Hemodynamic Metrics Research Articles

Hemodynamic relationship with angioarchitecture of cerebral arteriovenous malformation and changes after embolization: a pilot study by 4D flow MR.

The hemodynamics of cerebral arteriovenous malformation (cAVM) is difficult to evaluate with conventional imaging or clinical grading. The aim of this study is to: (I) investigate the association between the angioarchitecture and hemodynamic parameters in cAVM based on 4-dimentional flow magnetic resonance (4D flow MR); (II) quantify flow changes during follow-up after embolization and explore the potential of flow-guided staged embolization. Twenty-one patients with digital subtraction angiography (DSA)-diagnosed cAVM were prospectively enrolled in a tertiary hospital consecutively from April 2022 to January 2024 for a cohort study. Lesion angioarchitecture at baseline was assessed by DSA. 4D flow MR was performed to assess hemodynamics. Flow-derived parameters included velocity, flow, time averaged wall shear stress (WSS) of the main feeding artery, and inflow-to-outflow ratio. Hemodynamic metrics were compared between groups with different angioarchitecture and rupture status. Seven patients had a post embolization follow-up 4D flow MR scan with a median interval of 8.9 months. Among multiple angioarchitectural features, supply by a single feeding artery (6/7 in the ruptured group and 0/14 in the unruptured group, P<0.001) and intra nidal aneurysm (7/7 in the ruptured group and 5/14 in the unruptured group, P=0.007) were significantly associated with lesion rupture. The ruptured cAVM showed lower total flow of feeding arteries (2.09±3.15 vs. 6.05±3.76 mL/s, P=0.029), lower WSS (0.99±0.73 vs. 2.10±0.45 Pa, P=0.023) and higher inflow-to-outflow ratio (2.46±0.79 vs. 1.46±0.55, P=0.041). During follow-up, the total flow of the lesions decreased by 10-100% after the embolization. The nidus volume decreased significantly (reduction rate: 59.6-100%, P=0.009). The flow of the minor feeding artery increased in 2 cases out of 5, indicating flow remodeling. Three patients had a second embolization guided by the follow-up imaging. cAVM lesions tend to have heterogeneous hemodynamics even with similar angioarchitecture. This could be captured and quantified on an individual basis using 4D flow MR. Flow analysis by MR offers the potential to guide a second embolization.

MicroRNA Profiling to Inform Disease Classification, Severity, and Treatment Response in Pediatric Pulmonary Hypertension.

Pediatric pulmonary hypertension is a heterogeneous disease associated with significant morbidity and mortality. MicroRNAs have been implicated as both pathologic drivers of disease and potential therapeutic targets in pediatric pulmonary hypertension. We sought to characterize the circulating microRNA profiles of a diverse array of pediatric pulmonary hypertension patients using high throughput sequencing technology. Peripheral blood samples were drawn from patients recruited at the time of a clinically indicated cardiac catheterization and microRNA sequencing followed by differential expression and target/pathway enrichment analyses were performed. Among 63 pediatric pulmonary hypertension patients, we identified specific microRNA signatures that uniquely classified patients by disease subtype, correlated with indicators of disease severity including invasive hemodynamic metrics, and changed over the course of treatment for pulmonary hypertension. These microRNA profiles include a number of specific microRNA molecules known to function in signaling pathways critical to pulmonary vascular biology and disease, including TGFβ beta, VEGF, PI3K/Akt, cGMP-PKG, and HIF-1 signaling. Circulating levels of miR-122-5p, miR-124-3p, miR-204-5p, and miR-9-5p decreased over the course of treatment in a subset of patients who had multiple samples drawn during the study period. Our findings support the further investigation of specific microRNAs as mechanistic mediators, biomarkers, and therapeutic targets in pulmonary hypertension.

Abstract 4124342: Invasive CPET-based hemodynamic correlates of abnormal peak VO 2 and V E /VCO 2 in HFpEF and pre-capillary Pulmonary Hypertension

