The microvascular resistance reserve (MRR) was introduced as a means to characterize the vasodilator reserve capacity of the coronary microcirculation while accounting for the influence of concomitant epicardial disease and the impact of administration of potent vasodilators on aortic pressure. This study aimed to evaluate the diagnostic and prognostic performance of MRR. A total of 1481 patients with stable symptoms and a clinical indication for coronary angiography were included from the global ILIAS Registry. MRR was derived as a function of the coronary flow reserve (CFR) divided by the fractional flow reserve (FFR) and corrected for driving pressure. The median MRR was 2.97 [Q1–Q3: 2.32–3.86] and the overall relationship between MRR and CFR was good [correlation coefficient (R_s) = 0.88, P < 0.005]. The difference between CFR and MRR increased with decreasing FFR [coefficient of determination (R²) = 0.34; Coef.—2.88, 95% confidence interval (CI): -3.05–−2.73; P < 0.005]. MRR was independently associated with major adverse cardiac events (MACE) at 5-year follow-up [hazard ratio (HR) 0.78; 95% CI 0.63–0.95; P = 0.024] and with target vessel failure (TVF) at 5-year follow-up (HR 0.83; 95% CI 0.76–0.97; P = 0.047). The optimal cut-off value of MRR was 3.0. Based on this cut-off value, only abnormal MRR was significantly associated with MACE and TVF at 5-year follow-up in vessels with functionally significant epicardial disease (FFR <0.75). MRR seems a robust indicator of the microvascular vasodilator reserve capacity. Moreover, in line with its theoretical background, this study suggests a diagnostic advantage of MRR over other indices of vasodilatory capacity in patients with hemodynamically significant epicardial coronary artery disease. Diagnostic and prognostic value of the microvascular resistance reserve (MRR).The MRR is a novel index of the coronary vasodilatory capacity. The MMR is an index that corrects the assessment of the vasodilatory capacity for concomitant epicardial disease and the administration of vasodilatory indices. The MRR shows an excellent correlation with the coronary flow reserve (CFR), which decreases with decreasing fractional flow reserve (FFR) values. The MRR is an independent and significant predictor of both major adverse cardiac events (MACE) and target vessel failure (TVF) at 5-year follow-up.

Background: In the absence of obstructive coronary stenoses, abnormality of noninvasive stress tests (NIT) in patients with chronic coronary syndromes may indicate myocardial ischemia of nonobstructive coronary arteries (INOCA). The differential prognosis of INOCA according to the presence of coronary microvascular dysfunction (CMD) and incremental prognostic value of CMD with intracoronary physiologic assessment on top of NIT information remains unknown. Methods and Results: From the international multicenter registry of intracoronary physiologic assessment (ILIAS [Inclusive Invasive Physiological Assessment in Angina Syndromes] registry, N=2322), stable patients with NIT and nonobstructive coronary stenoses with fractional flow reserve >0.80 were selected. INOCA was diagnosed when patients showed positive NIT results. CMD was defined as coronary flow reserve ≤2.5. According to the presence of INOCA and CMD, patients were classified into 4 groups: group 1 (no INOCA nor CMD, n=116); group 2 (only CMD, n=90); group 3 (only INOCA, n=41); and group 4 (both INOCA and CMD, n=40). The primary outcome was major adverse cardiovascular events, a composite of all‐cause death, target vessel myocardial infarction, or clinically driven target vessel revascularization at 5 years. Among 287 patients with nonobstructive coronary stenoses (fractional flow reserve=0.91±0.06), 81 patients (38.2%) were diagnosed with INOCA based on positive NIT. By intracoronary physiologic assessment, 130 patients (45.3%) had CMD. Regardless of the presence of INOCA, patients with CMD showed a significantly lower coronary flow reserve and higher hyperemic microvascular resistance compared with patients without CMD ( P <0.001 for all). The cumulative incidence of major adverse cardiovascular events at 5 years were 7.4%, 21.3%, 7.7%, and 34.4% in groups 1 to 4. By documenting CMD (groups 2 and 4), intracoronary physiologic assessment identified patients at a significantly higher risk of major adverse cardiovascular events at 5 years compared with group 1 (group 2: adjusted hazard ratio [HR _adjusted ], 2.88; 95% CI, 1.52–7.19; P =0.024; group 4: HR _adjusted , 4.00; 95% CI, 1.41–11.35; P =0.009). Conclusions: In stable patients with nonobstructive coronary stenoses, a diagnosis of INOCA based only on abnormal NIT did not identify patients with higher risk of long‐term cardiovascular events. Incorporating intracoronary physiologic assessment to NIT information in patients with nonobstructive disease allowed identification of patient subgroups with up to 4‐fold difference in long‐term cardiovascular events. Registration: URL: https://www.clinicaltrials.gov ; Unique identifier: NCT04485234.

