Integrated morphologic and functional assessment of the aortic root after different tissue valve root replacement procedures

Lifetime Management of Adolescents and Young Adults with Congenital Aortic Valve Disease

In this invited expert review, we focus on evolving lifetime management strategies for adolescents and young adults with congenital aortic valve disease, acknowledging that these patients often require multiple interventions during their lifetime. Our goal is to preserve the native aortic valve when feasible. Leveraging advanced multimodality imaging, a detailed assessment of the aortic valve and root complex can be obtained, and a surgically approach tailored to an individual patient's anatomy and pathology can be used. In turn, aortic valve repair and reconstruction can be offered to a greater number of patients, either as a definitive strategy or as a component of a staged strategy to delay the need for aortic valve replacement until later in life when more options are available.

Ross procedure: valve function, clinical outcomes and predictors after 25 years' follow-up

OBJECTIVE

To describe long-term outcomes of the Ross procedure in a single center and retrospective series after 25 years follow-up.

METHODS

From 1997-2019 we included all consecutive patients who underwent Ross procedure at our center. Clinical and echocardiographic evaluations were performed at least yearly. Echocardiographic valvular impairment was defined as at least moderate autograft or homograft dysfunction. Reintervention outcomes included surgical and percutaneous approach.

RESULTS

151 Ross procedures were performed (mean age 28±12years, 21 %<16years, 70 %male). After 25 years follow-up (median 18 years, interquartile range 9-21, only 3 patients lost) 12 patients died (8 %); Autograft, homograft or any valve dysfunction were present in 38(26 %), 48(32 %) and 75(51 %), respectively; and reintervention in 22(15%), 17(11%) and 38(26 %) respectively. At 20 years of follow-up, probabilities of survival free from autograft, homograft or any valve dysfunction were 63 %, 60 % and 35 %; and from reintervention, 80 %, 85 % and 67 %, respectively. The learning curve period (first 12 cases) was independently associated to autograft dysfunction (HR 2.78, 95 %CI:1.18-6.53, p = 0.02) and reintervention (HR 3.76, 95 %CI: 1.46-9.70, p = 0.006). Larger native pulmonary diameter was also an independent predictor of autograft reintervention (HR 1.22, 95 %CI:1.03-1.45, p = 0.03). Homograft dysfunction was associated with younger age (HR 5.35, 95 %CI: 2.13-13.47, p<0.001) and homograft reintervention, with higher left ventricle ejection fraction (HR 1,10, 95 %CI:1.02-1.19, p<0.02).

CONCLUSIONS

In this 25 years' experience after the Ross procedure, global survival was high, although autograft and homograft dysfunction and reintervention rates were not negligible. Clinical and echocardiographic variables can identify patients with higher risk of events in follow up.

Asymmetry of flow in aortic root and its application in hypertrophic obstructive cardiomyopathy

The aortic root (AR) performs sophisticated functions regulating the blood dynamics during the cardiac cycle. Such complex function depends on the nature of flow in the AR. Here, we investigate the potential of new quantitative parameters of flow asymmetry that could have clinical implications. We developed a MATLAB program to study the AR hemodynamics in each sinus of Valsalva using two-dimensional (2-D) cardiac magnetic resonance imaging during systole and particularly at peak systolic flow in 13 healthy volunteers and compared with 10 patients with hypertrophic obstructive cardiomyopathy (HOCM). We show that the effective area of the aortic jet in healthy volunteers is significantly higher at peak systolic flow and on average during systole. The flow asymmetry index, indicating how the jet is skewed away from the left coronary sinus (LCS), is small in healthy volunteers and much larger in HOCM at peak systole. The average of this index over systole is significantly more different between cohorts. Looking in more detail at the flow in the sinuses during systole, we show that the AR jet in healthy volunteers is more symmetrical, affecting the three sinuses almost equally, unlike the asymmetric AR jet in patients with HOCM that has decreased flow rate in the LCS and increased fractional area of backward flow in the LCS. The percentage of backward flow in the sinuses of Valsalva calculated over systole is a potential indicator of perturbed AR hemodynamics and the distribution of vortical flow and could be used as a measure of flow asymmetry.NEW & NOTEWORTHY The aortic root is a vital organ responsible for performing sophisticated functions to regulate the blood flow dynamics during the cardiac cycle. Such synchronized complex performance affects and is affected by the flow symmetry and type of flow reaching the aorta. Here, we report flow asymmetry in the aortic root which could have clinical implications, and we investigate the potential of various quantitative parameters as measures of flow asymmetry in hypertrophic obstructive cardiomyopathy.

