Viscous energy loss in the presence of abnormal aortic flow

Multiscale structure and function of the aortic valve apparatus

Whereas studying the aortic valve in isolation has facilitated the development of life-saving procedures and technologies, the dynamic interplay of the aortic valve and its surrounding structures is vital to preserving their function across the wide range of conditions encountered in an active lifestyle. Our view is that these structures should be viewed as an integrated functional unit, here referred to as the aortic valve apparatus (AVA). The coupling of the aortic valve and root, left ventricular outflow tract, and blood circulation is crucial for AVA's functions: unidirectional flow out of the left ventricle, coronary perfusion, reservoir function, and support of left ventricular function. In this review, we explore the multiscale biological and physical phenomena that underlie the simultaneous fulfillment of these functions. A brief overview of the tools used to investigate the AVA, such as medical imaging modalities, experimental methods, and computational modeling, specifically fluid-structure interaction (FSI) simulations, is included. Some pathologies affecting the AVA are explored, and insights are provided on treatments and interventions that aim to maintain quality of life. The concepts explained in this article support the idea of AVA being an integrated functional unit and help identify unanswered research questions. Incorporating phenomena through the molecular, micro, meso, and whole tissue scales is crucial for understanding the sophisticated normal functions and diseases of the AVA.

Interactive effect of hemodynamics in transverse sigmoid sinus and bone morphology on venous pulsatile tinnitus: a four-dimensional (4D) flow magnetic resonance imaging (MRI) study

Background

The hemodynamic pathogenesis of venous pulsatile tinnitus (VPT) is still unclear. This study aimed to explore the mechanism of bone morphology and hemodynamic changes in transverse sigmoid sinus (TSS) on VPT patients.

Methods

49 patients with unilateral VPT, 26 patients with subjective tinnitus and 36 healthy controls were included in this retrospective clinical trial. Four-dimensional (4D) flow magnetic resonance imaging (MRI) was used to evaluate the hemodynamics of the TSS. High-resolution computed tomography was used to assess the perivenous bone structures. All images were independently assessed for each participant by two trained neuroradiologists. Kolmogorov-Smirnov test was used to determine the normal distribution of the data. Chi-square test and nonparametric test were used to compare classified or continuous variables. Stepwise linear regression and mediation effect analysis was used to explore the relationship between bone dehiscence (BD), hemodynamic factors and VPT symptoms.

Results

Peak velocity (P=0.001) and maximum energy loss (P=0.041) in VPT group were risk factors for the severity of tinnitus. Energy loss [indirect effect =0.692, P<0.005, 95% confidence interval (CI): 0.201-1.377] and peak velocity (indirect effect =0.899, P<0.005, 95% CI: 0.406-1.582) demonstrated the complete mediation effect between the BD and VPT. BD showed a complete mediation effect between the wall shear stress (WSS) and VPT (indirect effect =15.181, P<0.005, 95% CI: 3.448-35.493).

Conclusions

Cross-talk between the hemodynamic changes of TSS and BD can regulate the VPT symptoms. This type of analysis might be helpful in establishing the possible occurrence and development mechanism of the hemodynamics and bone morphology of the VPT.

Abnormal Cardiac Magnetic Resonance-Derived Ascending Aortic Area Strain Demonstrates Altered Ventriculo-Vascular Function in Marfan Syndrome

PURPOSE

There remains a need for improved imaging markers for risk stratification and treatment guidance in Marfan syndrome (MFS). After aortic root replacement (ARR), vascular remodeling and progressive aneurysm formation can occur due to alterations in up- and downstream wall biomechanics and hemodynamics. We aim to compare the ventriculo-vascular properties of patients with MFS with controls, and investigate the correlation between ascending aortic area strain and descending aortic area strain (DAAS) with other clinical variables.

PATIENTS AND METHODS

Nineteen patients with MFS (47% males), including 6 with ARR were studied. In 26 studies, aortic area strain was measured using cross-sectional cardiac magnetic resonance images at the ascending and proximal descending aortic levels. Left atrial, left ventricular longitudinal, and left ventricle circumferential strain (left atrial longitudinal strain, left ventricular longitudinal strain, and left ventricular circumferential strain, respectively) were measured using cardiac magnetic resonance-feature tracking.

RESULTS

Compared with healthy controls, patients with MFS had significantly impaired left ventricular longitudinal strain and left ventricular circumferential strain (-15.8 ± 4.7 vs -19.7 ± 4.8, P = 0.005, and -17.7 ± 4.0 vs -27.0 ± 4.1, P < 0.001). Left atrial longitudinal strain was comparable between patients with MFS and controls. AAAS was significantly reduced (19.0 [11.9, 23.7] vs 46.1 ± 11.3, P < 0.001), whereas DAAS was not significantly decreased. AAAS and DAAS were negatively correlated with age, whereas no significant associations were identified with left ventricle function indices. No significant differences were observed between the ventriculo-vascular properties of patients with MFS who underwent ARR and those who did not.

CONCLUSION

Patients with MFS demonstrated impaired ventricular and vascular function compared with healthy controls. Further investigations are warranted to determine clinical utility of aortic stiffness indices for predicting primary and repeat aortic events.

Multidirectional myocardial function in bicuspid aortic valve stenosis patients: a three-dimensional speckle tracking analysis

Purpose

The impact of aortic stenosis (AS) severity on multidirectional myocardial function in patients with bicuspid aortic valve (BAV) remains unclear, despite the recognized presence of early left ventricular longitudinal myocardial dysfunction in BAV patients with normal valve function. The aim of the study was to evaluate the multidirectional myocardial functions of BAV patients.

Methods

A total of 86 BAV patients (age 46.71 ± 13.62 years, 69.4% men) with normally functioning (BAV-nf), mild AS, moderate AS, and severe AS with preserved left ventricular ejection fraction (LVEF ≥ 52%) were included. 30 healthy volunteers were recruited as the control group. Multidirectional strain and volume analysis were performed by three-dimensional speckle tracking echocardiography(3D-STE).

Results

Global longitudinal strain (GLS), and global radial strain (GRS) were reduced in BAV-nf patients compared with the controls. With each categorical of AS severity from BAV-nf to severe AS, there was an associated progressive impairment of GLS and GRS (all P < 0.001). Global circumferential strain (GCS) did not show a significant decrease from BAV-nf to mild AS but began to decrease from moderate AS. Multiple linear regressions indicated that indexed aortic valve area (AVA/BSA), as a measure of AS severity, was an independent determinant of GLS, GCS and GRS.

Conclusions

Left ventricular longitudinal myocardial reduction is observed even in patients with well-functioning bicuspid aortic valves. With each categorical increase in the grade of AS severity from normally functioning to severe aortic stenosis, there was an associated progressive impairment of longitudinal myocardial function. Furthermore, circumferential myocardial function was starting damaged from moderate AS. AVA/BSA was independently associated with multidirectional myocardial function injuries.

Interval changes in four-dimensional flow-derived in vivo hemodynamics stratify aortic growth in type B aortic dissection patients

BACKGROUND

Aortic diameter growth in type B aortic dissection (TBAD) is associated with progressive aortic dilation, resulting in increased mortality in patients with both de novo TBAD (dnTBAD) and residual dissection after type A dissection repair (rTAAD). Preemptive thoracic endovascular aortic repair may improve mortality in patients with TBAD, although it is unclear which patients may benefit most from early intervention. In vivo hemodynamic assessment using four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has been used to characterize TBAD patients with growing aortas. In this longitudinal study, we investigated whether changes over time in 4D flow-derived true and false lumen (TL and FL) hemodynamic parameters correlate with aortic growth rate, which is a marker of increased risk.

METHODS

We retrospectively identified TBAD patients with baseline and follow-up 4D flow CMR at least 120 days apart. Patients with TBAD intervention before baseline or between scans were excluded. 4D flow CMR data analysis included segmentation of the TL and FL, followed by voxel-wise calculation of TL and FL total kinetic energy (KE), maximum velocity (MV), mean forward flow (FF), and mean reverse flow (RF). Changes over time (Δ) were calculated for all hemodynamic parameters. Maximal diameter in the descending aorta was measured from magnetic resonance angiogram images acquired at the time of 4D flow. Aortic growth rate was defined as the change in diameter divided by baseline diameter and standardized to scan interval.

RESULTS

Thirty-two patients met inclusion criteria (age: 56.9 ± 14.1 years, female: 13, n = 19 rTAAD, n = 13 dnTBAD). Mean follow-up time was 538 days (range: 135-1689). Baseline aortic diameter did not correlate with growth rate. In the entire cohort, Δ FL MV (Spearman's rho [rho] = 0.37, p = 0.04) and Δ FL RF (rho = 0.45, p = 0.01) correlated with growth rate. In rTAAD only, Δ FL MV (rho = 0.48, p = 0.04) and Δ FL RF (rho = 0.51, p = 0.03) correlated with growth rate, while in dnTBAD only, Δ TL KE (rho = 0.63, p = 0.02) and Δ TL MV (rho = 0.69, p = 0.01) correlated with growth rate.

CONCLUSION

4D flow-derived longitudinal hemodynamic changes correlate with aortic growth rate in TBAD and may provide additional prognostic value for risk stratification. 4D flow MRI could be integrated into existing imaging protocols to allow for the identification of TBAD patients who would benefit from preemptive surgical or endovascular intervention.

Thoracic aorta injury detected by 4D flow MRI predicts subsequent main adverse cardiovascular events in breast cancer patients receiving anthracyclines: A longitudinal study

PURPOSE

To investigate longitudinal thoracic aorta injury using 3-dimensional phase-contrast magnetic resonance imaging (4D flow MRI) parameters and to evaluate their value for predicting the subsequent main adverse cardiovascular events (MACEs) in breast cancer patients receiving anthracyclines.

