Perioperative evaluation of regional aortic wall shear stress patterns in patients undergoing aortic valve and/or proximal thoracic aortic replacement

Mid- and long-term outcomes after surgical correction of subaortic stenosis: a 27-year experience

OBJECTIVES

We reviewed the mid- and long-term surgical outcomes of patients with subaortic stenosis (SAS).

METHODS

Patients operated for SAS from April 1990 to August 2016 were reviewed retrospectively. Patients with major associations such as aortic arch obstruction were excluded. Time to reintervention and predictors of recurrence were assessed using Kaplan-Meier analysis, log-rank test and uni/multivariable Cox regression.

RESULTS

120 patients at a median age of 4.7 years (interquartile range 2.9, 8.1) underwent primary operation (median peak preoperative left ventricular outflow tract gradient 52.5 mmHg, interquartile range 40, 70) involving fibrous tissue excision (n = 120) with septal myectomy (93%; n = 112) as the procedure of choice.At median follow-up of 13 years (interquartile range 7, 18), freedom from reintervention at 1, 3, 5 and 10 years was 99% (95% confidence interval 94%, 99%), 94% (87%, 97%), 93% (86%, 96%) and 90% (82%, 94%), respectively. Recurrence occurred in 18% (n = 20) with 15 patients undergoing reinterventions, 13 of whom required radical reoperation. Multivariable analysis revealed higher preoperative peak left ventricular outflow tract gradient (hazard risk 1.06, confidence interval 1.03, 1.09, P < 0.001), and presence of bicuspid aortic valve (hazard risk 14.13, confidence interval 3.32, 60.1, P < 0.001) as predictors for reintervention. Mild/moderate aortic regurgitation occurred in 49% (n = 55) of patients at the most recent follow-up.

CONCLUSIONS

Reintervention for recurrent SAS is common, predicted by higher preoperative peak left ventricular outflow tract gradient, and presence of bicuspid aortic valve, and frequently involves a radical procedure. Aortic regurgitation is a major consequence of SAS, but its severity usually remains low.

CLINICAL REGISTRATION NUMBER

SCHN HREC reference number 2019/ETH02729, approved on 09 July 2019.

Aortic shape variation after frozen elephant trunk procedure predicts aortic events: Principal component analysis study

Objective

The frozen elephant trunk procedure is a well-established technique for the repair of type A ascending aortic dissection and complex aortic arch pathology. The ultimate shape created by the repair may have consequences in long-term complications. The purpose of this study was to apply a machine learning technique to comprehensively describe 3-dimensional aortic shape variations after the frozen elephant trunk procedure and associate these variations with aortic events.

Methods

Computed tomography angiography acquired before discharge of patients (n = 93) who underwent the frozen elephant trunk procedure for type A ascending aortic dissection or ascending aortic arch aneurysm was preprocessed to yield patient-specific aortic models and centerlines. Aortic centerlines were subjected to principal component analysis to describe principal components and aortic shape modulators. Patient-specific shape scores were correlated with outcomes defined by composite aortic event, including aortic rupture, aortic root dissection or pseudoaneurysm, new type B dissection, new thoracic or thoracoabdominal pathologies, residual descending aortic dissection with residual false lumen flow, or thoracic endovascular aortic repair complications.

Results

The first 3 principal components accounted for 36.4%, 26.4%, and 11.6% of aortic shape variance, respectively, and cumulatively for 74.5% of the total shape variation in all patients. The first principal component described variation in arch height-to-length ratio, the second principal component described angle at the isthmus, and the third principal component described variation in anterior-to-posterior arch tilt. Twenty-one aortic events (22.6%) were encountered. The degree of aortic angle at the isthmus described by the second principal component was associated with aortic events in logistic regression (hazard ratio, 0.98; 95% confidence interval, 0.97-0.99; P = .046).

Conclusions

The second principal component, describing angulation at the region of the aortic isthmus, was associated with adverse aortic events. Observed shape variation should be evaluated in the context of aortic biomechanical properties and flow hemodynamics.

Changes of aortic hemodynamics after aortic valve replacement-A four dimensional flow cardiovascular magnetic resonance follow up study

Objectives

Non-invasive assessment of aortic hemodynamics using four dimensional (4D) flow magnetic resonance imaging (MRI) provides new information on blood flow patterns and wall shear stress (WSS). Aortic valve stenosis (AS) and/or bicuspid aortic valves (BAV) are associated with altered aortic flow patterns and elevated WSS. Aim of this study was to investigate changes in aortic hemodynamics over time in patients with AS and/or BAV with or without aortic valve replacement.

