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: We 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 that had undergone proximal left anterior descending artery stenting, we created four 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) in order 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 hyperaemic 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). CONCLUSION: 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.

International evaluation of an artificial intelligence-powered electrocardiogram model detecting acute coronary occlusion myocardial infarction.

Aims: A majority of acute coronary syndromes (ACS) present without typical ST elevation. One-third of non-ST-elevation myocardial infarction (NSTEMI) patients have an acutely occluded culprit coronary artery [occlusion myocardial infarction (OMI)], leading to poor outcomes due to delayed identification and invasive management. In this study, we sought to develop a versatile artificial intelligence (AI) model detecting acute OMI on single-standard 12-lead electrocardiograms (ECGs) and compare its performance with existing state-of-the-art diagnostic criteria. Methods and results: An AI model was developed using 18 616 ECGs from 10 543 patients with suspected ACS from an international database with clinically validated outcomes. The model was evaluated in an international cohort and compared with STEMI criteria and ECG experts in detecting OMI. The primary outcome of OMI was an acutely occluded or flow-limiting culprit artery requiring emergent revascularization. In the overall test set of 3254 ECGs from 2222 patients (age 62 ± 14 years, 67% males, 21.6% OMI), the AI model achieved an area under the curve of 0.938 [95% confidence interval (CI): 0.924-0.951] in identifying the primary OMI outcome, with superior performance [accuracy 90.9% (95% CI: 89.7-92.0), sensitivity 80.6% (95% CI: 76.8-84.0), and specificity 93.7 (95% CI: 92.6-94.8)] compared with STEMI criteria [accuracy 83.6% (95% CI: 82.1-85.1), sensitivity 32.5% (95% CI: 28.4-36.6), and specificity 97.7% (95% CI: 97.0-98.3)] and with similar performance compared with ECG experts [accuracy 90.8% (95% CI: 89.5-91.9), sensitivity 73.0% (95% CI: 68.7-77.0), and specificity 95.7% (95% CI: 94.7-96.6)]. Conclusion: The present novel ECG AI model demonstrates superior accuracy to detect acute OMI when compared with STEMI criteria. This suggests its potential to improve ACS triage, ensuring appropriate and timely referral for immediate revascularization.

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.

Predictors of percutaneous coronary intervention derived from CCTA in patients with chronic coronary syndrome.

BACKGROUND: To identify anatomical and morphological plaque features predictors of PCI and create a multiparametric score to increase the predictive yield. Moreover, we assessed the incremental predictive value of FFRCT (Fractional Flow Reserve derived from CCTA) trans-lesion gradient (ΔFFRCT) when integrated into the score. METHODS: Observational cohort study including patients undergoing CCTA for suspected coronary artery disease, with FFRCT available, referred to invasive coronary angiogram and assessment of fractional flow reserve. Plaque analysis was performed using validated semi-automated software. Logistic regression was performed to identify anatomical and morphological plaque features predictive of PCI. Optimal thresholds were defined by area under the receiver-operating characteristics curve (AUC) analysis. A scoring system was developed in a derivation cohort (70 â€‹% of the study population) and tested in a validation cohort (30 â€‹% of patients). RESULTS: The overall study population included 340 patients (455 vessels), among which 238 patients (320 vessels) were included in the derivation cohort. At multivariate logistic regression analysis, absence of left main disease, diameter stenosis (DS), non-calcified plaque (NCP) volume, and percent atheroma volume (PAV) were independent predictors of PCI. Optimal thresholds were: DS â€‹≥ â€‹50 â€‹%, volume of NCP>113 â€‹mm3 and PAV>17 â€‹%. A weighted score (CT-PCI Score) ranging from 0 to 11 was obtained. The AUC of the score was 0.80 (95%CI 0.74-0.86). The integration of ΔFFRCT in the CT-PCI score led to a mild albeit not significant increase in the AUC (0.82, 95%CI 0.77-0.87, p â€‹= â€‹0.328). CONCLUSIONS: Plaque anatomy and morphology derived from CCTA could aid in identifying patients amenable to PCI.

Characterisation of coronary microvascular dysfunction in patients with severe aortic stenosis undergoing TAVI.