METHODS

Between July 2020 and July 2021, eighty-eight female participants with breast cancer scheduled to receive anthracyclines with or without trastuzumab prospectively enrolled. Each subjects underwent 4D flow MRI at baseline, 3 and 6 months in relation to baseline. The diameter, peak velocity (Vpeak), wall shear stress (WSS), pulse wave velocity (PWV), energy loss (EL) and pressure gradient (PG) of thoracic aorta were measured. The association between these parameters and subsequent MACEs was performed by Cox proportional hazard models.

RESULTS

Ten participants had subsequently MACEs. The Vpeak and PG gradually decreased and the WSS, PWV and EL progressively increased at 3 and 6 months compared with baseline. Adjusted multivariable analysis showed that the WSS of the proximal, mid- and distal ascending aorta [HR, 1.314 (95% confidence interval (CI): 1.003, 1.898)], [HR, 1.320 (95% CI: 1.002, 1.801)] and [HR, 1.322 (95% CI: 1.001, 1.805)] and PWV of ascending aorta [HR, 2.223 (95% CI: 1.010, 4.653)] at 3 months were associated with subsequent MACEs. Combined WSS and PWV of ascending aorta at 3 months yielded the highest AUC (0.912) for predicting subsequent MACEs.

CONCLUSION

Combined WSS and PWV of ascending aorta at 3 months is helpful for predicting the subsequent MACEs in breast cancer patients treated by anthracyclines.

Assessment of aortic hemodynamics in patients with thoracoabdominal aortic aneurysm using four-dimensional magnetic resonance imaging: a cross-sectional study

Background

Thoracoabdominal aortic aneurysms (TAAAs) are rare but complicated aortic pathologies that can result in high morbidity and mortality. The whole-aorta hemodynamic characteristics of TAAA survivors remains unknown. This study sought to obtain a comprehensive view of flow hemodynamics of the whole aorta in patients with TAAA using four-dimensional flow (4D flow) magnetic resonance imaging (MRI).

Methods

This study included patients who had experienced TAAA or abdominal aortic aneurysm (AAA) and age- and sex-matched volunteers who had attended China Hospital from December 2021 to December 2022 in West. Patients with unstable ruptured aneurysm or other cardiovascular diseases were excluded. 4D-flow MRI that covered the whole aorta was acquired. Both planar parameters [(regurgitation fraction (RF), peak systolic velocity (Vmax), overall wall shear stress (WSS)] and segmental parameters [pulse wave velocity (PWV) and viscous energy loss (VEL)] were generated during postprocessing. The Student's t-test or Mann-Whitney test was used to compare flow dynamics among the three groups.

Results

A total of 11 patients with TAAA (mean age 53.2±11.9 years; 10 males), 19 patients with AAA (mean age 58.0±11.7 years; 16 males), and 21 controls (mean age 55.4±15.0 years; 19 males) were analyzed. The patients with TAAA demonstrated a significantly higher RF and lower Vmax in the aortic arch compared to healthy controls. The whole length of the aorta in patients with TAAA was characterized by lower WSS, predominantly in the planes of pulmonary artery bifurcation and the middle infrarenal planes (all P values <0.001). As for segmental hemodynamics, compared to controls, patients with TAAA had a significantly higher PWV in the thoracic aorta (TAAA: median 11.41 m/s, IQR 9.56-14.32 m/s; control: median 7.21 m/s, IQR 5.57-7.79 m/s; P<0.001) as did those with AAA (AAA: median 8.75 m/s, IQR 7.35-10.75 m/s; control: median 7.21 m/s, IQR 5.57-7.79 m/s; P=0.024). Moreover, a greater VEL was observed in the whole aorta and abdominal aorta in patients with TAAA.

Conclusions

Patients with TAAA exhibited a stiffer aortic wall with a lower WSS and a greater VEL for the whole aorta, which was accompanied by a higher RF and lower peak velocity in the dilated portion of the aorta.

Patient-specific tissue engineered vascular graft for aortic arch reconstruction

Objectives

The complexity of aortic arch reconstruction due to diverse 3-dimensional geometrical abnormalities is a major challenge. This study introduces 3-dimensional printed tissue-engineered vascular grafts, which can fit patient-specific dimensions, optimize hemodynamics, exhibit antithrombotic and anti-infective properties, and accommodate growth.

Methods

We procured cardiac magnetic resonance imaging with 4-dimensional flow for native porcine anatomy (n = 10), from which we designed tissue-engineered vascular grafts for the distal aortic arch, 4 weeks before surgery. An optimal shape of the curved vascular graft was designed using computer-aided design informed by computational fluid dynamics analysis. Grafts were manufactured and implanted into the distal aortic arch of porcine models, and postoperative cardiac magnetic resonance imaging data were collected. Pre- and postimplant hemodynamic data and histology were analyzed.

Results

Postoperative magnetic resonance imaging of all pigs with 1:1 ratio of polycaprolactone and poly-L-lactide-co-ε-caprolactone demonstrated no specific dilatation or stenosis of the graft, revealing a positive growth trend in the graft area from the day after surgery to 3 months later, with maintaining a similar shape. The peak wall shear stress of the polycaprolactone/poly-L-lactide-co-ε-caprolactone graft portion did not change significantly between the day after surgery and 3 months later. Immunohistochemistry showed endothelization and smooth muscle layer formation without calcification of the polycaprolactone/poly-L-lactide-co-ε-caprolactone graft.

Conclusions

Our patient-specific polycaprolactone/poly-L-lactide-co-ε-caprolactone tissue-engineered vascular grafts demonstrated optimal anatomical fit maintaining ideal hemodynamics and neotissue formation in a porcine model. This study provides a proof of concept of patient-specific tissue-engineered vascular grafts for aortic arch reconstruction.

Evaluating a Phase-Specific Approach to Aortic Flow: A 4D Flow MRI Study

BACKGROUND

Aortic flow parameters can be quantified using 4D flow MRI. However, data are sparse on how different methods of analysis influence these parameters and how these parameters evolve during systole.

PURPOSE

To assess multiphase segmentations and multiphase quantification of flow-related parameters in aortic 4D flow MRI.

STUDY TYPE

Prospective.

POPULATION

40 healthy volunteers (50% male, 28.9 ± 5.0 years) and 10 patients with thoracic aortic aneurysm (80% male, 54 ± 8 years).

FIELD STRENGTH/SEQUENCE

4D flow MRI with a velocity encoded turbo field echo sequence at 3 T.

ASSESSMENT

Phase-specific segmentations were obtained for the aortic root and the ascending aorta. The whole aorta was segmented in peak systole. In all aortic segments, time to peak (TTP; for flow velocity, vorticity, helicity, kinetic energy, and viscous energy loss) and peak and time-averaged values (for velocity and vorticity) were calculated.

STATISTICAL TESTS

Static vs. phase-specific models were assessed using Bland-Altman plots. Other analyses were performed using phase-specific segmentations for aortic root and ascending aorta. TTP for all parameters was compared to TTP of flow rate using paired t-tests. Time-averaged and peak values were assessed using Pearson correlation coefficient. P < 0.05 was considered statistically significant.

RESULTS

In the combined group, velocity in static vs. phase-specific segmentations differed by 0.8 cm/sec for the aortic root, and 0.1 cm/sec (P = 0.214) for the ascending aorta. Vorticity differed by 167 sec-1  mL-1 (P = 0.468) for the aortic root, and by 59 sec-1  mL-1 (P = 0.481) for the ascending aorta. Vorticity, helicity, and energy loss in the ascending aorta, aortic arch, and descending aorta peaked significantly later than flow rate. Time-averaged velocity and vorticity values correlated significantly in all segments.

DATA CONCLUSION

Static 4D flow MRI segmentation yields comparable results as multiphase segmentation for flow-related parameters, eliminating the need for time-consuming multiple segmentations. However, multiphase quantification is necessary for assessing peak values of aortic flow-related parameters.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 3.

Multimodality magnetic resonance evaluating the effect of enhanced physical exercise on the growth rate, flow haemodynamics, aneurysm wall and ventricular-aortic coupling of patients with small abdominal aortic aneurysms (AAA MOVE trial): a study protocol for an open-label randomised controlled trial

INTRODUCTION

The best lifestyle for small abdominal aortic aneurysms (sAAA) is essential for its conservative management. Physical exercise can improve the cardiopulmonary function of the patients, but it remains unclear which specific type of exercise is most beneficial for individuals with sAAA. The current study was designed to investigate the effect of physician-guided enhanced physical exercise programme on the aorto-cardiac haemodynamic environment, aneurysm sac wall, cardiac function and growth rate of sAAA by multimodality MRI.

METHODS AND ANALYSIS

AAA MOVE study is a prospective, parallel, equivalence, randomised controlled trial. Eligible individuals will be recruited if they are diagnosed with sAAA (focal dilation of abdominal aorta with maximum diameter <5 cm), without contraindication for MRI scanning, or severe heart failure, or uncontrolled arrhythmia. Participants will be randomly allocated to intervention group (physician-guided enhanced physical exercise programme: mainly aerobic training) and control group (standard clinical care) separately in a 1:1 ratio. The primary outcome is 12-month growth rate of sAAA. The first set of secondary outcomes involve multimodality MRI parameters covering flow haemodynamics, aortic wall inflammation and cardiac function. The other secondary outcome (safety end point) is a composite of exercise-related injury, aneurysm rupture and aneurysm intervention. Follow-up will be conducted at 6 and 12 months after intervention.