Introduction: Pulmonary hypertension (PH) is a heterogeneous disease characterized by impaired gas exchange (CO 2 , O 2 ) in the pulmonary circulation, leading to dyspnea and exercise intolerance. We hypothesize that specific hemodynamic metrics correlate with poor gas exchange in PH phenotypes, which can be leveraged to define therapeutically relevant hemodynamic targets. Aim: This study aims to define hemodynamic correlates of poor gas exchange (peak VO 2 , V E /VCO 2 slope) in heart failure with preserved ejection fraction (HFpEF) and pre-capillary PH. Methods: We retrospectively analyzed 170 participants with invasive cardiopulmonary exercise testing: HFpEF (n=91), pre-capillary PH (n=54), and non-cardiac dyspnea (NCD, n=25). Linear regression models, adjusted for patient groups with interaction, were used to assess the association of peak VO 2 and V E /VCO 2 slope with predictors (pulmonary vascular resistance [PVR], distensibility, and pulmonary arterial compliance [PAC]). Results: In the order of NCD vs. HFpEF vs. pre-capillary PH, rest PAC (5.5±1.6 vs 3.8±1.7 vs 2.6±1.3 mL/mmHg), rest PVR (1.4±0.6 vs 3.2±2.0 vs 5.7±3.0 Woods unit), and distensibility (1.5±0.5 vs 0.8±0.4 vs 0.5±0.2 % per mmHg). In comparison to a non-significant correlation with rest PVR and distensibility, peak VO 2 (%predicted) showed significant correlation with rest PAC (p&lt;0.01) with significantly positive slope of +6 in HFpEF and +10 in pre-capillary PH. Similarly, significant slopes were noted with rest PAC and V E /VCO 2 relationship (p&lt;0.01) in HFpEF (-3) and pre-capillary PH (-4). Conclusion: Pulmonary arterial compliance (PAC) is the best correlate of poor gas exchange. Improving rest PAC by 1.0 mL/mmHg can lead to improvement in peak VO 2 predicted (+10% in pre-capillary PH, +6% in HFpEF), and V E /VCO 2 slope (-4 in pre-capillary PH, and -3 in HFpEF). In comparison to pre-capillary PH, more limited improvement in HFpEF is likely due to multi-organ dysfunction leading to exercise intolerance.

Development of a minimally invasive technique to measure the interstitial fluid pressure for remote monitoring of heart failure

Abstract Background Heart failure (HF) induces fluid interstitial retention, leading to oedema and elevated interstitial fluid pressure (IFP).1-3 There is a clinical need for remotely assessing IFP and understanding its correlation with cardiopulmonary haemodynamics for early treatment optimization in HF. IFP can be measured from a preserved fluid pocket formed by a subcutaneous perforated capsule in animals.4 However, the structural understanding of tissue neovascularization within a perforated capsule and the temporal relationship between altered cardiopulmonary haemodynamics and IFP remains unknown. Purpose To determine the neovascularisation of the perforated capsule over time and demonstrate the relationship between haemodynamic metrics of congestion (CVP, PAP, and LVEDP) and IFP during HF development. Methods Ten 45-55kg swine were implanted with subcutaneous perforated capsules. Perforated capsule characterisation included MicroCT using MicroFil cast (Fig. 1A) and microscopy initially at 3 and 6 weeks. A perforated capsule containing a PTFE (polytetrafluoroethylene) membrane was subcutaneously implanted in animals and chronic stability was studied at 90 using MicroCT and microscopy. After 3 weeks of perforated capsule implantation, HF was induced under general anaesthesia with 12-16 mg/kg/hour of esmolol (i.v.) and 0.9% NaCl (10% body weight, i.v.) and fluid was removed to euvolemia via ultrafiltration (Fig 2A). Concurrent measurements of IFP from perforated capsules and haemodynamic metrics of congestion were made using interventional techniques. Results MicroCT and microscopy have demonstrated perforated capsule neovascularization containing a central fluid pocket at 3 weeks and loss at 6 weeks due to continued tissue growth (Fig 1B-E). The perforated capsule at 90 days demonstrated fluid pocket preservation due to the PTFE membrane on MicroCT and microscopy (Fig. 1F-G). During the development of HF and offloading, there is a strong correlation between IFP and haemodynamic metrics of congestion (Fig. 2B). Conclusion We have developed a minimally invasive technique for continuous IFP measurement demonstrating a relationship between IFP and cardiac filling pressure in HF. IFP assessment offers a direct measure of fluid status and an indirect measure of haemodynamics, facilitating early treatment optimisation.

Poor correlation of venous lactate with systemic oxygen saturation in the paediatric cardiac ICU: a pilot study.

Cardiac intensive care providers require a comprehensive understanding of cardiac output and oxygen delivery. The estimation of cardiac output in clinical practice often relies on thermodilution and the Fick principle. Central venous saturation and lactate levels are commonly used indicators for cardiac output assessment. However, the relationship between venous lactate levels and venous oxygen saturation in paediatric cardiac intensive care patients remains unclear. This is a single-centre retrospective pilot study aimed to investigate the correlation between venous lactate and venous oxygen saturation in paediatric patients. Data collected included venous saturation, heart rate, mean arterial blood pressure, arterial saturation by pulse oximetry, cerebral and renal near-infra-red spectroscopy values, and the presence of a functionally univentricular heart. Statistical analyses included Bayesian Pearson correlation and regression analyses. A total of 203 data points from 37 unique patients were included in the analysis. There was no significant correlation between serum lactate and venous saturation (correlation coefficient = -0.01; Bayes factor 10 = 0.06). Serum lactate also did not correlate with other haemodynamic metrics. Venous saturation showed correlations with arterial saturation and cerebral and renal near-infra-red spectroscopy. Regression analysis revealed that parallel circulation, arterial saturation, and cerebral near-infra-red spectroscopy were predictive of venous saturation. The following equation resulted from the regression analysis: 68.0 - (12.7 x parallel circulation) - (0.8 x arterial saturation) + (0.3 x cerebral near-infra-red spectroscopy). This model had a Bayes factor 10 of 0.03 and adjusted R-squared was 0.29. In paediatric cardiac intensive care patients, there is no significant correlation between venous lactate and venous saturation, suggesting that lactate may not be a reliable marker for assessing the adequacy of oxygen delivery in this population. Only a weak correlation could be identified once the venous saturation was 70% or lower. Additional research is needed to explore alternative markers for monitoring oxygen delivery in critically ill paediatric patients.

