnormalities in the microvasculature is associated with adverse cardiac events and mortality in both sexes. Women may be particularly susceptible to vasomotor disorders and CMD due to unique factors such as inflammation, mental stress, autonomic, and neuroendocrine dysfunction, which predispose to endothelial dysfunction and CMD. CMD can be detected with coronary reactivity testing and non-invasive imaging modalities; however, it remains underdiagnosed. This review focuses on sex differences in presentation, pathophysiologic risk factors, diagnostic testing, and prognosis of CMD.

Blood haemoglobin, renal insufficiency, fractional flow reserve and plasma NT-proBNP is associated with index of microcirculatory resistance in chronic coronary syndrome

BACKGROUND

Coronary microvascular dysfunction (CMVD) is associated with adverse cardiovascular outcome. We aimed to determine the prevalence of CMVD and factors related to index of microcirculatory resistance (IMR) in consecutive patients with chronic coronary syndrome (CCS) undergoing elective coronary angiography.

METHODS AND RESULTS

Non-interventional physicians enrolled 274 patients with CCS before angiography, to minimize selection bias by PCI-operators. Fractional flow reserve (FFR) and IMR were measured in the LAD. Subjects with extensively diseased LAD, no measures due to technical reasons or violation of protocol were excluded from the analysis (n = 54). The proportion of patients with IMR corrected for collateral flow (IMR_corr) >25 units was 25% (95% confidence interval [CI] 19%-31%) in all 220 patients. In subjects with FFR ≤0.80 in the LAD the proportion of IMR_corr > 25 units was 21% (95% CI 13%-30%) as compared to subjects with FFR >0.80, 29% (95% CI 21%-36%), p = .268. Haemoglobin (p < .005; r2 = 0.084), FFR in the LAD (p = .001; r2 = 0.049), creatinine clearance (p = .001; r² = 0.049; inversely), and NT-proBNP (p = .038; r² = 0.021) were independently associated with IMR_corr in multivariate linear regression analysis.

CONCLUSIONS

We report that IMR_corr is associated with renal dysfunction, NT-proBNP, FFR in the LAD and, for the first time, blood haemoglobin. One in four of patients referred for coronary angiography due to CCS have CMVD defined as IMR_corr > 25 in the LAD.

Coronary flow reserve and microcirculatory resistance in patients with coronary tortuosity and without atherosclerosis

Objective

Coronary tortuosity may affect epicardial coronary arterial blood flow. This study aimed to investigate the effect of coronary tortuosity on coronary flow reserve and the coronary microcirculation in patients without apparent coronary atherosclerosis.

Methods

Prospective patients (n = 8, 3 men, mean age: 58 ± 6.0 years) with coronary tortuosity and without apparent coronary atherosclerosis were enrolled. Coronary tortuosity was defined by the finding of ≥three bends (defined as a ≥45° change in vessel direction) along the main trunk of the left anterior descending artery or left circumflex artery. Coronary flow reserve and the index of microcirculatory resistance were measured by the thermodilution technique.

Results

A total of eight coronary arteries with coronary tortuosity were analyzed. The mean fractional flow reserve was 0.98 ± 0.007. The mean coronary flow reserve was 1.5 ± 0.3, which is much lower than that in the normal coronary artery as reported in the literature. The mean index of microcirculatory resistance was 26.7 ± 2.3, which is much higher than that in the normal coronary artery.

Conclusions

Coronary tortuosity is associated with decreased coronary flow reserve and an increased index of microcirculatory resistance.

Trial registration: This study is registered at the Chinese Clinical Trial Registry, NCT No: ChiCTR2000033671

End-stage renal failure is associated with impaired coronary microvascular function

BACKGROUND

Cardiovascular disease is the leading cause of death in patients with chronic kidney disease. Studies investigating the disproportionate burden of cardiovascular disease have occurred predominantly in the peripheral vasculature, often used noninvasive imaging modalities, and infrequently recruited patients receiving dialysis. This study sought to evaluate invasive coronary dynamic vascular function in patients with end-stage renal failure (ESRF).