New insights into the hemodynamics of pulmonary homograft patients under stress echocardiography: The contribution of pressure recovery

BACKGROUND

The importance of pulmonary artery pressure recovery (PR) in patients with Ross procedures in whom a homograft substitutes the resected pulmonary valve, is unknown. The aim of the study was to evaluate the occurrence and extent of PR in the pulmonary artery in 65 asymptomatic patients with pulmonary homograft after Ross surgery during rest and exercise.

METHODS

Stress echocardiography was performed in 65 pulmonary homograft patients and 31 controls with native pulmonary valves up to 75 W. Right ventricular systolic pressure (RVSP), transvalvular flow, mean pressure gradient (Pmean ), valve resistance, and RV stroke work were determined in the exercise (max. 75 W) and recovery phases in increments of 25 W each.

RESULTS

Pulmonary homografts demonstrated significantly elevated Pmean compared to controls at all stages. When considering pressure recovery (absolute and relative PR at rest 3.8 ± 1.8 mm Hg, 42.6 ± 7.2%, respectively) and transvalvular energy loss (EL; at rest 4.5 ± 4.3 mm Hg) the homograft hemodynamics reached the level of controls. In a subgroup of patients with tricuspid regurgitation, resting RVSP was the same in homograft patients and controls (21.3 ± 6.1 vs. 20.4 ± 6.3, p = .62), despite significant different Pmax values.

CONCLUSIONS

Ross patients with pulmonary homograft showed systematically increased hemodynamic parameters compared to normal pulmonary valves. These differences were abolished when PR was considered for homograft patients. The equality of RVSP values at rest in both groups shows non-invasive evidence for PR in the pulmonary system after homograft implantation. Therefore, PR appears to be an important measure in calculating the actual hemodynamics in pulmonary homografts.

Reciprocal interferences of the left ventricular assist device and the aortic valve competence

Patients suffering from end-stage heart failure tend to have high mortality rates. With growing numbers of patients progressing into severe heart failure, the shortage of available donors is a growing concern, with less than 10% of patients undergoing cardiac transplantation (CTx). Fortunately, the use of left ventricular assist devices (LVADs), a variant of mechanical circulatory support has been on the rise in recent years. The expansion of LVADs has led them to be incorporated into a variety of clinical settings, based on the goals of therapy for patients ailing from heart failure. However, with an increase in the use of LVADs, there are a host of complications that arise with it. One such complication is the development and progression of aortic regurgitation (AR) which is noted to adversely influence patient outcomes and compromise pump benefits leading to increased morbidity and mortality. The underlying mechanisms are likely multifactorial and involve the aortic root-aortic valve (AV) complex, as well as the LVAD device, patient, and other factors, all of them alter the physiological mechanics of the heart resulting in AV dysfunction. Thus, it is imperative to screen patients before LVAD implantation for AR, as moderate or greater AR requires a concurrent intervention at the time of LVADs implantation. No current strict guidelines were identified in the literature search on how to actively manage and limit the development and/or progression of AR, due to the limited information. However, some recommendations include medical management by targeting fluid overload and arterial blood pressure, along with adjusting the settings of the LVADs device itself. Surgical interventions are to be considered depending on patient factors, goals of care, and the underlying pathology. These interventions include the closure of the AV, replacement of the valve, and percutaneous approach via percutaneous occluding device or transcatheter aortic valve implantation. In the present review, we describe the interaction between AV and LVAD placement, in terms of patient management and prognosis. Also it is provided a comprehensive echocardiographic strategy for the precise assessment of AV regurgitation severity.

