Hemodynamic Modeling of Surgically Repaired Coarctation of the Aorta

A 3D scaling law for supravalvular aortic stenosis suited for stethoscopic auscultations

In this study a frequency scaling law for 3D anatomically representative supravalvular aortic stenosis (SVAS) cases is proposed. The law is uncovered for stethoscopy's preferred auscultation range (70-120 Hz). LES simulations are performed on the CFD solver Fluent, leveraging Simulia's Living Heart Human Model (LHHM), modified to feature hourglass stenoses that range between 30 to 80 percent (mild to severe) in addition to the descending aorta. For physiological hemodynamic boundary conditions the Windkessel model is implemented via a UDF subroutine. The flow-generated acoustic signal is then extracted using the FW-H model and analyzed using FFT. A preferred receiver location that matches clinical practice is confirmed (right intercostal space) and a correlation between the degree of stenosis and a corresponding acoustic frequency is obtained. Five clinical auscultation signals are tested against the scaling law, with the findings interpreted in relation to the NHS classification of stenosis and to the assessments of experienced cardiologists. The scaling law is thus shown to succeed as a potential quantitative decision-support tool for clinicians, enabling them to reliably interpret stethoscopic auscultations for all degrees of stenosis, which is especially useful for moderate degrees of SVAS. Computational investigation of more complex stenotic cases would enhance the clinical relevance of this proposed scaling law, and will be explored in future research.

In-silico investigations of haemodynamic parameters for a blunt thoracic aortic injury case

Accounting for 1.5% of thoracic trauma, blunt thoracic aortic injury (BTAI) is a rare disease with a high mortality rate that nowadays is treated mostly via thoracic endovascular aortic repair (TEVAR). Personalised computational models based on fluid-solid interaction (FSI) principals not only support clinical researchers in studying virtual therapy response, but also are capable of predicting eventual outcomes. The present work studies the variation of key haemodynamic parameters in a clinical case of BTAI after successful TEVAR, using a two-way FSI model. The three-dimensional (3D) patient-specific geometries of the patient were coupled with three-element Windkessel model for both prior and post intervention cases, forcing a correct prediction of blood flow over each section. Results showed significant improvement in velocity and pressure distribution after stenting. High oscillatory, low magnitude shear (HOLMES) regions require careful examination in future follow-ups, since thrombus formation was confirmed in some previously clinically reported cases of BTAI treated with TEVAR. The strength of swirling flows along aorta was also damped after stent deployment. Highlighting the importance of haemodynamic parameters in case-specific therapies. In future studies, compromising motion of aortic wall due to excessive cost of FSI simulations can be considered and should be based on the objectives of studies to achieve a more clinical-friendly patient-specific CFD model.

Personalized Pre- and Post-Operative Hemodynamic Assessment of Aortic Coarctation from 3D Rotational Angiography

PURPOSE

Coarctation of Aorta (CoA) is a congenital disease consisting of a narrowing that obstructs the systemic blood flow. This proof-of-concept study aimed to develop a framework for automatically and robustly personalizing aortic hemodynamic computations for the assessment of pre- and post-intervention CoA patients from 3D rotational angiography (3DRA) data.

METHODS

We propose a framework that combines hemodynamic modelling and machine learning (ML) based techniques, and rely on 3DRA data for non-invasive pressure computation in CoA patients. The key features of our framework are a parameter estimation method for calibrating inlet and outlet boundary conditions, and regional mechanical wall properties, to ensure that the computational results match the patient-specific measurements, and an improved ML based pressure drop model capable of predicting the instantaneous pressure drop for a wide range of flow conditions and anatomical CoA variations.

RESULTS

We evaluated the framework by investigating 6 patient datasets, under pre- and post-operative setting, and, since all calibration procedures converged successfully, the proposed approach is deemed robust. We compared the peak-to-peak and the cycle-averaged pressure drop computed using the reduced-order hemodynamic model with the catheter based measurements, before and after virtual and actual stenting. The mean absolute error for the peak-to-peak pressure drop, which is the most relevant measure for clinical decision making, was 2.98 mmHg for the pre- and 2.11 mmHg for the post-operative setting. Moreover, the proposed method is computationally efficient: the average execution time was of only [Formula: see text] minutes on a standard hardware configuration.

CONCLUSION

The use of 3DRA for hemodynamic modelling could allow for a complete hemodynamic assessment, as well as virtual interventions or surgeries and predictive modeling. However, before such an approach can be used routinely, significant advancements are required for automating the workflow.

Isolating the Effect of Arch Architecture on Aortic Hemodynamics Late After Coarctation Repair: A Computational Study

Objectives

Effective management of aortic coarctation (CoA) affects long-term cardiovascular outcomes. Full appreciation of CoA hemodynamics is important. This study aimed to analyze the relationship between aortic shape and hemodynamic parameters by means of computational simulations, purposely isolating the morphological variable.