BACKGROUND: Microvascular resistance reserve (MRR) is a validated measure of coronary microvascular function independent of epicardial resistances. AIMS: We sought to assess whether MRR is associated with adverse cardiac remodelling, a low-flow phenotype and extravalvular cardiac damage (EVCD) in patients with severe aortic stenosis (AS) undergoing transcatheter aortic valve implantation (TAVI). METHODS: Invasive thermodilution-based assessment of the coronary microvascular function of the left anterior descending artery was performed in a prospective, multicentre cohort of patients undergoing TAVI. Coronary microvascular dysfunction (CMD) was defined as the lowest MRR tertile of the study cohort. Haemodynamic measurements were performed at baseline and then repeated immediately after TAVI. EVCD and markers of a low-flow phenotype were assessed with echocardiography. RESULTS: A total of 134 patients were included in this study. Patients with low MRR were more frequently females, had a lower estimated glomerular filtration rate and a higher rate of atrial fibrillation. MRR was significantly lower in patients with advanced EVCD (median 1.80 [1.26-3.30] vs 2.50 [1.87-3.41]; p=0.038) and in low-flow, low-gradient AS (LF LG-AS) (median 1.85 [1.20-3.04] vs 2.50 [1.87-3.40]; p=0.008). Overall, coronary microvascular function tended to improve after TAVI and, in particular, MRR increased significantly after TAVI in the subgroup with low MRR at baseline. However, MRR was significantly impaired in 38 (28.4%) patients immediately after TAVI. Advanced EVCD (adjusted odds ratio 3.08 [1.22-7.76]; p=0.017) and a low-flow phenotype (adjusted odds ratio 3.36 [1.08-10.47]; p=0.036) were significant predictors of CMD. CONCLUSIONS: In this observational, hypothesis-generating study, CMD was associated with extravalvular cardiac damage and a low-flow phenotype in patients with severe AS undergoing TAVI.

Combined Cardiac Damage Staging by Echocardiography and Cardiac Catheterization in Patients With Clinically Significant Aortic Stenosis.

BACKGROUND: Cardiac damage (CD) staging enhances risk stratification in patients with clinically significant aortic stenosis (AS). We aimed to assess the prognostic value and reclassification rate of right heart catheterization (RHC) compared with transthoracic echocardiography (TTE) in characterising CD staging at 3-year follow-up in patients with clinically significant AS, to identify patients that would benefit from RHC for prognostic stratification, and to test the prognostic value of combined CD staging. METHODS: An observational cohort study of 432 AS patients undergoing TTE and RHC were divided into moderate or asymptomatic severe (m/asAS) and symptomatic severe (ssAS) AS. Kaplan-Meier curves were used to compare survival. The accuracy in prognostic stratification was tested by area under the receiver operating characteristic curve analysis and Delong test. RESULTS: In both cohorts, TTE- and RHC-derived staging systems had prognostic value, although the agreement between them appeared moderate. A higher proportion of patients were assigned to stage 2 by TTE than by RHC. Patients in TTE-derived stage 2 had a high reclassification rate, with 40%-50% presenting with right chamber involvement (stages 3-4) according to RHC. Discordant cases were significantly older, with higher prevalence of atrial fibrillation, markedly elevated N-terminal pro-B-type natriuretic peptide, and higher indexed left atrial volume, E/e', and systolic pulmonary artery pressure vs concordant cases (P < 0.05). The combined CD staging, integrating TTE and RHC, was more accurate in predicting mortality than the TTE-derived system (P < 0.05). CONCLUSIONS: In patients with m/asAS and ssAS, the combined CD staging, derived from TTE and RHC, was more accurate in predicting mortality than TTE alone. In a subset of AS patients, the integration of RHC may significantly improve prognostic stratification.

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.

Widely Split P Waves After Pharmacologic Cardioversion in a Patient With Atrial Fibrillation.

We report a case of a clinically asymptomatic patient with extreme P-wave separation on the electrocardiogram mimicking atrial tachycardia with atrioventricular block. The accurate examination of the patient, analysis of the electrocardiogram, and echocardiographic findings led to proper diagnosis, management, and treatment. (Level of Difficulty: Intermediate.).

Continuous vs Bolus Thermodilution to Assess Microvascular Resistance Reserve.

