Palombi, Andrea; (2022) Measuring aortic annulus size using a soft robotic balloon catheter. Masters thesis (M.Phil), UCL (University College London).

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Abstract

Transcatheter aortic valve implantation (TAVI) is a minimally invasive surgical technique to treat aortic heart valve diseases. According to current clinical guidelines, the implanted prosthetic valve replacing the native one is selected based on pre-operative size assessment of the aortic annulus through different imaging techniques. That very often leads to suboptimal device selection resulting in major complications, such as aortic regurgitation and atrioventricular blocks. In this work, we propose a new, intra-operative approach to determine the diameter of the aortic annulus exploiting intra-balloon pressure and volume (p-v) data, acquired from a robotised valvuloplasty balloon catheter. This strategy, combined with current imaging-based sizing methods, would allow to obtain more accurate measurements and check whether the implantation region has changed as a consequence of the valvuloplasty procedure. That would improve TAVI device selection, potentially reducing the occurrence of the aforementioned complications. Two robotic inflation devices, capable of collecting real-time intra-balloon p-v data, were designed and interfaced with a commercially available valvuloplasty balloon catheter. A sizing algorithm that can precisely estimate the annular diameter from acquired p-v data was also implemented. The algorithm relies on a mathematical model of the balloon free inflation and an iterative method based on linear regression. Two different mathematical models of the balloon free inflation, one analytical and one numerical, were developed and compared in terms of sizing accuracy. In vitro tests were performed on idealised aortic phantoms. Experimental results show that pressure-volume data can be used to determine annular diameters bigger than the unstretched diameter of the balloon catheter. This conclusion applies to both rigid and compliant phantoms characterised by a rigidity greater than 100 kPa/%. For these cases, the proposed approach exhibited good precision (maximum average error 1.972%) and good repeatability (maximum standard deviation ±0.263 mm).

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