Biomechanics of Pulmonary Autograft as Living Tissue: A Systematic Review

Introduction: The choice of valve substitute for aortic valve surgery is tailored to the patient with specific indications and contraindications to consider. The use of an autologous pulmonary artery (PA) with a simultaneous homograft in the pulmonary position is called a Ross procedure. It permits somatic growth and the avoidance of lifelong anticoagulation. Concerns remain on the functionality of a pulmonary autograft in the aortic position when exposed to systemic pressure. Methods: A literature review was performed incorporating the following databases: Pub Med (1996 to present), Ovid Medline (1958 to present), and Ovid Embase (1982 to present), which was run on 1 January 2022 with the following targeted words: biomechanics of pulmonary autograft, biomechanics of Ross operation, aortic valve replacement and pulmonary autograph, aortic valve replacement and Ross procedure. To address the issues with heterogeneity, studies involving the pediatric cohort were also analyzed separately. The outcomes measured were early- and late-graft failure alongside mortality. Results: a total of 8468 patients were included based on 40 studies (7796 in pediatric cohort and young adult series and 672 in pediatric series). There was considerable experience accumulated by various institutions around the world. Late rates of biomechanical failure and mortality were low and comparable to the general population. The biomechanical properties of the PA were superior to other valve substitutes. Mathematical and finite element analysis studies have shown the potential stress-shielding effects of the PA root. Conclusion: The Ross procedure has excellent durability and longevity in clinical and biomechanical studies. The use of external reinforcements such as semi-resorbable scaffolds may further extend their longevity.

Improved Outcomes Following the Ross Procedure Compared With Bioprosthetic Aortic Valve Replacement

BACKGROUND

The ideal aortic valve substitute for young and middle-aged adults remains elusive.

OBJECTIVES

This study sought to compare the long-term outcomes of patients undergoing the Ross procedure and those receiving bioprosthetic aortic valve replacements (AVRs).

METHODS

Consecutive patients aged 16-60 years who underwent a Ross procedure or surgical bioprosthetic AVR at the Toronto General Hospital between 1990 and 2014 were identified. Propensity score matching was used to account for differences in baseline characteristics. The primary outcome was all-cause mortality. Secondary outcomes included valve reintervention, valve deterioration, endocarditis, thromboembolic events, and permanent pacemaker implantation.

RESULTS

Propensity score matching yielded 108 pairs of patients. The median age was 41 years (IQR: 34-47 years). Baseline characteristics were similar between the matched groups. There was no operative mortality in either group. Mean follow-up was 14.5 ± 7.2 years. All-cause mortality was lower following the Ross procedure (HR: 0.35; 95% CI: 0.14-0.90; P = 0.028). Using death as a competing risk, the Ross procedure was associated with lower rates of reintervention (HR: 0.21; 95% CI: 0.10-0.41; P < 0.001), valve deterioration (HR: 0.25; 95% CI: 0.14-0.45; P < 0.001), thromboembolic events (HR: 0.15; 95% CI: 0.05-0.50; P = 0.002), and permanent pacemaker implantation (HR: 0.22; 95% CI: 0.07-0.64; P = 0.006).

CONCLUSIONS

In this propensity-matched study, the Ross procedure was associated with better long-term survival and freedom from adverse valve-related events compared with bioprosthetic AVR. In specialized centers with sufficient expertise, the Ross procedure should be considered the primary option for young and middle-aged adults undergoing AVR.

Supporting the Ross procedure: preserving root physiology while mitigating autograft dilatation

PURPOSE OF REVIEW

The purpose of this article is to describe the optimized approach to nonrepairable aortic valve disease in young adults with a Ross procedure, while preserving the dynamic physiology of the aortic root.

