The autograft inclusion: An obligatory step to avoid late failure following the Ross procedure?

Wall stresses of early remodeled pulmonary autografts

OBJECTIVE

The Ross procedure is an excellent option for children or young adults who need aortic valve replacement because it can restore survival to that of the normal aged-matched population. However, autograft remodeling can lead to aneurysmal formation and reoperation, and the biomechanics of this process is unknown. This study investigated postoperative autograft remodeling after the Ross procedure by examining patient-specific autograft wall stresses.

METHODS

Patients who have undergone the Ross procedure who had intraoperative pulmonary root and aortic specimens collected were recruited. Patient-specific models (n = 16) were developed using patient-specific material property and their corresponding geometry from cine magnetic resonance imaging at 1-year follow-up. Autograft ± Dacron for aneurysm repair and ascending aortic geometries were reconstructed to develop patient-specific finite element models, which incorporated material properties and wall thickness experimentally measured from biaxial stretching. A multiplicative approach was used to account for prestress geometry from in vivo magnetic resonance imaging. Pressure loading to systemic pressure (120/80) was performed using LS-DYNA software (LSTC Inc, Livermore, Calif).

RESULTS

At systole, first principal stresses were 809 kPa (25%-75% interquartile range, 691-1219 kPa), 567 kPa (485-675 kPa), 637 kPa (555-755 kPa), and 382 kPa (334-413 kPa) at the autograft sinotubular junction, sinuses, annulus, and ascending aorta, respectively. Second principal stresses were 360 kPa (310-426 kPa), 355 kPa (320-394 kPa), 272 kPa (252-319 kPa), and 184 kPa (147-222 kPa) at the autograft sinotubular junction, sinuses, annulus, and ascending aorta, respectively. Mean autograft diameters were 29.9 ± 2.7 mm, 38.3 ± 5.3 mm, and 26.6 ± 4.0 mm at the sinotubular junction, sinuses, and annulus, respectively.

CONCLUSIONS

Peak first principal stresses were mainly located at the sinotubular junction, particularly when Dacron reinforcement was used. Patient-specific simulations lay the foundation for predicting autograft dilatation in the future after understanding biomechanical behavior during long-term follow-up.

Biomechanical future of the growing pulmonary autograft in Ross operation

It has been few years since the preliminary translational research study on mechanics performance of autologous pulmonary tissue were published to circumvent complication relies to SVD. Several studies reported the modification of pulmonary native autograft root subjected to dynamic stress strain in long-term outcomes of aortic valve replacement. Our multidisciplinary research team firstly describe the weave relationship between stress-strain, growth and remodelling in an experimental model of Ross Operation. From a biomechanical point of view, the rapid absorption of polydioxanone constituting the internal part of the device may limit the potential negative effect of excessive stretching and improvement of steeper curve in the circumferential response. Improvement of longitudinal stretching of pulmonary autograft by external component of device are indicative of auxetic effect of e-PTFE. Successful reinforcement with semiresorbable device can also be favourable to pulmonary autograft function in growing patients needing to match somatic growth. The attendant decrease in PA expansion and the preserved features of the valve leaflets enhances durability of Ross operation. Strengthening of the distal pulmonary root anastomosis using external reinforcement, modifying the ascending phase of the circumferential stress curve, might be advisable as previously described. PA is an ideal substitute for aortic valve replacement not only in Mr. Ross's dreams but also from the biomechanical point of view.

The use of allogenic and autologous tissue to treat aortic valve endocarditis

The surgical treatment of aortic valve endocarditis (AVE) is generally performed using conventional mechanical or biological xenograft prosthesis, with limited use of aortic homograft (Ao-Homo) or pulmonary autograft (PA). Clinical evidence has demonstrated a clear contradiction between the proven benefits of Ao-Homo and PA in the context of infection and the very limited use of allogenic or autologous tissue in everyday clinical practice. This review aims to summarize the most recent and relevant literature in order to foster the scientific debate on the use of the use of allogenic and autologous tissue to treat AVE. The decisional process of the Heart Team should also include the preferences of the patient, his/her family, the general cardiologist or primary care physician. The use of allogenic or autologous valve substitute is beneficial if there is a high risk of recurrence of infection, avoiding extensive adhesiolysis and debridement of synthetic material. In any case, those procedures should be performed by highly trained centers to optimize outcomes.