Methods

We rescheduled 20 patients for a second 4D flow MRI examination, whose first examination was at least 3 years prior. A total of 7 patients received an aortic valve replacement between baseline and follow up examination (=operated group = OP group). Aortic flow patterns (helicity/vorticity) were assessed using a semi-quantitative grading approach from 0 to 3, flow volumes were evaluated in 9 planes, WSS in 18 and peak velocity in 3 areas.

Results

While most patients had vortical and/or helical flow formations within the aorta, there was no significant change over time. Ascending aortic forward flow volumes were significantly lower in the OP group than in the NOP group at baseline (NOP 69.3 mL ± 14.2 mL vs. OP 55.3 mL ± 1.9 mL p = 0.029). WSS in the outer ascending aorta was significantly higher in the OP group than in the NOP group at baseline (NOP 0.6 ± 0.2 N/m² vs. OP 0.8 ± 0.2 N/m², p = 0.008). Peak velocity decreased from baseline to follow up in the aortic arch only in the OP group (1.6 ± 0.6 m/s vs. 1.2 ± 0.3 m/s, p = 0.018).

Conclusion

Aortic valve replacement influences aortic hemodynamics. The parameters improve after surgery.

Modelling blood flow in patients with heart valve disease using deep learning: A computationally efficient method to expand diagnostic capabilities in clinical routine

Introduction

The computational modelling of blood flow is known to provide vital hemodynamic parameters for diagnosis and treatment-support for patients with valvular heart disease. However, most diagnosis/treatment-support solutions based on flow modelling proposed utilize time- and resource-intensive computational fluid dynamics (CFD) and are therefore difficult to implement into clinical practice. In contrast, deep learning (DL) algorithms provide results quickly with little need for computational power. Thus, modelling blood flow with DL instead of CFD may substantially enhances the usability of flow modelling-based diagnosis/treatment support in clinical routine. In this study, we propose a DL-based approach to compute pressure and wall-shear-stress (WSS) in the aorta and aortic valve of patients with aortic stenosis (AS).

Methods

A total of 103 individual surface models of the aorta and aortic valve were constructed from computed tomography data of AS patients. Based on these surface models, a total of 267 patient-specific, steady-state CFD simulations of aortic flow under various flow rates were performed. Using this simulation data, an artificial neural network (ANN) was trained to compute spatially resolved pressure and WSS using a centerline-based representation. An unseen test subset of 23 cases was used to compare both methods.

Results

ANN and CFD-based computations agreed well with a median relative difference between both methods of 6.0% for pressure and 4.9% for wall-shear-stress. Demonstrating the ability of DL to compute clinically relevant hemodynamic parameters for AS patients, this work presents a possible solution to facilitate the introduction of modelling-based treatment support into clinical practice.

Impact of extra-anatomical bypass on coarctation fluid dynamics using patient-specific lumped parameter and Lattice Boltzmann modeling

Accurate hemodynamic analysis is not only crucial for successful diagnosis of coarctation of the aorta (COA), but intervention decisions also rely on the hemodynamics assessment in both pre and post intervention states to minimize patient risks. Despite ongoing advances in surgical techniques for COA treatments, the impacts of extra-anatomic bypass grafting, a surgical technique to treat COA, on the aorta are not always benign. Our objective was to investigate the impact of bypass grafting on aortic hemodynamics. We investigated the impact of bypass grafting on aortic hemodynamics using a patient-specific computational-mechanics framework in three patients with COA who underwent bypass grafting. Our results describe that bypass grafting improved some hemodynamic metrics while worsened the others: (1) Doppler pressure gradient improved (decreased) in all patients; (2) Bypass graft did not reduce the flow rate substantially through the COA; (3) Systemic arterial compliance increased in patients #1 and 3 and didn't change (improve) in patient 3; (4) Hypertension got worse in all patients; (5) The flow velocity magnitude improved (reduced) in patient 2 and 3 but did not improve significantly in patient 1; (6) There were elevated velocity magnitude, persistence of vortical flow structure, elevated turbulence characteristics, and elevated wall shear stress at the bypass graft junctions in all patients. We concluded that bypass graft may lead to pseudoaneurysm formation and potential aortic rupture as well as intimal hyperplasia due to the persistent abnormal and irregular aortic hemodynamics in some patients. Moreover, post-intervention, exposures of endothelial cells to high shear stress may lead to arterial remodeling, aneurysm, and rupture.