RECENT FINDINGS

As the techniques for supporting pulmonary autografts continue to be refined, and the applicability of the Ross procedure continues to expand, an assessment of the various techniques based on aortic root physiology is warranted. Semi-resorbable scaffolds show promise in ovine models for improving the Ross procedure. Recent long-term outcomes for the Dacron inclusion technique in comparison to more physiologic methods of support emphasize the importance of balancing the prevention of early dilatation with the preservation of root haemodynamics. As this review will synthesize, the dynamic physiology of the root may be preserved even in patients at a higher risk of autograft dilatation.

SUMMARY

The favourable long-term outcomes of the Ross procedure can be partly attributed to the ability of the autograft to restore dynamism to the neoaortic root. Patient-specific modifications that respect root physiology can tailor the Ross procedure to address each patient's risk factors for early dilatation and late failure. As such, the Ross procedure should be recognized as an increasingly favourable solution for a wide spectrum of nonpreservable aortic valve disease in young adults.

Propensity-Matched Comparison of the Ross Procedure and Prosthetic Aortic Valve Replacement in Adults

BACKGROUND

There has recently been renewed interest in the Ross procedure in adults.

OBJECTIVES

The goal of this study was to compare long-term outcomes after the Ross procedure vs biological and mechanical aortic valve replacement (AVR) in adults (aged 18-50 years) undergoing aortic valve surgery.

METHODS

Mandatory California and New York databases were queried between 1997 and 2014. Exclusion criteria included: ≥1 concomitant procedure, reoperations, infective endocarditis, intravenous drug use, hemodialysis, and out-of-state residency. Propensity matching (1:1:1) was used, resulting in 434 patients per group. The primary endpoint was all-cause mortality. Secondary endpoints were stroke, major bleeding, reoperation, and endocarditis. Median follow-up was 12.5 years (IQR: 9.3-15.7 years).

RESULTS

At 15 years, actuarial survival after the Ross procedure was 93.1% (95% CI: 89.1%-95.7%), similar to that of the age-, sex-, and race-matched U.S. general population. It was significantly lower after biological AVR (HR: 0.42; 95% CI: 0.23-0.075; P = 0.003) and mechanical AVR (HR: 0.45; 95% CI: 0.26-0.79; P = 0.006). At 15 years, the Ross procedure was associated with a lower cumulative risk of reintervention (P = 0.008) and endocarditis (P = 0.01) than biological AVR. In contrast, at 15 years, the Ross procedure was associated with a higher cumulative incidence of reoperation (P < 0.001) but lower risks of stroke (P = 0.03) and major bleeding (P = 0.016) than mechanical AVR. Thirty-day mortality after valve-related complications was lowest after a reintervention.

CONCLUSIONS

In young adults, the Ross procedure is associated with better long-term survival and freedom from valve-related complications compared with prosthetic AVR. This confirms the notion that a living valve substitute in the aortic position translates into improved clinically relevant outcomes.

Understanding Pulmonary Autograft Remodeling After the Ross Procedure: Stick to the Facts

The Ross, or pulmonary autograft, procedure presents a fascinating mechanobiological scenario. Due to the common embryological origin of the aortic and pulmonary root, the conotruncus, several authors have hypothesized that a pulmonary autograft has the innate potential to remodel into an aortic phenotype once exposed to systemic conditions. Most of our understanding of pulmonary autograft mechanobiology stems from the remodeling observed in the arterial wall, rather than the valve, simply because there have been many opportunities to study the walls of dilated autografts explanted at reoperation. While previous histological studies provided important clues on autograft adaptation, a comprehensive understanding of its determinants and underlying mechanisms is needed so that the Ross procedure can become a widely accepted aortic valve substitute in select patients. It is clear that protecting the autograft during the early adaptation phase is crucial to avoid initiating a sequence of pathological remodeling. External support in the freestanding Ross procedure should aim to prevent dilatation while simultaneously promoting remodeling, rather than preventing dilatation at the cost of vascular atrophy. To define the optimal mechanical properties and geometry for external support, the ideal conditions for autograft remodeling and the timeline of mechanical adaptation must be determined. We aimed to rigorously review pulmonary autograft remodeling after the Ross procedure. Starting from the developmental, microstructural and biomechanical differences between the pulmonary artery and aorta, we review autograft mechanobiology in relation to distinct clinical failure mechanisms while aiming to identify unmet clinical needs, gaps in current knowledge and areas for further research. By correlating clinical and experimental observations of autograft remodeling with established principles in cardiovascular mechanobiology, we aim to present an up-to-date overview of all factors involved in extracellular matrix remodeling, their interactions and potential underlying molecular mechanisms.

