Transapical Aortic Valve Implantation

Transapical aortic valve implantation (TA-AVI) is a new minimally invasive treatment of aortic stenosis for high-risk patients. Through a left lateral mini-thoracotomy and the apex of left ventricle, a stented valve bioprosthesis is inserted into the aortic root using a catheter. After reaching the correct position, the aortic valve prosthesis (AVP) is deployed by an inflatable balloon to reach its final diameter, thus fixing the prosthesis to the aortic wall.

The correct placement of the prosthesis is crucial. If the AVP is placed too high, the coronary arteries may be blocked, resulting in an emergency sternotomy. If the AVP is placed too low, the mitral valve leaflets might be damaged by the stent.

The motivation of this research is to develop a new guidance system that is capable of automatically defining the optimal placement of AVP during the intervention, preventing the misplacement of the valve.

ICCAS developed therefore a new guidance system for assisting TA-AVI. The developed system currently includes two stand-alone modules: a surgical planning software and an intra-operative tracking system.

The Surgical planning software has been developed to measure the optimal size of the prosthesis and to determine its position before implantation of the valve. The software imports 3-D images directly from the Dyna-CT imaging device or from a PACS server. In a semi-automatic process, the user selects anatomical landmarks on the reconstructed surface segmentation of the aortic root. Once the user accepts the landmark positions, the size and position of the AVP into the aortic root are automatically calculated. An appropriate AVP template is then selected from a DICOM prosthesis database and aligned with the patient data. After planning, the generated information is sent to a PACS server using DICOM syntax. From the PACS server, intra-operative systems can retrieve the planning information.

During the intervention, placement of the AVP is done under 2-D X-ray fluoroscopy guidance. However, the contrast agent is injected to visualize shortly the aortic root with the coronary ostia. Also the amount of contrast agent is limited to avoid renal dysfunctions. The Intra-operative tracking system has been developed for tracking the AVP and the coronary ostia in 2-D fluoroscopic image sequences. AVP tracking is performed using the template matching approach and a proposed shape model of the prosthesis. For tracking the coronary ostia even without the contrast agent, the image sequence is frozen as soon as the contrast agent is detected to manually provide the initialization of coronary ostium locations. In the following, the motion of the AVP is used to extrapolate the motion of the coronary ostia. Then the safe area of implantation can be defined and tracked in each image of the sequence based on the information of surgical planning and the coronary ostia tracking.

The next planned task is the integration of our developed guidance system with the current intra-operative systems for assisting TA-AVI at the Heart Center Leipzig.