ETHICS AND DISSEMINATION

This study was approved by the Ethics Committee on Biomedical Research of West China Hospital (approval number: 2023-783) on 16 June 2023. Main findings from the trial will be disseminated through presentations at conferences, peer-reviewed publications and directly pushed to smartphone of participants.

TRIAL REGISTRATION NUMBER

ChiCTR2300073334.

Biomechanical Evaluation of Aortic Valve Stenosis by Means of a Virtual Stress Test: A Fluid-Structure Interaction Study

The impact of aortic valve stenosis (AS) extends beyond the vicinity of the narrowed leaflets into the left ventricle (LV) and into the systemic vasculature because of highly unpredictable valve behavior and complex blood flow in the ascending aorta that can be attributed to the strong interaction between the narrowed cusps and the ejected blood. These effects can become exacerbated during exercise and may have implications for disease progression, accurate diagnosis, and timing of intervention. In this 3-D patient-specific study, we employ strongly coupled fluid-structure interaction (FSI) modeling to perform a comprehensive biomechanical evaluation of systolic ejection dynamics in a stenosed aortic valve (AV) during increasing LV contraction. Our model predictions reveal that the heterogeneous ∆P vs. Q relationship that was observed in our previous clinical study can be attributed to a non-linear increase (by ~ 1.5-fold) in aortic valve area as LV heart rate increases from 70 to 115 bpm. Furthermore, our results show that even for a moderately stenotic valve, increased LV contraction during exercise can lead to high-velocity flow turbulence (Re = 11,700) in the aorta similar to that encountered with a severely stenotic valve (Re ~ 10,000), with concomitant greater viscous loss (~3-fold increase) and elevated wall stress in the ascending aorta. Our FSI predictions also reveal that individual valve cusps undergo distinct and highly non-linear increases (>100%) in stress during exercise, potentially contributing to progressive calcification. Such quantitative biomechanical evaluations from realistic FSI workflows provide insights into disease progression and can be integrated with current stress testing for AS patients to comprehensively predict hemodynamics and valve function under both baseline and exercise conditions.

A hemodynamic analysis of energy loss in abdominal aortic aneurysm using three-dimension idealized model

Objective: The aim of this study is to perform specific hemodynamic simulations of idealized abdominal aortic aneurysm (AAA) models with different diameters, curvatures and eccentricities and evaluate the risk of thrombosis and aneurysm rupture. Methods: Nine idealized AAA models with different diameters (3 cm or 5 cm), curvatures (0° or 30°) and eccentricities (centered on or tangent to the aorta), as well as a normal model, were constructed using commercial software (Solidworks; Dassault Systemes S.A, Suresnes, France). Hemodynamic simulations were conducted with the same time-varying volumetric flow rate extracted from the literature and 3-element Windkessel model (3 EWM) boundary conditions were applied at the aortic outlet. Several hemodynamic parameters such as time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), endothelial cell activation potential (ECAP) and energy loss (EL) were obtained to evaluate the risk of thrombosis and aneurysm rupture under different conditions. Results: Simulation results showed that the proportion of low TAWSS region and high OSI region increases with the rising of aneurysm diameter, whereas decreases in the curvature and eccentric models of the corresponding diameters, with the 5 cm normal model having the largest low TAWSS region (68.5%) and high OSI region (40%). Similar to the results of TAWSS and OSI, the high ECAP and high RRT areas were largest in the 5 cm normal model, with the highest wall-averaged value (RRT: 5.18 s, ECAP: 4.36 Pa-1). Differently, the increase of aneurysm diameter, curvature, and eccentricity all lead to the increase of mean flow EL and turbulent EL, such that the highest mean flow EL (0.82 W · 10-3) and turbulent EL (1.72 W · 10-3) were observed in the eccentric 5 cm model with the bending angle of 30°. Conclusion: Collectively, increases in aneurysm diameter, curvature, and eccentricity all raise mean flow EL and turbulent flow EL, which may aggravate the damage and disturbance of flow in aneurysm. In addition, it can be inferred by conventional parameters (TAWSS, OSI, RRT and ECAP) that the increase of aneurysm diameter may raise the risk of thrombosis, whereas the curvature and eccentricity appeared to have a protective effect against thrombosis.

Measurement of Turbulent Kinetic Energy in Hypertrophic Cardiomyopathy Using Triple-velocity Encoding 4D Flow MR Imaging

PURPOSE

The turbulent kinetic energy (TKE) estimation based on 4D flow MRI has been currently developed and can be used to estimate the pressure gradient. The objective of this study was to validate the clinical value of 4D flow-based TKE measurement in patients with hypertrophic cardiomyopathy (HCM).

METHODS

From April 2018 to March 2019, we recruited 28 patients with HCM. Based on echocardiography, they were divided into obstructed HCM (HOCM) and non-obstructed HCM (HNCM). Triple-velocity encoding 4D flow MRI was performed. The volume-of-interest from the left ventricle to the aortic arch was drawn semi-automatically. We defined peak turbulent kinetic energy (TKEpeak) as the highest TKE phase in all cardiac phases.

RESULTS

TKEpeak was significantly higher in HOCM than in HNCM (14.83 ± 3.91 vs. 7.11 ± 3.60 mJ, P < 0.001). TKEpeak was significantly higher in patients with systolic anterior movement (SAM) than in those without SAM (15.60 ± 3.96 vs. 7.44 ± 3.29 mJ, P < 0.001). Left ventricular (LV) mass increased proportionally with TKEpeak (P = 0.012, r = 0.466). When only the asymptomatic patients were extracted, a stronger correlation was observed (P = 0.001, r = 0.842).

CONCLUSION

TKE measurement based on 4D flow MRI can detect the flow alteration induced by systolic flow jet and LV outflow tract geometry, such as SAM in patients with HOCM. The elevated TKE is correlated with increasing LV mass. This indicates that increasing cardiac load, by pressure loss due to turbulence, induces progression of LV hypertrophy, which leads to a worse prognosis.

Hemi-Fontan and bidirectional Glenn operations result in flow-mediated viscous energy loss at the time of stage II palliation

Background

Superior cavopulmonary connection (SCPC) for stage II palliation of hypoplastic left heart syndrome (HLHS) is achieved most frequently by either a bidirectional Glenn (BDG) or hemi-Fontan (HF) operation. The comparison of flow hemodynamic efficiency at the region of surgical reconstruction and in proximal pulmonary arteries has been evaluated primarily using computational modeling techniques with conflicting reports. The purpose of this descriptive study was to compare flow hemodynamics following stage II (BDG vs HF) using 4-dimensional flow magnetic resonance imaging (4D-Flow MRI) with particular focus on flow-mediated viscous energy loss (EL') under matched hemodynamic conditions.

Methods

Patients with hypoplastic left heart syndrome (HLHS) who underwent either HF or BDG as part of stage II palliation underwent pre-Fontan 4D-Flow MRI. Patients were matched by the pulmonary vascular resistance index, net superior vena cava (SVC) flow, right pulmonary artery (RPA) and left pulmonary artery (LPA) size, and age. Maximum EL' throughout the cardiac cycle was calculated along the SVC-RPA and SVC-LPA tracts.

Results

Eight patients who underwent HF as part of their stage II single ventricle palliation were matched with 8 patients who underwent BDG. There were no differences between the 2 groups in median volumetric indices, including end-diastolic volume (P = .278) and end-systolic volume (P = .213). Moreover, no differences were observed in ejection fraction (P = .091) and cardiac index (P = .324). There also were no differences in peak EL' measured along the SVC-RPA tract (median, 0.05 mW for HF vs 0.04 mW for BDG; P = .365) or along the SVC-LPA tract (median, 0.05 mW vs 0.04 mW; P = .741).

Conclusions

The second stage of surgical palliation of HLHS using either HF or BDG results in similar flow-mediated viscous energy loss throughout the SCPC junction. 4D-Flow MRI and computational methods should be applied together to investigate flow hemodynamic patterns throughout the Fontan palliation and overall efficiency of the Fontan circuit.

Highly accelerated compressed sensing 4D flow MRI in congenital and acquired heart disease: comparison of aorta and main pulmonary artery flow parameters with conventional 4D flow MRI in children and young adults

BACKGROUND

Four-dimensional flow (4D flow) MRI has become a clinically utilized cardiovascular flow assessment tool. However, scans can be lengthy and may require anesthesia in younger children. Adding compressed sensing can decrease scan time, but its impact on hemodynamic data accuracy needs additional assessment.

OBJECTIVE

To compare 4D flow hemodynamics acquired with and without compressed sensing.

MATERIALS AND METHODS

Twenty-seven patients (median age: 13 [IQR: 9.5] years) underwent conventional and compressed sensing cardiovascular 4D flow following informed consent. Conventional 4D flow was performed using parallel imaging and an acceleration factor of 2. Compressed sensing 4D flow was performed with an acceleration factor of 7.7. Regions of interest were placed to compare flow parameters in the ascending aorta and main pulmonary artery. Paired Student's t-tests, Wilcoxon signed-rank tests, Bland-Altman plots, and intraclass correlation coefficients were conducted. A P-value of < 0.05 was considered statistically significant.

RESULTS

Mean scan acquisition time was reduced by 59% using compressed sensing (3.4 vs. 8.2 min, P < 0.001). Flow quantification was similar for compressed sensing and conventional 4D flow for the ascending aorta net flow: 47 vs. 49 ml/beat (P = 0.28); forward flow: 49 vs. 50 ml/beat (P = 0.07), and main pulmonary artery net flow: 49 vs. 51 ml/beat (P = 0.18); forward flow: 50 vs. 55 ml/beat (P = 0.07). Peak systolic velocity was significantly underestimated by compressed sensing 4D flow in the ascending aorta: 114 vs. 128 cm/s (P < 0.001) and main pulmonary artery: 106 vs. 112 cm/s (P = 0.02).