Methods

Computational simulations were run in three aortic models. MRI-derived aortic geometries were generated using a statistical shape modeling methodology. Starting from n = 108 patients, the mean aortic configuration was derived in patients without CoA (n = 37, "no-CoA"), with surgically repaired CoA (n = 58, "r-CoA") and with unrepaired CoA (n = 13, "CoA"). As such, the aortic models represented average configurations for each scenario. Key hemodynamic parameters (i.e., pressure drop, aortic velocity, vorticity, wall shear stress WSS, and length and number of strong flow separations in the descending aorta) were measured in the three models at three time points (peak systole, end systole, end diastole).

Results

Comparing no-CoA and CoA revealed substantial differences in all hemodynamic parameters. However, simulations revealed significant increases in vorticity at the site of CoA repair, higher WSS in the descending aorta and a 12% increase in power loss, in r-CoA compared to no-CoA, despite no clinically significant narrowing (CoA index >0.8) in the r-CoA model.

Conclusions

Small alterations in aortic morphology impact on key hemodynamic indices. This may contribute to explaining phenomena such as persistent hypertension in the absence of any clinically significant narrowing. Whilst cardiovascular events in these patients may be related to hypertension, the role of arch geometry may be a contributory factor.

Right ventricular afterload in repaired D-TGA is associated with inefficient flow patterns, rather than stenosis alone

Treatment of D- transposition of great arteries (DTGA) involves the Arterial Switch Operation (ASO), which can create PA branch stenosis (PABS) and alter PA blood flow energetics. This altered PA flow may contribute to elevated right ventricular (RV) afterload more significantly than stenosis alone. Our aim was to correlate RV afterload and PA flow characteristics using 4D flow cardiac magnetic resonance (CMR) imaging of a mock circulatory system (MCS) incorporating 3D printed replicas. CMR imaging and clinical characteristics were analyzed from 22 ASO patients (age 11.9 ± 8.7 years, 68% male). Segmentation was performed to create 3D printed PA replicas that were mounted in an MRI-compatible MCS. Pressure drop across the PA replica was recorded and 4D flow CMR acquisitions were analyzed for blood flow inefficiency (energy loss, vorticity). In post-ASO patients, there is no difference in RV mass (p = 0.07), nor RV systolic pressure (p = 0.26) in the presence or absence of PABS. 4D flow analysis of MCS shows energy loss is correlated to RV mass (p = 0.01, r = 0.67) and MCS pressure differential (p = 0.02, r = 0.57). Receiver operating characteristic curve shows energy loss detects elevated RV mass above 30 g/m² (p = 0.02, AUC 0.88) while index of PA dimensions (Nakata) does not (p = 0.09, AUC 0.79). PABS alone does not account for differences in RV mass or afterload in post-ASO patients. In MCS simulations, energy loss is correlated with both RV mass and PA pressure, and can moderately detect elevated RV mass. Inefficient PA flow may be an important predictor of RV afterload in this population.

Altered hemodynamics by 4D flow cardiovascular magnetic resonance predict exercise intolerance in repaired coarctation of the aorta: an in vitro study

BACKGROUND

Coarctation of the aorta (CoA) is associated with decreased exercise capacity despite successful repair. Altered flow patterns have been identified due to abnormal aortic arch geometry. Our previous work demonstrated aorta size mismatch to be associated with exercise intolerance in this population. In this study, we studied aortic flow patterns during simulations of exercise in repaired CoA using 4D flow cardiovascular magnetic resonance (CMR) using aortic replicas connected to an in vitro flow pump and correlated findings with exercise stress test results to identify biomarkers of exercise intolerance.

METHODS

Patients with CoA repair were retrospectively analyzed after CMR and exercise stress test. Each aorta was manually segmented and 3D printed. Pressure gradient measurements from ascending aorta (AAo) to descending aorta (DAo) and 4D flow CMR were performed during simulations of rest and exercise using a mock circulatory flow loop. Changes in wall shear stress (WSS) and secondary flow formation (vorticity and helicity) from rest to exercise were quantified, as well as estimated DAo Reynolds number. Parameters were correlated with percent predicted peak oxygen consumption (VO2max) and aorta size mismatch (DAAo/DDAo).

RESULTS

Fifteen patients were identified (VO2max 47 to 126% predicted). Pressure gradient did not correlate with VO2max at rest or exercise. VO2max correlated positively with the change in peak vorticity (R = 0.55, p = 0.03), peak helicity (R = 0.54, p = 0.04), peak WSS in the AAo (R = 0.68, p = 0.005) and negatively with peak WSS in the DAo (R = - 0.57, p = 0.03) from rest to exercise. DAAo/DDAo correlated strongly with change in vorticity (R = - 0.38, p = 0.01), helicity (R = - 0.66, p = 0.007), and WSS in the AAo (R = - 0.73, p = 0.002) and DAo (R = 0.58, p = 0.02). Estimated DAo Reynolds number negatively correlated with VO2max for exercise (R = - 0.59, p = 0.02), but not rest (R = - 0.28, p = 0.31). Visualization of streamline patterns demonstrated more secondary flow formation in aortic arches with better exercise capacity, larger DAo, and lower Reynolds number.