Patients with aortic stenosis exhibit early improved endothelial function following transcatheter aortic valve replacement: The eFAST study

BACKGROUND

Patients with severe aortic stenosis (AS) exhibit systemic endothelial dysfunction, which can be associated with myocardial ischaemia in absence of obstructive coronary disease. Transcatheter aortic valve replacement (TAVR) is used to treat severe AS in patients with high or prohibitive surgical risk. However, it remains unknown whether endothelial function recovers post-TAVR. We therefore sought to assess the early and late changes in flow-mediated dilation (FMD), a measure of endothelial function, following TAVR.

METHODS

Patients undergoing TAVR for severe AS had ultrasound assessment of brachial endothelial-independent and -dependent FMD. Measurements were performed pre-TAVR, at early follow-up (<48 h post-TAVR) and late follow-up (4-6 weeks post-TAVR).

RESULTS

27 patients (mean age 82.0 ± 7.0; 33.3% female) were recruited; 37.0% had diabetes mellitus and 59.3% had hypertension. Brachial artery FMD increased from 4.2 ± 1.6% (pre-TAVR) to 9.7 ± 3.5% at early follow-up (p < 0.0001). At late follow-up, improvement compared with early follow-up was sustained (8.7 ± 1.9%, p = 0.27). Resting brachial arterial flow velocities decreased significantly at late follow-up (11.24 ± 5.16 vs. 7.73 ± 2.79 cm/s, p = 0.003). Concordantly, at late follow-up, there was decrease in resting wall shear stress (WSS; 14.8 ± 7.8 vs. 10.6 ± 4.8dyne/cm2, p = 0.01), peak WSS (73.1 ± 34.1 vs. 58.8 ± 27.8dyne/cm2, p = 0.03) and cumulative WSS (3543 ± 1852 vs. 2504 ± 1089dyne·s/cm², p = 0.002). Additionally, a favourable inverse correlation between cumulative WSS and FMD was restored at late follow-up (r = -0.21 vs. r = 0.49).

CONCLUSION

Endothelial function in patients with AS improves early post-TAVR and this improvement is sustained. This likely occurs as a result of improved arterial haemodynamics, leading to lower localised WSS and release of vasoactive mediators that may also alleviate myocardial ischaemia.

Hemodynamic Profiles Before and After Surgery in Bicuspid Aortic Valve Disease-A Systematic Review of the Literature

Bicuspid aortic valve (BAV) disease presents a unique management challenge both pre- and post-operatively. 4D flow MRI offers multiple tools for the assessment of the thoracic aorta in aortic valve disease. In particular, its assessment of flow patterns and wall shear stress have led to new understandings around the mechanisms of aneurysm development in BAV disease. Novel parameters have now been developed that have the potential to predict pathological aortic dilatation and may help to risk stratify BAV patients in future. This systematic review analyses the current 4D flow MRI literature after aortic valve and/or ascending aortic replacement in bicuspid aortic valve disease. 4D flow MRI has also identified distinct challenges posed by this cohort at the time of valve replacement compared to standard management of tri-leaflet disorders, and may help tailor the type and timing of replacement. Eccentric pathological flow patterns seen after bioprosthetic valve implantation, but not with mechanical prostheses, might be an important future consideration in intervention planning. 4D flow MRI also has promising potential in supporting the development of artificial valve prostheses and aortic conduits with more physiological flow patterns.

The long-term fate of ascending aorta aneurysm after wrapping versus replacement

OBJECTIVE

The study objective was to examine the long-term fate of aortic diameter expansion at 4 cardiac regions (annulus, sinus, ascending aorta, and proximal arch) after wrapping or replacement during aortic valve surgery of the moderately dilated ascending aorta.

METHODS

From January 1995 to December 2018, 964 consecutive patients who underwent aortic valve replacement at our institution were reviewed. Of them, 204 (mean age, 60.7 ± 7.4 years) underwent ascending aorta wrapping (n = 96) or replacement (n = 108) for a moderately dilated ascending aorta (40 to 55 mm). The overall fate of the aortic diameter was analyzed with a linear mixed-effect model. The median follow-up duration was 7.1 years.

RESULTS

After propensity score matching, the baseline maximal ascending aortic diameter median value was 47.3 ± 3.1 mm and 49.4 ± 13.5 mm in the wrapping and replacement groups, respectively. The annulus, sinus, and ascending aorta did not redilate in either group. The proximal aortic arch diameter significantly increased over time (0.343 mm/year; P = .006) in the wrapping group but not in the replacement group (0.066 mm/year; P = .649). Multivariable competing risk analysis identified the initial ascending aorta diameter at the wrapping procedure as an independent risk factor of proximal arch redilation (0.071 ± 0.037, P < .001). The cutoff value was an initial ascending aorta diameter of 47.2 mm for the prediction proximal arch redilation (area under the curve, 0.703; P = .014).

