Aortic root dynamism, geometry, and function after the remodeling operation: Clinical relevance

Multiscale structure and function of the aortic valve apparatus

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

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.

Aortic Valve Embryology, Mechanobiology, and Second Messenger Pathways: Implications for Clinical Practice

During the Renaissance, Leonardo Da Vinci was the first person to successfully detail the anatomy of the aortic root and its adjacent structures. Ever since, novel insights into morphology, function, and their interplay have accumulated, resulting in advanced knowledge on the complex functional characteristics of the aortic valve (AV) and root. This has shifted our vision from the AV as being a static structure towards that of a dynamic interconnected apparatus within the aortic root as a functional unit, exhibiting a complex interplay with adjacent structures via both humoral and mechanical stimuli. This paradigm shift has stimulated surgical treatment strategies of valvular disease that seek to recapitulate healthy AV function, whereby AV disease can no longer be seen as an isolated morphological pathology which needs to be replaced. As prostheses still cannot reproduce the complexity of human nature, treatment of diseased AVs, whether stenotic or insufficient, has tremendously evolved, with a similar shift towards treatments options that are more hemodynamically centered, such as the Ross procedure and valve-conserving surgery. Native AV and root components allow for an efficient Venturi effect over the valve to allow for optimal opening during the cardiac cycle, while also alleviating the left ventricle. Next to that, several receptors are present on native AV leaflets, enabling messenger pathways based on their interaction with blood and other shear-stress-related stimuli. Many of these physiological and hemodynamical processes are under-acknowledged but may hold important clues for innovative treatment strategies, or as potential novel targets for therapeutic agents that halt or reverse the process of valve degeneration. A structured overview of these pathways and their implications for cardiothoracic surgeons and cardiologists is lacking. As such, we provide an overview on embryology, hemodynamics, and messenger pathways of the healthy and diseased AV and its implications for clinical practice, by relating this knowledge to current treatment alternatives and clinical decision making.

Long-Term Outcomes of Cardiovascular Operations in Children With Connective Tissue Disorders

Connective tissue disorders can be associated with significant cardiovascular morbidity needing cardiac surgery during childhood. In this retrospective study, we used the Pediatric Cardiac Care Consortium, a multicenter United States-based registry of pediatric cardiac interventions, to describe the long-term outcomes of patients who underwent their first surgery for connective tissue-related cardiovascular conditions aged <21 years. Between 1982 and 2003, a total of 103 patients were enrolled who underwent cardiac surgery for a connective tissue-related cardiovascular disorder, including 3 severe infantile cases operated on within the first year of life. Most patients underwent aortic site surgery (n = 85) as a composite graft (n = 50), valve-sparing (n = 33), or other aortic surgery (n = 2). The remaining patients underwent atrioventricular valve surgery (mitral 17, tricuspid 1). Of the 99 patients surviving to discharge, 80 (including the 3 infantile) had adequate identifiers for tracking long-term outcomes through 2019 through linkage with the National Death Index and the Organ Procurement. Over a median period of 19.5 years (interquartile range 16.0 to 23.1), 29 deaths and 1 transplant occurred in the noninfantile group, whereas all 3 infantile patients died before the age of 4 years. The postdischarge survival for the noninfantile group was 92.2%, 68.2%, and 56.7% at 10, 20, and 25 years, respectively. Cardiovascular-related pathology contributed to all deaths in the infantile and 89% (n = 27) of deaths for the noninfantile cases after hospital discharge. The significant late attrition from cardiovascular causes emphasizes the need for close monitoring and ongoing management in this population.

Utility of 4D Flow MRI in Thoracic Aortic Diseases: A Literature Review of Clinical Applications and Current Evidence

Despite the recent technical developments, surgery on the thoracic aorta remains challenging and is associated with significant mortality and morbidity. Decisions about when and if to operate are based on a balance between surgical risk and the hazard of aortic rupture. These decisions are sometimes difficult in elective cases of thoracic aortic diseases, including aneurysms and dissections. Abnormal wall stress derived from flow alterations influences disease progression. Therefore, a better understanding of the complex hemodynamic environment inside the aortic lumen will facilitate patient-specific risk assessments of complications, which enable clinicians to provide timely prophylactic interventions. Time-resolved 3D phase-contrast (4D flow) MRI has many advantages for the in vivo assessment of flow dynamics. Recent developments in 4D flow imaging techniques has led to significant advances in our understanding of physiological flow dynamics in healthy subjects and patients with thoracic aortic diseases. In this clinically focused review of thoracic aortic diseases, we demonstrate the clinical advances acquired with 4D flow MRI from published studies. We provide a systematic overview of key evidences and considerations regarding normal thoracic aortas, thoracic aortic aneurysms, aortic dissections, and thoracic aortas with prosthetic graft replacement.

Microstructure of the juvenile sheep aortic valve hinge region and the trilamellar sliding hypothesis

Background: The aortic valve mechanism performs extremely sophisticated functions which depend on the microstructure of its component parts. The hinge mechanism of the aortic leaflets plays a crucial part in the overall function. However, the detailed microstructure and its relation to function has not been adequately studied.