Assessment of abnormal transvalvular flow and wall shear stress direction for pediatric/young adults with bicuspid aortic valve: a cross-sectional 4D flow study

BackgroundAortic dilation is seen in pediatric/young adult patients with bicuspid aortic valve (BAV), and hemodynamic markers to predict aortic dilation are necessary for monitoring. Although promising hemodynamic metrics, such as abnormal wall shear stress (WSS) magnitude, have been proposed for adult BAV patients using 4D flow cardiovascular magnetic resonance, those for pediatric BAV patients have less frequently been reported, partly due to scarcity of data to define normal WSS range. To circumvent this challenge, this study aims to investigate if a recently proposed 4D flow-based hemodynamic measurement, abnormal flow directionality, is associated with aortic dilation in pediatric/young adult BAV patients. Methods4D flow scans for BAV patients (<20 years old) and age-matched controls were retrospectively enrolled. Static segmentation for the aorta and pulmonary arteries was obtained to quantify peak systolic hemodynamics and diameters in the proximal aorta. In addition to peak velocity, wall shear stress (WSS), vorticity, helicity, and viscous energy loss, direction of aortic velocity and WSS in BAV patients was compared with that of control atlas using registration technique; angle differences of >60deg and >120deg were defined as moderately and severely abnormal, respectively. Association between the obtained metrics and normalized diameters (Z-scores) were evaluated at the sinotubular junction, mid ascending aorta, and distal ascending aorta. ResultsFifty-three BAV patients, including eighteen with history of repaired aortic coarctation, and seventeen controls were enrolled. Correlation between moderately abnormal velocity/WSS direction and aortic Z-scores was moderate to strong at the sinotubular junction and mid ascending aorta (R=0.62-0.81; p<0.001) while conventional measurements exhibited weaker correlation (|R|=0.003-0.47, p=0.009-0.99) in all subdomains. Multivariable regression analysis found moderately abnormal velocity direction and existence of aortic regurgitation (only for isolated BAV group) were independently associated with mid ascending aortic Z-scores. ConclusionAbnormal velocity and WSS directionality in the proximal aorta was strongly associated with aortic Z-scores in pediatric/young adult BAV patients.

Cardiac power output ratio: Novel survival predictor after percutaneous ventricular assist device in cardiogenic shock.

Currently, there is limited data on prognostic indicators after insertion of percutaneous ventricular assist device (PVAD) in the treatment of cardiogenic shock (CS). This study evaluated the prognostic role of cardiac power output (CPO) ratio, defined as CPO at 24h divided by early CPO (30min to 2h), in CS patients after PVAD. Consecutive CS patients from the QEH-PVAD Registry were followed up for survival at 90days after PVAD. Among 121 consecutive patients, 98 underwent right heart catheterization after PVAD, with CPO ratio available in 68 patients. The CPO ratio and 24-h CPO, but not the early CPO post PVAD, were significantly associated with 90-day survival, with corresponding area under curve in ROC analysis of 0.816, 0.740, and 0.469, respectively. In multivariate analysis, only the CPO ratio and lactate level at 24h remained as independent survival predictors. The CPO ratio was not associated with age, sex, and body size. Patients with lower CPO ratio had significantly lower coronary perfusion pressure, worse right heart indices, and higher pulmonary vascular resistance. A lower CPO ratio was also significantly associated with mechanical ventilation and higher creatine kinase levels in myocardial infarction patients. In post-PVAD patients, the CPO ratio outperformed the absolute CPO values and other haemodynamic metrics in predicting survival at 90days. Such a proportional change of CPO over time, likely reflecting native heart function recovery, may help to guide management of CS patients post-PVAD.

Description of the local hemodynamic environment in intracranial aneurysm wall subdivisions.

