Alterations in blood flow in the aortic valve, such as stenosis and regurgitation, are increasingly common as the population ages. To solve these disorders in a minimally invasive manner, the transcatheter aortic valve implantation procedure (TAVI) is used, a technique that allows the replacement of the damaged aortic valve without open-heart surgery. This technique has estab lished itself as the main therapeutic solution, as it reduces post-operative mortality and almost completely restores the patient’s functional capacity, making it particularly suitable for frail indi viduals. However, TAVI placement remains a complex procedure, due to the anatomical intervari ability of patients and the difficulties in positioning it accurately, risking incorrect installation or rotation of the prosthesis. This study examined the haemodynamic impact of TAVI misalignment and rotation, using global mock loop measurements and local analysis with in silico simulations. After designing silicone valves and resin stents inspired by the SAPIEN XT TAVI, three experimen tal setups were developed: reference, casting and mock TAVI, which were subsequently compared to each other. Three degrees of misalignment were also assessed in the TAVI mock: mild (15 degrees), moderate (30 degrees) and severe (60 degrees) rotation. In silico analyses to characterise local haemodynamics were performed using 2D fluid-structure interaction (FSI) modelling. The results showed that the silicone valves accurately replicated the pressure and flow curves. Stent insertion resulted in a significant reduction in ventricular pressure from 130 mmHg in the absence of the stent to 110 mmHg with the stent. In addition, an increase in the difference between the aortic and ventricular pressure curves was observed as the misalignment increased, specifically in the transition from 15◦ to 30◦ degrees the gap between the curves increased by 3.8 mmHg. The 2D simulations showed that the stent misalignment reduces the valve leaflet opening by 0.251 mm, increasing the blood flow velocity at the end of the geometry to 3 m/s compared to 1.8 m/s in the configuration without the stent. In conclusion, the study demonstrated how the combination of silicone valves and resin stents adequately reproduces the haemodynamic conditions of TAVI, allowing a detailed analysis of the impact of misalignment on local fluid dynamics. Experimentally, severe to moderate misalignment showed an increase in the gap between the pressure curves, while in silico analysis revealed that misalignment accentuates blood flow velocity, especially in the inlet, leaflet opening and outlet areas, destabilising blood flow.
Le alterazioni del flusso sanguigno nella valvola aortica, come stenosi e rigurgito, sono sempre più comuni con l’invecchiamento della popolazione. Per risolvere questi disturbi in maniera minima mente invasinva, viene adoperata la procedura di impianto transcatetere di valvola aortica (TAVI), una tecnica che consente la sostituzione della valvola aortica danneggiata senza intervento chirur gico a cuore aperto. Questa tecnica si è affermata come la principale soluzione terapeutica, in quanto riduce la mortalità post-operatoria e ripristina quasi completamente la capacità funzionale del paziente, risultando particolarmente indicata per soggetti fragili. Tuttavia, il posizionamento della TAVI rimane un intervento complesso, dovuto all’intervariabilità anatomica dei pazienti e alle difficoltà nel posizionarla con precisione, rischiando un’installazione non corretta o una rotazione della protesi. Questo studio esaminato l’impatto emodinamico del disallineamento e della rotazione della TAVI, utilizzando misurazioni globali tramite mock loop e analisi locali con simulazioni in silico. Dopo aver progettato valvole in silicone e stent in resina ispirandosi alla TAVI SAPIEN XT, sono stati sviluppati tre setup sperimentali: reference, casting e mock TAVI, successivamente con frontati tra loro. Nel mock TAVI sono stati inoltre valutati tre gradi di disallineamento: rotazione lieve (15 gradi), moderata (30 gradi) e severa (60 gradi). Le analisi in silico, atte a caratterizzare l’emodinamica locale sono state eseguite con una modellazione interazione fluido-struttura (FSI) 2D. I risultati hanno dimostrato che le valvole in silicone replicano accuratamente le curve pressorie e di flusso. L’inserimento dello stent ha comportato una significativa riduzione della pressione ventricolare, passando da 130 mmHg in assenza di stent a 110 mmHg con lo stent. Inoltre, si è osservato un aumento della differenza tra le curve pressorie aortiche e ventricolari con l’aumentare del disallineamento, in particolare nel passaggio da 15◦ a 30◦ gradi il gap tra le curve è aumentato di 3.8 mmHg. Le simulazioni 2D hanno evidenziato che il disallineamento dello stent riduce l’apertura dei foglietti valvolari di 0.251 mm, aumentando la velocità del flusso sanguigno nella parte finale della geometria raggiungendo i 3 m/s rispetto agli 1.8 m/s nella configurazione senza lo stent. In conclusione, lo studio ha dimostrato come la combinazione di valvole in silicone e stent in resina permetta di riprodurre adeguatamente le condizioni emodinamiche della TAVI, consentendo un’analisi dettagliata dell’impatto del disallineamento sulla fluidodinamica locale. Sperimental mente, un disallineamento severo o moderato ha mostrato un incremento del divario tra le curve pressorie, mentre l’analisi in silico ha rilevato che il disallineamento accentua la velocità del flusso sanguigno, specialmente nelle zone di inlet, apertura dei foglietti e outlet, destabilizzando il flusso ematico.
Impostazione del mock-loop per la valutazione dell’emodinamica post-TAVI
ROSSI, EDOARDO
2023/2024
Abstract
Alterations in blood flow in the aortic valve, such as stenosis and regurgitation, are increasingly common as the population ages. To solve these disorders in a minimally invasive manner, the transcatheter aortic valve implantation procedure (TAVI) is used, a technique that allows the replacement of the damaged aortic valve without open-heart surgery. This technique has estab lished itself as the main therapeutic solution, as it reduces post-operative mortality and almost completely restores the patient’s functional capacity, making it particularly suitable for frail indi viduals. However, TAVI placement remains a complex procedure, due to the anatomical intervari ability of patients and the difficulties in positioning it accurately, risking incorrect installation or rotation of the prosthesis. This study examined the haemodynamic impact of TAVI misalignment and rotation, using global mock loop measurements and local analysis with in silico simulations. After designing silicone valves and resin stents inspired by the SAPIEN XT TAVI, three experimen tal setups were developed: reference, casting and mock TAVI, which were subsequently compared to each other. Three degrees of misalignment were also assessed in the TAVI mock: mild (15 degrees), moderate (30 degrees) and severe (60 degrees) rotation. In silico analyses to characterise local haemodynamics were performed using 2D fluid-structure interaction (FSI) modelling. The results showed that the silicone valves accurately replicated the pressure and flow curves. Stent insertion resulted in a significant reduction in ventricular pressure from 130 mmHg in the absence of the stent to 110 mmHg with the stent. In addition, an increase in the difference between the aortic and ventricular pressure curves was observed as the misalignment increased, specifically in the transition from 15◦ to 30◦ degrees the gap between the curves increased by 3.8 mmHg. The 2D simulations showed that the stent misalignment reduces the valve leaflet opening by 0.251 mm, increasing the blood flow velocity at the end of the geometry to 3 m/s compared to 1.8 m/s in the configuration without the stent. In conclusion, the study demonstrated how the combination of silicone valves and resin stents adequately reproduces the haemodynamic conditions of TAVI, allowing a detailed analysis of the impact of misalignment on local fluid dynamics. Experimentally, severe to moderate misalignment showed an increase in the gap between the pressure curves, while in silico analysis revealed that misalignment accentuates blood flow velocity, especially in the inlet, leaflet opening and outlet areas, destabilising blood flow.| File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14239/33304