CONCLUSIONS

There are important associations between secondary flow characteristics and exercise capacity in repaired CoA that are not captured by traditional pressure gradient, likely due to increased turbulence and inefficient flow. These 4D flow CMR parameters are a target of investigation to identify optimal aortic arch geometry and improve long term clinical outcomes after CoA repair.

Congenital Heart Disease: An Immunological Perspective

Congenital heart disease (CHD) poses a significant global health and economic burden-despite advances in treating CHD reducing the mortality risk, globally CHD accounts for approximately 300,000 deaths yearly. Children with CHD experience both acute and chronic cardiac complications, and though treatment options have improved, some remain extremely invasive. A challenge in addressing these morbidity and mortality risks is that little is known regarding the cause of many CHDs and current evidence suggests a multifactorial etiology. Some studies implicate an immune contribution to CHD development; however, the role of the immune system is not well-understood. Defining the role of the immune and inflammatory responses in CHD therefore holds promise in elucidating mechanisms underlying these disorders and improving upon current diagnostic and treatment options. In this review, we address the current knowledge coinciding CHDs with immune and inflammatory associations, emphasizing conditions where this understanding would provide clinical benefit, and challenges in studying these mechanisms.

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.

The effect of coarctation degrees on wall shear stress indices

Coarctation of the aorta (CoA) is a congenital tightening of the proximal descending aorta. Flow quantification can be immensely valuable for an early and accurate diagnosis. However, there is a lack of appropriate diagnostic approaches for a variety of cardiovascular diseases, such as CoA. An accurate understanding of the disease depends on measurements of the global haemodynamics (criteria for heart function) and also the local haemodynamics (detailed data on the dynamics of blood flow). Playing a significant role in clinical processes, wall shear stress (WSS) cannot be measured clinically; thus, computation tools are needed to give an insight into this crucial haemodynamic parameter. In the present study, in order to enable the progress of non-invasive approaches that quantify global and local haemodynamics for different CoA severities, innovative computational blueprint simulations that include fluid-solid interaction models are developed. Since there is no clear approach for managing the CoA regarding its severity, this study proposes the use of WSS indices and pressure gradient to better establish a framework for treatment procedures in CoA patients with different severities. This provides a platform for improving CoA therapy on a patient-specific level, in which physicians can perform treatment methods based on WSS indices on top of using a mere experience. Results show how severe CoA affects the aorta in comparison to the milder cases, which can give the medical community valuable information before and after any intervention.

Modified technique for coarctation of aorta with hypoplastic distal aortic arch

BACKGROUND

A combination of coarctation of aorta with various severity of distal arch hypoplasia frequently occurs in newborns. Traditional techniques in the neonatal period such as extended end-to-end anastomosis or inner curve patch are controversial. Arch geometry has a marked role in long-term outcomes. We introduce a modified Amato technique of distal aortic arch enlargement with native tissue-to-tissue reconstruction.

METHODS

Neonatal patients with coarctation of aorta and distal aortic arch hypoplasia who underwent surgical reconstruction using this technique between January 2016 and December 2019 in our center were included. Patients with concomitant complex heart defects were excluded. Data were obtained from echo protocols, CT scans before and after repair. The dimensions of the arch were assessed using Z-score, arch geometry was evaluated with height/width ratio.

RESULTS

Thirty-two patients (22 males, 10 females) were included. Median age and weight were 7 days (5; 18) and 3.5 kg (3.1; 4.0), respectively. The Z-score of distal part of the arch before and after procedure was significantly different (<0.01). No mortality, recoarctation, or bronchial compression was found during 18 (6-38) months of follow-up.

CONCLUSION

Modified technique for coarctation of aorta with hypoplastic distal aortic arch provides favorable geometry of the aorta with a low risk of morbidity. The proper selection and accurate technique could minimize potential risks. This method is relatively safe and might improve long-term outcomes associated with the geometry of aorta.

Aortic Arch Enlargement and Coarctation Repair of Preserving the Lesser Curvature of the Aortic Arch Through a Left Thoracotomy in Neonates

The aim of this study was to analyze the aortic arch repair technique for preserving the lesser curvature without cardiopulmonary bypass through a left thoracotomy in neonates with coarctation of the aorta (CoA) and a hypoplastic distal aortic arch (HDAA). HDAA was defined as z-score of the aortic arch < - 2.5. Twenty-four neonates with CoA and HDAA were retrospectively studied. Patients underwent enlargement of the HDAA associated with CoA repair when their z-scores were < - 4. They were divided into 2 groups on the basis of the preoperative z-score of the distal aortic arch: group 1 (n = 14), z-score ≥ - 4; group 2 (n = 10), z-score < - 4. Twenty-two patients had intracardiac defects. Follow-up ranged from 0.9 to 20.1 years (median 11.6 years). The z-scores of the distal aortic arch were significantly smaller in group 2 than group 1 (- 5.09 ± 1.05 vs - 3.19 ± 0.36, p < 0.001). There were no hospital deaths and no hypertension. All dimensions of the aortic arch in both groups revealed significant catch-up growth (p < 0.02). All patients showed a pressure gradient ≤  5 mmHg across the aortic arch and between the arms and legs at the latest follow-up. Two patients showed an angulated arch deformity over 10 years later. This technique provided good catch-up growth and a low incidence of reobstruction and deformity of reconstructed aortic arch in both groups. These results suggest that this modification might be considered as one choice of technique for CoA and HDAA.