The Ross procedure is the optimal solution for young adults with unrepairable aortic valve disease

While aortic valve repair remains the ideal intervention to restore normal valvular function, the optimal aortic valve substitute for patients with a non-repairable aortic valve remains an ongoing subject for debate. In particular, younger patients with a non-repairable valve represent a unique challenge because of their active lifestyle and long life expectancy, which carries a higher cumulative risk of prosthesis-related complications. The Ross procedure, unlike prosthetic or homograft aortic valve replacement (AVR), provides an expected survival equivalent to that of the age and gender-matched general population. Contemporary data has shown that the Ross procedure can be performed safely in centers with expertise, and is associated with improved valvular durability, hemodynamics and quality of life.

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.

A review of pulmonary autograft external support in the Ross procedure

Introduction: Although the Ross procedure offers several advantages over standard prosthetic AVR, its use remains limited. The risk of pulmonary autograft dilatation requiring reintervention remains one of the main concerns. Consequently, multiple techniques have been developed in attempt to mitigate this complication.Areas covered: This article reviews the incidence of pulmonary autograft dilatation, its risk factors and pathophysiology. The techniques of external pulmonary autograft support are discussed along with their respective advantages and limitations. Finally, future areas of research and developments are examined.Expert opinion: The risk of autograft dilatation is mainly prevalent in patients with aortic regurgitation and a dilated aortic annulus. In these selected patients, an external support may prevent dilatation of the autograft. However, any permanent support potentially restricts autograft root motion, mitigating some of the advantages associated with the Ross procedure. A bioresorbable matrix that could support the root during its initial adaptative phase could alleviate this problem. In our opinion, aggressive blood pressure control during the first postoperative year along with annular and sino-tubular junction support in selected patients provides optimal stability of autograft root dimensions while preserving root dynamics. Serial imaging and clinical follow-up are necessary to define the role of these various strategies.

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

OBJECTIVES

To assess in patients with aortopathy perioperative changes in thoracic aortic wall shear stress (WSS), which is known to affect arterial remodeling, and the effects of specific surgical interventions.

METHODS

Presurgical and postsurgical aortic 4D flow MRI were performed in 33 patients with aortopathy (54 ± 14 years; 5 women; sinus of Valsalva (d_SOV)/midascending aortic (d_MAA) diameters = 44 ± 5/45 ± 6 mm) scheduled for aortic valve (AVR) and/or root (ARR) replacement. Control patients with aortopathy who did not have surgery were matched for age, sex, body size, and d_MAA (n = 20: 52 ± 14 years; 3 women; d_SOV/d_MAA = 42 ± 4/42 ± 4 mm). Regional aortic 3D systolic peak WSS was calculated. An atlas of WSS normal values was used to quantify the percentage of at-risk tissue area with abnormally high WSS, excluding the area to be resected/graft.

RESULTS

Peak WSS and at-risk area showed low interobserver variability (≤0.09 [-0.3; 0.5] Pa and 1.1% [-7%; 9%], respectively). In control patients, WSS was stable over time (follow-up-baseline differences ≤0.02 Pa and 0.0%, respectively). Proximal aortic WSS decreased after AVR (n = 5; peak WSS difference ≤-0.41 Pa and at-risk area ≤-10%, P < .05 vs controls). WSS was increased after ARR in regions distal to the graft (peak WSS difference ≥0.16 Pa and at-risk area ≥4%, P < .05 vs AVR). Follow-up duration had no significant effects on these WSS changes, except when comparing ascending aortic peak WSS between ARR and AVR (P = .006).