Methods: The aortic roots of juvenile sheep were fixed under physiologic pressure. Sections through all three sinuses were then performed to illustrate the microstructure of the hinge mechanism in different regions of the aortic root.

Results: The hinge region in the different sinuses showed unique microstructure with a trilamellar topology with a dominant core consisting of glycosaminoglycans. The exact arrangement of the trilamellar structures varies around the aortic sinuses, which could have functional implications. These features allow the hinge to perform its complex functions through what we have described as “the trilamellar sliding hypothesis”.

Conclusion: The microstructure of the hinge mechanism is unique and enables it to perform it sophisticated functions.

A New Technique for Shaping the Aortic Sinuses and Conserving Dynamism in the Remodeling Operation

BACKGROUND

Preserving dynamism and recreating the sinuses in the Dacron graft are thought to be important for optimizing results of aortic valve-conserving operations.

METHODS

We describe a novel technique that preserves dynamism and recreates the sinotubular junction. In addition, it tailors 3 sinuses of defined longitudinal and transverse curvatures in a straight Dacron tube during the operation. The technique has been used in 6 patients with varied aortic root pathology. We performed preoperative and postoperative multimodality imaging using computerized image analysis as well as 3-dimensional models.

RESULTS

There was no early or midterm death. Upon discharge, patients were clinically well, with echocardiographic evidence of minimal (3 patients) or mild (3 patients) aortic regurgitation. Computed tomography and cardiac magnetic resonance imaging with extensive image analysis of the aortic root size, shape, and function showed partial or complete normalization of these parameters. This included the shape and dynamism of the aortic annulus and the size and shape of the geometric (effective) orifice. The 4-dimensional magnetic resonance imaging pattern of flow in the sinuses and ascending aorta showed favorable vortices in the sinuses, right-handed helical flow, and marked diminution of energy loss in the ascending aorta.

CONCLUSIONS

The novel technique described here is simple, practical, and cost-effective because it uses a widely available straight Dacron tube. The technique does not use rigid internal or external support. The early results are encouraging. Larger series with longer follow-up are required.

Valve sparing root replacement: an update

PURPOSE OF REVIEW

Until the year 2000, the publications concerning aortic valve sparing (AVS) did not exceed 20 articles; in the following years almost 300 publications have appeared. Over 35 years from the introduction of valve sparing techniques and 500 years after the death of Leonardo da Vinci, this review highlights the significant steps in modern imaging techniques and the excellent clinical results in the field of reconstructive aortic root surgery.

RECENT FINDINGS

AVS operations underwent significant modifications over the last few years making it reproducible with satisfactory outcomes. The extraordinary potential of imaging opens new boundless horizons in the perspective of an increasingly patient-tailored surgical planning. The basic surgical concepts include the preservation and resuspension of the aortic valve in a near-normal environment (with the creation of functionally suited neo-aortic sinuses) and the re-establishment of a normal relationship of the aortic root components.

SUMMARY

Today is possible to perform a reimplantation procedure with the creation of neo-sinuses or a remodeling procedure with the addition of annular support. Both procedures can now guarantee an anatomical root reconstruction and an increased long-term durability. AVS operations have become established alternatives to Bentall procedures for patients with aortic root pathology, especially in young patients.

Does the Aortic Annulus Dilate After Aortic Root Remodeling?

BACKGROUND

The 2 main techniques of valve-sparing aortic root replacement (VSRR) are remodeling and reimplantation. There is concern that the aortic annulus, which is not stabilized in remodeling technique, may dilate over time and cause aortic regurgitation. Our aim was to assess whether the aortic annulus dilates after VSRR with remodeling technique without aortic annuloplasty.

METHODS

Data on patients undergoing elective or urgent VSRR remodeling technique between 2005 and 2018 were collected. Patients undergoing arch and emergency surgery for acute type A aortic dissection were excluded. Preoperative aortic annulus diameter was measured by transthoracic echocardiography, and this was compared with the annulus diameter measured from the most recently available transthoracic echocardiography. The requirement for reintervention during follow-up was recorded.

RESULTS

Between 2005 and 2018, 98 patients underwent VSRR. Sixty-six (67.3%) had Marfan syndrome or Loeys-Dietz syndrome. Median age was 60 (interquartile range, 18-68) years and 71 (72.4%) were men. Median cross-clamp and cardiopulmonary bypass times were 122 (interquartile range, 104-164) minutes and 138 (interquartile range, 121-198) minutes, respectively. Median intensive care unit and hospital stay were 1 day and 6 days, respectively. No patients suffered perioperative stroke. There was no in-hospital mortality. At median follow-up of 7.1 years (interquartile range, 5-129 months), mean postoperative annular diameter was 25.7 mm, from 24.2 mm preoperatively (P = .403). One patient required aortic valve replacement during follow-up. Freedom from moderate or severe aortic regurgitation was 97%.

CONCLUSIONS

There was no significant aortic annular dilatation in selected patients undergoing remodeling VSRR. Our data do not support routine use of annuloplasty in patients with annular diameter less than or equal to 25 mm.