Steerable Balloon Endoscopes for Transcatheter Intracardiac Procedures
Authors: McCandless Max , Otto Silvan , Dupont Pierre E. 
Published: September 2024

While the repair and replacement of heart valves previ- ously required the risk and trauma of open-heart surgery, transcatheter procedures and devices are rapidly devel- oping as low-risk low-trauma alternatives [1]. A contin- uing challenge in the development of these techniques is the lack of direct visualization of valve tissue as is possible in open surgery. The standard catheter imaging modalities are fluoroscopy and ultrasound. Fluoroscopy enables visualization of the catheter, but not the tissue. Ultrasound images both the catheter and the tissue, but provides very noisy images. To fill this imaging gap, cardioscopy (endoscopy inside the blood-filled heart) has been developed as a means of providing detailed visualization of the con- tact region between the catheter tip and the valve tis- sue [2]. Furthermore, cardioscopic imaging can enable autonomous robotic catheter procedures as demonstrated in [3]. Cardioscopes use an optically-clear “cap” or optical window on the imaging element. When the optical window is in the blood pool, the cardioscopic image is completely red, but when placed in contact with tissue, the optical window displaces the blood and so enables imaging of the contacting tissue. When designing the optical window, the diameter of its distal face is a critical parameter since it determines the diameter of the cardioscopic field of view. The field of view diameter needs to be large enough to be able to identify what the catheter tip is touching inside the heart. For many applications, the minimum diameter for localization is 1cm. Prior cardioscopes designed for valve repair used solid optical windows, which had to be inserted through the heart wall since their 1cm diameter was too large to introduce through the vasculature. For percutaneous access, an ideal optical window design should be col- lapsible during introduction into the vasculature, but capable of expansion once positioned inside the heart. Saline-filled optically-clear balloons represent a promising approach which is explored in this paper. A prototype cardioscope balloon is depicted in Fig. 1. In this design, the distal tail of the balloon is inverted and glued to the tube forming the working channel so as to reate a smooth distal surface on the optical window. A chip camera with integrated LEDs for illumination is positioned inside the balloon. Since the working channel appears within the field of view (Fig. 1(d)), the cardio- scope makes it possible to visualize the precise location of the working channel on heart valve tissue. This eccen- tric working channel differentiates the cardioscope from past works that are capable of observing and evaluating tissue, but not performing tissue modification [4]. Using existing technology, positioning the working channel inside the heart involves delivering the cardio- scope using one or more telescoping steerable sheaths. Since these sheaths are ∼1m long and contact vascular and cardiac tissue over much of their length, precise motions of the tip based on sheath bending can be challenging. This paper investigates an alternative approach to fine positioning of the working channel which is based on building flexural degrees of freedom into the cardiocopic balloon. We demonstrate a balloon design in which inflation to an initial pressure fully inflates the optical window. Increases in pressure from this value produce flexure of the cardioscope while maintaining the original diameter of the optical window.