Intracranial aneurysms (IAs) pose severe health risks influenced by hemodynamics. This study focuses on the intricate characterization of hemodynamic conditions within the IA walls and their influence on bleb development, aiming to enhance understanding of aneurysm stability and the risk of rupture. The methods emphasized utilizing a comprehensive dataset of 359 IAs and 213 IA blebs from 268 patients to reconstruct patient-specific vascular models, analyzing blood flow using finite element methods to solve the unsteady Navier-Stokes equations, the segmentation of aneurysm wall subregions and the hemodynamic metrics wall shear stress (WSS), its metrics, and the critical points in WSS fields were computed and analyzed across different aneurysm subregions defined by saccular, streamwise, and topographical divisions. The results revealed significant variations in these metrics, correlating distinct hemodynamic environments with wall features on the aneurysm walls, such as bleb formation. Critical findings indicated that regions with low WSS and high OSI, particularly in the body and central regions of aneurysms, are prone to conditions that promote bleb formation. Conversely, areas exposed to high WSS and positive divergence, like the aneurysm neck, inflow, and outflow regions, exhibited a different but substantial risk profile for bleb development, influenced by flow impingements and convergences. These insights highlight the complexity of aneurysm behavior, suggesting that both high and low-shear environments can contribute to aneurysm pathology through distinct mechanisms.

Reproducibility of semi-quantitative assessment of aortic valve calcification and valve motion on echocardiography: a small-scale study

BackgroundAortic stenosis (AS) is the most common degenerative valve disease in high income countries. While hemodynamic metrics are commonly used to assess severity of stenosis, they are impacted by loading conditions and stroke volume and are often discordant. Anatomic valve assessments such as aortic valve calcification (AVC) and valve motion (VM) during transthoracic echocardiography (TTE) can offer clues to disease severity. The reliability of these semi-quantitatively assessed anatomic imaging parameters is unknown.MethodsThis is a retrospective study of semi-quantitative assessment of AVC and valve VM on TTE. TTEs representing a range of AS severities were identified. The degree of calcification of the aortic valve and the degree of restricted VM were assessed in standard fashion. AVC scores and valve motion were assessed by readers with varied training levels blinded to the severity of AS. Correlation and inter-reader reliability between readers were assessed.Results420 assessments (210 each for AVC and VM) were collected for 35 TTEs. Correlation of AVC for imaging trainees (fellows and students, respectively), ranged from 0.49 (95% CI 0.18–0.70) to 0.62 (95% CI 0.36–0.79) and 0.58 (95% CI 0.30–0.76) to 0.54 (95% CI 0.25–0.74) for VM. Correlation of anatomic assessments between echocardiographer-assigned AVC grades was r = 0.76 (95% CI 0.57–0.87)). The correlation between echocardiographer-assigned assessment of VM was r = 0.73 (95% CI 0.53–0.86), p < 0.00001 for both. For echocardiographer AVC assessment, weighted kappa was 0.52 (0.32–0.72), valve motion weighted kappa was 0.60 (0.42–0.78).ConclusionThere was good inter-reader correlation between TTE-based semi-quantitative assessment of AVC and VM when assessed by board certified echocardiographers. There was modest inter-reader reliability of semi-quantitative assessments of AVC and VM between board certified echocardiographers. Inter-reader correlation and reliability between imaging trainees was lower. More reliable methods to assess TTE based anatomic assessments are needed in order to accurately track disease progression.Clinical Trial NumberSTUDY00003100.

Subjects with carotid webs demonstrate pro-thrombotic hemodynamics compared to subjects with carotid atherosclerosis

Carotid artery webs (CaW) are non-atherosclerotic projections into the vascular lumen and have been linked to up to one-third of cryptogenic strokes in younger patients. Determining how CaW affects local hemodynamics is essential for understanding clot formation and stroke risk. Computational fluid dynamics simulations were used to investigate patient-specific hemodynamics in carotid artery bifurcations with CaW, bifurcations with atherosclerotic lesions having a similar degree of lumen narrowing, and with healthy carotid bifurcations. Simulations were conducted using segmented computed tomography angiography geometries with inlet boundary conditions extracted from 2D phase contrast MRI scans. The study included carotid bifurcations with CaW (n = 13), mild atherosclerosis (n = 7), and healthy bifurcation geometries (n = 6). Hemodynamic parameters associated with vascular dysfunction and clot formation, including shear rate, oscillatory shear index (OSI), low velocity, and flow stasis were calculated and compared between the subject groups. Patients with CaW had significantly larger regions containing low shear rate, high OSI, low velocity, and flow stasis in comparison to subjects with mild atherosclerosis or normal bifurcations. These abnormal hemodynamic metrics in patients with CaW are associated with clot formation and vascular dysfunction and suggest that hemodynamic assessment may be a tool to assess stroke risk in these patients.

