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Background: Absolute hyperaemic coronary blood flow (Q, in mL/min) and resistance (R, in Wood units [WU]) can be measured invasively by continuous thermodilution. Aims: The aim of this study was to assess normal reference values of Q and R. Methods: In 177 arteries (69 patients: 25 controls, i.e., without identifiable coronary atherosclerosis; 44 patients with mild, non-obstructive atherosclerosis), thermodilution-derived hyperaemic Q and total, epicardial, and microvascular absolute resistances (R tot, R epi, and R micro) were measured. In 20 controls and 29 patients, measurements were obtained in all three major coronary arteries, thus allowing calculations of Q and R for the whole heart. In 15 controls (41 vessels) and 25 patients (71 vessels), vessel-specific myocardial mass was derived from coronary computed tomography angiography. Results: Whole heart hyperaemic Q tended to be higher in controls compared to patients (668±185 vs 582±138 mL/min, p=0.068). In the left anterior descending coronary artery (LAD), hyperaemic Q was significantly higher (293±102 mL/min versus 228±71 mL/min, p=0.004) in controls than in patients. This was driven mainly by a difference in R epi (43±23 vs 83±41 WU, p=0.048), without significant differences in R micro. After adjustment for vessel-specific myocardial mass, hyperaemic Q was similar in the three vascular territories (5.9±1.9, 4.9±1.7, and 5.3±2.1 mL/min/g, p=0.44, in the LAD, left circumflex and right coronary artery, respectively). Conclusions: The present report provides reference values of absolute coronary hyperaemic Q and R. Q was homogeneously distributed in the three major myocardial territories but the large ranges of observed hyperaemic values of flow and of microvascular resistance preclude their clinical use for inter-patient comparison.

Assessment of the microcirculation of the heart has gained interest over recent years. This is partly due to the fact that up to 50% of patients with chest pain visiting the catherization laboratory do not present with significant epicardial stenosis (so-called Angina with Non Obstructive Coronary Artery disease (ANOCA).1Most knowledge regarding microvascular resistance came from non-invasive imaging, from invasive index of microvascular resistance2, or from doppler wires3, both being semi-quantitative and operator dependent.Recently, direct quantitative measurement of coronary blood flow and microvascular resistancehas become possible by thermodilution with saline infusion, using a pressure-temperature guidewire and a multisidehole infusion catheter. Such measurements have been validated versus Positron Emission Tomography (PET)4, have a high reproducibility and are operator independent.5 Procedural safety has been reported before5, but long term safety and absence of late complications have not been described yet. The present study evaluates the safety of absolute flow measurements, both periprocedural, at 30 days and to one year follow-up.

Background: It would be ideal for a non-hyperaemic index to predict fractional flow reserve (FFR) more accurately, given FFR's extensive validation in a multitude of clinical settings. Aims: The aim of this study was to derive a novel non-hyperaemic algorithm based on deep learning and to validate it in an internal validation cohort against FFR. Methods: The ARTIST study is a post hoc analysis of three previously published studies. In a derivation cohort (random 80% sample of the total cohort) a deep neural network was trained (deep learning) with paired examples of resting coronary pressure curves and their FFR values. The resulting algorithm was validated against unseen resting pressure curves from a random 20% sample of the total cohort. The primary endpoint was diagnostic accuracy of the deep learning-derived algorithms against binary FFR ≤0.8. To reduce the variance in the precision, we used a fivefold cross-validation procedure. Results: A total of 1,666 patients with 1,718 coronary lesions and 2,928 coronary pressure tracings were included. The diagnostic accuracy of our convolutional neural network (CNN) and recurrent neural networks (RNN) against binary FFR ≤0.80 was 79.6±1.9% and 77.6±2.3%, respectively. There was no statistically significant difference between the accuracy of our neural networks to predict binary FFR and the most accurate non-hyperaemic pressure ratio (NHPR). Conclusions: Compared to standard derivation of resting pressure ratios, we did not find a significant improvement in FFR prediction when resting data are analysed using artificial intelligence approaches. Our findings strongly suggest that a larger class of hidden information within resting pressure traces is not the main cause of the known disagreement between resting indices and FFR. Therefore, if clinicians want to use FFR for clinical decision making, hyperaemia induction should remain the standard practice.

In ST-elevation myocardial infarction (STEMI), early restoration of blood flow, preferably by primary percutaneous coronary intervention (PPCI), is paramount to limit infarct size (IS) and improve long-term outcomes 1. However, reperfusion by itself may also cause damage to the myocardium and increase IS. This has been termed myocardial reperfusion injury 2. In animal models of acute myocardial infarction, it has been demonstrated that hypothermia decreases IS 3. In contrast, human studies applying systemic cooling methods have not yet been able to confirm this protective effect. Recently, we developed a new method to provide selective intracoronary hypothermia during PPCI 4. The EUROpean Intracoronary Cooling Evaluation in patients with ST-elevation myocardial infarction (EURO-ICE) trial will assess the efficacy of this method. Methods STUDY OBJECTIVES The primary objective of the EURO-ICE trial is to evaluate the effect of selective intracoronary hypothermia (SIH) on IS.

AIMS: Randomised controlled trials have reported instantaneous wave-free ratio (iFR) to be non-inferior to fractional flow reserve (FFR) for major adverse cardiovascular events at one year; however, iFR is limited by sensitive landmarking of the pressure waveform, and the assumption that maximal flow and minimal resistance occur during a fixed period of diastole. We sought to validate the resting full-cycle ratio (RFR), a novel non-hyperaemic index of coronary stenosis severity based on unbiased identification of the lowest distal coronary pressure to aortic pressure ratio (Pd/Pa), independent of the ECG, landmark identification, and timing within the cardiac cycle.METHODS AND RESULTS: VALIDATE-RFR was a retrospective study designed to derive and validate the RFR. The primary endpoint was the agreement between RFR and iFR. RFR was retrospectively determined in 651 waveforms in which iFR was measured using a proprietary Philips/Volcano wire. RFR was highly correlated to iFR (R2=0.99, pCONCLUSIONS: RFR is diagnostically equivalent to iFR but unbiased in its ability to detect the lowest Pd/Pa during the full cardiac cycle, potentially unmasking physiologically significant coronary stenoses that would be missed by assessment dedicated to specific segments of the cardiac cycle.