CONCLUSION

For both the aorta and main pulmonary artery, compressed sensing 4D flow provided equivalent net and forward flow values compared to conventional 4D flow but underestimated peak systolic velocity. By reducing scan time, compressed sensing 4D flow may decrease the need for anesthesia and increase scanner output without significantly compromising data integrity.

Valvular and ascending aortic hemodynamics of the On-X aortic valved conduit by same-day echocardiography and 4D flow MRI

This study aims to assess whether the On-X aortic valved conduit better restores normal valvular and ascending aortic hemodynamics than other commonly used bileaflet mechanical valved conduit prostheses from St. Jude Medical and Carbomedics by using same-day transthoracic echocardiography (TTE) and 4D flow magnetic resonance imaging (MRI) examinations. TTE and 4D flow MRI were performed back-to-back in 10 patients with On-X, six patients with St. Jude (two) and Carbomedics (four) prostheses, and 36 healthy volunteers. TTE evaluated valvular hemodynamic parameters: transvalvular peak velocity (TPV), mean and peak transvalvular pressure gradient (TPG), and effective orifice area (EOA). 4D flow MRI evaluated the peak systolic 3D viscous energy loss rate (VELR) density and mean vorticity magnitude in the ascending aorta (AAo). While higher TPV and mean and peak TPG were recorded in all patients compared to healthy subjects, the values in On-X patients were closer to those in healthy subjects (TPV 1.9 ± 0.3 vs. 2.2 ± 0.3 vs. 1.2 ± 0.2 m/s, mean TPG 7.4 ± 1.9 vs. 9.2 ± 2.3 vs. 3.1 ± 0.9 mmHg, peak TPG 15.3 ± 5.2 vs. 18.9 ± 5.2 vs. 6.1 ± 1.8 mmHg, p < 0.001). Likewise, while higher VELR density and mean vorticity magnitude were recorded in all patients than in healthy subjects, the values in On-X patients were closer to those in healthy subjects (VELR: 50.6 ± 20.1 vs. 89.8 ± 35.2 vs. 21.4 ± 9.2 W/m3, p < 0.001) and vorticity (147.6 ± 30.0 vs. 191.2 ± 26.0 vs. 84.6 ± 20.5 s-1, p < 0.001). This study demonstrates that the On-X aortic valved conduit may produce less aberrant hemodynamics in the AAo while maintaining similar valvular hemodynamics to St. Jude Medical and Carbomedics alternatives.

Flow Dynamics in Children With Bicuspid Aortic Valve: A Blood Speckle Tracking Study

OBJECTIVE

Bicuspid aortic valve (BAV) is associated with progressive aortic dilation. Although the etiology is complex, altered flow dynamics is thought to play an important role. Blood speckle tracking (BST) allows for visualization and quantification of complex flow, which could be useful in identifying patients at risk of root dilation and could aid in surgical planning. The aims of this study were to assess and quantify flow in the aortic root and left ventricle using BST in children with bicuspid aortic valves.

METHODS AND RESULTS

A total of 38 children <10 y of age were included (24 controls, 14 with BAV). Flow dynamics were examined using BST in the aortic root and left ventricle. Children with BAV had altered systolic flow patterns in the aortic root and higher aortic root average vorticity (25.9 [23.4-29.2] Hz vs. 17.8 [9.0-26.2] Hz, p < 0.05), vector complexity (0.17 [0.14-0.31] vs. 0.05 [0.02-0.13], p < 0.01) and rate of energy loss (7.9 [4.9-12.1] mW/m vs. 2.7 [1.2-7.4] mW/m, p = 0.01). Left ventricular average diastolic vorticity (20.9 ± 5.8 Hz vs. 11.4 ± 5.2 Hz, p < 0.01), kinetic energy (0.11 ± 0.05 J/m vs. 0.04 ± 0.02 J/m, p < 0.01), vector complexity (0.38 ± 0.1 vs. 0.23 ± 0.1, p < 0.01) and rate of energy loss (11.1 ± 4.8 mW/m vs. 2.7 ± 1.9 mW/m, p < 0.01) were higher in children with BAV.

CONCLUSION

Children with BAV exhibit altered flow dynamics in the aortic root and left ventricle in the absence of significant aortic root dilation. This may represent a substrate and potential predictor for future dilation and diastolic dysfunction.

Energy loss is related to CT fractional flow reserve progression in type 2 diabetes mellitus patients

Background

We aimed to investigate the diagnostic value of energy loss (EL) and baseline CT fractional flow reserve (CT-FFR) computed using computational fluid dynamics to predict functional progression of coronary stenosis in patients with type 2 diabetes mellitus.

Methods

This single-center prospective study included 61 patients with type 2 diabetes mellitus (mean age, 61 years ±9 [SD]; 43 men) showing 20-70 % stenosis who underwent serial coronary CT performed at 2-year interval between October 2015 and March 2020. A mesh-free simulation was performed to calculate the CT-FFR and EL. Functional progression was defined as ≥ 0.05 decrease in CT-FFR on the second coronary CT. Models using baseline CT-FFR and EL were compared by analyzing the receiver operating characteristic (ROC) curve.

Results

Of the 94 vessels evaluated, 25 vessels (27 %) showed functional progression. EL at distal stenosis (ELdis) of vessels with functional progression was higher than that of vessels without functional progression (27.6 W/m3 [interquartile range (IQR): 15.0, 53.0] vs. 5.7 W/m3 [IQR: 2.3, 10.1], p < 0.001). Multivariable analysis showed that ELdis (per unit Ln(EL); odds ratio, 11.8; 95 % CI: 4.0-34.9; p < 0.001) remained as a predictor of functional progression after adjustment for diameter stenosis and baseline CT-FFR. The area under the ROC curve using ELdis (0.89; 95 % CI: 0.82-0.96) was higher than that using baseline CT-FFR (0.71; 95 % CI: 0.59-0.83; p < 0.001).

Conclusion

When ELdis and baseline CT-FFR were considered, ELdis was a better predictor of functional progression of coronary stenosis.

Mechanisms of Aortic Dilation in Patients With Bicuspid Aortic Valve: JACC State-of-the-Art Review

Bicuspid aortic valve is the most common congenital heart disease and exposes patients to an increased risk of aortic dilation and dissection. Aortic dilation is a slow, silent process, leading to a greater risk of aortic dissection. The prevention of adverse events together with optimization of the frequency of the required lifelong imaging surveillance are important for both clinicians and patients and motivated extensive research to shed light on the physiopathologic processes involved in bicuspid aortic valve aortopathy. Two main research hypotheses have been consolidated in the last decade: one supports a genetic basis for the increased prevalence of dilation, in particular for the aortic root, and the second supports the damaging impact on the aortic wall of altered flow dynamics associated with these structurally abnormal valves, particularly significant in the ascending aorta. Current opinion tends to rule out mutually excluding causative mechanisms, recognizing both as important and potentially clinically relevant.

A clinician's guide to understanding aortic 4D flow MRI

Four-dimensional flow magnetic resonance imaging is an emerging technique which may play a role in diagnosis and risk-stratification of aortic disease. Some knowledge of flow dynamics and related parameters is necessary to understand and apply this technique in clinical workflows. The purpose of the current review is to provide a guide for clinicians to the basics of flow imaging, frequently used flow-related parameters, and their relevance in the context of aortic disease.Clinical relevance statement Understanding normal and abnormal aortic flow could improve clinical care in patients with aortic disease.

Clinical Use of Blood Flow Analysis through 4D-Flow Imaging in Aortic Valve Disease

Bicuspid aortic valve (BAV), which affects 1% of the general population, results from the abnormal fusion of the cusps of the aortic valve. BAV can lead to the dilatation of the aorta, aortic coarctation, development of aortic stenosis (AS), and aortic regurgitation. Surgical intervention is usually recommended for patients with BAV and bicuspid aortopathy. This review aims to examine 4D-flow imaging as a tool in cardiac magnetic resonance imaging for assessing abnormal blood flow and its clinical application in BAV and AS. We present a historical clinical approach summarizing evidence of abnormal blood flow in aortic valve disease. We highlight how abnormal flow patterns can contribute to the development of aortic dilatation and novel flow-based biomarkers that can be used for a better understanding of the disease progression.

Postendovascular Aneurysmal Repair Increase in Local Energy Loss for Fusiform Abdominal Aortic Aneurysm: Assessments With 4D flow MRI

BACKGROUND

Although endovascular aneurysmal repair (EVAR) is a preferred treatment for abdominal aortic aneurysm (AAA) owing to its low invasiveness, its impact on the local hemodynamics has not been fully assessed.

PURPOSE

To elucidate how EVAR affects the local hemodynamics in terms of energy loss (EL).

STUDY TYPE

Prospective single-arm study.

FIELD STRENGTH/SEQUENCE

A 3.0 T/4D flow MRI using a phase-contrast three-dimensional cine-gradient-echo sequence.

POPULATION

A total of 13 consecutive patients (median [interquartile range] age: 77.0 [73.0, 78.8] years, 11 male) scheduled for EVAR as an initial treatment for fusiform AAA.