A prospective observational study on hemodynamic risk in cerebral aneurysm growth

Introduction: Hemodynamic factors are thought to play a major role in the development, growth, and rupture of cerebral aneurysms, but the hemodynamics related to enlargement remain unclear. We prospectively enrolled patients with unruptured cerebral aneurysms and performed Computational Fluid Dynamics (CFD) analysis using 3D CT images to investigate differences in hemodynamic environments between aneurysms that grew and those that did not grow over a 3-year period. Methods: This prospective observational study was approved by the National Hospital Organization Central Ethics Review Board. Hemodynamic distributions were examined using ANSYS-CFX software. Patient-specific arterial geometries and inflow velocities were obtained from 3D-CTA and carotid ultrasound Doppler examinations. The distributions of hemodynamic metrics of 17 enlarged and 70 unenlarged aneurysms was compared. In addition, the distributions of hemodynamic metrics of the neck, body, and dome of the aneurysm was also examined in 9 enlarged and 41 non-enlarged cases. A multivariate logistic analysis was performed to investigate the influence of the six hemodynamic metrics, i.e., the time-averaged wall shear stress (TAWSS), time-averaged WSS gradient (TAWSSG), oscillatory shear index (OSI), gradient oscillatory number (GON), transverse WSS (transWSS), and normalized transWSS (NtransWSS) after adjustment forknown risk factors for aneurysm growth, i.e., age, sex, hypertension, smoking history, and aneurysm location, size, and history of subarachnoid hemorrhage. Results: Regarding the distributions of hemodynamic metrics throughout the aneurysm, NtransWSS was significantly higher in the cases with growth than in the cases without growth (odds ratio 2.09, 95% CI 1.02-4.29). the distributions of hemodynamic metrics at each cerebral aneurysm growth site showed that NtransWSS at the dome was significantly higher in the growth cases than in the non-enlargement cases (odds ratio 4.14, 95% CI 1.02-16.80). Conclusion: The data suggest that multidirectional disturbance of wall shear stress is involved in cerebral aneurysm growth, and the disturbance at the dome of the aneurysm may be particularly strongly related. This study was supported by a Grant-in-Aid from the Japanese National Hospital Organization Multi-Center Clinical Research, AMED under grant no. JP15gm0810006h0301 and a JSPS KAKENHI Grant, no. 15K10323. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Abstract 1089: Noninvasive Assessment Of Aortic Biomechanics Using 4-D Flow And Cardiovascular Magnetic Resonance In A Porcine Model Of Aortic Coarctation

Objectives: Aortic coarctation (COA) is a congenital heart disease that results from narrowing of the aorta, contributing to increased cardiovascular morbidity. Current animal models are limited by stenotic mechanism and study longevity. We introduce a porcine model of COA, treated with a novel growth stent and imaged with advanced MRI techniques, to obtain hemodynamic metrics. Methods: A total of 14 piglets, 4 sham, 4 coarcted controls (CC) and 6 coarcted stents (CS), underwent surgical creation of a COA. The timeline is detailed in Figure 1. Serial imaging was obtained on a 3.0T MRI scanner. Hemodynamic metrics were acquired in predefined vascular planes (Ensight, CEI) to assess net flow, velocities and helical or vortical flow. CMR image analysis using cvi42 (Circle, Canada) included T1 maps and cardiac function. Results: Analyses are shown at 20 weeks. For CMR, there were no differences in cardiac function metrics, left ventricular mass or T1 mapping. In the 4D Flow analysis, shown in Figure 2, ascending aortic flow averages 62.5 mL/cycle in the CS group, higher than the sham and CC groups (p= &lt;0.05). Both CS and CC animals have increased post-stenotic velocities (&gt;1.5m/s), compared to the sham aorta (p= 0.01). All coarcted aortas, both CS and CC, exhibited helical flow and post-stenotic dilatation. Conclusions: No hemodynamic differences were seen with CMR, reflecting minimal adverse myocardial remodeling. 4D MRI data revealed locational differences in flow, velocity and collateralization. In conclusion, this work illustrates a successful longitudinal large animal model of COA and validates advanced imaging methods in the study of vascular hemodynamics.

Changes in aorta hemodynamics in Left-Right Type 1 bicuspid aortic valve patients after replacement with bioprosthetic valves: An in-silico study.

Bicuspid aortic valve (BAV) is the most common cardiac congenital abnormality with a high rate of concomitant aortic valve and ascending aorta (AAo) pathologic changes throughout the patient's lifetime. The etiology of BAV-related aortopathy was historically believed to be genetic. However, recent studies theorize that adverse hemodynamics secondary to BAVs also contribute to aortopathy, but their precise role, specifically, that of wall shear stress (WSS) magnitude and directionality remains controversial. Moreover, the primary therapeutic option for BAV patients is aortic valve replacement (AVR), but the role of improved post-AVR hemodynamics on aortopathy progression is also not well-understood. To address these issues, this study employs a computational fluid dynamics model to simulate personalized AAo hemodynamics before and after TAVR for a small cohort of 6 Left-Right fused BAV patients. Regional distributions of five hemodynamic metrics, namely, time-averaged wall shear stress (TAWSS) and oscillating shear index (OSI), divergence of wall shear (DWSS), helicity flux integral & endothelial cell activation potential (ECAP), which are hypothesized to be associated with potential aortic injury are computed in the root, proximal and distal ascending aorta. BAVs are characterized by strong, eccentric jets, with peak velocities exceeding 4 m/s and axially circulating flow away from the jets. Such conditions result in focused WSS loading along jet attachment regions on the lumen boundary and weaker, oscillating WSS on other regions. The jet attachment regions also show alternating streaks of positive and negative DWSS, which may increase risk for local tissue stretching. Large WSS magnitudes, strong helical flows and circumferential WSS have been previously implicated in the progression of BAV aortopathy. Post-intervention hemodynamics exhibit weaker, less eccentric jets. Significant reductions are observed in flow helicity, TAWSS and DWSS in localized regions of the proximal AAo. On the other hand, OSI increases post-intervention and ECAP is observed to be low in both pre- and post-intervention scenarios, although significant increases are also observed in this ECAP. These results indicate a significant alleviation of pathological hemodynamics post AVR.

