Article

Biomechanical implications of the bicuspid aortic valve: A finite element study from in vivo data

Department of Bioengineering, Politecnico di Milano, Milan, Italy.
The Journal of thoracic and cardiovascular surgery (Impact Factor: 4.17). 04/2010; 140(4):890-6, 896.e1-2. DOI: 10.1016/j.jtcvs.2010.01.016
Source: PubMed

ABSTRACT

Congenital bicuspid aortic valves frequently cause aortic stenosis or regurgitation. Improved understanding of valve and root biomechanics is needed to achieve advancements in surgical repair techniques. By using imaging-derived data, finite element models were developed to quantify aortic valve and root biomechanical alterations associated with bicuspid geometry.
A dynamic 3-dimensional finite element model of the aortic root with a bicuspid aortic valve (type 1 right/left) was developed. The model's geometry was based on measurements from 2-dimensional magnetic resonance images acquired in 8 normotensive and otherwise healthy subjects with echocardiographically normal function of their bicuspid aortic valves. Numeric results were compared with those obtained from our previous model representing the normal root with a tricuspid aortic valve. The effects of raphe thickening on valve kinematics and stresses were also evaluated.
During systole, the bicuspid valve opened asymmetrically compared with the normal valve, resulting in an elliptic shape of its orifice. During diastole, the conjoint cusp occluded a larger proportion of the valve orifice and leaflet bending was altered, although competence was preserved. The bicuspid model presented higher stresses compared with the tricuspid model, particularly in the central basal region of the conjoint cusp (+800%). The presence of a raphe partially reduced stress in this region but increased stress in the other cusp.
Aortic valve function is altered in clinically normally functioning bicuspid aortic valves. Bicuspid geometry per se entails abnormal leaflet stress. The stress location suggests that leaflet stress may play a role in tissue remodeling at the raphe region and in early leaflet degeneration.

