Development of a balloon catheter for fetal aortic valvuloplasty

Abstract

This thesis describes the design process of a new instrument that can be used to perform a fetal aortic valvuloplasty procedure. Congenital heart defects occur in 8 to 12 out of every 1000 live births. Aortic stenosis (AS) is one of the most common congenital heart defects. When AS occurs, the opening and closing of the aortic valve does not work well. This is often caused by two leaflets being fused together. If left untreated, aortic stenosis could have severe consequences such as the development of hypoplastic left heart syndrome (HLHS). To prevent this, the fetal aortic valvuloplasty (FAV) procedure is performed. In this procedure, a balloon catheter is advanced percutaneously into the fetal heart at   26 weeks of gestation. The problem with this procedure is that still many complications occur, of which some can be attributed to the used instruments. The currently used instruments are designed for an angioplasty procedure in adults, and therefore quite large. This led to the need for the design of a dedicated device for FAV, which was the goal of this thesis. The thesis started off with a literature study and clinical interviews to determine the design focus, requirements and wishes. It was found that reduction of cannula diameter reduces the risk of complications, which therefore became the aim of this project. Currently an 18G cannula is used, which has an outer diameter of 1.27 mm. It would however be preferable to use a 20G cannula, which has an outer diameter of 0.91 mm. The 18G cannula is now required due to the crossing profile of the balloon that is used, which does not fit through a smaller needle. The crossing profile of a balloon refers to the maximum diameter found between the proximal and distal end of the balloon catheter, while it is still folded. To be able to use a smaller needle, this crossing profile needs to be reduced. Therefore, it was determined that the design focus should be on reducing the crossing profile of the balloon catheter, while still being able to reach the required diameter at inflation. After exploring multiple ideas and concepts, the final concept was generated. This concept is based on the fact that the FAV procedure requires other balloon properties than an angioplasty procedure. Less pressure is required, the procedure is performed under ultrasound instead of x-ray guidance and the guidewire does not have to be changed and used for complex steering. Based on these differences, several design choices were made that lead to a smaller crossing profile and enhance the performance of the FAV procedure. Amongst others, this new design contains a fixed guidewire, longer cones and a low wall thickness. Multiple prototypes were developed for testing and validation, which was done on both clinical and mechanical level. The clinical tests gave insights regarding preferred shape and configuration, and established that there was enough control and steerability provided with the fixed guidewire. The mechanical tests provided information regarding the force exerted by the balloon, (burst) pressure and diameter of the balloon. The prototypes had crossing profiles of around 0.6 mm, which is a significant reduction compared to the crossing profile of 0.8 mm of the current balloon. This allows for the use of a 20G cannula instead of an 18G cannula, which has an outer diameter that is almost 0.4 mm smaller. The final design fulfilled all requirements and wishes, and therefore a proof of principle for a suitable alternative instrument for the FAV procedure was provided. Further research is recommended concerning the production of a more accurate prototype and elaborate clinical testing to optimize the design and gain more insights in the behaviour of this balloon.