Dynamic load modulation predicts right heart tolerance of left ventricular cardiovascular assist in a porcine model of cardiogenic shock.

Ventricular assist devices (VADs) offer mechanical support for patients with cardiogenic shock by unloading the impaired ventricle and increasing cardiac outflow and subsequent tissue perfusion. Their ability to adjust ventricular assistance allows for rapid and safe dynamic changes in cardiac load, which can be used with direct measures of chamber pressures to quantify cardiac pathophysiologic state, predict response to interventions, and unmask vulnerabilities such as limitations of left-sided support efficacy due to intolerance of the right heart. We defined hemodynamic metrics in five pigs with dynamic peripheral transvalvular VAD (pVAD) support to the left ventricle. Metrics were obtained across a spectrum of disease states, including left ventricular ischemia induced by titrated microembolization of a coronary artery and right ventricular strain induced by titrated microembolization of the pulmonary arteries. A sweep of different pVAD speeds confirmed mechanisms of right heart decompensation after left-sided support and revealed intolerance. In contrast to the systemic circulation, pulmonary vascular compliance dominated in the right heart and defined the ability of the right heart to adapt to left-sided pVAD unloading. We developed a clinically accessible metric to measure pulmonary vascular compliance at different pVAD speeds that could predict right heart efficiency and tolerance to left-sided pVAD support. Findings in swine were validated with retrospective hemodynamic data from eight patients on pVAD support. This methodology and metric could be used to track right heart tolerance, predict decompensation before right heart failure, and guide titration of device speed and the need for biventricular support.

A comparative study of altered hemodynamics in iliac vein compression syndrome.

Introduction: Iliac vein compression syndrome (IVCS) is present in over 20% of the population and is associated with left leg pain, swelling, and thrombosis. IVCS symptoms are thought to be induced by altered pelvic hemodynamics, however, there currently exists a knowledge gap on the hemodynamic differences between IVCS and healthy patients. To elucidate those differences, we carried out a patient-specific, computational modeling comparative study. Methods: Computed tomography and ultrasound velocity and area data were used to build and validate computational models for a cohort of IVCS (N = 4, Subject group) and control (N = 4, Control group) patients. Flow, cross-sectional area, and shear rate were compared between the right common iliac vein (RCIV) and left common iliac vein (LCIV) for each group and between the Subject and Control groups for the same vessel. Results: For the IVCS patients, LCIV mean shear rate was higher than RCIV mean shear rate (550 ± 103s-1 vs. 113 ± 48s-1, p = 0.0009). Furthermore, LCIV mean shear rate was higher in the Subject group than in the Control group (550 ± 103s-1 vs. 75 ± 37s-1, p = 0.0001). Lastly, the LCIV/RCIV shear rate ratio was 4.6 times greater in the Subject group than in the Control group (6.56 ± 0.9 vs. 1.43 ± 0.6, p = 0.00008). Discussion: Our analyses revealed that IVCS patients have elevated shear rates which may explain a higher thrombosis risk and suggest that their thrombus initiation process may share aspects of arterial thrombosis. We have identified hemodynamic metrics that revealed profound differences between IVCS patients and Controls, and between RCIV and LCIV in the IVCS patients. Based on these metrics, we propose that non-invasive measurement of shear rate may aid with stratification of patients with moderate compression in which treatment is highly variable. More investigation is needed to assess the prognostic value of shear rate and shear rate ratio as clinical metrics and to understand the mechanisms of thrombus formation in IVCS patients.

A computational model-based study on the feasibility of predicting post-splenectomy thrombosis using hemodynamic metrics.