CONCLUSIONS

Aortic wrapping and replacement may be long-term durable treatment options in patients with a moderately enlarged ascending aorta. We suggest careful evaluation of redilation in the proximal arch after an aorta wrapping procedure.

Highly accelerated aortic 4D flow MRI using compressed sensing: Performance at different acceleration factors in patients with aortic disease

PURPOSE

To systematically assess the feasibility and performance of a highly accelerated compressed sensing (CS) 4D flow MRI framework at three different acceleration factors (R) for the quantification of aortic flow dynamics and wall shear stress (WSS) in patients with aortic disease.

METHODS

Twenty patients with aortic disease (58 ± 15 y old; 19 M) underwent four 4D flow scans: one conventional (GRAPPA, R = 2) and three CS 4D flows with R = 5.7, 7.7, and 10.2. All scans were acquired with otherwise equivalent imaging parameters on a 1.5T scanner. Peak-systolic velocity (V_max ), peak flow (Q_max ), and net flow (Q_net ) were quantified at the ascending aorta (AAo), arch, and descending aorta (DAo). WSS was calculated at six regions within the AAo and arch.

RESULTS

Mean scan times for the conventional and CS 4D flows with R = 5.7, 7.7, and 10.2 were 9:58 ± 2:58 min, 3:40 ± 1:19 min, 2:50 ± 0:56 min, and 2:05 ± 0:42 min, respectively. V_max , Q_max , and Q_net were significantly underestimated by all CS protocols (underestimation ≤ -7%, -9%, and -10% by CS, R = 5.7, 7.7, and 10.2, respectively). WSS measurements showed the highest underestimation by all CS protocols (underestimation ≤ -9%, -12%, and -14% by CS, R = 5.7, 7.7, and 10.2).

CONCLUSIONS

Highly accelerated aortic CS 4D flow at R = 5.7, 7.7, and 10.2 showed moderate agreement with the conventional 4D flow, despite systematically underestimating various hemodynamic parameters. The shortened scan time may enable the clinical translation of CS 4D flow, although potential hemodynamic underestimation should be considered when interpreting the results.

Aortic stenosis exacerbates flow aberrations related to the bicuspid aortic valve fusion pattern and the aortopathy phenotype

OBJECTIVES

A bicuspid aortic valve (BAV) is characterized by variable phenotypic manifestations, as well as longitudinal evolution of valve dysfunction and ascending aorta dilatation. The present study investigated the impact of severe aortic stenosis (AS) on the flow patterns and wall shear stress (WSS) distribution in BAV patients with right-left (RL) and right-non-coronary (RN) cusp fusion types, and the study aimed to reveal whether aortic dysfunction could further alter intrinsic aortic haemodynamic aberrations generated by abnormal BAV cusp fusion patterns.

METHODS

Four-dimensional flow magnetic resonance imaging was performed in 120 BAV subjects and 20 tricuspid aortic valve controls. BAV patients were evenly categorized into 4 cohorts, including RL and RN BAV with no more than mild aortic dysfunction as well as RL and RN BAV-AS with isolated severe AS.

RESULTS

BAV subjects exhibited eccentric outflow jets resulting in regional WSS elevation at the right-anterior position of the ascending aorta in the RL group and the right-posterior location in the RN group (P < 0.005). The presence of severe AS resulted in accelerated outflow jets and more prominent flow and WSS eccentricity (P < 0.005) by marked helical (P = 0.014) and vortical flow formation (P < 0.005), as well as increased prevalence of tubular and transverse arch dilatation. The changes to the flow jet in BAV-AS subjects blurred the differences in peak flow velocity and WSS distribution between RL and RN BAV. Differences in the phenotypes of aortopathy were associated with changes in functional haemodynamic parameters such as flow displacement and WSS eccentricity.

CONCLUSIONS

Severe AS markedly exacerbated aortic flow aberrations in BAV patients and masked the existing distinct flow features deriving from RL and RN fusion types. Longitudinal studies are needed to investigate the evolution of ascending aortic dilatation relative to the interaction between intrinsic cusp fusion types and acquired severe valve dysfunction.

Influence of TEVAR on blood pressure in subacute type B aortic dissection (TBAD) patients with refractory and non-refractory arterial hypertension

BACKGROUND

Aim of this study was to compare the modifications of systemic blood pressure in patients with subacute type b aortic dissection (TBAD) and refractory (rHTN) and non-refractory arterial hypertension (N-rHTN) treated by thoracic endovascular aortic repair (TEVAR).