Acute and medium term results of balloon expandable stent placement in the transverse arch-a multicenter pediatric interventional cardiology early career society study

OBJECTIVES AND BACKGROUND

Coarctation of the aorta represents 5-8% of all congenital heart disease. Although balloon expandable stents provide an established treatment option for native or recurrent coarctation, outcomes from transverse arch (TAO) stenting, including resolution of hypertension have not been well studied. This study aims to evaluate immediate and midterm results of TAO stenting in a multi-center retrospective cohort.

METHODS

TAO stenting was defined as stent placement traversing any head and neck vessel, with the primary intention of treating narrowing in the transverse aorta. Procedural details, complications and medications were assessed immediately post procedure, at 6 month follow-up and at most recent follow-up.

RESULTS

Fifty-seven subjects, 12 (21%) native, and 45 (79%) surgically repaired aortic arches, from seven centers were included. Median age was 14 years (4 days-42 years), median weight 54 kg (1.1-141 kg). After intervention, the median directly measured arch gradient decreased from 20 mmHg (0-57 mmHg) to 0 mmHg (0-23 mmHg) (p < .001). The narrowest arch diameter increased from 9 mm (1.4-16 mm) to 14 mm (2.9-25 mm) (p < .001), with a median increase of 4.9 mm (1.1-10.1 mm). One or more arch branches were covered by the stent in 55 patients (96%). There were no serious adverse events. Two patients warranted stent repositioning following migration during deployment. There were no late complications. There were 8 reinterventions, 7 planned, and 1 unplanned (6 catheterizations, 2 surgeries). Antihypertensive management was continued in 19 (40%) at a median follow-up of 3.2 years (0.4-7.3 years).

CONCLUSIONS

TAO stenting can be useful in selected patients for resolution of stenosis with minimal complications. This subset of patients are likely to continue on antihypertensive medications despite resolution of stenosis.

Prediction of Stress Map in Ascending Aorta - Optimization of the Coaxial Position in Transcatheter Aortic Valve Replacement

BACKGROUD

Transcatheter aortic valve replacement (TAVR) can reduce mortality among patients with aortic stenosis. Knowledge of pressure distribution and shear stress at the aortic wall may help identify critical regions, where aortic remodeling process may occur. Here a numerical simulation study of the influence of positioning of the prosthetic valve orifice on the flow field is presented.

OBJECTIVE

The present analysis provides a perspective of great variance on flow behavior due only to angle changes.

METHODS

A 3D model was generated from computed tomography angiography of a patient who had undergone a TAVR. Different mass flow rates were imposed at the inlet valve.

RESULTS

Small variations of the tilt angle could modify the nature of the flow, displacing the position of the vortices, and altering the prerssure distribution and the location of high wall shear stress.

CONCLUSION

These hemodynamic features may be relevant in the aortic remodeling process and distribution of the stress mapping and could help, in the near future, the optimization of the percutaneous prosthesis implantation. (Arq Bras Cardiol. 2020; [online].ahead print, PP.0-0).

Prediction of post-stenting biomechanics in coarcted aortas: A pilot finite element study

Endovascular stenting has recently become a standard treatment for native coarctation of the aorta (CoA) in children and young adults, given the efficacy in relieving vessel obstruction with a low incidence of adverse events. Yet, despite the short-term success of the technique, late hypertension remains an endemic risk. To assess the impact of the percutaneous procedure on the aortic wall biomechanics, we designed a novel finite element (FE) protocol for the simulation of endovascular stenting in three patient-specific CoA anatomies, developing a remeshing procedure that allows for coping with different CoA severities. Our FE protocol was able to yield numerical results on stent distortions and stresses, as well as on changes in aortic wall stresses and distensibility. These results were consistent with intraprocedural in-vivo evidences and with previous findings from the literature, and they suggest that our numerical approach could be used to understand the role of patient specific anatomical features (CoA severity and arch type) on the post-stenting aortic biomechanics. If soundly validated on a vast cohort of patients, our approach could support patient selection for the procedure.

Personalized Interventions: A Reality in the Next 20 Years or Pie in the Sky

There is no better representation of the need for personalization of care than the breadth and complexity of congenital heart disease. Advanced imaging modalities are now standard of care in the field, and the advancements being made to three-dimensional visualization technologies are growing as a means of pre-procedural preparation. Incorporating emerging modeling approaches, such as computational fluid dynamics, will push the limits of our ability to predict outcomes, and this information may be both obtained and utilized during a single procedure in the future. Artificial intelligence and customized devices may soon surface as realistic tools for the care of patients with congenital heart disease, as they are showing growing evidence of feasibility within other fields. This review illustrates the great strides that have been made and the persistent challenges that exist within the field of congenital interventional cardiology, a field which must continue to innovate and push the limits to achieve personalization of the interventions it provides.