CONCLUSIONS

Serial perioperative 4D flow MRI investigations showed distinct patterns of postsurgical changes in aortic WSS, which included both reductions and translocations. Larger longitudinal studies are warranted to validate these findings with clinical outcomes and prediction of risk of future aortic events.

Current state of the art and future of myectomy

Surgical relief of left ventricular outflow tract obstruction (LVOTO) in hypertrophic cardiomyopathy (HCM) requires more than septal myectomy. The procedure is currently the gold standard for all symptomatic HCM patients except those with comorbidities. The operation requires an individualized approach to restore the sophisticated functions of the left ventricular outflow tract (LVOT) without injury to the surrounding vital structures. The procedure should be tailored to deal with all the varied components of the obstruction including fibrous trigones, accessory tissues, and papillary muscle fusion. Preoperative multimodality imaging and numerical modeling combined with intraoperative transesophageal echocardiography (TEE) are essential to define existing anomalies as well as assess the adequacy of the repair. The mitral valve can be conserved in virtually all patients. The operation can be conducted with very low mortality and morbidity with predictable good outcomes both in the short and long term. Nevertheless, surgical relief of LVOTO is still grossly underused.

Assessment of Hemodynamic Conditions in the Aorta Following Root Replacement with Composite Valve-Conduit Graft

This paper presents the analysis of detailed hemodynamics in the aortas of four patients following replacement with a composite bio-prosthetic valve-conduit. Magnetic resonance image-based computational models were set up for each patient with boundary conditions comprising subject-specific three-dimensional inflow velocity profiles at the aortic root and central pressure waveform at the model outlet. Two normal subjects were also included for comparison. The purpose of the study was to investigate the effects of the valve-conduit on flow in the proximal and distal aorta. The results suggested that following the composite valve-conduit implantation, the vortical flow structure and hemodynamic parameters in the aorta were altered, with slightly reduced helical flow index, elevated wall shear stress and higher non-uniformity in wall shear compared to normal aortas. Inter-individual analysis revealed different hemodynamic conditions among the patients depending on the conduit configuration in the ascending aorta, which is a key factor in determining post-operative aortic flow. Introducing a natural curvature in the conduit to create a smooth transition between the conduit and native aorta may help prevent the occurrence of retrograde and recirculating flow in the aortic arch, which is particularly important when a large portion or the entire ascending aorta needs to be replaced.

In-vivo assessment of the morphology and hemodynamic functions of the BioValsalva™ composite valve-conduit graft using cardiac magnetic resonance imaging and computational modelling technology

BACKGROUND

The evaluation of any new cardiac valvular prosthesis should go beyond the classical morbidity and mortality rates and involve hemodynamic assessment. As a proof of concept, the objective of this study was to characterise for the first time the hemodynamics and the blood flow profiles at the aortic root in patients implanted with BioValsalva™ composite valve-conduit using comprehensive MRI and computer technologies.

METHODS

Four male patients implanted with BioValsalva™ and 2 age-matched normal controls (NC) underwent cardiac magnetic resonance imaging (MRI). Phase-contrast imaging with velocity-mapping in 3 orthogonal directions was performed at the level of the aortic root and descending thoracic aorta. Computational fluid dynamic (CFD) simulations were performed for all the subjects with patient-specific flow information derived from phase-contrast MR data.