METHODS

Patients were divided into two groups, rHTN defined as blood pressure >140/90 mmHg with ≥5 antihypertensive drugs and patients with N-rHTN. Primary endpoint was the variation of mean systolic, diastolic and overall pressure (MSP, MDP and MAP) before and after antihypertensive treatment or TEVAR. Secondary endpoints were the 30-days mortality. Fifty-seven patients were included in this study.

RESULTS

Of the 44 Patients of the TEVAR group 21 were included in the N-rHTN group. The MSP before and after surgery for the N-rHTN group was 130 (±10 SD) and 111 (±22 SD) mmHg, P=0.01. In the rHTN group 164 (±17 SD) and 118 (±17 SD) mmHg (P=0.01). The reduction of MSP was greater in the rHTN group (P=0.01). The MAP before and after the TEVAR for the N-rHTN group was 90 (±10 SD) and 74 (±12 SD) mmHg (P=0.01), in the rHTN group 111 (±14 SD) and 70 (±9 SD) mmHg (P=0.01). The overall mortality rate group was 2.2% (1/44).

CONCLUSIONS

TEVAR for TBAD appears to positively affect blood pressure in patients with rHTN and N-rHTN.

Impact of sequence type and field strength (1.5, 3, and 7T) on 4D flow MRI hemodynamic aortic parameters in healthy volunteers

PURPOSE

4D flow magnetic resonance imaging (4D-MRI) allows time-resolved visualization of blood flow patterns, quantification of volumes, velocities, and advanced parameters, such as wall shear stress (WSS). As 4D-MRI enters the clinical arena, standardization and awareness of confounders are important. Our aim was to evaluate the equivalence of 4D flow-derived aortic hemodynamics in healthy volunteers using different sequences and field strengths.

METHODS

4D-MRI was acquired in 10 healthy volunteers at 1.5T using three different prototype sequences, at 3T and at 7T (Siemens Healthineers). After evaluation of diagnostic quality in three segments (ascending-, descending aorta, aortic arch), peak velocity, flow volumes, and WSS were investigated. Equivalence limits for comparison of field strengths/sequences were based on the limits of Bland-Altman analyses of the intraobserver variability.

RESULTS

Non-diagnostic quality was found in 10/144 segments, 9/10 were obtained at 7T. Apart for the comparison of forward flow between sequence 1 and 3, the differences in measurements between field strengths/sequences exceeded the range of agreement. Significant differences were found between field strengths/sequences for forward flow (1.5T vs. 3T, 3T vs. 7T, sequence 1 vs. 3, 2 vs. 3 [P < .001]), WSS (1.5T vs. 3T [P < .05], sequence 1 vs. 2, 1 vs. 3, 2 vs. 3 [P < .001]), and peak velocity (1.5T vs. 7T, sequence 1 vs. 3 [P > .001]). All parameters at all field strengths/with all sequences correlated moderately to strongly (r ≥ 0.5).

CONCLUSION

Data from all sequences could be acquired and resulting images showed sufficient quality for further analysis. However, the variability of the measurements of peak velocity, flow volumes, and WSS was higher when comparing field strengths/sequences as the equivalence limits defined by the intraobserver assessments.

4D Flow with MRI

Magnetic resonance imaging (MRI) has become an important tool for the clinical evaluation of patients with cardiac and vascular diseases. Since its introduction in the late 1980s, quantitative flow imaging with MRI has become a routine part of standard-of-care cardiothoracic and vascular MRI for the assessment of pathological changes in blood flow in patients with cardiovascular disease. More recently, time-resolved flow imaging with velocity encoding along all three flow directions and three-dimensional (3D) anatomic coverage (4D flow MRI) has been developed and applied to enable comprehensive 3D visualization and quantification of hemodynamics throughout the human circulatory system. This article provides an overview of the use of 4D flow applications in different cardiac and vascular regions in the human circulatory system, with a focus on using 4D flow MRI in cardiothoracic and cerebrovascular diseases.

Four-dimensional-flow Magnetic Resonance Imaging of the Aortic Valve and Thoracic Aorta

Blood flow through the heart and great vessels is sensitive to time and multiple velocity directions. The assessment of its three-dimensional nature has been limited. Recent advances in magnetic resonance imaging (MRI) allow the comprehensive visualization and quantification of in vivo flow dynamics using four-dimensional (4D)-flow MRI. In addition, the technique provides the opportunity to obtain advanced hemodynamic measures. This article introduces 4D-flow MRI as it is currently used for blood flow visualization and quantification of cardiac hemodynamic parameters. It discusses its advantages relative to other flow MRI techniques and describes its potential clinical applications.