PATIENTS AND METHODS

Patients referred for invasive coronary angiography prior to renal transplantation were invited to participate. Control patients were recruited in parallel. Baseline characteristics were obtained. Coronary diameter (via quantitative coronary angiography) and coronary blood flow (via Doppler Flowire) were measured; macrovascular endothelial-dependent and independent effects were evaluated in response to intracoronary acetylcholine infusion (10 and 10 mol/l) and intracoronary glyceryl trinitrate, respectively. Microvascular function was evaluated by response to adenosine and expressed as coronary flow velocity reserve. Mean values were compared.

RESULTS

Thirty patients were evaluated: 15 patients with ESRF (mean age 52.1 ± 9, male 73%) and 15 control patients (mean age 53.3 ± 13, male 60%). Comorbidity profile, aside from ESRF, was well matched. Baseline coronary blood flow was similar between groups (101.6 ± 10.3 vs. 103.4 ± 9.1 ml/min, P = 0.71), as was endothelial-dependent response to acetylcholine (159.1 ± 16.9 vs. 171.1 ± 16.8 ml/min, P = 0.41). Endothelial-independent response to glyceryl trinitrate was no different between groups (14.3 ± 3.1 vs. 13.1 ± 2.3%, P = 0.73. A significantly reduced coronary flow velocity reserve was observed in the ESRF cohort compared to controls (2.34 ± 0.4 vs. 3.05 ± 0.3, P = 0.003).

CONCLUSION

Patients with ESRF had preserved endothelial-dependent function however compared to controls, demonstrated significantly attenuated microvascular reserve. An impaired response to adenosine may not only represent a component of the pathophysiological milieu in patients with ESRF but may also provide a basis for the suboptimal diagnostic performance of vasodilatory stress in this population.

Coronary Microcirculation Downstream Non-Infarct-Related Arteries in the Subacute Phase of Myocardial Infarction: Implications for Physiology-Guided Revascularization

Background

Concerns exist about reliability of pressure‐wire‐guided coronary revascularization of non‐infarct‐related arteries (non‐IRA). We investigated whether physiological assessment of non‐IRA during the subacute phase of myocardial infarction might be flawed by microcirculatory dysfunction.

Methods and Results

We analyzed non‐IRA that underwent fractional flow reserve, coronary flow reserve, and the index of microcirculatory resistance assessment. Microcirculation and hyperemic response were evaluated in 49 acute myocardial infarction patients (59 non‐IRA) and compared with a matched control group of 46 stable angina (SA) patients (59 vessels). Time between acute myocardial infarction to physiological interrogation was 5.9±2.4 days. Fractional flow reserve was similar in both groups (0.79±0.11 in non‐IRA versus 0.80±0.13 in SA vessels, P=0.527). Lower coronary flow reserve values were found in non‐IRA compared with SA vessels (1.77 [1.25–2.76] versus 2.44 [1.63–4.00], P=0.018), primarily driven by an increased baseline flow in non‐IRA (rest mean transit time 0.58 [0.32–0.83] versus 0.65 s [0.39–1.20], P=0.045), whereas the hyperemic flow was similar (hyperemic mean transit time 0.26 [0.20–0.42] versus 0.26 s [0.18–0.35], P=0.873). No differences were found regarding index of microcirculatory resistance (15.6 [10.4–21.8] in non‐IRA versus 16.7 [11.6–23.6] U in SA vessels, P=0.559). During adenosine infusion, the hyperemic response was similar in both groups (non‐IRA versus SA vessels) in terms of the resistive reserve ratio (3.1±2.1 versus 3.7±2.2, P=0.118).

Conclusions

In the subacute phase of myocardial infarction, non‐IRA show an increased baseline flow that may cause abnormal coronary flow reserve despite preserved hyperemic flow. In non‐IRA, microcirculatory resistance and adenosine‐induced hyperemic response are similar to those found in SA patients. From a physiological perspective, these findings support the use of fractional flow reserve to interrogate non‐IRA during the subacute phase of myocardial infarction.

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