BACKGROUND: Coronary flow reserve (CFR) and microvascular resistance reserve (MRR) can, in principle, be derived by any method assessing coronary flow. OBJECTIVES: The aim of this study was to compare CFR and MRR as derived by continuous (CFRcont and MRRcont) and bolus thermodilution (CFRbolus and MRRbolus). METHODS: A total of 175 patients with chest pain and nonobstructive coronary artery disease were studied. Bolus and continuous thermodilution measurements were performed in the left anterior descending coronary artery. MRR was calculated as the ratio of CFR to fractional flow reserve and corrected for changes in systemic pressure. In 102 patients, bolus and continuous thermodilution measurements were performed in duplicate to assess test-retest reliability. RESULTS: Mean CFRbolus was higher than CFRcont (3.47 ± 1.42 and 2.67 ± 0.81 [P < 0.001], mean difference 0.80, upper limit of agreement 3.92, lower limit of agreement -2.32). Mean MRRbolus was also higher than MRRcont (4.40 ± 1.99 and 3.22 ± 1.02 [P < 0.001], mean difference 1.2, upper limit of agreement 5.08, lower limit of agreement -2.71). The correlation between CFR and MRR values obtained using both methods was significant but weak (CFR, r = 0.28 [95% CI: 0.14-0.41]; MRR, r = 0.26 [95% CI: 0.16-0.39]; P < 0.001 for both). The precision of both CFR and MRR was higher when assessed using continuous thermodilution compared with bolus thermodilution (repeatability coefficients of 0.89 and 2.79 for CFRcont and CFRbolus, respectively, and 1.01 and 3.05 for MRRcont and MRRbolus, respectively). CONCLUSIONS: Compared with bolus thermodilution, continuous thermodilution yields lower values of CFR and MRR accompanied by an almost 3-fold reduction of the variability in the measured results.

Association of Mild-to-Moderate Aortic Regurgitation With Outcomes in Heart Failure With Preserved Ejection Fraction.

OBJECTIVE: To assess aortic regurgitation (AR) prevalence, its hemodynamic effect, and long-term prognostic implications in patients admitted with de novo or worsened heart failure with preserved ejection fraction (HFpEF). METHODS: Consecutive patients hospitalized with de novo or worsened HFpEF between 2014 and 2020 were enrolled. Patients with more than moderate aortic and/or mitral valve disease were excluded. Based on the presence and degree of AR, patients were divided into those without AR, those with mild, and those with moderate AR. Data on cardiovascular death, heart failure (HF) rehospitalization, and their composite (major adverse cardiovascular events) were collected. RESULTS: The final study population consisted of 458 HFpEF patients: 156 (34.1%) with mild-AR, 153 (33.4%) with moderate-AR, and the remaining 149 (32.5%) with no AR. Mild-to-moderate AR patients were older, with larger left atrium-left ventricle (LV) volumes, greater LV mass index, higher filling pressure, and prevalence of diastolic dysfunction compared with the no-AR group (all P<.05). During 5-year follow-up, 113 patients died of cardiovascular causes, 124 patients were rehospitalized for HF, whereas 196 experienced the composite endpoint. Mild-to-moderate AR was identified as an independent predictor of all-cause death (HR, 1.62; 95% CI, 1.14 to 1.58; P=.04) and major adverse cardiovascular event occurrence (HR, 1.48; 95% CI, 1.05 to 2.09; P=.02). A total of 126 (35.5%) of 355 patients showed progression of AR at follow-up echocardiography. CONCLUSION: Mild-to-moderate AR is common among patients hospitalized for HFpEF. It is associated with adverse LV remodeling and worse long-term outcomes. These findings warrant further prospective studies addressing the importance of AR in prognostic stratification and exploring therapeutic strategies to mitigate its hemodynamic effect on HF.

Comprehensive invasive evaluation of coronary microcirculation in patients with Takotsubo syndrome.

BACKGROUND AND AIMS: The etiology and pathophysiology of Takotsubo syndrome (TTS) remain a matter of debate. In murine models of coronary microvascular dysfunction (CMD), abnormalities in myocardial perfusion led to the development of TTS. Importantly, TTS was reversible when normal perfusion was restored. However, in clinical practice, the assessment of coronary microcirculation in patients with TTS has primarily relied on non-invasive or indirect, angiography-derived methods. METHODS AND RESULTS: For the first time, we performed invasive microcirculatory assessment, by both validated techniques currently available in the catheterization laboratory, namely intracoronary bolus and continuous thermodilution, in patients with TTS, upon hospital admission and at short term follow-up. Our findings demonstrate that CMD was consistently present in all patients upon hospital admission, as assessed by both techniques. At a median follow-up of 3 months, after the recovery of left ventricular ejection fraction, two third of patients no longer exhibited CMD. CONCLUSIONS: These findings support the hypothesis that an acute and transient worsening in coronary microvascular function plays a pivotal role in the pathophysiology of TTS.