Current spectrum, challenges and new developments in the surgical care of adults with congenital heart disease

Today, more than two thirds of patients with congenital heart disease (CHD) are adults. Cardiac surgery plays an essential role in restoring and maintaining cardiac function, aside from evolving medical treatment and catheter-based interventions. The aim of the present publication was to describe the spectrum of operations performed on adults with CHD (ACHD) by reviewing current literature. Currently, surgery for ACHD is predominantly valve surgery, since valvular pathologies are often either a part of the basic heart defect or develop as sequelae of corrective or palliative surgery. Surgical techniques for valve repair, established in patients with acquired heart disease (non-ACHD), can often be transferred to ACHD. New valve substitutes may help to reduce the number of redo operations. Most of valve operations yield good results in terms of survival and quality of life, with the precondition that the ventricular function is preserved. Heart failure due to end-stage CHD is the most frequent cause of mortality in ACHD. However, surgical treatment by means of mechanical circulatory support (MCS) is still uncommon and the mortality exceeds the one following other operations in ACHD. Currently, different devices are used and new technical developments are in progress. However, there still is no ideal assist device available. Therefore, heart transplantation remains the only valid option for end-stage CHD. Despite higher early mortality following heart transplantation in ACHD compared to non-ACHD, the long-term survival compares favorably to non-ACHD. There is room for improvement by refining the indications, the time of listing, and the perioperative care of ACHD transplant patients. Sudden death is the second most frequent cause of mortality in ACHD. Ventricular tachycardia is the most frequent cause of sudden death followed by coronary artery anomaly. Due to the increasing awareness of physicians and the improved imaging techniques, coronary artery anomalies are coming more into the focus of cardiac surgeons. However, the reported experience is limited and it is currently difficult to provide a standardized and generally applicable recommendation for the indication and the adequate surgical technique. With the increasing age and complexity of ACHD, treatment of rhythm disturbances by surgical ablation, pacemaker or implantable cardioverter defibrillator (ICD) implantation and resynchronisation gains importance. A risk score specifically designed for surgery in ACHD is among the newest developments in predicting the outcome of surgical treatment of ACHD. This evidence-based score, derived from and validated with data from the Society of Thoracic Surgeons Congenital Heart Surgery Database, enables comparison of risk-adjusted performance of the whole spectrum of procedures performed in ACHD and helps in understanding the differences in surgical outcomes. The score is thus a powerful tool for quality control and quality improvement. In conclusion, new developments in surgery for ACHD are currently made with regard to valve surgery, which comprises more than half of all operations in ACHD and in treatment of end-stage CHD, which still yields high mortality and morbidity.

Pulmonary autograft in aortic position: is everything known?

The Ross operation provides several advantages compared to other valve substitutes to manage aortic valve disease, such as growth potential, excellent hemodynamics, freedom from oral anticoagulation and hemolysis, and better durability. However, progressive dilatation of the pulmonary autografts after Ross operation reflects the inadequate remodeling of the native pulmonary root in the systemic circulation, which results in impaired adaptability to systemic pressure and risk of reoperation after the first decade. A recently published article showed that remodeling increased wall thickness and decreased stiffness in the failed specimens after Ross operation, and the increased compliance might play a key role in determining the progressive long-term autograft root dilatation. Late dilatation can be counteracted by an external barrier which prevents failure. Therefore, an inclusion cylinder technique with a native aorta or a synthetic external support, such as Dacron, might stabilize the autograft root and improve long-term outcomes. In this article, we offer a prospective about the importance of biomechanical features in future developments of the Ross operation. Pre-clinical and clinical evaluations of the biomechanical properties of these reinforced pulmonary autografts might shed new light on the current debate about the long-term fate of the pulmonary autograft after Ross procedure.

Biomechanics drive histological wall remodeling of neoaortic root: A mathematical model to study the expression levels of ki 67, metalloprotease, and apoptosis transition