Applications of a Specialty Bicuspid Aortic Valve Program: Clinical Continuity and Translational Collaboration

Bicuspid aortic valve (BAV) is a common congenital heart diagnosis and is associated with aortopathy. Current guidelines for aortic resection have been validated but are based on aortic diameter, which is insufficient to predict acute aortic events. Clinical and translational collaboration is necessary to identify biomarkers that can individualize the timing of prophylactic surgery for BAV aortopathy. We describe our multidisciplinary BAV program, including research protocols aimed at biomarker discovery and results from our longitudinal clinical registry. From 2012–2018, 887 patients enrolled in our clinical BAV registry with the option to undergo four dimensional flow cardiovascular magnetic resonance imaging (4D flow CMR) and donate serum plasma or tissue samples. Of 887 patients, 388 (44%) had an elective BAV-related procedure after initial presentation, while 499 (56%) continued with medical management. Of medical patients, 44 (9%) had elective surgery after 2.3 ± 1.4 years. Surgery patients’ biobank donations include 198 (46%) aorta, 374 (86%) aortic valve, and 314 (73%) plasma samples. The 4D flow CMR was completed for 215 (50%) surgery patients and 243 (49%) medical patients. Patients with BAV aortopathy can be safely followed by a multidisciplinary team to detect indications for surgery. Paired tissue and hemodynamic analysis holds opportunity for biomarker development in BAV aortopathy.

Phase-contrast magnetic resonance imaging and computational fluid dynamics assessment of thoracic aorta blood flow: a literature review

The death rate from thoracic aortic disease is on the rise and represents a growing global health concern as patients are often asymptomatic before acute events, which have devastating effects on health-related quality of life. Biomechanical factors have been found to play a major role in the development of both acquired and congenital aortic diseases. However, much is still unknown and translational benefits of this knowledge are yet to be seen. Phase-contrast cardiovascular magnetic resonance imaging of thoracic aortic blood flow has emerged as an exceptionally powerful non-invasive tool enabling visualization of complex flow patterns, and calculation of variables such as wall shear stress. This has led to multiple new findings in the areas of phenotype-dependent bicuspid valve flow patterns, thoracic aortic aneurysm formation and aortic prosthesis performance assessment. Phase-contrast cardiovascular magnetic resonance imaging has also been used in conjunction with computational fluid modelling techniques to produce even more sophisticated analyses, by allowing the calculation of haemodynamic variables with exceptional temporal and spatial resolution. Translationally, these technologies may potentially play a major role in the emergence of precision medicine and patient-specific treatments in patients with aortic disease. This clinically focused review will provide a systematic overview of key insights from published studies to date.

Evaluating medical device and material thrombosis under flow: current and emerging technologies

This review highlights the importance of flow in medical device thrombosis and explores current and emerging technologies to evaluate dynamic biomaterial Thrombosis in vitro.

Familial Aortopathies - State of the Art Review

Aortopathies are conditions that result in aortic dilatation, aneurysm formation and dissection. Familial aortopathies (perhaps better known as heritable thoracic aortic aneurysm and dissection, h-TAAD, as not all have a positive family history) are recognised to have an underlying genetic cause and affect the aorta, predisposing it to the above pathologies. These conditions can also affect the extra-aortic vasculature, particularly large elastic arteries and other body systems. Mutations in a number of genes have been associated with h-TAAD. However, not all affected families have a pathogenic gene variant identified-highlighting the importance of a three-generational family history and the likely role of both environmental factors and future gene discoveries in furthering knowledge. Survival has improved over the last few decades, essentially due to surgical intervention. The benefit of identifying affected individuals depends upon a regular surveillance program and timely referral for surgery before complications such as dissection. Further research is required to appreciate fully the effects of individual gene variants and improve evidence for prophylactic medical therapy, as well as to understand the effect of h-TAAD on quality of life and life choices, particularly around exercise and pregnancy, for affected individuals. This will be complemented by laboratory-based research that seeks to understand the tissue pathways that underlie development of arterial pathology, ideally providing targets for novel medical therapies and a means of non-invasively identifying individuals at increased vascular risk to reduce dissection, which remains a devastating life-threatening event.

