Michael Gessat

Safety and feasibility of novel technology fusing echocardiography and fluoroscopy images during MitraClip interventions.

AIMS The EchoNavigator (EN) software (Philips Healthcare, Best, The Netherlands) enables real-time fusion of echocardiography and fluoroscopy by co-registration of the echocardiography probe on the x-ray image. We aimed to evaluate the feasibility and safety of this novel software during MitraClip procedures. METHODS AND RESULTS Twenty-one patients were treated with the support of EchoNavigator software (EN+ patients). The primary (safety) endpoint was the total radiation dose. Secondary endpoints were fluoroscopy and total procedure time. The measurements were compared to those of 21 patients treated immediately before the installation of EchoNavigator (EN- patients). More MitraClips (45 vs. 36) were implanted in the EN+ group, mirroring more complex interventions in this group. In EN+ patients, radiation dose (Gy/cm2) was similar compared to EN- patients (146.5±123.6 vs.146.8±134.1, p=0.9). Total procedure time (minutes) was similar in the EN+ group compared to EN- patients (136.2±50.2 vs. 125.7±51.2, p=0.5). The main benefit of the EchoNavigator is the automated real-time fusion of echocardiography and fluoroscopy, leading to easier catheter manipulation. CONCLUSIONS The use of EchoNavigator software was feasible and safe in all study patients. Further studies are necessary to confirm the benefits of using this software.

A planning system for transapical aortic valve implantation

Stenosis of the aortic valve is a common cardiac disease. It is usually corrected surgically by replacing the valve with a mechanical or biological prosthesis. Transapical aortic valve implantation is an experimental minimally invasive surgical technique that is applied to patients with high operative risk to avoid pulmonary arrest. A stented biological prosthesis is mounted on a catheter. Through small incisions in the fifth intercostal space and the apex of the heart, the catheter is positioned under flouroscopy in the aortic root. The stent is expanded and unfolds the valve which is thereby implanted into the aortic root. Exact targeting is crucial, since major complications can arise from a misplaced valve. Planning software for the perioperative use is presented that allows for selection of the best fitting implant and calculation of the safe target area for that implant. The software uses contrast enhanced perioperative DynaCT images acquired under rapid pacing. In a semiautomatic process, a surface segmentation of the aortic root is created. User selected anatomical landmarks are used to calculate the geometric constraints for the size and position of the implant. The software is integrated into a PACS network based on DICOM communication to query and receive the images and implants templates from a PACS server. The planning results can be exported to the same server and from there can be rertieved by an intraoperative catheter guidance device.

Simulation of transcatheter aortic valve implantation under consideration of leaflet calcification

Transcatheter aortic valve implantation (TAVI) is a minimally invasive off-pump procedure to replace diseased aortic heart valves. Known complications include paravalvular leaks, atrioventricular blocks, coronary obstruction and annular rupture. Careful procedure planning including appropriate stent selection and sizing are crucial. Few patient-specific geometric parameters, like annular diameters, annular perimeter and measurement of the distance to the coronary ostia, are currently used within this process. Biomechanical simulation allows the consideration of extracted anatomy and material parameters for the intervention, which may improve planning and execution phases. We present a simulation workflow using a fully segmented aortic root anatomy, which was extracted from pre-operative CT-scan data and apply individual material models and parameters to predict the procedure outcome. Our results indicate the high relevance of calcification location and size for intervention planning, which are not sufficiently considered at this time. Our analysis can further provide guidance for accurate, patient-specific device positioning and future adaptations to stent design.

