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.

Influence of intracoronary hemodynamic forces on atherosclerotic plaque phenotypes.

BACKGROUND AND AIMS: Coronary hemodynamics impact coronary plaque progression and destabilization. The aim of the present study was to establish the association between focal vs. diffuse intracoronary pressure gradients and wall shear stress (WSS) patterns with atherosclerotic plaque composition. METHODS: Prospective, international, single-arm study of patients with chronic coronary syndromes and hemodynamic significant lesions (fractional flow reserve [FFR] ≤ 0.80). Motorized FFR pullback pressure gradient (PPG), optical coherence tomography (OCT), and time-average WSS (TAWSS) and topological shear variation index (TSVI) derived from three-dimensional angiography were obtained. RESULTS: One hundred five vessels (median FFR 0.70 [Interquartile range (IQR) 0.56-0.77]) had combined PPG and WSS analyses. TSVI was correlated with PPG (r = 0.47, [95% Confidence Interval (95% CI) 0.30-0.65], p < 0.001). Vessels with a focal CAD (PPG above the median value of 0.67) had significantly higher TAWSS (14.8 [IQR 8.6-24.3] vs. 7.03 [4.8-11.7] Pa, p < 0.001) and TSVI (163.9 [117.6-249.2] vs. 76.8 [23.1-140.9] m-1, p < 0.001). In the 51 vessels with baseline OCT, TSVI was associated with plaque rupture (OR 1.01 [1.00-1.02], p = 0.024), PPG with the extension of lipids (OR 7.78 [6.19-9.77], p = 0.003), with the presence of thin-cap fibroatheroma (OR 2.85 [1.11-7.83], p = 0.024) and plaque rupture (OR 4.94 [1.82 to 13.47], p = 0.002). CONCLUSIONS: Focal and diffuse coronary artery disease, defined using coronary physiology, are associated with differential WSS profiles. Pullback pressure gradients and WSS profiles are associated with atherosclerotic plaque phenotypes. Focal disease (as identified by high PPG) and high TSVI are associated with high-risk plaque features. CLINICAL TRIAL REGISTRATION: https://clinicaltrials,gov/ct2/show/NCT03782688.

Coronary CT Angiography in the Cath Lab: Leveraging Artificial Intelligence to Plan and Guide Percutaneous Coronary Intervention.

The role of coronary CT angiography for the diagnosis and risk stratification of coronary artery disease is well established. However, its potential beyond the diagnostic phase remains to be determined. The current review focuses on the insights that coronary CT angiography can provide when planning and performing percutaneous coronary interventions. We describe a novel approach incorporating anatomical and functional pre-procedural planning enhanced by artificial intelligence, computational physiology and online 3D CT guidance for percutaneous coronary interventions. This strategy allows the individualisation of patient selection, optimisation of the revascularisation strategy and effective use of resources.

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.

Diagnostic performance of exercise stress tests for detection of epicardial and microvascular coronary artery disease: the UZ Clear study.

BACKGROUND: Cardiac stress tests remain the cornerstone for evaluating patients suspected of having obstructive coronary artery disease (CAD). Coronary microvascular dysfunction (CMD) can lead to abnormal non-invasive tests. AIMS: We sought to assess the diagnostic performance of exercise stress tests with indexes of epicardial and microvascular resistance as reference. METHODS: This was a prospective, single-arm, multicentre study of patients with an intermediate pretest probability of CAD and positive exercise stress tests who were referred for invasive angiography. Patients underwent an invasive diagnostic procedure (IDP) with measurement of fractional flow reserve (FFR) and index of microvascular resistance (IMR) in at least one coronary vessel. Obstructive CAD was defined as diameter stenosis (DS) >50% by quantitative coronary angiography (QCA). The objective was to determine the false discovery rate (FDR) of cardiac exercise stress tests with both FFR and IMR as references. RESULTS: One hundred and seven patients (137 vessels) were studied. The mean age was 62.1±8.7, and 27.1% were female. The mean diameter stenosis was 37.2±27.5%, FFR was 0.84±0.10, coronary flow reserve was 2.74±2.07, and IMR 20.3±11.9. Obstructive CAD was present in 39.3%, whereas CMD was detected in 20.6%. The FDR was 60.7% and 62.6% with QCA and FFR as references (p-value=0.803). The combination of FFR and IMR as clinical reference reduced the FDR by 25% compared to QCA (45.8% vs 60.7%; p-value=0.006). CONCLUSIONS: In patients with evidence of ischaemia, an invasive functional assessment accounting for the epicardial and microvascular compartments led to an improvement in the diagnostic performance of exercise tests, driven by a significant FDR reduction.

Radiofrequency Current Versus Balloon-Based Ablation for Atrial Fibrillation.