For portal hypertensive patients with splenomegaly and hypersplenism, splenectomy is an effective surgery to relieve the complications. However, patients who have undergone splenectomy often suffer from portal venous system thrombosis, a sequela that requires prophylaxis and timely treatment to avoid deterioration and death. The aim of this study is to investigate the feasibility of predicting post-splenectomy thrombosis using hemodynamic metrics based on computational models. First, 15 portal hypertensive patients who had undergone splenectomy were enrolled, and their preoperative clinical data and postoperative follow-up results were collected. Next, computational models of the portal venous system were constructed based on the preoperative computed tomography angiography images and ultrasound-measured flow velocities. On this basis, splenectomy was mimicked and the postoperative area of low wall shear stress (ALWSS) was simulated for each patient-specific model. Finally, model-simulated ALWSS was statistically compared with the patient follow-up results to investigate the feasibility of predicting post-splenectomy thrombosis using hemodynamic metrics. Results showed that ALWSS could predict the occurrence of post-splenectomy thrombosis with the area under the receiver operating characteristic curve (AUC) equal to 0.75. Moreover, statistical analysis implied that the diameter of the splenic vein is positively correlated with ALWSS (r = 0.883, p < 0.0001), and the anatomical structures of the portal venous system also influence the ALWSS. These findings demonstrated that the computational model-based hemodynamic metric ALWSS, which is associated with the anatomorphological features of the portal venous system, is capable of predicting the occurrence of post-splenectomy thrombosis, promoting better prophylaxis and postoperative management for portal hypertensive patients receiving splenectomy.

Assessing Passive Leg Raise Test in Pediatric Shock Using Electrical Cardiometry

AbstractPassive leg raise (PLR) is widely used to incite an autobolus to assess fluid responsiveness in adults; however, there is a paucity of studies exploring its utility in children. Our study aimed to analyze the efficacy of PLR in determining fluid responsiveness in children presenting with shock using electrical cardiometry. Patients in the age group of 0 to 20 years who presented in shock to our children's hospital emergency department were evaluated. Multiple hemodynamic metrics including, heart rate, systolic/diastolic blood pressure, cardiac output (CO), stroke index, stroke volume (SV), flow time corrected (FTC), and left ventricular ejection time (LVET) were recorded using the noninvasive ICON device and compared at baseline and post-PLR. A total of 68 patients had pre- and post-PLR data available for review between June and July 2022. Median age was 7 years (54% male); most common etiology was hypovolemic (67.6%) shock. Following PLR, there was no significant change in most hemodynamic parameters, including SV and CO; however, there was a significant difference in FTC (301 [pre-PLR] vs. 307 [post-PLR], p = 0.016) (ms) and LVET (232 [pre-PLR] vs. 234 [post-PLR], p = 0.014) (ms). A significantly higher proportion of children diagnosed with septic shock demonstrated fluid responsiveness (ΔSV ≥ 10% from baseline) compared with those with hypovolemic shock (p = 0.036). This study demonstrated no identifiable fluid responsiveness (ΔSV ≥ 10% from baseline) following PLR; however, a significantly higher proportion of children suffering from septic shock demonstrated fluid responsiveness compared with those with hypovolemic shock. Larger studies are needed to further assess the utility of PLR, as well as other modalities, in determining fluid responsiveness in children.

GRASP reconstruction amplified with view-sharing and KWIC filtering reduces underestimation of peak velocity in highly-accelerated real-time phase-contrast MRI: A preliminary evaluation in pediatric patients with congenital heart disease.

To develop a highly-accelerated, real-time phase contrast (rtPC) MRI pulse sequence with 40 fps frame rate (25 ms effective temporal resolution). Highly-accelerated golden-angle radial sparse parallel (GRASP) with over regularization may result in temporal blurring, which in turn causes underestimation of peak velocity. Thus, we amplified GRASP performance by synergistically combining view-sharing (VS) and k-space weighted image contrast (KWIC) filtering. In 17 pediatric patients with congenital heart disease (CHD), the conventional GRASP and the proposed GRASP amplified by VS and KWIC (or GRASP + VS + KWIC) reconstruction for rtPC MRI were compared with respect to clinical standard PC MRI in measuring hemodynamic parameters (peak velocity, forward volume, backward volume, regurgitant fraction) at four locations (aortic valve, pulmonary valve, left and right pulmonary arteries). The proposed reconstruction method (GRASP + VS + KWIC) achieved better effective spatial resolution (i.e., image sharpness) compared with conventional GRASP, ultimately reducing the underestimation of peak velocity from 17.4% to 6.4%. The hemodynamic metrics (peak velocity, volumes) were not significantly (p > 0.99) different between GRASP + VS + KWIC and clinical PC, whereas peak velocity was significantly (p < 0.007) lower for conventional GRASP. RtPC with GRASP + VS + KWIC also showed the ability to assess beat-to-beat variation and detect the highest peak among peaks. The synergistic combination of GRASP, VS, and KWIC achieves 25 ms effective temporal resolution (40 fps frame rate), while minimizing the underestimation of peak velocity compared with conventional GRASP.

