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LA PATOLOGIA AORTICA NELLA BICUSPIDIA VALVOLARE: MODELLI MATEMATICI AD ELEMENTIFINITI E CORRELAZIONI FLUIDODINAMICHE
No full textScopo della tesi: Nella bicuspidia aortica (BAV), il ruolo dei fattori genetici ed emodinamici che influenzano la patologia vascolare a carico dell'aorta ascendente è controverso. Per testare l'effetto della geometria valvolare sul flusso in aorta ascendente è stato utilizzato un modello ad elementi finiti.
Metodi: Un modello della superficie della radice aortica ed aorta ascendente è stato ottenuto da immagini di risonanza magnetica di pazienti con BAV e valvola tricuspide (TAV), con l'utilizzo delle capacità di segmentazione del software Vascular Modelling Toolkit. Modelli analitici dell'orifizio bicuspide (antero-posteriore, AP e latero-laterale, L-L) e tricuspide sono stati matematicamente definiti. I modelli sono stati trasformati in mesh volumetriche di tetraedri lineari per eseguire le simulazioni fluidodinamiche con l'utilizzo del codice ad elementi finiti LifeV. Il campi di velocità del flusso aortico sono stati definiti a quattro livelli: annulus, seni di Valsalva, giunzione sino-tubulare ed aorta ascendente.
Risultati: Da un confronto mediante analisi ad elementi finiti del modello bicuspide e tricuspide si ottiene un pattern di flusso completamente diverso. Il flusso aortico nelle configurazioni bicuspidi mostra una distribuzione asimmetrica del campo di velocità verso la convessità dell'aorta ascendente media, tornando simmetrico a livello dell'aorta ascendente distale. Il flusso nel modello tricuspide è, al contrario, simmetrico in tutti i segmenti aortici. Paragonando poi i modelli bicuspidi A-P e L-L si notano zone di ricircolo più pronunciate in quest'ultimo. Infine lo stress a parete massimo per entrambi i modelli bicuspidi è localizzato alla convessità dell'aorta ascendente media.
Conclusioni: Il confronto tra i modelli proposti mostra flusso asimmetrico e con maggior velocità nei modelli bicuspidi, in particolare l'A-P. Lo stress a parete è massimo nella zona aortica maggiormente sottoposta a formazione di aneurismi. Questi risultati supportano l'ipotesi che fattori emodinamici possano contribuire alla patologia aneurismatica dell'aorta ascendente nei pazienti bicuspidi.Purpose: In bicuspid aortic valve disease (BAV) role of genetic and hemodynamic factors influencing ascending aortic pathology is controversial. To test the effect of BAV geometry on ascending aortic flow, a Finite Element Model analysis was undertaken.
Methods: A surface model of the aortic root and ascending aorta was obtained from magnetic resonance images of patients with BAV and tricuspid valve using segmentation facilities of the image processing code Vascular Modelling Toolkit. Analytical models of bicuspid (antero-posterior, AP and latero-lateral, LL) and
tricuspid orifices were mathematically defined. Models were then turned into volumetric meshes of linear tetrahedra for computational fluid dynamics simulations. Numerical simulations were performer with the Finite Element code LifeV. Flow
velocity fields were assessed ad four levels: aortic annulus, sinuses of Valsalva, sinotubular junction, ascending aorta.
Results: Comparison of finite-element analysis of bicuspid and tricuspid aortic valve shows different blood flow velocity pattern.
Flow in bicuspid configurations shows asymmetrical distribution of velocity field towards the convexity of mid-ascending aorta, returning symmetrical in distal ascending aorta. On the contrary, tricuspid flow is symmetrical in each aortic segment. Comparing AP-BAV with LL-BAV, more pronounced recirculation zones have been noticed in the latter. Finally, we found that in both BAV configurations maximum wall shear stress is highly localized at the convex portion of mid-ascending aorta.
Conclusions: Comparison between models show asymmetrical and higher flow velocity in bicuspid models, in particolar in AP configuration. Wall shear stress is maximum at the aortic level known to be more exposed to aneurysm formation in bicuspid patients. This supports the hypothesis that hemodynamic factors may contribute to ascending aortic pathology in this subset of patients
Influence of bicuspid valve geometry on ascending aortic fluid-dynamics: a parametric study
No full textBicuspid aortic valve (BAV) predisposes to aortic aneurysms with a high prevalence. A first hypothesis of this phenomenon is related to fibrillin deficiency (genetic hypothesis). In this paper we focus on a complementary, haemodynamic hypothesis stating that is the peculiar fluid-dynamics of the blood in the ascending aorta in BAV configurations which leads to those conditions that facilitate the aneurysms’ formation. To corroborate that hypothesis, we perform a parametric study based on numerical simulations of ascending aorta hemodynamics in different configurations of orifice area and valve orientation. We investigate the resulting WSS distributions and degrees of asymmetry of the blood jet, and we introduce surrogate indices which may find direct application in clinical environments
Comparative finite-element model analysis of ascending aortic flow in bicuspid and tricuspid aortic valve
No full textPurpose: In bicuspid aortic valve (BAV) disease the role of genetic and haemodynamic factors influencing ascending aortic pathology is controversial. In order to test the effect of BAV geometry on ascending aortic flow, a Finite Element model analysis was undertaken.