Background: Coronary function testing in patients with ischemia and nonobstructive coronary arteries (INOCA) commonly includes assessment of adenosine-mediated vasodilation and acetylcholine spasm provocation. The purpose of this study was to evaluate the diagnostic value of additional endothelial function testing for the diagnosis of vasomotor dysfunction in patients with INOCA. Methods: In this retrospective cohort study, we included patients with INOCA who underwent clinically indicated comprehensive coronary function testing. Endothelial dysfunction was defined as a <50% increase in coronary blood flow, determined by Doppler flow, and/or epicardial vasoconstriction compared to baseline, in response to low-dose acetylcholine. Coronary artery spasm (CAS) was defined as vasospastic angina or microvascular angina in response to coronary high-dose acetylcholine. An impaired adenosine-mediated vasodilation was defined as a coronary flow reserve <2.5 and/or hyperemic microvascular resistance ≥2.5. Results: Among all 110 patients, 79% had endothelial dysfunction, 62% had CAS, and 29% had an impaired adenosine-mediated vasodilation. Endothelial dysfunction was present in 80% of patients who tested positively for CAS and/or an impaired adenosine-mediated vasodilation. Endothelial function testing increases the diagnostic yield of coronary function testing that only incorporates adenosine testing and spasm provocation by 17% to 92%. Of patients with normal adenosine-mediated vasodilation and no inducible CAS, 68% had endothelial dysfunction. Conclusions: Concomitant endothelial dysfunction was prevalent in the vast majority of patients with INOCA with inducible CAS and/or an impaired adenosine-mediated vasodilation. In patients with INOCA without inducible CAS and normal adenosine-mediated vasodilation, two-thirds had endothelial dysfunction. These results indicate the relevance to perform endothelial function testing in patients with INOCA in view of its therapeutic implication.

Background and Aims: Invasive coronary function testing (CFT) identifies coronary vasomotor disorders in up to 90% of patients with angina with non-obstructive coronary arteries (ANOCA). The ILIAS ANOCA trial hypothesized that routine ad hoc CFT would be feasible, safe, and effective in providing an early, comprehensive diagnosis. Additionally, it was anticipated that combining CFT with a disease-specific treatment protocol would significantly improve quality of life in ANOCA patients compared with standard care. Methods: After excluding patients with obstructive coronary artery disease (CAD) during clinically indicated invasive coronary angiography (ICA), eligible patients underwent CFT and were randomized to either the standard care group, where CFT results remained blinded, or the intervention group, where CFT results were disclosed along with a tailored medical therapy protocol. The primary outcome was the mean difference in the within-subject change in Seattle Angina Questionnaire summary score (SAQSS) between groups from baseline to a follow-up of 6 months. The trial is registered with the International Clinical Trials Registry Platform (NL-OMON20739). Results: A total of 255 patients consented, of whom 153 patients (60%) without CAD underwent CFT and were randomized 1:1 to the standard care (n = 76) or intervention group (n = 77). All CFT procedures were successful without adverse events. A vasomotor disorder was identified in 120 patients (78%). At 6-month follow-up, the SAQSS improved significantly in the intervention group compared with the control group, with an intervention effect of 9.4 units (95% confidence interval 3.9–14.9, P = .001). There were no major adverse cardiac events at the 6-month follow-up. Conclusions: Routine CFT during the initial ICA was feasible, safe, and had high diagnostic yield. Implementing a pragmatic CFT protocol combined with a disease-specific treatment protocol significantly improved disease-related quality of life in patients with ANOCA compared with standard care.

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.