The pulmonary artery autograft (PA) is the ideal substitute for aortic valve disease in children and young adult. However, it is harnessed by the issue of long-term dilation and regurgitation, often requiring surgery. PA implanted in aortic position during the growth phase in children undergoes a process of mechanical remodeling. We previously developed a semiresorbable armored prosthesis able to mechanically sustain the neoaorta preventing dilation and to gradually integrate with the PA wall inducing a progressive arterial-like tissue positive remodeling. We also described the mechanisms of growth, remodeling and stress shielding of the reinforced PA through a mathematical model. We sought to demonstrate the biological counterpart and the potential molecular mechanisms underlying this histological and mechanical remodeling. A specific mathematical model was developed to describe mechanical behavior of the PA. Mallory trichrome red staining and immunohistochemistry for MMP-9 were performed to elucidate extracellular matrix remodeling phenomena. Apoptosis and cell proliferation were determined by TUNEL assay and immunohistochemistry for Ki67, respectively. An histological remodeling phenomenon sustained by increased level of MMP-9, augmented cell proliferation and reduced apoptosis in the reinforced PA was demonstrated. The mathematical model predicted the biomechanical behavior subtended by the histological changes of the PA in these settings. Changes in metalloproteinases (MMP-9), cell proliferation and apoptosis are the main actors in the remodeling process occurring after transposition of the PA into systemic regimens. Use of semiresorbable reinforcements might induce a positive remodeling of the PA in the context of Ross operation. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2785-2793, 2016.

Compliance mismatch and compressive wall stresses drive anomalous remodelling of pulmonary trunks reinforced with Dacron grafts

Synthetic grafts are often satisfactory employed in cardiac and vascular surgery, including expanded poly(ethylene terephthalate) or expanded poly(tetrafluoroethylene). However, accumulating evidences suggest the emergence of worrisome issues concerning the long-term fate of prosthetic grafts as large vessel replacement. Disadvantages related to the use of synthetic grafts can be traced in their inability of mimicking the elasto-mechanical characteristics of the native vascular tissue, local suture overstress leading to several prosthesis-related complications and retrograde deleterious effects on valve competence, cardiac function and perfusion. Motivated by this, in the present work it is analyzed - by means of both elemental biomechanical paradigms and more accurate in silico Finite Element simulations - the physical interaction among aorta, autograft and widely adopted synthetic (Dacron) prostheses utilized in transposition of pulmonary artery, highlighting the crucial role played by somehow unexpected stress fields kindled in the vessel walls and around suture regions, which could be traced as prodromal to the triggering of anomalous remodelling processes and alterations of needed surgical outcomes. Theoretical results are finally compared with histological and surgical data related to a significant experimental animal campaign conducted by performing pulmonary artery transpositions in 30 two-month old growing lambs, followed up during growth for six months. The in vivo observations demonstrate the effectiveness of the proposed biomechanical hypothesis and open the way for possible engineering-guided strategies to support and optimize surgical procedures.

A composite semiresorbable armoured scaffold stabilizes pulmonary autograft after the Ross operation: Mr Ross's dream fulfilled

OBJECTIVES

Use of resorbable external reinforcement of the pulmonary autograft during the Ross operation has been suggested, but the differential regional potential for dilation of the aorta, mainly regarding the neo-root and the neo-Valsalva sinuses, represents an unresolved issue. Auxetic materials could be useful in preventing dilation given their favorable mechanical properties. We designed a composite semiresorbable armoured bioprosthesis constituted by polydioxanone and expanded polytetrafluoroethylene and evaluated its effectiveness as a pulmonary autograft reinforcement device in an animal model of the Ross procedure.

METHODS

An experimental model of the Ross procedure was performed in 20 three-month-old growing lambs. The pulmonary autograft was alternatively nonreinforced (control group n = 10) or reinforced with composite bioprosthesis (reinforced group n = 10). Animals were followed up during growth for 6 months by angiography and echocardiography. Specific stainings for extracellular matrix and immunohistochemistry for metalloproteinase-9 were performed.

RESULTS

Reference aortic diameter increased from 14 ± 1 mm to 19 ± 2 mm over 6 months of growth. In the control group, pulmonary autograft distension (28 ± 2 mm) was immediately noted, followed by aneurysm development at 6 months (40 ± 2 mm, P < .001 vs reference). In the reinforced group, an initial dilation to 18 ± 1 mm was detected and the final diameter was 27 ± 2 mm (42% increase). Two deaths due to pulmonary autograft rupture occurred in the control group. On histology, the control group showed medial disruption with connective fibrous replacement, whereas in the reinforced group compensatory intimal hyperplasia was present in the absence of intimal tears. The bioprosthesis promoted a positive matrix rearrangement process favoring neoarterialization and elastic remodeling as demonstrated on specific staining for elastin collagen and metalloproteinase-9.

CONCLUSIONS

The device adapted and functionally compensated for the characteristics of autograft growth, guaranteeing a reasonable size of the autograft at 6 months, but more important, because the device is biocompatible, it did not disrupt the biological process of growth or cause inflammatory damage to the wall.