In vitro 4D Flow MRI evaluation of aortic valve replacements reveals disturbed flow distal to biological but not to mechanical valves

BACKGROUND AND AIM OF THE STUDY

Aortic hemodynamics influence the integrity of the vessel wall and cardiac afterload. The aim of this study was to compare hemodynamics distal to biological (BV) and mechanical aortic valve (MV) replacements by in vitro 4D Flow MRI excluding confounding factors of in-vivo testing potentially influencing hemodynamics.

METHODS

Two BV (Perimount MagnaEase [Carpentier-Edwards], Trifecta [Abbott]) and two MV (On-X [CryoLife], prototype trileaflet valve) were scanned in a flexible aortic phantom at 3T using a recommended 4D Flow MR sequence. A triphasic aortic flow profile with blood-mimicking fluid was established. Using GTFlow (Gyrotools), area and velocity of the ejection jet were measured. Presence and extent of sinus vortices and secondary flow patterns were graded on a 0 to 3 scale.

RESULTS

A narrow, accelerated central ejection jet (Area = 27 ± 7% of vessel area, Velocity = 166 ± 13 cm/s; measured at sinotubular junction) was observed in BV as compared to MV (Area = 53 ± 13%, Velocity = 109 ± 21 cm/s). As opposed to MV, the jet distal to BV impacted the outer curvature of the ascending aorta and resulted in large secondary flow patterns (BV: n = 4, grades 3, 3, 2, 1; MV: n = 1, grade 1). Sinus vortices only formed distal to MV. Although physiologically configured, they were larger than normal (grade 3).

CONCLUSIONS

In contrast to mechanical valves, biological valve replacements induced accelerated and increased flow patterns deviating from physiological ones. While it remains speculative whether this increases the risk of aneurysm formation through wall shear stress changes, findings are contrasted by almost no secondary flow patterns and typical, near-physiological sinus vortex formation distal to mechanical valves.

Seismocardiography and 4D flow MRI reveal impact of aortic valve replacement on chest acceleration and aortic hemodynamics

Aortic valve replacement (AVR) is a common treatment for severe aortic valve disease, which can adversely affect blood flow in the aorta. Seismocardiography (SCG) measures physical vibrations at the exterior of the chest, which can be sensitive to altered cardiac function and flow dynamics. Magnetic resonance imaging (MRI) can image blood movement, and it can provide depiction and quantification of aortic flow. Here we present SCG and MRI measurements from before and after AVR and ascending aorta replacement, in the case of a woman with bicuspid aortic valve disease and a dilated ascending aorta. SCG measurements show elevated energy during systole indicating stenotic flow before surgery and lowered systolic energy levels after replacement with a prosthetic valve. MRI shows jetting, helical flow before surgery, and cohesive flow after.

Two-Minute k-Space and Time-accelerated Aortic Four-dimensional Flow MRI: Dual-Center Study of Feasibility and Impact on Velocity and Wall Shear Stress Quantification

Purpose

To investigate the two-center feasibility of highly k-space and time (k-t)-accelerated 2-minute aortic four-dimensional (4D) flow MRI and to evaluate its performance for the quantification of velocities and wall shear stress (WSS).

Materials and Methods

This cross-sectional study prospectively included 68 participants (center 1, 11 healthy volunteers [mean age ± standard deviation, 61 years ± 15] and 16 patients with aortic disease [mean age, 60 years ± 10]; center 2, 14 healthy volunteers [mean age, 38 years ± 13] and 27 patients with aortic or cardiac disease [mean age, 78 years ± 18]). Each participant underwent highly accelerated 4D flow MRI (k-t acceleration, acceleration factor of 5) of the thoracic aorta. For comparison, conventional 4D flow MRI (acceleration factor of 2) was acquired in the participants at center 1 (n = 27). Regional aortic peak systolic velocities and three-dimensional WSS were quantified.

Results

k-t-accelerated scan times (center 1, 2:03 minutes ± 0:29; center 2, 2:06 minutes ± 0:20) were significantly reduced compared with conventional 4D flow MRI (center 1, 12:38 minutes ± 2:25; P < .0001). Overall good agreement was found between the two techniques (absolute differences ≤15%), but proximal aortic WSS was significantly underestimated in patients by using k-t-accelerated 4D flow when compared with conventional 4D flow (P ≤ .03). k-t-accelerated 4D flow MRI was reproducible (intra- and interobserver intraclass correlation coefficient ≥0.98) and identified significantly increased peak velocities and WSS in patients with stenotic (P ≤ .003) or bicuspid (P ≤ .04) aortic valves compared with healthy volunteers. In addition, k-t-accelerated 4D flow MRI-derived velocities and WSS were inversely related to age (r ≥-0.53; P ≤ .03) over all healthy volunteers.