Left atrial haemodynamic evaluation using 4D flow cardiac magnetic resonance imaging: application to hypertension and hypertrophic cardiomyopathy

Abstract Introduction Changes in left atrial (LA) hemodynamics have been suggested reflective of left ventricular (LV) disease progression. Kinetic energy (KE), viscous energy loss, and vorticity could be promising indices for the assessment of left atrial dynamics by time resolved four-dimensional cardiac magnetic resonance (4D flow CMR). Hypertrophic cardiomyopathy (HCM) patients are at risk of developing mitral regurgitation and left ventricular outflow tract obstruction, with poor outcome (1). Hypertensive myocardial remodelling has been suggested to be due to complex flow and tissue interactions leading to hypertrophy and diastolic dysfunction (2). Early detection of altered LA hemodynamic abnormalities may help non-invasive assessment, improving their long-term outcome (3). Purpose Quantitative and qualitative evaluation of left atrial hemodynamic metrics by 4D flow CMR in a cohort of HCM patients, hypertensive patients, and healthy controls with no known cardiovascular disease. Methods Eighteen HCM patients (50.0 [±18.2] years, 8 females), twenty-one hypertensive patients (55.2 [±6.2] years, 11 females), and seventeen controls (36.7 [±12.8] years, 1 female) underwent 4D flow CMR. Both patient groups had significantly higher LV-indexed mass, end-diastolic volume, and end-systolic volumes (P &amp;lt; 0.05). A semi-automated pipeline was used to segment the LA including pulmonary inflow and mitral outflow tracts using phase contrast magnetic resonance images derived from the 4D flow acquisition's phase and magnitude images. LA KE, viscous energy loss and vorticity were computed throughout the cardiac cycle. Results The HCM and hypertensive groups demonstrated significantly higher average KE integrated across the cardiac cycle (1.58 ± 0.79 and 1.32 ± 0.50 mJ respectively) compared to controls (1.20 ± 0.47 mJ) (P &amp;lt; 0.05), with the systolic curve in HCM showing the highest peak KE. Qualitatively, KE in the diastolic portion of the cardiac cycle appeared less variable between groups (Figure 1). Vorticity in HCM showed different configurations with loss of the central atrial vortex core (Figure 2). Viscous energy loss was also significantly higher in HCM patients confirming the increase in energy loss (Figure 2). Average KE across the cardiac cycle highly correlated with LA volume and pulmonary capillary wedge pressure calculated by a previously published regression method (4) (Pearson correlation: r= 0.76 and 0.71 respectively P &amp;lt; 0.05). There were also significant correlations with cardiac metrics such as indexed end-diastolic and indexed end-systolic volumes (Pearson correlation: r= 0.54 and 0.52 respectively P &amp;lt; 0.05) as well as indexed LV mass (r= 0.59 P &amp;lt; 0.05). Conclusion Hemodynamic metrics derived from 4D flow CMR may be valuable in establishing valuable predictive metrics of ventricular function. Integration of 4D flow MRI in clinical workflows could provide information that may be indicative of pathological onset before abnormal remodelling.Kinetic energy and viscous energy lossParticle pathlines and vorticity

Abstract 14195: Right Ventricular Outflow Tract Diameter Increase With the Low-Moderate Workload: A Prospective Simultaneous Exercise Echocardiography and Invasive Cardiopulmonary Exercise Testing Study

Background: While cardiac output at rest can be estimated non-invasively with echocardiogram, change in left ventricular or right ventricular outflow tract diameter (RVOTd) with exercise makes the cardiac output estimation inaccurate. Hypothesis: RVOTd increases with exercise proportionally with an incremental workload and is determined by stroke volume augmentation. Aims: 1. Define a workload-based change in RVOTd in subjects undergoing invasive cardiopulmonary exercise test (iCPET). 2. Correlate RVOTd at exercise stages with iCPET metrics. Methods: 20 subjects undergoing simultaneous echocardiogram and iCPET were enrolled in a prospective study. Exercise datapoints were acquired at 25 W (n=20), 50W (n=16), 75W (n=14), 100W (n=6). Three hemodynamic groups included: HFpEF (n=12), PAH (n=5), controls (n=3). Utilizing iCPET-based direct Fick cardiac output and stroke volume, RVOTd was reverse engineered with RVOT velocity time integral, per ASE guidelines. Pearson correlation was used to assess correlation of RVOTd with hemodynamic metrics. p&lt;0.05* Results: In overall cohort, age was 64±12 years, BMI 31.2±4.9 Kg/m 2 , female 60%, peak VO 2 13.7±5.7 mL/Kg.min -1 and V E /VCO 2 37±8. Increase in RVOTd with exercise is represented in the Figure. In comparison to rest, RVOTd increased significantly even at low-25W (+4.1±13.6%*) and moderate-50W (+7.6±17.2%*) workloads. Overall, RVOTd increased by 4-5% every 25W. At high workload (100W), the diameter increased by 24% (n=6). There were no differences in RVOT diameter between subgroups. RVOTd at four exercise stages (25W, 50W, 75W, 100W) correlated significantly with stroke volume index (r=0.68*, 0.80*, 0.23, 0.64) and cardiac output (r=0.50*, 0.80*, 0.08, 0.68), but non-significantly with heart rate (r=-0.15, 0.19, -0.10, 0.68). Conclusion: RVOTd increases by 4-5% every 25W on an incremental workload protocol. This behavior is predominantly associated with an increase in stroke volume index with exercise.