The effects of age at correction of aortic coarctation and recurrent obstruction on adolescent patients: MRI evaluation of wall shear stress and pulse wave velocity

Background

Coarctation patients before curative reconstruction are exposed to abnormal flow patterns which potentially could cause wall deterioration. This study evaluated the effect of age at correction on the pulse wave velocity (PWV) and peak wall shear stress (WSS) in adolescent patients with corrected coarctation. Effects of valve morphology and presence of reobstruction were also evaluated.

Methods

Twenty-one patients aged 13.7 ± 2.6 years (mean ± standard deviation) were included (bicuspid aortic valve, n = 14; reobstruction, n = 9). Mean age at correction was 1.0 ± 1.8 years. PWV was determined from two high-temporal through-plane phase-contrast magnetic resonance imaging (MRI) acquisitions, for two segments: ascending aorta plus aortic arch and descending aorta. WSS was determined from four-dimensional flow MRI. Peak WSS over five systolic phases was determined for ascending aorta, aortic arch, and descending aorta.

Results

Patients with tricuspid aortic valve showed a significant correlation between the age at correction and descending aorta PWV (r_s = 0.80, p = 0.010). Significant differences were found between patients without and with reobstruction for peak WSS in the aortic arch (3.9 ± 1.3 Pa versus 6.5 ± 2.2 Pa, respectively; p = 0.003) and descending aorta (5.0 ± 1.3 Pa versus 6.7 ± 1.1 Pa, respectively; p = 0.005).

Conclusions

A prolonged period of abnormal haemodynamic exposure may result in increased aortic wall stiffening. The increased peak WSS as results of a reobstruction possibly promotes different disease progression, which endorse longitudinal follow-up examination of corrected coarctation patients.

[Fatal renal and neurological complications after aortic arch repair in newborns]

AIM

To evaluate effectiveness and safety of various methods of cerebral and visceral protection during aortic arch surgery in infants.

MATERIAL AND METHODS

Retrospective analysis included 60 patients after aortic arch repair followed by different cerebral protection technique who have been assessed for neurological status and visceral injury in early and long-term postoperative period. Aortic arch surgery with deep hypothermic circulatory arrest for congenital diseases was performed in 26 patients (group 1) and antegrade unilateral selective cerebral perfusion in 34 patients (group 2).

RESULTS

Cerebral complications occurred in 28.5% of patients of the 1^st group and in 7.9% of patients of the 2^nd group.

CONCLUSION

Odds ratio for neurological event is significantly lower in group 2: 0.17 (0.06-0.69; p=0.02). However, there were more patients with renal dysfunction in this group compared with group 1: 58.7% vs. 23.7% (p=0.02).

Hemodynamic Evaluation of a Biological and Mechanical Aortic Valve Prosthesis Using Patient-Specific MRI-Based CFD

Modeling different treatment options before a procedure is performed is a promising approach for surgical decision making and patient care in heart valve disease. This study investigated the hemodynamic impact of different prostheses through patient-specific MRI-based CFD simulations. Ten time-resolved MRI data sets with and without velocity encoding were obtained to reconstruct the aorta and set hemodynamic boundary conditions for simulations. Aortic hemodynamics after virtual valve replacement with a biological and mechanical valve prosthesis were investigated. Wall shear stress (WSS), secondary flow degree (SFD), transvalvular pressure drop (TPD), turbulent kinetic energy (TKE), and normalized flow displacement (NFD) were evaluated to characterize valve-induced hemodynamics. The biological prostheses induced significantly higher WSS (medians: 9.3 vs. 8.6 Pa, P = 0.027) and SFD (means: 0.78 vs. 0.49, P = 0.002) in the ascending aorta, TPD (medians: 11.4 vs. 2.7 mm Hg, P = 0.002), TKE (means: 400 vs. 283 cm² /s² , P = 0.037), and NFD (means: 0.0994 vs. 0.0607, P = 0.020) than the mechanical prostheses. The differences between the prosthesis types showed great inter-patient variability, however. Given this variability, a patient-specific evaluation is warranted. In conclusion, MRI-based CFD offers an opportunity to assess the interactions between prosthesis and patient-specific boundary conditions, which may help in optimizing surgical decision making and providing additional guidance to clinicians.

Role of Computational Modelling in Planning and Executing Interventional Procedures for Congenital Heart Disease

Increasingly, computational modelling and numerical simulations are used to help plan complex surgical and interventional cardiovascular procedures in children and young adults with congenital heart disease. From its origins more than 30 years ago, surgical planning with analysis of flow hemodynamics and energy loss/efficiency has helped design and implement many modifications to existing techniques. On the basis of patient-specific medical imaging, surgical planning allows accurate model production that can then be manipulated in a virtual surgical environment, with the proposed solutions finally tested with advanced computational fluid dynamics to evaluate the results. Applications include a broad range of congenital heart disease, including patients with single-ventricle anatomy undergoing staged palliation, those with arch obstruction, with double outlet right ventricle, or with tetralogy of Fallot. In the present work, we focus on clinical applications of this exciting field. We describe the framework for these techniques, including brief descriptions of the engineering principles applied and the interaction between "benchtop" data with medical decision-making. We highlight some early insights learned from pioneers over the past few decades, including refinements in Fontan baffle geometries and configurations. Finally, we offer a glimpse into exciting advances that are presently being explored, including use of modelling for transcatheter interventions. In this era of personalized medicine, computational modelling and surgical planning allows patient-specific tailoring of interventions to optimize clinical outcomes.