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    • "Using an ex vivo animal AV model, investigators showed that BAV-related hemodynamics were associated with higher markers of endothelial activation, osteogenesis, and valvular remodeling than TAV-related hemodynamics[12]. BAVs are exposed to higher biomechanical stress[27], which can up-regulate BMP expression[28]. Pro-osteogenic signaling also presumably begins at a later age in TAVs compared to congenital BAVs. "
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    ABSTRACT: Background: Aortic valve replacement for calcific aortic valve stenosis is one of the more common cardiac surgical procedures. However, the underlying pathophysiology of calcific aortic valve stenosis is poorly understood. We therefore investigated the histologic findings of aortic valves excised for calcific aortic valve stenosis and correlated these findings with their associated clinical features. Results and methods: We performed a retrospective analysis on 6685 native aortic valves excised for calcific stenosis and 312 prosthetic tissue aortic valves with calcific degeneration at a single institution between 1987 and 2013. Patient demographics were correlated with valvular histologic features diagnosed on formalin-fixed, decalcified, and paraffin embedded hematoxylin and eosin stained sections. Of the analyzed aortic valves, 5200 (77.8%) were tricuspid, 1473 (22%) were bicuspid, 11 (0.2%) were unicuspid, and 1 was quadricuspid. The overall prevalence of osseous and/or chondromatous metaplasia was 15.6%. Compared to tricuspid valves, bicuspid valves had a higher prevalence of metaplasia (30.1% vs. 11.5%) and had an earlier mean age of excision (60.2 vs. 75.1 years old). In addition, the frequency of osseous metaplasia and/or chondromatous metaplasia increased with age at time of excision of bicuspid aortic valves, while tricuspid aortic valves showed the same incidence regardless of patient age. Males had a higher prevalence of metaplasia in both bicuspid (33.5% vs. 22.3%) and tricuspid (13.8% vs. 8.6%) aortic valves compared to females. Osseous metaplasia and/or chondromatous metaplasia was also more common in patients with bicuspid aortic valves and concurrent chronic kidney disease or atherosclerosis than in those without (33.6% vs. 28.3%). No osseous or chondromatous metaplasia was observed within the cusps of any of the prosthetic tissue valves. Conclusions: Osseous and chondromatous metaplasia are common findings in native aortic valves but do not occur in prosthetic tissue aortic valves. Bicuspid valves appear to have an inherent proclivity for metaplasia, as demonstrated by their higher rates of osseous metaplasia and/or chondromatous metaplasia both overall and at earlier age compared to tricuspid and prosthetic tissue aortic valves. This predilection could be due to aberrant hemodynamic forces on bicuspid valves, as well as intrinsic genetic changes associated with bicuspid valve formation. Aortic valve interstitial cells may play a central role in this process. Calcification of prosthetic tissue valves is most likely a primarily dystrophic phenomenon.
    Full-text · Article · Sep 2015 · Cardiovascular pathology: the official journal of the Society for Cardiovascular Pathology
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    • "Individual BAV phenotypes may be caused by unique pathogenetic mechanisms and may require tailored surgical approaches [9]. Recent in vitro and in vivo studies have provided major insight into the pathogenesis of the different phenotypes of BAV disease [10] [11] [12]. "
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    ABSTRACT: The purpose of this study was to analyse the correlation between preoperative systolic transvalvular flow patterns and proximal aortic wall lesions in patients undergoing surgery for bicuspid aortic valve (BAV) stenosis. A total of 48 consecutive patients with BAV stenosis (mean age 58 ± 9 years, 65% male) underwent aortic valve replacement (AVR) ± proximal aortic surgery from January 2012 through February 2013. Preoperative cardiac phase-contrast cine magnetic resonance imaging (MRI) assessment was performed in all patients in order to detect the area of maximal flow-induced stress in the proximal aorta. Based on these MRI data, two aortic wall samples (i.e. area of the maximal stress (jet sample) and the opposite aortic wall (control sample)) were collected during AVR surgery. Aortic wall changes were graded based on a summation of seven histological criteria (each scored from 0 to 3). Histological sum score (0-21) was separately calculated and compared between the two aortic samples (i.e. jet sample vs control sample). An eccentric transvalvular flow jet hitting the proximal aortic wall could be identified in all 48 (100%) patients. The mean histological sum score was significantly higher in the jet sample vs control sample areas of the aorta (i.e. 4.1 ± 1.8 vs 2.2 ± 1.5, respectively) (P = 0.02). None of the patients had a higher sum score value in the control sample. Our study demonstrates a strong correlation between the systolic pattern of the transvalvular flow jet and asymmetric proximal aortic wall changes in patients undergoing AVR for BAV stenosis.
    Full-text · Article · Jan 2014 · European journal of cardio-thoracic surgery: official journal of the European Association for Cardio-thoracic Surgery
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    • "In particular, was the risk of aortic dissection in BAV patients determined before or after aortic valve replacement (AVR) surgery? Considering the recently published evidence on BAV function and effects of transvalvular flow [4] [5] [6] [7] [8] [9] [10], AVR surgery may be a key factor in the natural history of BAV-associated aortopathy with considerable influence on the risk of future aortic events. "
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    ABSTRACT: The risk of acute aortic events in patients with bicuspid aortic valve (BAV) disease is a controversial issue. The real risk of aortic dissection in patients with BAV disease is unknown. An indirect assessment of this risk, however, could be gained with a more detailed understanding of the pathogenesis of BAV aortopathy. There are two major issues that should be clarified before one addresses the question of aortic dissection risk in BAV patients. The first issue, when analysing the data from previous BAV cohorts, is to determine what stage of BAV disease was present in the described patient population. In particular, was the risk of aortic dissection in BAV patients determined before or after aortic valve replacement (AVR) surgery? The second issue to consider is the functional state of the pathological valve within the observed population. In particular, did patients predominantly suffer from BAV stenosis or BAV insufficiency? Unfortunately, the vast majority of published reports do not separate between the different BAV phenotypes, thereby complicating interpretation of the results. Considering these two important clinical variables (i.e. the stage of BAV disease and the functional phenotype), we herein aim to explain the inconsistency of the published data with regard to the risk of aortic dissection in patients with BAV disease.
    Full-text · Article · Dec 2013 · Interactive Cardiovascular and Thoracic Surgery
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