Methods: A surface model of aortic root and ascending aorta was obtained from magnetic resonance images of patients with BAV and tricuspid aortic valve using the segmentation facilities of the image processing code Vascular Modeling Toolkit (developed at the Mario Negri Institute). Simplified and however reliable analytical models of bicuspid (antero-posterior, AP, and laterolateral, LL, commissures) and tricuspid orifices were mathematically defined. Final models were turned into a volumetric mesh of linear tetrahedra for computational fluid dynamics simulations. Numerical simulations were performed with the Finite Element code LifeV (developed by the research centers MOX-Milan, INRIA-Paris, EPFL-Lausanne). Physiological inflow boundary conditions at inlet were imposed by means of a mathematically sound and well tested method based on the introduction of a Lagrange multiplier in the problem formulation. The flow velocity fields were assessed for four levels: aortic annulus, sinus of Valsalva, sinotubular junction, ascending aorta.
Results: Comparison of finite-element model analysis of bicuspid and tricuspid aortic valve shows different blood flow velocity pattern. The flow in the AP bicuspid shows an asymmetrical distribution of velocity field towards the convexity of the mid-ascending aorta returning symmetrical in distal ascending aorta. In the LL bicuspid a less pronounced asymmetry is noted at the sinus of Valsalva level. On the contrary, tricuspid flow is symmetrical in each aortic segment. Moreover, aortic flow in bicuspid model gains a maximum velocity at the systole of 5.5 m/s for AP and of 5.7 m/s for LL, while in the tricuspid maximum velocity is 2.6 m/s.
Conclusions: Comparison between models shows an asymmetrical and higher flow velocity in the bicuspid models, in particular in the AP configuration. The asymmetry is more pronounced at the aortic level known to be more exposed to aneurysm formation in bicuspid patients. This supports the hypothesis that haemodynamic factors may contribute to ascending aortic pathology in this subset of patients
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Valve-sparing root replacement for pulmonary autograft dissection late after the Ross operation
No full textAortic valve replacement with the pulmonary autograft (ie, the Ross operation) is generally associated with satisfactory early and late results. Complications, however, can occur, including the tendency of the pulmonary autograft root to dilate with time.1 Whereas neoaortic root dilatation might be observed in as many as one third of patients late after the Ross operation,2 uncertainty still exists as to the rate of progression toward true aneurysmal disease (aortic diameter ≥5 cm).1,2 Furthermore, the actual risk of complications, such as neoaortic rupture or dissection, is also unknown. The yet undefined natural history of root dilatation after the Ross operation, the often satisfactory competence of the pulmonary autograft valve, the scarcity of valid therapeutic alternatives (particularly in the infant and child), and the complexity–risk of reintervention have thus far delayed standardization of therapeutic indications. In particular, timing and technique of reoperation on the aneurysmal neoaortic root are still controversial.1,2Here we present a case of potentially lethal evolution of progressive pulmonary autograft dilatation (ie, neoaortic root dissection) successfully treated with valve-sparing root replacement. The implications in terms of natural history and indications for reintervention are discussed
Seven-year performance of the Edwards Prima Plus stentless valve with the intact non-coronary sinus technique
No full textOBJECTIVES: Late results after stentless aortic valve replacement (AVR) may be jeopardized by progressive aortic dilatation. To define functional outcome using the intact non-coronary sinus technique, all patients operated using the stentless Edwards Prima Plus xenograft were assessed. METHODS: Between January 2000 and August 2007, 154 patients, aged 71 +/- 9 years, underwent stentless AVR using a technique, which replaces the non-coronary sinus and stabilizes two of three commissures. Indication was aortic valve stenosis (AS) in 103 (67%) patients: 33 (21%) had bicuspid valve and four endocarditis. Ninety-six (62%) patients were in NYHA III-IV, and 13 (8%) had LVEF <30%. Associated procedures were required in 59 (38%) patients (CABG, 34; ascending aorta, 22; others 3). Study endpoints were survival, freedom from valve-related events, clinical status, and graft function. RESULTS: There were two hospital and two late deaths during a 48 +/- 19 months (1-92) follow-up (97 +/- 3% survival at seven years). Seven-year freedom from structural failure, nonstructural failure, and endocarditis was 99 +/- 1%, 97 +/- 3%, and 98 +/- 2%. Follow-up NYHA (96 vs ten patients in class III-IV, p = 0.001), and cardiac function (13 vs one patient with LVEF <30%, p = 0.02) were improved. Xenograft performance was satisfactory: 0-2 + aortic insufficiency (AI) in 147 (98%) patients, mean trans-prosthetic pressure gradient 8 +/- 4 (0-25 mmHg). Aortic root diameters were comparable to postoperative values (sinus of Valsalva, 36 +/- 8 vs 35 +/- 9 mm, p = ns; sinotubular junction, 32 +/- 7 vs 34 +/- 8 mm, p = ns). CONCLUSIONS: Stentless AVR with non-coronary sinus replacement affords excellent late outcome and low rate of valve-related events, even in complex patients (bicuspid valve, LV failure, and endocarditis). Aortic root dimensions remain stable over time allowing rewarding xenograft function
Unusual lesion of the tricuspid valve in a small infant with pulmonary arterial hypertension
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