The basis for selection of contemporary ablation technologies for pulmonary vein isolation (PVI) in patients with atrial fibrillation (AF) remains unclear. We compared procedural data and efficacy in a propensity score-matched cohort treated with 4 ablation technologies in a center mainly using cryoballoon (CB). A total of 819 consecutive patients with AF underwent PVI, using radiofrequency current (RFC) (65 patients), CB (693 patients), hot balloon (HB) (74 patients), and laser balloon (LB) (52 patients). Fifty patients (82% paroxysmal AF) were selected from each group according to the propensity score. Procedural data and freedom from atrial tachyarrhythmia recurrence after the index procedure were compared. All pulmonary veins were isolated in all groups. Procedure time was shorter in CB and HB groups (RFC: 148 ± 53 vs CB: 85 ± 37 vs HB: 102 ± 31 vs LB: 140 ± 28 minutes, p <0.001). RFC touch-up was most commonly required for PVI in the HB group among balloon groups (40%) (p <0.001). Total complication rate was 4% to 18% without any statistical differences between groups (p = 0.123). Phrenic nerve injury occurred most often in the CB group (16%) (p <0.001). During a mean follow-up of 21 ± 6 months, there were no significant differences among groups for freedom from atrial tachyarrhythmia recurrence after the index procedure (RFC: 68% vs CB: 78% vs HB: 76% vs LB: 76%, p = 0.440). In conclusion, all the ablation technologies facilitate safe and efficient PVI, with slight differences in the procedural data and complications.

Prognostic predictors and echocardiographic time course after device replacement in patients treated chronically with cardiac resynchronization therapy devices.

The prognostic predictors of death or heart failure hospitalization and the echocardiographic response after initial cardiac resynchronization therapy (CRT) device replacement (CRT-r) remain unclear. We evaluated the predictors and the echocardiographic time course in patients after CRT-r. Consecutive 60 patients underwent CRT-r because of battery depletion. Patients were divided into two groups depending on the chronic echocardiographic response to CRT (left ventricular end-systolic volume [LVESV] reduction of ≥ 15%) at the time of CRT-r: CRT responders (group A; 35 patients) and CRT nonresponders (group B; 25 patients). The primary endpoint was a composite of death from any cause or heart failure hospitalization. Changes in LVESV and left ventricular ejection fraction (LVEF) after CRT-r were also analyzed. During the mean follow-up of 46 ± 33 months after CRT-r, the primary endpoint occurred more frequently in group B (group A versus group B; 8/35 [23%] patients versus 19/25 [76%] patients, p < 0.001). No significant changes in LVESV and LVEF were observed at the mean of 46 ± 29 months after CRT-r in both groups. A multivariate analysis identified echocardiographic nonresponse to CRT, chronic kidney disease, atrial fibrillation, and New York Heart Association functional class III or IV at the time of CRT-r as independent predictors of the primary endpoint in all patients. Residual echocardiographic nonresponse, comorbidities, and heart failure symptoms at the time of CRT-r predict the subsequent very long-term prognosis after CRT-r. No further echocardiographic response to CRT was found after CRT-r.

Evaluation of different ablation strategies verifying the optimal overlap ratio in point-by-point laser balloon ablation for patients with atrial fibrillation.

BACKGROUND: Optimal overlap ratio remains unclear in point-by-point laser balloon (LB) ablation. OBJECTIVE: This study sought to determine the optimal overlap strategy with target energies on the acute and chronic outcomes in LB pulmonary vein (PV) isolation (PVI). METHODS: Consecutive 38 patients (148 PVs) with atrial fibrillation underwent the first-generation LB PVI with the following protocols based on the overlap ratios for each PV anterior/posterior wall: 50%/50% (13 patients [49 PVs], group A), 50%/25% (15 patients [60 PVs], group B), and 25%/25% (10 patients [39 PVs], group C). High energies (240-255 J: 12 W / 20 seconds, 8.5 W / 30 seconds), moderate energies (200-210 J: 10 W / 20 seconds, 7 W / 30 seconds), and low-to-moderate energies (low, 165-170 J: 5.5 W / 30 seconds, 8.5 W / 20 seconds) were targeted for left PV anterior walls, right PV anterior walls, and bilateral PV posterior walls, respectively. First-pass PVI, the other procedure-related data, and atrial tachyarrhythmia recurrences were analyzed. RESULTS: First-pass PVI rate per PV was higher in group A (94%) than in group B (88%) and group C (62%) (P < .001). All PVs were finally isolated. First-pass time, total LB PVI time, complications, and atrial tachyarrhythmia recurrences during a mean follow-up of 11 ± 5 months did not differ between the groups. A few residual gaps after first-pass LB ablations were found for PV anterior walls even in group A and group B. CONCLUSION: Sufficiently overlapped LB ablation promises a high rate of first-pass PVI without adverse outcomes. High energy could be required for PV anterior walls.

Pacemaker implantation using the SelectSecure system for a patient with persistent left superior vena cava and absent right superior vena cava: Insights into techniques for stable lead fixation.

The techniques for successful pacemaker implantation via the PLSVC with the SelectSecure system (Medtronic, Minneapolis, Minnesota, USA) are unknown. Regarding the techniques, we presented a case in which we implanted a pacemaker via the PLSVC in patient with absent RSVC using the SelectSecure system.