Clinical Impact of Stent Implantation for Coarctation of the Aorta with Associated Hypoplasia of the Transverse Aortic Arch

The aim of this study was to explore the clinical impact of transverse aortic arch hypoplasia (TAH) after stent implementation for isthmal coarctation of the aorta (CoA). From a retrospective chart review, 51 children (median age 11.1 years) were identified who had TAH and a CoA stent implanted between 10/1995 and 4/2015. Arm-leg cuff blood pressure measurements, echocardiographic arch imaging, and 24-h ambulatory blood pressure monitoring, prior to and after stent implantation, were reviewed. At catheterization, peak systolic gradients across the CoA's were 25 mmHg before and 4 mmHg after stent implantation. At a median 37-month follow-up, echocardiographic imaging showed no significant catch-up growth in the transverse arch (median z-score; proximal and distal arch -1.54 and -1.99 vs. -1.78 and -1.63, p = 0.13 and 0.90). A trend to increasing systolic blood pressure (SBP) differentials between the right and left arms was noted (11 mmHg [prior to]; 16 mmHg [follow-up], p = 0.09). Age-adjusted percentiles for right arm SBP decreased from 99.7% prior to, and 87.6% in follow-up (p < 0.001). The median time to re-intervention was 5.6 years (95% CI [2.8, 7.8]) and the proportion of children using anti-hypertensive in follow-up was not significantly different before the implantation (38% [prior to]; 45% [follow-up]). Elevated right arm blood pressure persists after successful stent implantation in the setting of associated TAH and there appears to be no catch-up growth of the transverse arch with time. Medical management can be difficult and approaches to surgical arch augmentation or stent implantation should be considered to avoid unilateral arm hypertension.

Mechanical stress is associated with right ventricular response to pulmonary valve replacement in patients with repaired tetralogy of Fallot

OBJECTIVE

Patients with repaired tetralogy of Fallot account for a substantial proportion of cases with late-onset right ventricular failure. The current surgical approach, which includes pulmonary valve replacement/insertion, has yielded mixed results. Therefore, it may be clinically useful to identify parameters that can be used to predict right ventricular function response to pulmonary valve replacement.

METHODS

Cardiac magnetic resonance data before and 6 months after pulmonary valve replacement were obtained from 16 patients with repaired tetralogy of Fallot (8 male, 8 female; median age, 42.75 years). Right ventricular ejection fraction change from pre- to postpulmonary valve replacement was used as the outcome. The patients were divided into group 1 (n = 8, better outcome) and group 2 (n = 8, worst outcome). Cardiac magnetic resonance-based patient-specific computational right ventricular/left ventricular models were constructed, and right ventricular mechanical stress and strain, wall thickness, curvature, and volumes were obtained for analysis.

RESULTS

Our results indicated that right ventricular wall stress was the best single predictor for postpulmonary valve replacement outcome with an area under the receiver operating characteristic curve of 0.819. Mean values of stress, strain, wall thickness, and longitudinal curvature differed significantly between the 2 groups with right ventricular wall stress showing the largest difference. Mean right ventricular stress in group 2 was 103% higher than in group 1.

CONCLUSIONS

Computational modeling and right ventricular stress may be used as tools to identify right ventricular function response to pulmonary valve replacement. Large-scale clinical studies are needed to validate these preliminary findings.

[Surgical treatment of aortic arch malformations in infants under cardiopulmonary bypass]

AIM

To evaluate long-term results and the causes of complications in congenital obstructive pathology of the aortic arch.

MATERIAL AND METHODS

Retrospective study enrolled 62 patients aged 55 ± 14 days who underwent aortic arch surgery under cardiopulmonary bypass. It was compared two methods of aortic archplasty: use of xenopericardial material in group 1 and Rajasinghe's autoplastic method in group 2.

RESULTS

Follow-up was 42 ± 14 months. In the long-term recoarctation occurred in 7 (13.7%) cases including 6 (18.75%) patients in group 1 and one (3.3%) patient in group 2. Residual hypertension was observed in 12 (23.5%) cases including 10 (37%) patients in group 1 and 2 (8.3%) patients in group 2. Six (50%) patients receive antihypertensive therapy, 5 (41.6%) patients who receive antihypertensive drugs have persistent increase of blood pressure without evidence of anatomic aortic obstruction. Hypertensive response to functional tests was observed in one patient.

CONCLUSIONS

Aortic arch reconstruction using autoplasty is associated with lower risk of recoarctationand residual hypertension compared with xenopericardial patch application.