ASSESSMENT

4D flow MRI covering the abdominal aorta and bilateral common iliac arteries and the corresponding stent-graft (SG) lumen was performed before and after EVAR. Plasma brain natriuretic peptide (BNP) was measured within 1 week before and 1 month after EVAR. The hemodynamic data, including mean velocity and the local EL, were compared pre-/post-EVAR. EL was correlated with AAA neck angle and with BNP. Patients were subdivided into deformed (N = 5) and undeformed SG subgroups (N = 8) and pre-/post-EVAR BNP compared in each.

STATISTICS

Parametric or nonparametric methods. Spearman's rank correlation coefficients (r). The interobserver/intraobserver variabilities with Bland-Altman plots. A P value < 0.05 is considered significant.

RESULTS

The mean velocity (cm/sec) at the AAA was five times greater after EVAR: 4.79 ± 0.32 vs. 0.91 ± 0.02. The total EL (mW) increased by 1.7 times after EVAR: 0.487 (0.420, 0.706) vs. 0.292 (0.192, 0.420). The total EL was proportional to the AAA neck angle pre-EVAR (r = 0.691) and post-EVAR (r = 0.718). BNP (pg/mL) was proportional to the total EL post-EVAR (r = 0.773). In the deformed SG group, EL (0.349 [0.261, 0.416]) increased 2.4-fold to 0.848 (0.597, 1.13), and the BNP 90.3 (53.6, 105) to 100 (67.2, 123) post-EVAR.

CONCLUSION

The local EL showed a 1.7-fold increase after EVAR. The larger increase in the EL in the deformed SG group might be a potential concern for frail patients.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 2.

Analysis of Upper Airway Flow Dynamics in Robin Sequence Infants Using 4-D Computed Tomography and Computational Fluid Dynamics

Robin Sequence (RS) is a potentially fatal craniofacial condition characterized by undersized jaw, posteriorly displaced tongue, and resultant upper airway obstruction (UAO). Accurate assessment of UAO severity is crucial for management and diagnosis of RS, yet current evaluation modalities have significant limitations and no quantitative measures of airway resistance exist. In this study, we combine 4-dimensional computed tomography and computational fluid dynamics (CFD) to assess, for the first time, UAO severity using fluid dynamic metrics in RS patients. Dramatic intrapopulation differences are found, with the ratio between most and least severe patients in breathing resistance, energy loss, and peak velocity equal to 40:1, 20:1, and 6:1, respectively. Analysis of local airflow dynamics characterized patients as presenting with primary obstructions either at the location of the tongue base, or at the larynx, with tongue base obstructions resulting in a more energetic stenotic jet and greater breathing resistance. Finally, CFD-derived flow metrics are found to correlate with the level of clinical respiratory support. Our results highlight the large intrapopulation variability, both in quantitative metrics of UAO severity (resistance, energy loss, velocity) and in the location and intensity of stenotic jets for RS patients. These results suggest that computed airflow metrics may significantly improve our understanding of UAO and its management in RS.

Evaluation of aortic stenosis: From Bernoulli and Doppler to Navier-Stokes

Uni-dimensional Doppler echocardiography data provide the mainstay of quantative assessment of aortic stenosis, with the transvalvular pressure drop a key indicator of haemodynamic burden. Sophisticated methods of obtaining velocity data, combined with improved computational analysis, are facilitating increasingly robust and reproducible measurement. Imaging modalities which permit acquisition of three-dimensional blood velocity vector fields enable angle-independent valve interrogation and calculation of enhanced measures of the transvalvular pressure drop. This manuscript clarifies the fundamental principles of physics that underpin the evaluation of aortic stenosis and explores modern techniques that may provide more accurate means to grade aortic stenosis and inform appropriate management.

Four-dimensional magnetic resonance after ascending aorta replacement and aortic valve repair with HAART 300 internal annuloplasty ring

BACKGROUND

The hemispherical aortic annuloplasty reconstructive technology (HAART) is an internal geometric annuloplasty ring designed to restore a natural elliptical shape to the aortic annulus as part of aortic valve repair. We present four-dimensional flow hemodynamic analysis before and after implementation of the HAART ring in patients undergoing ascending aortic replacement.

METHODS

Aortic hemodynamics over the cardiac cycle were visualized using time-resolved three-dimensional pathlines. Velocity streamlines tangent to the time-resolved velocity vector field were used to demonstrate instantaneous aortic hemodynamics. Peak velocities, forward and retrograde flow were calculated at nine planes placed along the midline of the thoracic aorta. Systolic wall shear stress and peak viscous energy loss over the cardiac cycle were calculated.

RESULTS

HAART patients displayed similar or improved flow profiles after surgery when compared to a patient undergoing ascending aortic replacement alone.

CONCLUSION

There may be a trend towards improved flow dynamics in patients undergoing HAART ring implantation.

The role of 4-dimensional flow in the assessment of bicuspid aortic valve and its valvulo-aortopathies

Bicuspid aortic valve is the most common congenital cardiac malformation and the leading cause of aortopathy and aortic stenosis in younger patients. Aortic wall remodelling secondary to altered haemodynamic flow patterns, changes in peak velocity, and wall shear stress may be implicated in the development of aortopathy in the presence of bicuspid aortic valve and dysfunction. Assessment of these parameters as potential predictors of disease severity and progression is thus desirable. The anatomic and functional information acquired from 4D flow MRI can allow simultaneous visualisation and quantification of the pathological geometric and haemodynamic changes of the aorta. We review the current clinical utility of haemodynamic quantities including velocity, wall sheer stress and energy losses, as well as visual descriptors such as vorticity and helicity, and flow direction in assessing the aortic valve and associated aortopathies.

Aortic Viscous Energy Loss for Assessment of Valve-related Hemodynamics in Asymptomatic Severe Aortic Stenosis

Purpose

To investigate whether functional assessment of aberrant flow patterns by viscous energy loss (E′L ) using four-dimensional (4D) flow MRI could determine aortic stenosis (AS) severity in accordance with transvalvular energy loss and aid in surgical decision-making in asymptomatic patients with severe AS.

Materials and Methods

In this prospective, single-center study, E′L was measured in the thoracic aorta of 74 consecutive asymptomatic patients with severe AS and preserved left ventricular ejection fraction who presented between January 2015 and December 2017, and 23 healthy volunteers using 4D flow MRI. Transvalvular energy loss was assessed based on the energy loss index (ELI) measured using Doppler echocardiography. The association between E′L and AS-related events including aortic valve replacement was evaluated by receiver operating characteristic curve analysis, Kaplan-Meier analysis, and multivariable Cox regression analysis.

Results

Among 74 asymptomatic patients with severe AS (mean age, 60 years ± 9 [SD]; 43 men; 56 with bicuspid aortic valve), 33 experienced AS-related events during a median follow-up of 42 months (IQR, 30–53 months). Altered flow patterns in severe AS resulted in a sevenfold increase in peak systolic E′L in the ascending aorta compared with controls (13.9 mW ± 3.4 vs 1.80 mW ± 0.44; P < .001). Peak systolic E′L in the ascending aorta was independently associated with the ELI (standardized β, −0.52; P < .001) and showed better discrimination for AS-related events (area under the curve, 0.83; 95% CI: 0.74, 0.93; P < .001) than conventional echocardiographic parameters. After adjustment for confounding variables, peak systolic E′L in the ascending aorta was associated with a significant increase in AS-related events (P < .001 for adjusted hazard ratio).

Conclusion

Changes in AS-mediated poststenotic three-dimensional outflow patterns can be quantified by 4D flow MRI-derived energetic markers to aid in the risk stratification and clinical management of asymptomatic patients with severe AS.

Keywords: Aortic Stenosis, 4D Flow MRI, Flow Energetics, Vascular, Aorta, Aortic Valve, MR Angiography

Supplemental material is available for this article.

© RSNA, 2022

Location matters: Offset in tissue-engineered vascular graft implantation location affects wall shear stress in porcine models

Objective

Although surgical simulation using computational fluid dynamics has advanced, little is known about the accuracy of cardiac surgical procedures after patient-specific design. We evaluated the effects of discrepancies in location for patient-specific simulation and actual implantation on hemodynamic performance of patient-specific tissue-engineered vascular grafts (TEVGs) in porcine models.

Methods

Magnetic resonance angiography and 4-dimensional (4D) flow data were acquired in porcine models (n = 11) to create individualized TEVGs. Graft shapes were optimized and manufactured by electrospinning bioresorbable material onto a metal mandrel. TEVGs were implanted 1 or 3 months postimaging, and postoperative magnetic resonance angiography and 4D flow data were obtained and segmented. Displacement between intended and observed TEVG position was determined through center of mass analysis. Hemodynamic data were obtained from 4D flow analysis. Displacement and hemodynamic data were compared using linear regression.

Results

Patient-specific TEVGs were displaced between 1 and 8 mm during implantation compared with their surgically simulated, intended locations. Greater offset between intended and observed position correlated with greater wall shear stress (WSS) in postoperative vasculature (P < .01). Grafts that were implanted closer to their intended locations showed decreased WSS.

Conclusions

Patient-specific TEVGs are designed for precise locations to help optimize hemodynamic performance. However, if TEVGs were implanted far from their intended location, worse WSS was observed. This underscores the importance of not only patient-specific design but also precision-guided implantation to optimize hemodynamics in cardiac surgery and increase reproducibility of surgical simulation.

Hemolytic anemia caused by an excessively kinked prosthetic graft after total arch replacement detected by 4-dimensional flow magnetic resonance imaging: A case report

RATIONALE

Hemolytic anemia is a rare postoperative complication of aortic surgery, which may be caused by an excessively kinked graft that causes abnormal blood flow. It has been reported that 4-dimensional flow magnetic resonance imaging (4D flow MRI) can identify abnormal flow. Herein, we report the guidance of 4D flow MRI in performing the revision procedure for a patient with hemolytic anemia by evaluating abnormal blood flow based on this method.