Detection of transthyretin amyloid cardiomyopathy by automated data extraction from electronic health records.

AIMS: Transthyretin amyloid cardiomyopathy (ATTR-CM), a progressive and fatal cardiomyopathy, is frequently misdiagnosed or entails diagnostic delays, hindering patients from timely treatment. This study aimed to generate a systematic framework based on data from electronic health records (EHRs) to assess patients with ATTR-CM in a real-world population of heart failure (HF) patients. Predictive factors or combinations of predictive factors related to ATTR-CM in a European population were also assessed. METHODS AND RESULTS: Retrospective unstructured and semi-structured data from EHRs of patients from OLV Hospital Aalst, Belgium (2012-20), were processed using natural language processing (NLP) to generate an Observational Medical Outcomes Partnership Common Data Model database. NLP model performance was assessed on a random subset of EHRs by comparing algorithm outputs to a physician-generated standard (using precision, recall, and their harmonic mean, or F1-score). Of the 3127 HF patients, 103 potentially had ATTR-CM (age 78 ± 9 years; male 55%; ejection fraction of 48% ± 16). The mean diagnostic delay between HF and ATTR-CM diagnosis was 1.8 years. Besides HF and cardiomyopathy-related phenotypes, the strongest cardiac predictor was atrial fibrillation (AF; 72% in ATTR-CM vs. 60% in non-ATTR-CM, P = 0.02), whereas the strongest non-cardiac predictor was carpal tunnel syndrome (21% in ATTR-CM vs. 3% in non-ATTR-CM, P < 0.001). The strongest combination predictor was AF, joint disorders, and HF with preserved ejection fraction (29% in ATTR-CM vs. 18% in non-ATTR-CM: odds ratio = 2.03, 95% confidence interval = 1.28-3.22). CONCLUSIONS: Not only well-known variables associated with ATTR-CM but also unique combinations of cardiac and non-cardiac phenotypes are able to predict ATTR-CM in a real-world HF population, aiding in early identification of ATTR-CM patients.

Dual left anterior descending coronary artery and anomalous origin of left circumflex artery: a novel coronary anomaly revealed by CCTA.

In the rare coronary anomaly of Dual LAD, two segments of the vessel reside within the anterior interventricular sulcus. In our case, the short LAD originated from the Left Coronary Sinus (LCS), while the long LAD emerged from the Right Coronary Sinus (RCS). The LCx arose from the RCS, and the RCA displayed typical features. This anomaly was deemed incidental, prompting routine follow-up. It underscores the significance of integrating CCTA for a thorough assessment, offering crucial insights for patient management.

Innovative Device-Based Strategies for Managing Acute Decompensated Heart Failure.

Acute decompensated heart failure (ADHF) is a major cause of hospitalizations in older adults, leading to high mortality, morbidity, and healthcare costs. To address the persistent poor outcomes in ADHF, novel device-based approaches targeting specific pathophysiological mechanisms are urgently needed. The recently introduced DRI2P2S classification categorizes these innovative therapies based on their mechanisms. Devices include dilators (increasing venous capacitance), removers (directly removing sodium and water), inotropes (enhancing left ventricular contractility), interstitials (accelerating lymph removal), pushers (increasing renal arterial pressure), pullers (decreasing renal venous pressure), and selective drippers (selective intrarenal drug infusion). Some are tailored for chronic HF, while others focus on the acute setting. Most devices are in early development, necessitating further research to understand mechanisms, assess clinical effectiveness, and ensure safety before routine use in ADHF management. Exploring these innovative device-based strategies may lead to improved outcomes and revolutionize HF treatment in the future.

Assessment of E/A ratio helps emergency clinicians in the management of patients with acute dyspnea.