Differential impact of local stiffening and narrowing on hemodynamics in repaired aortic coarctation: an FSI study

Even after successful treatment of aortic coarctation, a high risk of cardiovascular morbidity and mortality remains. Uncertainty exists on the factors contributing to this increased risk among which are the presence of (1) a residual narrowing leading to an additional resistance and (2) a less distensible zone disturbing the buffer function of the aorta. As the many interfering factors and adaptive physiological mechanisms present in vivo prohibit the study of the isolated impact of these individual factors, a numerical fluid-structure interaction model is developed to predict central hemodynamics in coarctation treatment. The overall impact of a stiffening on the hemodynamics is limited, with a small increase in systolic pressure (up to 8 mmHg) proximal to the stiffening which is amplified with increasing stiffening and length. A residual narrowing, on the other hand, affects the hemodynamics significantly. For a short segment (10 mm), the combination of a stiffening and narrowing (coarctation index 0.5) causes an increase in systolic pressure of 58 mmHg, with 31 mmHg due to narrowing and an additional 27 mmHg due to stiffening. For a longer segment (25 mm), an increase in systolic pressure of 50 mmHg is found, of which only 9 mmHg is due to stiffening.

Aortic coarctation repair in neonates with intracardiac defects: the importance of preservation of the lesser curvature of the aortic arch

BACKGROUND AND AIM

The aim of this study was to evaluate the mid-term outcomes of a strategy for repair of coarctation of the aorta (CoA) and hypoplastic aortic arch (HAA) with a modified, extended end-to-end repair that preserves the lesser curvature of the aortic arch in neonates with intracardiac defects.

METHODS

We studied 21 neonates who underwent CoA repair and remote intracardiac repair (2000-2013). Fifteen patients had HAA, and six patients had no HAA. Follow-up ranged from 0.4 to 12.8 years (median, 7.5 years), and all patients underwent cardiac catheterization and blood pressure measurement in both the arms and legs.

RESULTS

The overall median age at the time of CoA repair was seven days and the median age at the time of intracardiac defect repair was 18.6 months. There were no hospital deaths and one case had recoarctation (4.8%). The overall mean pressure gradient at the latest follow-up was 3.4 ± 5.7 mmHg. Critical deformation of arch geometry was not found. No patient had hypertension or an abnormal arm-leg gradient. There was no difference in the cardiac catheterization data or blood pressure between patients with and without HAA.

CONCLUSIONS

A modified, extended end-to-end repair for CoA and HAA resulted in a low rate of recoarctation, no operative mortality, maintenance of a smooth rounded arch, and normal blood pressures in the arms and legs during mid-term follow-up. These results suggest that this technique may be acceptable for repair of CoA and HAA in neonates with intracardiac defects.

Computational Models of Aortic Coarctation in Hypoplastic Left Heart Syndrome: Considerations on Validation of a Detailed 3D model

Background

Reliability of computational models for cardiovascular investigations strongly depends on their validation against physical data. This study aims to experimentally validate a computational model of complex congenital heart disease (i.e., surgically palliated hypoplastic left heart syndrome with aortic coarctation) thus demonstrating that hemodynamic information can be reliably extrapolated from the model for clinically meaningful investigations.

Materials and methods

A patient-specific aortic arch model was tested in a mock circulatory system and the same flow conditions were re-created in silico, by setting an appropriate lumped parameter network (LPN) attached to the same three-dimensional (3D) aortic model (i.e., multi-scale approach). The model included a modified Blalock-Taussig shunt and coarctation of the aorta. Different flow regimes were tested as well as the impact of uncertainty in viscosity.

Results

Computational flow and pressure results were in good agreement with the experimental signals, both qualitatively, in terms of the shape of the waveforms, and quantitatively (mean aortic pressure 62.3 vs. 65.1 mmHg, 4.8% difference; mean aortic flow 28.0 vs. 28.4% inlet flow, 1.4% difference; coarctation pressure drop 30.0 vs. 33.5 mmHg, 10.4% difference), proving the reliability of the numerical approach. It was observed that substantial changes in fluid viscosity or using a turbulent model in the numerical simulations did not significantly affect flows and pressures of the investigated physiology. Results highlighted how the non-linear fluid dynamic phenomena occurring in vitro must be properly described to ensure satisfactory agreement.

Conclusions

This study presents methodological considerations for using experimental data to preliminarily set up a computational model, and then simulate a complex congenital physiology using a multi-scale approach.

MRI-based computational fluid dynamics for diagnosis and treatment prediction: clinical validation study in patients with coarctation of aorta

PURPOSE

To reduce the need for diagnostic catheterization and optimize treatment in a variety of congenital heart diseases, magnetic resonance imaging (MRI)-based computational fluid dynamics (CFD) is proposed. However, data about the accuracy of CFD in a clinical context are still sparse. To fill this gap, this study compares MRI-based CFD to catheterization in the coarctation of aorta (CoA) setting.

MATERIALS AND METHODS

Thirteen patients with CoA were investigated by routine MRI prior to catheterization. 3D whole-heart MRI was used to reconstruct geometries and 4D flow-sensitive phase-contrast MRI was used to acquire flows. Peak systolic flows were simulated using the program FLUENT.