PATIENT CONCERNS

A 70-year-old woman presented with dizziness and fatigue. She had undergone total arch replacement with a frozen elephant trunk 5 years prior. We diagnosed hemolytic anemia caused by a kinked graft after total arch replacement.

DIAGNOSIS

Although computed tomography findings revealed 3 lesions of the kinked graft at the ascending portion and cervical branches, 4D flow MRI findings showed that only the kinked graft at the ascending portion caused hemolytic anemia due to an elevated viscous energy loss around it.

INTERVENTION

We performed surgery to remove the kinked section instead of revision surgery consisting of total arch replacement.

OUTCOMES

The patient's postoperative course was uneventful and there were no complications. Postoperative enhanced computed tomography findings showed that the repaired graft had an adequate length and smoothly curved shape. The 4D flow MRI findings revealed smooth flow in the ascending portion and decreased viscous energy loss.

LESSONS

Based on the 4D flow MRI findings, we adopted a less invasive approach, repairing only the ascending portion of the graft, instead of performing revision surgery comprising total arch replacement.

Four-dimensional flow cardiac magnetic resonance assessment of left ventricular diastolic function

Left ventricular diastolic dysfunction is a major cause of heart failure and carries a poor prognosis. Assessment of left ventricular diastolic function however remains challenging for both echocardiography and conventional phase contrast cardiac magnetic resonance. Amongst other limitations, both are restricted to measuring velocity in a single direction or plane, thereby compromising their ability to capture complex diastolic hemodynamics in health and disease. Time-resolved three-dimensional phase contrast cardiac magnetic resonance imaging with three-directional velocity encoding known as '4D flow CMR' is an emerging technology which allows retrospective measurement of velocity and by extension flow at any point in the acquired 3D data volume. With 4D flow CMR, complex aspects of blood flow and ventricular function can be studied throughout the cardiac cycle. 4D flow CMR can facilitate the visualization of functional blood flow components and flow vortices as well as the quantification of novel hemodynamic and functional parameters such as kinetic energy, relative pressure, energy loss and vorticity. In this review, we examine key concepts and novel markers of diastolic function obtained by flow pattern analysis using 4D flow CMR. We consolidate the existing evidence base to highlight the strengths and limitations of 4D flow CMR techniques in the surveillance and diagnosis of left ventricular diastolic dysfunction.

Component quantification of aortic blood flow energy loss using computational fluid-structure interaction hemodynamics

BACKGROUND AND OBJECTIVES

The aorta serves as the main tube of the human blood circulation system. Energy loss (EL) occurs when blood flows through the aorta and there may be a potential correlation between EL and aortic diseases. However, the components of blood flow EL are still not fully understood. This study aims to quantitatively reveal the EL components in healthy and diseased aortas.

METHODS

We construct an idealized healthy aorta and three idealized representative diseased aortas: aortic aneurysm, coarctation of the aorta, and aortic dissection. Computational hemodynamic studies are carried out by using the fluid-structure interaction simulation framework.

RESULTS

Four kinds of EL components: viscous friction, turbulence dissipation, wall deformation, and local lesion are firstly acquired in healthy and diseased aortas based on the high-resolution blood flow information. Viscous friction contributes most to the EL (45.69%-57.22%). EL caused by the deformation of the aortic wall ranks second (15.18%-33.12%). The proportions of turbulence dissipation and local lesion depend on individual geometric characteristics. Besides, the buffering efficiency of the healthy and diseased aorta is about 80%.

CONCLUSIONS

This study quantitatively reports the components of blood flow EL in healthy and diseased aortas, the finding may provide novel insights into the pathogenesis of aortic diseases.

Turbulent Intensity of Blood Flow in the Healthy Aorta Increases With Dobutamine Stress and is Related to Cardiac Output

Introduction: The blood flow in the normal cardiovascular system is predominately laminar but operates close to the threshold to turbulence. Morphological distortions such as vascular and valvular stenosis can cause transition into turbulent blood flow, which in turn may cause damage to tissues in the cardiovascular system. A growing number of studies have used magnetic resonance imaging (MRI) to estimate the extent and degree of turbulent flow in different cardiovascular diseases. However, the way in which heart rate and inotropy affect turbulent flow has not been investigated. In this study we hypothesized that dobutamine stress would result in higher turbulence intensity in the healthy thoracic aorta.

Method: 4D flow MRI data were acquired in twelve healthy subjects at rest and with dobutamine, which was infused until the heart rate increased by 60% when compared to rest. A semi-automatic segmentation method was used to segment the thoracic aorta in the 4D flow MR images. Subsequently, flow velocity and several turbulent kinetic energy (TKE) parameters were calculated in the ascending aorta, aortic arch, descending aorta and whole thoracic aorta.

Results: With dobutamine infusion there was an increase in heart rate (66 ± 9 vs. 108 ± 13 bpm, p < 0.001) and stroke volume (88 ± 13 vs. 102 ± 25 ml, p < 0.01). Additionally, there was an increase in Peak Average velocity (0.7 ± 0.1 vs. 1.2 ± 0.2 m/s, p < 0.001, Peak Max velocity (1.3 ± 0.1 vs. 2.0 ± 0.2 m/s, p < 0.001), Peak Total TKE (2.9 ± 0.7 vs. 8.0 ± 2.2 mJ, p < 0.001), Peak Median TKE (36 ± 7 vs. 93 ± 24 J/m3, p = 0.002) and Peak Max TKE (176 ± 33 vs. 334 ± 69 J/m3, p < 0.001). The relation between cardiac output and Peak Total TKE in the whole thoracic aorta was very strong (R² = 0.90, p < 0.001).

Conclusion: TKE of blood flow in the healthy thoracic aorta increases with dobutamine stress and is strongly related to cardiac output. Quantification of such turbulence intensity parameters with cardiac stress may serve as a risk assessment of aortic disease development.

Fully Three-Dimensional Hemodynamic Characterization of Altered Blood Flow in Bicuspid Aortic Valve Patients With Respect to Aortic Dilatation: A Finite Element Approach

Background and Purpose

Prognostic models based on cardiovascular hemodynamic parameters may bring new information for an early assessment of patients with bicuspid aortic valve (BAV), playing a key role in reducing the long-term risk of cardiovascular events. This work quantifies several three-dimensional hemodynamic parameters in different patients with BAV and ranks their relationships with aortic diameter.

Materials and Methods

Using 4D-flow CMR data of 74 patients with BAV (49 right-left and 25 right-non-coronary) and 48 healthy volunteers, aortic 3D maps of seventeen 17 different hemodynamic parameters were quantified along the thoracic aorta. Patients with BAV were divided into two morphotype categories, BAV-Non-AAoD (where we include 18 non-dilated patients and 7 root-dilated patients) and BAV-AAoD (where we include the 49 patients with dilatation of the ascending aorta). Differences between volunteers and patients were evaluated using MANOVA with Pillai's trace statistic, Mann–Whitney U test, ROC curves, and minimum redundancy maximum relevance algorithm. Spearman's correlation was used to correlate the dilation with each hemodynamic parameter.

Results

The flow eccentricity, backward velocity, velocity angle, regurgitation fraction, circumferential wall shear stress, axial vorticity, and axial circulation allowed to discriminate between volunteers and patients with BAV, even in the absence of dilation. In patients with BAV, the diameter presented a strong correlation (&gt; |+/−0.7|) with the forward velocity and velocity angle, and a good correlation (&gt; |+/−0.5|) with regurgitation fraction, wall shear stress, wall shear stress axial, and vorticity, also for morphotypes and phenotypes, some of them are correlated with the diameter. The velocity angle proved to be an excellent biomarker in the differentiation between volunteers and patients with BAV, BAV morphotypes, and BAV phenotypes, with an area under the curve bigger than 0.90, and higher predictor important scores.

Conclusions

Through the application of a novel 3D quantification method, hemodynamic parameters related to flow direction, such as flow eccentricity, velocity angle, and regurgitation fraction, presented the best relationships with a local diameter and effectively differentiated patients with BAV from healthy volunteers.

Patient-Specific Inverse Modeling of In Vivo Cardiovascular Mechanics with Medical Image-Derived Kinematics as Input Data: Concepts, Methods, and Applications

Inverse modeling approaches in cardiovascular medicine are a collection of methodologies that can provide non-invasive patient-specific estimations of tissue properties, mechanical loads, and other mechanics-based risk factors using medical imaging as inputs. Its incorporation into clinical practice has the potential to improve diagnosis and treatment planning with low associated risks and costs. These methods have become available for medical applications mainly due to the continuing development of image-based kinematic techniques, the maturity of the associated theories describing cardiovascular function, and recent progress in computer science, modeling, and simulation engineering. Inverse method applications are multidisciplinary, requiring tailored solutions to the available clinical data, pathology of interest, and available computational resources. Herein, we review biomechanical modeling and simulation principles, methods of solving inverse problems, and techniques for image-based kinematic analysis. In the final section, the major advances in inverse modeling of human cardiovascular mechanics since its early development in the early 2000s are reviewed with emphasis on method-specific descriptions, results, and conclusions. We draw selected studies on healthy and diseased hearts, aortas, and pulmonary arteries achieved through the incorporation of tissue mechanics, hemodynamics, and fluid-structure interaction methods paired with patient-specific data acquired with medical imaging in inverse modeling approaches.