RESULTS

The maximum and mean flow rates throughout the cardiac cycle at the aortic root level were very comparable between NC and BioValsalva™ patients (541 ± 199 vs. 567 ± 75 ml/s) and (95 ± 46 vs. 96 ± 10 ml/s), respectively. The maximum velocity (cm/s) was higher in patients (314 ± 49 vs. 223 ± 20; P = 0.06) due to relatively smaller effective orifice area (EOA), 2.99 ± 0.47 vs. 4.40 ± 0.24 cm2 (P = 0.06), however, the BioValsalva™ EOA was comparable to other reported prosthesis. The cross-sectional area and maximum diameter at the root were comparable between the two groups. BioValsalva™ conduit was stiffer than the native aortic wall, compliance (mm2 • mmHg(-1) • 10(-3)) values were (12.6 ± 4.2 vs 25.3 ± 0.4.; P = 0.06). The maximum time-averaged wall shear stress (Pa), at the ascending aorta was equivalent between the two groups, 17.17 ± 2.7 (NC) vs. 17.33 ± 4.7 (BioValsalva™ ). Flow streamlines at the root and ascending aorta were also similar between the two groups apart from a degree of helical flow that occurs at the outer curvature at the angle developed near the suture line.

CONCLUSIONS

BioValsalva™ composite valve-conduit prosthesis is potentially comparable to native aortic root in structural design and in many hemodynamic parameters, although it is stiffer. Surgeons should pay more attention to the surgical technique to maximise the reestablishment of normal smooth aortic curvature geometry to prevent unfavourable flow characteristics.

The living aortic valve: From molecules to function

The aortic valve lies in a unique hemodynamic environment, one characterized by a range of stresses (shear stress, bending forces, loading forces and strain) that vary in intensity and direction throughout the cardiac cycle. Yet, despite its changing environment, the aortic valve opens and closes over 100,000 times a day and, in the majority of human beings, will function normally over a lifespan of 70–90 years. Until relatively recently heart valves were considered passive structures that play no active role in the functioning of a valve, or in the maintenance of its integrity and durability. However, through clinical experience and basic research the aortic valve can now be characterized as a living, dynamic organ with the capacity to adapt to its complex mechanical and biomechanical environment through active and passive communication between its constituent parts. The clinical relevance of a living valve substitute in patients requiring aortic valve replacement has been confirmed. This highlights the importance of using tissue engineering to develop heart valve substitutes containing living cells which have the ability to assume the complex functioning of the native valve.

Blood flow characteristics in the ascending aorta after aortic valve replacement--a pilot study using 4D-flow MRI

BACKGROUND

Aortic remodeling after aortic valve replacement (AVR) might be influenced by the postoperative blood flow pattern in the ascending aorta. This pilot study used flow-sensitive four-dimensional magnetic resonance imaging (4D-flow) to describe ascending aortic flow characteristics after various types of AVR.

METHODS

4D-flow was acquired in 38 AVR patients (n=9 mechanical, n=8 stentless bioprosthesis, n=14 stented bioprosthesis, n=7 autograft) and 9 healthy controls. Analysis included grading of vortex and helix flow (0-3 point scale), assessment of systolic flow eccentricity (1-3 point scale), and quantification of the segmental distribution of peak systolic wall shear stress (WSS(peak)) in the ascending aorta.

RESULTS

Compared to controls, mechanical prostheses showed the most distinct vorticity (2.7±0.5 vs. 0.7±0.7; p<0.001), while stented bioprostheses exhibited most distinct helicity (2.6±0.7 vs. 1.6±0.5; p=0.002). Instead of a physiologic central flow, all stented, stentless and mechanical prostheses showed eccentric flow jets mainly directed towards the right-anterior aortic wall. Stented and stentless prostheses showed an asymmetric distribution of WSS(peak) along the aortic circumference, with significantly increased local WSS(peak) where the flow jet impinged on the aortic wall. Local WSS(peak) was higher in stented (1.4±0.7 N/m(2)) and stentless (1.3±0.7 N/m(2)) compared to autografts (0.6±0.2 N/m(2); p=0.005 and p=0.008) and controls (0.7±0.1 N/m(2); p=0.017 and p=0.027). Autografts exhibited lower absolute WSS(peak) than controls (0.4±0.1 N/m(2) vs. 0.7±0.2 N/m(2); p=0.003).

CONCLUSIONS

Flow characteristics in the ascending aorta after AVR are different from native aortic valves and differ between various types of AVR.