Conclusion

k-t-accelerated aortic 4D flow MRI providing 2-minute scan times was feasible and reproducible at two centers. Although consistent healthy aging- and disease-related changes in aortic hemodynamics were observed, care should be taken when considering WSS, which can be underestimated in patients.© RSNA, 2019See also the commentary by François in this issue.

Ascending aortic aneurysm exposed to direct impingement of eccentric flow jets through a tilting-disc valve prosthesis

Single-leaflet tilting-disc aortic valve prostheses are known to generate eccentric transvalvular flow jets. These prostheses are routinely inserted with the major valve opening directed toward the non-coronary sinus to achieve more favorable hemodynamic performance. From the viewpoint of blood flow dynamics, the structural and functional properties of tilting-disc aortic valves resemble those of congenital bicuspid aortic valves with right- and left-coronary leaflet fusion, which have been associated with aortopathy in the ascending aorta. Here we describe the case of a patient who had undergone aortic valve replacement in 1987 with a Björk-Shiley tilting-disc valve and required reoperation for ascending aortic aneurysm 29 years later. Eccentric flow jets through the tilting-disc valve directly impinged on the posterior wall of the ascending aorta including the aortotomy suture line, possibly contributing to the development of the saccular aneurysm in the ascending aorta.

Structural valve deterioration does not alter tissue valves' radiopaque landmarks: Implications for valve-in-valve therapy

BACKGROUND

Valve-in-valve is established as a safe and efficient alternative to redo surgery in the treatment of structural valve deterioration (SVD). In vitro models rely on the radiopaque landmarks of undeteriorated tissue valves to establish the optimal implantation level of the transcatheter heart valves inside the deteriorated valves. In computed assisted procedures, the radiopaque landmarks of the deteriorated valves may be used to guide valve implantation through image fusion. The purpose of this study is to determine whether SVD alters the radiopaque landmarks of stented tissue valves.

METHODS

Our approach was based on the computation of relevant anatomical measurements from CT images. Radiopaque landmarks of degenerated bioprostheses and the corresponding undeteriorated valves were extracted to create surface meshes and cloud points using grey-level thresholding. 3D registration using an iterative closest point algorithm was used to align the corresponding cloud points, while the modified Hausdorff Distance was applied to determine the differences between them.

RESULTS

The proposed evaluation was performed on 19 degenerated tissue valves. 15 valves were scanned from patients evaluated for valve-in-valve procedures, and 4 bioprostheses were scanned after surgical extraction during redo aortic valve replacement. All the degenerated valves were compared to the corresponding undeteriorated models. Overall, the mean difference between degenerated and undeteriorated valves was 0.33 ± 0.12 mm. The maximum observed registration error was 0.66 mm.

CONCLUSIONS

Our study demonstrates no significant difference between the radiopaque landmarks of deteriorated and undeteriorated bioprostheses after the occurrence of SVD. Our findings suggest therefore that SVD does not alter radiopaque landmarks of stented tissue valves. These results validate in-vitro studies of optimal transcatheter heart valves implantation inside deteriorated tissue valves based on their radiopaque landmarks, and allow the use of non-deteriorated valves' imaging features in computer assisted valve-in-valve procedures.

Discrete Subaortic Stenosis: Perspective Roadmap to a Complex Disease

Discrete subaortic stenosis (DSS) is a congenital heart disease that results in the formation of a fibro-membranous tissue, causing an increased pressure gradient in the left ventricular outflow tract (LVOT). While surgical resection of the membrane has shown some success in eliminating the obstruction, it poses significant risks associated with anesthesia, sternotomy, and heart bypass, and it remains associated with a high rate of recurrence. Although a genetic etiology had been initially proposed, the association between DSS and left ventricle (LV) geometrical abnormalities has provided more support to a hemodynamic etiology by which congenital or post-surgical LVOT geometric derangements could generate abnormal shear forces on the septal wall, triggering in turn a fibrotic response. Validating this hypothetical etiology and understanding the mechanobiological processes by which altered shear forces induce fibrosis in the LVOT are major knowledge gaps. This perspective paper describes the current state of knowledge of DSS, articulates the research needs to yield mechanistic insights into a significant pathologic process that is poorly understood, and proposes several strategies aimed at elucidating the potential mechanobiological synergies responsible for DSS pathogenesis. The proposed roadmap has the potential to improve DSS management by identifying early targets for prevention of the fibrotic lesion, and may also prove beneficial in other fibrotic cardiovascular diseases associated with altered flow.