Acute dyspnea (AD) is one of the main reasons for admission to the Emergency Department (ED). In the last years integrated ultrasound examination (IUE) of lung, heart and inferior vena cava (IVC) has become an extension of clinical examination for a fast differential diagnosis. The aim of present study is to assess the feasibility and diagnostic accuracy of E/A ratio for diagnosing acute heart failure (aHF) in patients with acute dyspnea. We included 92 patients presenting to the ED of CTO Hospital in Naples (Italy) for AD. All patients underwent IUE of lung-heart-IVC with a portable ultrasound device. Left ventricle diastolic function was assessed using pulse wave doppler at the tips of the mitral valve and E wave velocity and E/A ratio were recorded. The FINAL diagnosis was determined by two expert reviewers: acute HF or non-acute HF (non-aHF). We used 2 × 2 contingency tables to analyze sensitivity, specificity, positive predictive and negative predictive value of ultrasound parameters for the diagnosis of AD, comparing with the FINAL diagnosis. Lung ultrasound (LUS) showed high sensitivity, good specificity and accuracy in identification of patients with aHF. However, the highest accuracy was obtained by diastolic function parameters. The E/A ratio showed the highest diagnostic performance with an AUC for aHF of 0.93. In patients presenting with AD, E/A ratio is easy to obtain in a fast ultrasound protocol and showed an excellent accuracy for diagnosis of aHF.

Same Day Discharge Strategy by Default in a Tertiary Catheterization Laboratory in Belgium: Value Based Healthcare-Change in Practice.

AIMS: To assess the effects on outcomes and hospital revenues (societal cost) of a by default strategy of same day discharge (SDD) in patients undergoing a cardiac catheterization procedure in a Belgian Hospital. METHODS AND RESULTS: Outcome and complete financial data were obtained in all consecutive patients with a cardiac catheterization performed in 2019 (n=5237) and in 2021 (n=5377). Patient-reported experience, patient satisfaction and Net promotor score were obtained prospectively for the SDD cohort in 2021. The proportion of patients receiving catheterization procedure in SDD increased from 28 to 44 % (p<0.001). This translates to the saving of 889 conventional hospitalizations in 2021. All-cause death and readmission rate remained unchanged (0,17% vs 0,15% (p=0,004); and 0,7% vs 1,8% (p>0,05)) in 2019 and 2021, respectively. Patients satisfaction top box score was 91% and the Net Promotor Score was 89,5. The by default SDD strategy was associated with reduction in in-hospital health care spending, on average 3206€ per procedure is saved. This means a 57% decrease in hospital revenues and translates into an important decrease in physician income. CONCLUSION: Implementing a by default SDD cardiac catheterization strategy results in a reduction of societal cost, excellent patient satisfaction and unchanged clinical outcome. Yet, in the given context this approach negatively impacts hospital and physician revenues precluding the sustainability of such protocol.

Reproducibility of bolus versus continuous thermodilution for assessment of coronary microvascular function in patients with ANOCA.

BACKGROUND: A bolus thermodilution-derived index of microcirculatory resistance (IMR) has emerged as the standard for assessing coronary microvascular dysfunction (CMD). Continuous thermodilution has recently been introduced as a tool to quantify absolute coronary flow and microvascular resistance directly. Microvascular resistance reserve (MRR) derived from continuous thermodilution has been proposed as a novel metric of microvascular function, which is independent of epicardial stenoses and myocardial mass. AIMS: We aimed to assess the reproducibility of bolus and continuous thermodilution in assessing coronary microvascular function. METHODS: Patients with angina and non-obstructive coronary artery disease (ANOCA) at angiography were prospectively enrolled. Bolus and continuous intracoronary thermodilution measurements were obtained in duplicate in the left anterior descending artery (LAD). Patients were randomly assigned in a 1:1 ratio to undergo either bolus thermodilution first or continuous thermodilution first. RESULTS: A total of 102 patients were enrolled. The mean fractional flow reserve (FFR) was 0.86±0.06. Coronary flow reserve (CFR) calculated with continuous thermodilution (CFRcont) was significantly lower than bolus thermodilution-derived CFR (CFRbolus; 2.63±0.65 vs 3.29±1.17; p<0.001). CFRcont showed a higher reproducibility than CFRbolus (variability: 12.7±10.4% continuous vs 31.26±24.85% bolus; p<0.001). MRR showed a higher reproducibility than IMR (variability 12.4±10.1% continuous vs 24.2±19.3% bolus; p<0.001). No correlation was found between MRR and IMR (r=0.1, 95% confidence interval: -0.09 to 0.29; p=0.305). CONCLUSIONS: In the assessment of coronary microvascular function, continuous thermodilution demonstrated significantly less variability on repeated measurements than bolus thermodilution.