Pulmonary Artery Remodeling and Advanced Hemodynamics: Magnetic Resonance Imaging Biomarkers of Pulmonary Hypertension

Poorly characterized by non-invasive diagnostic imaging techniques, pulmonary hypertension (PHT) is commonly associated with changes in vascular hemodynamics and remodeling of pulmonary artery architecture. These disease phenotypes represent potential biomarkers of interest in clinical environment. In this retrospective clinical study, 33 patients with pulmonary hypertension and seventeen controls were recruited. Architectural remodeling was characterized using 3D-contrast enhanced angiogram via the measurement of pulmonary artery diameters, bifurcation distances, and angles. Hemodynamics were characterized using 4D-flow magnetic resonance imaging (MRI) via wall shear stress, kinetic energy, vorticity, and directional flow dynamics. Parameters were compared using independent samples student’s t-tests. Correlational analysis was performed using Pearson’s correlation. PHT patients demonstrated dilation in the main and right branch of the pulmonary artery (p < 0.05). Furthermore, these patients also exhibited increases in bifurcation distances in the left and right pulmonary arteries (p < 0.05). Wall shear stress, maximum kinetic energy, and energy loss were decreased in the pulmonary artery (p < 0.001). Correlations were observed between peak velocities and right ventricle ejection fraction (r = 0.527, p < 0.05). These findings suggest that pulmonary artery remodeling and hemodynamic changes may possess clinical utility as MRI biomarkers for PHT.

Unlocking the Non-invasive Assessment of Conduit and Reservoir Function in the Aorta

Aortic surgeries in congenital conditions, such as hypoplastic left heart syndrome (HLHS), aim to restore and maintain the conduit and reservoir functions of the aorta. We proposed a method to assess these two functions based on 4D flow MRI, and we applied it to study the aorta in pre-Fontan HLHS. Ten pre-Fontan HLHS patients and six age-matched controls were studied to derive the advective pressure difference and viscous dissipation for conduit function, and pulse wave velocity and elastic modulus for reservoir function. The reconstructed neo-aorta in HLHS subjects achieved a good conduit function at a cost of an impaired reservoir function (69.7% increase of elastic modulus). The native descending HLHS aorta displayed enhanced reservoir (elastic modulus being 18.4% smaller) but impaired conduit function (three-fold increase in peak advection). A non-invasive and comprehensive assessment of aortic conduit and reservoir functions is feasible and has potentially clinical relevance in congenital vascular conditions.

Hemodynamic Parameters for Cardiovascular System in 4D Flow MRI: Mathematical Definition and Clinical Applications

Blood flow imaging becomes an emerging trend in cardiology with the recent progress in computer technology. It not only visualizes colorful flow velocity streamlines but also quantifies the mechanical stress on cardiovascular structures; thus, it can provide the detailed inspections of the pathophysiology of diseases and predict the prognosis of cardiovascular functions. Clinical applications include the comprehensive assessment of hemodynamics and cardiac functions in echocardiography vector flow mapping (VFM), 4D flow MRI, and surgical planning as a simulation medicine in computational fluid dynamics (CFD).For evaluation of the hemodynamics, novel mathematically derived parameters obtained using measured velocity distributions are essential. Among them, the traditional and typical parameters are wall shear stress (WSS) and its related parameters. These parameters indicate the mechanical damages to endothelial cells, resulting in degenerative intimal change in vascular diseases. Apart from WSS, there are abundant parameters that describe the strength of the vortical and/or helical flow patterns. For instance, vorticity, enstrophy, and circulation indicate the rotating flow strength or power of 2D vortical flows. In addition, helicity, which is defined as the cross-linking number of the vortex filaments, indicates the 3D helical flow strength and adequately describes the turbulent flow in the aortic root in cases with complicated anatomies. For the description of turbulence caused by the diseased flow, there exist two types of parameters based on completely different concepts, namely: energy loss (EL) and turbulent kinetic energy (TKE). EL is the dissipated energy with blood viscosity and evaluates the cardiac workload related to the prognosis of heart failure. TKE describes the fluctuation in kinetic energy during turbulence, which describes the severity of the diseases that cause jet flow. These parameters are based on intuitive and clear physiological concepts, and are suitable for in vivo flow measurements using inner velocity profiles.

Improving transcatheter aortic valve interventional predictability via fluid-structure interaction modelling using patient-specific anatomy

Transcatheter aortic valve replacement (TAVR) is now a standard treatment for high-surgical-risk patients with severe aortic valve stenosis. TAVR is being explored for broader indications including degenerated bioprosthetic valves, bicuspid valves and for aortic valve (AV) insufficiency. It is, however, challenging to predict whether the chosen valve size, design or its orientation would produce the most-optimal haemodynamics in the patient. Here, we present a novel patient-specific evaluation framework to realistically predict the patient's AV performance with a high-fidelity fluid-structure interaction analysis that included the patient's left ventricle and ascending aorta (AAo). We retrospectively evaluated the pre- and post-TAVR dynamics of a patient who underwent a 23 mm TAVR and evaluated against the patient's virtually de-calcified AV serving as a hypothetical benchmark. Our model predictions were consistent with clinical data. Stenosed AV produced a turbulent flow during peak-systole, while aortic flow with TAVR and de-calcified AV were both in the laminar-to-turbulent transitional regime with an estimated fivefold reduction in viscous dissipation. For TAVR, dissipation was highest during early systole when valve deformation was the greatest, suggesting that an efficient valve opening may reduce energy loss. Our study demonstrates that such patient-specific modelling frameworks can be used to improve predictability and in the planning of AV interventions.

Hemodynamic features underlying pulmonary vein stump thrombus formation after left upper lobectomy: four-dimensional flow magnetic resonance imaging study

BACKGROUND

We previously reported that to-and-fro blood movement near the pulmonary vein stump was particularly prominent after left upper lobectomy compared with other lobectomy, which may be the cause of the high susceptibility of pulmonary vein thrombus after left upper lobectomy. The aim of the present study was to compare the hemodynamics in patients who developed pulmonary vein thrombus after left upper lobectomy with those in patients who did not develop pulmonary vein thrombus using four-dimensional flow magnetic resonance imaging (4D MRI).

METHODS

This was a retrospective evaluation of a prospectively collected clinical and radiological database of 37 patients who underwent 4D MRI 7 days after left upper lobectomy for lung cancer (n=37). We obtained two parameters by 4D MRI: the grade of to-and-fro blood movement and the flow energy loss around the pulmonary vein stump. The length of the pulmonary vein stump, a known risk factor for pulmonary vein thrombus, was also measured.

RESULTS

According to a scatterplot of the grade of to-and-fro blood movement versus the flow energy loss, patients with pulmonary vein thrombus (n=15) were concentrated in an area which appears to be a 'dangerous' hemodynamic condition. There were few patients without pulmonary vein thrombus in this 'dangerous' area, except for one who unfortunately developed delayed pulmonary vein thrombus and cerebral infarction. We proposed a formula using the 4D MRI-derived parameters based on a stepwise multiple regression analysis that was more closely associated with the development of pulmonary vein thrombus than the length of the pulmonary vein stump (area under the receiver operating characteristics curve: 0.918 vs. 0.705, P=0.0500).

CONCLUSIONS

We proposed the existence of a 'dangerous' hemodynamic condition responsible for pulmonary vein thrombus formation. 4D MRI before the development of pulmonary vein thrombus may help identify patients requiring preventive therapy against pulmonary vein thrombus and subsequent thromboembolic complications.

Initial experience with intensity distribution analysis of hemodynamic parameters in the thoracic aorta using four-dimensional magnetic resonance imaging: A comparison between groups with different ejection fractions

The purpose of this study was to investigate whether there were significant differences in the intensity distributions of thoracic aorta hemodynamic parameters between groups with different ejection fractions (EF) using four-dimensional flow magnetic resonance imaging and to investigate the relationships between each parameter.A total of 26 patients, 13 each with EF of >60% and <30%, underwent cardiac four-dimensional flow magnetic resonance imaging (EF >60%: mean age: 54 ± 11.6 years, EF <30%: mean age: 49.2 ± 17.2 years). The thoracic aorta was divided into the proximal and distal ascending aorta (AAo), aortic arch, and the proximal and distal descending aorta, and each section was further divided into the anterior wall, posterior wall, lesser curvature, and greater curvature. The intensity distributions of wall shear stress (WSS), energy loss (EL), and vorticity (Vort) (hemodynamic parameters) and the concordance rates between these distributions were analyzed.The concordance rate between the intensity distributions of EL and Vort was high. Only the intensity distributions of EL and Vort in the distal AAo differed significantly between the groups (P < .001). In the EF >60% group, these intensity distributions showed higher values in the greater curvature of the AAo, whereas in the EF <30% group higher values were seen in the lesser curvature of the AAo.Although there was no significant intergroup difference in the WSS intensity distribution, in the EF <30% group the WSS intensity distribution tended to exhibit higher values in the lesser curvature of the distal AAo, and the WSS intensity distribution values for the greater curvature tended to gradually increase from the arch to the proximal descending aorta.The only significant differences between the EF groups were found in the intensity distributions of EL and Vort in the distal AAo. This suggests that the distributions of atherosclerosis may be EF-dependent.

Alcohol septal ablation markedly reduces energy loss in hypertrophic cardiomyopathy with left ventricular outflow tract obstruction: A four-dimensional flow cardiac magnetic resonance study

Background

Functional follow-up modalities of hypertrophic cardiomyopathy (HCM) with left ventricular (LV) outflow tract obstruction (LVOTO) subjected to alcohol septal ablation (ASA) are limited.

Methods

This retrospective cohort study included patients of HCM with LVOTO who underwent ASA and four-dimensional (4D) flow cardiac magnetic resonance imaging (MRI) both before and after ASA. We analyzed energy loss in one cardiac cycle within the three-chamber plane of the LV and aortic root, and compared between pre- and post-ASA measurements.