RESULTS

Peak systolic pressure drops in CoA measured by catheterization and CFD correlated significantly for both pre- and posttreatment measurements (pre: r = 0.98, p = 0.00; post: r = 0.87, p = 0.00). The pretreatment bias was -0.5 ± 3.33 mmHg (95% confidence interval -2.55 to 1.47 mmHg). CFD predicted a reduction of the peak systolic pressure drop after treatment that ranged from 17.6 ± 5.56 mmHg to 6.7 ± 5.58 mmHg. The posttreatment bias was 3.0 ± 2.91 mmHg (95% CI -1.74 to 5.43 mmHg).

CONCLUSION

Peak systolic pressure drops can be reliably calculated using MRI-based CFD in a clinical setting. Therefore, CFD might be an attractive noninvasive alternative to diagnostic catheterization.

Computational fluid dynamics simulation to evaluate aortic coarctation gradient with contrast-enhanced CT

Coarctation of aorta (CoA) is a narrowing of the aorta leading to a pressure gradient (ΔP) across the coarctation, increased afterload and reduced peripheral perfusion pressures. Indication to invasive treatment is based on values of maximal (systolic) trans-coarctation ΔP. A computational fluid dynamic (CFD) approach is herein presented for the non-invasive haemodynamic assessment of ΔP across CoA. Patient-specific CFD simulations were created from contrast-enhanced computed tomography (CT) and appropriate flow boundary conditions. Computed ΔP was validated with invasive intravascular trans-CoA pressure measurements. Haemodynamic indices, including pressure loss coefficient (PLc), time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI), were also quantified. CFD-estimated ΔP values were comparable to the invasive ones. Moreover, the aorta proximal to CoA was exposed to altered TAWSS and OSI suggesting hypertension. PLc was found as a further geometric marker of CoA severity. Finally, CFD-estimated ΔP confirmed a significant reduction after percutaneous balloon dilatation and stenting of the CoA in one patient (e.g. from ΔP∼52 mmHg to ΔP∼3 mmHg). The validation of the ΔP computations with catheterisation measurements suggests that CFD simulation, based on CT-derived anatomical data, is a useful tool to readily quantify CoA severity.

Endovascular treatment of late thoracic aortic aneurysms after surgical repair of congenital aortic coarctation in childhood

Background

In some patients, local surgery-related complications are diagnosed many years after surgery for aortic coarctation. The purposes of this study were: (1) to systematically evaluate asymptomatic adults after Dacron patch repair in childhood, (2) to estimate the formation rate of secondary thoracic aortic aneurysms (TAAs) and (3) to assess outcomes after intravascular treatment for TAAs.

Methods

This study involved 37 asymptomatic patients (26 female and 11 male) who underwent surgical repair of aortic coarctation in the childhood. After they had reached adolescence, patients with secondary TAAs were referred to endovascular repair.

Results

Follow-up studies revealed TAA in seven cases (19%) (including six with the gothic type of the aortic arch) and mild recoarctation in other six (16%). Six of the TAA patients were treated with stentgrafts, but one refused to undergo an endovascular procedure. In three cases, stengrafts covered the left subclavian artery (LSA), in another the graft was implanted distally to the LSA. In two individuals, elective hybrid procedures were performed with surgical bypass to the supraaortic arteries followed by stengraft implantation. All subjects survived the secondary procedures. One patient developed type Ia endoleak after stentgraft implantation that was eventually treated with a debranching procedure.

Conclusions

The long-term course of clinically asymptomatic patients after coarctation patch repair is not uncommonly complicated by formation of TAAs (particularly in individuals with the gothic pattern of the aortic arch) that can be treated effectively with stentgrafts. However, in some patients hybrid procedures may be necessary.

The impact of MRI-based inflow for the hemodynamic evaluation of aortic coarctation

Aortic coarctation (CoA) accounting for 3-11% of congenital heart disease can be successfully treated. Long-term results, however, have revealed decreased life expectancy associated with abnormal hemodynamics. Accordingly, an assessment of hemodynamics is the key factor in treatment decisions and successful long-term results. In this study, 3D angiography whole heart (3DWH) and 4D phase-contrast magnetic resonance imaging (MRI) data were acquired. Geometries of the thoracic aorta with CoAs were reconstructed using ZIB-Amira software. X-ray angiograms were used to evaluate the post-treatment geometry. Computational fluid dynamics models in three patients were created to simulate pre- and post-treatment situations using the FLUENT program. The aim of the study was to investigate the impact of the inlet velocity profile (plug vs. MRI-based) with a focus on the peak systole pressure gradient and wall shear stress (WSS). Results show that helical flow at the aorta inlet can significantly affect the assessment of pressure drop and WSS. Simplified plug inlet velocity profiles significantly (p < 0.05) overestimate the pressure drop in pre- and post-treatment geometries and significantly (p < 0.05) underestimate surface-averaged WSS. We conclude that the use of the physiologically correct but time-expensive 4D MRI-based in vivo velocity profile in CFD studies may be an important step towards a patient-specific analysis of CoA hemodynamics.