Results

Of the 26 included patients, 10 (39%) were male, and median age was 71 (interquartile range 58–78) years. ASA significantly reduced not only LVOT pressure gradient (70 [19–50] to 9 [3–16], P < 0.001), but also energy loss during one cardiac cycle within the three-chamber plane of the LV and aortic root (80 [65–99] to 56 [45–70], P < 0.001). A linear association was observed between the reductions of energy loss and pressure gradient (R² = 0.58, P < 0.001).

Conclusions

ASA significantly reduced energy loss within the LV and aortic root as quantified by 4D flow MRI, reflecting the decreased cardiac workload. This approach is a promising candidate for serial functional follow-up in patients undergoing ASA.

Analysis of Turbulence Effects in a Patient-Specific Aorta with Aortic Valve Stenosis

Blood flow in the aorta is often assumed laminar, however aortic valve pathologies may induce transition to turbulence and our understanding of turbulence effects is incomplete. The aim of the study was to provide a detailed analysis of turbulence effects in aortic valve stenosis (AVS).

METHODS

Large-eddy simulation (LES) of flow through a patient-specific aorta with AVS was conducted. Magnetic resonance imaging (MRI) was performed and used for geometric reconstruction and patient-specific boundary conditions. Computed velocity field was compared with 4D flow MRI to check qualitative and quantitative consistency. The effect of turbulence was evaluated in terms of fluctuating kinetic energy, turbulence-related wall shear stress (WSS) and energy loss.

RESULTS

Our analysis suggested that turbulence was induced by a combination of a high velocity jet impinging on the arterial wall and a dilated ascending aorta which provided sufficient space for turbulence to develop. Turbulent WSS contributed to 40% of the total WSS in the ascending aorta and 38% in the entire aorta. Viscous and turbulent irreversible energy losses accounted for 3.9 and 2.7% of the total stroke work, respectively.

CONCLUSIONS

This study demonstrates the importance of turbulence in assessing aortic haemodynamics in a patient with AVS. Neglecting the turbulent contribution to WSS could potentially result in a significant underestimation of the total WSS. Further work is warranted to extend the analysis to more AVS cases and patients with other aortic valve diseases.

Novel concepts and early results of repairing common arterial trunk

OBJECTIVES

Common Arterial Trunk (CAT) continues to have a very poor prognosis globally. To address that, we have developed a novel technique targeting key concepts for the correction of all components of the anomaly, using autologous arterial tissue. This aims to enhance results, availability worldwide, and importantly to avoid the need for repeated reoperations.

METHODS

From January 2019 to 4 January 2021, all patients with isolated CAT had repair of the defect using autologous arterial trunk tissue with direct right ventricle (RV) to pulmonary artery (PA) connection. Clinical outcomes, follow-up which included multi-slice computed tomography 3D segmentation and 4D cardiovascular magnetic resonance flow, are presented.

RESULTS

Twenty patients were included in the study (median age 4.5 months). There were 2 hospital deaths due to systemic infection and pulmonary hypertensive crisis, respectively. Following discharge all patients remained asymptomatic with no signs of heart failure and improved pattern of growth (median follow-up: 8 months). Early postoperative 3D segmentation showed a conical shaped neo-right ventricular outflow chamber connecting the body of the RV to the main PA through a valveless ostium, and normal crossing of PA and neo-aorta. 4D cardiovascular magnetic resonance pattern of flow showed normal rapid laminar flow through the atrioventricular valves followed by a vortex towards the outflow tracts. There was laminar flow through the neo-aorta and neo-PA with velocity not exceeding 2.5 m/s. The PA regurgitant fraction was 25 ± 5% and was limited to early diastole.

CONCLUSIONS

The initial results of utilizing the key concepts, using autologous arterial tissue for the repair of CAT, are encouraging, both clinically and by multimodality imaging.

Bicuspid aortic valve disease is associated with abnormal wall shear stress, viscous energy loss, and pressure drop within the ascending thoracic aorta: A cross-sectional study

Bicuspid aortic valve (BAV) disease has significant gaps in its clinical management practices. To highlight the potential utility of advanced hemodynamic biomarkers in strengthening BAV assessment, we used 4-dimentional flow magnetic resonance imaging to investigate altered hemodynamics in the ascending aorta (AAo).A total of 32 healthy controls and 53 age-matched BAV patients underwent cardiac magnetic resonance imaging at 3T, with cine imaging and 4D-flow. Analysis planes were placed along 3D-segmented aortas at the left ventricular outflow tract (LVOT), sinuses of Valsalva, mid-ascending aorta (MAA), and proximal to the first aortic branch. Locations were analyzed for aortic diameter (normalized to body surface area), pressure drop (PD), viscous energy loss (EL), and wall shear stress (WSS) sub-vectors (axial wall shear stress, circumferential wall shear stress [WSSC], magnitude wall shear stress). Student's t tests, or non-parametric equivalents, compared parameters between cohorts. Univariable and multivariable analyses explored the associations of AAo diameter with hemodynamics within the BAV cohort.Compared to control cohort, BAV patients showed significantly greater PD (MAA: 9.5 ± 8.0 vs 2.8 ± 2.4 mm Hg; P < .01), EL (from LVOT-AA1: 7.39 ± 4.57 mW vs 2.90 ± 1.07 mW; P < .01), and WSSC (MAA: 0.3 ± 0.1 vs 0.2 ± 0.06 Pa; P ≤ .01) throughout the AAo. Correlational analyses revealed an inverse association between AAo diameter and both magnitude wall shear stress and axial wall shear stress.BAV patients exhibited increased PD, EL, and WSSC in the AAo, and an inverse association between AAo diameter and WSS sub-vectors. This demonstrated the impact of PD, EL, and WSS in BAV disease and the importance of altered hemodynamics in aortic remodelling.

Aorta size mismatch predicts decreased exercise capacity in patients with successfully repaired coarctation of the aorta

OBJECTIVE

Coarctation of the aorta (CoA) is associated with decreased exercise capacity despite successful repair with no residual stenosis; however, the hemodynamic mechanism remains unknown. This study aims to correlate aortic arch geometry with exercise capacity in patients with successfully repaired CoA and explain hemodynamic changes using 3-dimensional-printed aorta models in a mock circulatory flow loop.

METHODS

A retrospective chart review identified patients with CoA repair who had cardiac magnetic resonance imaging and an exercise stress test. Measurements included aorta diameters, arch height to diameter ratio, left ventricular function, and percent descending aorta (%DAo) flow. Each aorta was printed 3-dimensionally for the flow loop. Flow and pressure were measured at the ascending aorta (AAo) and DAo during simulated rest and exercise. Measurements were correlated with percent predicted peak oxygen consumption (VO2 max).

RESULTS

Fifteen patients (mean age 26.8 ± 8.6 years) had a VO2 max between 47% and 126% predicted (mean 92 ± 20%) with normal left ventricular function. DAo diameter and %DAo flow positively correlated with VO2 (P = .007 and P = .04, respectively). AAo to DAo diameter ratio (DAAo/DDAo) negatively correlated with VO2 (P < .001). From flow loop simulations, the ratio of %DAo flow in exercise to rest negatively correlated with VO2 (P = .02) and positively correlated with DAAo/DDAo (P < .01).

CONCLUSIONS

This study suggests aorta size mismatch (DAAo/DDAo) is a novel, clinically important measurement predicting exercise capacity in patients with successful CoA repair, likely due to increased resistance and altered flow distribution. Aorta size mismatch and %DAo flow are targets for further clinical evaluation in repaired CoA.

Blood flow dynamics with four-dimensional flow cardiovascular magnetic resonance in patients with aortic stenosis before and after transcatheter aortic valve replacement

BACKGROUND

Pre- and post-procedural hemodynamic changes which could affect adverse outcomes in aortic stenosis (AS) patients who undergo transcatheter aortic valve replacement (TAVR) have not been well investigated. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) enables accurate analysis of blood flow dynamics such as flow velocity, flow pattern, wall shear stress (WSS), and energy loss (EL). We sought to examine the changes in blood flow dynamics of patients with severe AS who underwent TAVR.

METHODS

We examined 32 consecutive severe AS patients who underwent TAVR between May 2018 and June 2019 (17 men, 82 ± 5 years, median left ventricular ejection fraction 61%, 6 self-expanding valve), after excluding those without CMR because of a contraindication or inadequate imaging from the analyses. We analyzed blood flow patterns, WSS and EL in the ascending aorta (AAo), and those changes before and after TAVR using 4D flow CMR.

RESULTS

After TAVR, semi-quantified helical flow in the AAo was significantly decreased (1.4 ± 0.6 vs. 1.9 ± 0.8, P = 0.002), whereas vortical flow and eccentricity showed no significant changes. WSS along the ascending aortic circumference was significantly decreased in the left (P = 0.038) and left anterior (P = 0.033) wall at the basal level, right posterior (P = 0.011) and left (P = 0.010) wall at the middle level, and right (P = 0.012), left posterior (P = 0.019) and left anterior (P = 0.028) wall at the upper level. EL in the AAo was significantly decreased (15.6 [10.8-25.1 vs. 25.8 [18.6-36.2]] mW, P = 0.012). Furthermore, a significant negative correlation was observed between EL and effective orifice area index after TAVR (r = - 0.38, P = 0.034).

CONCLUSIONS

In severe AS patients undergoing TAVR, 4D flow CMR demonstrates that TAVR improves blood flow dynamics, especially when a larger effective orifice area index is obtained.