DICOM for Implantations—Overview and Application

Surgeons have to deal with many devices from different vendors within the operating room during surgery. Independent communication standards are necessary for the system integration of these devices. For implantations, three new extensions of the Digital Imaging and Communications in Medicine (DICOM) standard make use of a common communication standard that may optimise one of the surgeons presently very time-consuming daily tasks. The paper provides a brief description of these DICOM Supplements and gives recommendations to their application in practice based on workflows that are proposed to be covered by the new standard extension. Two of the workflows are described in detail and separated into phases that are supported by the new data structures. Examples for the application of the standard within these phases give an impression of the potential usage. Even if the presented workflows are from different domains, we identified a generic core that may benefit from the surgical DICOM Supplements. In some steps of the workflows, the surgical DICOM Supplements are able to replace or optimise conventional methods. Standardisation can only be a means for integration and interoperability. Thus, it can be used as the basis for new applications and system architectures. The influence on current applications and communication processes is limited. Additionally, the supplements provide the basis for further applications, such as the support of surgical navigation systems. Given the support of all involved stakeholders, it is possible to provide a benefit for surgeons and patients.

Implantation of personalized, biocompatible mitral annuloplasty rings: feasibility study in an animal model

OBJECTIVES Implantation of an annuloplasty ring is an essential component of a durable mitral valve repair. Currently available off-the-shelf rings still do not cover all the variations in mitral annulus anatomy and pathology from subject to subject. Computed tomography (CT) and echo imaging allow for 3-D segmentation of the mitral valve and mitral annulus. The concept of tailored annuloplasty rings has been proposed although, to date, no surgically applicable implementation of patient-specific annuloplasty rings has been seen. The objective of this trial was to prove the concept of surgical implantation of a model-guided, personalized mitral annuloplasty ring, manufactured based on individual CT-scan models. METHODS ECG-gated CT angiography was performed in six healthy pigs under general anaesthesia. Based on the individual shape of the mitral annulus in systole, a customized solid ring with integrated suturing holes was designed and manufactured from a biocompatible titanium alloy by a rapid process using laser melting. The ring was implanted three days later and valve function was assessed by intraoperative echocardiography. The macroscopic annulus-annuloplasty match was assessed after heart explantation. RESULTS CT angiography provided good enough image quality in all animals to allow for segmentation of the mitral annulus. The individually tailored mitral rings were manufactured and successfully implanted in all pigs. In 50%, a perfect matching of the implanted ring and the mitral annulus was achieved. In one animal, a slight deviation of the ring shape from the circumference was seen postoperatively. The rings implanted in the first two animals were significantly oversized but the deviation did not affect valve competence. CONCLUSIONS CT image quality and accuracy of the dimensions of the mitral annulus were sufficient for digital modelling and rapid manufacturing of mitral rings. Implantation of individually tailored annuloplasty rings is feasible.

Stent Maps — Comparative Visualization for the Prediction of Adverse Events of Transcatheter Aortic Valve Implantations

Transcatheter aortic valve implantation (TAVI) is a minimally-invasive method for the treatment of aortic valve stenosis in patients with high surgical risk. Despite the success of TAVI, side effects such as paravalvular leakages can occur postoperatively. The goal of this project is to quantitatively analyze the co-occurrence of this complication and several potential risk factors such as stent shape after implantation, implantation height, amount and distribution of calcifications, and contact forces between stent and surrounding structure. In this paper, we present a two-dimensional visualization (stent maps), which allows (1) to comprehensively display all these aspects from CT data and mechanical simulation results and (2) to compare different datasets to identify patterns that are typical for adverse effects. The area of a stent map represents the surface area of the implanted stent - virtually straightened and uncoiled. Several properties of interest, like radial forces or stent compression, are displayed in this stent map in a heatmap-like fashion. Important anatomical landmarks and calcifications are plotted to show their spatial relation to the stent and possible correlations with the color-coded parameters. To provide comparability, the maps of different patient datasets are spatially adjusted according to a corresponding anatomical landmark. Also, stent maps summarizing the characteristics of different populations (e.g. with or without side effects) can be generated. Up to this point several interesting patterns have been observed with our technique, which remained hidden when examining the raw CT data or 3D visualizations of the same data. One example are obvious radial force maxima between the right and non-coronary valve leaflet occurring mainly in cases without leakages. These observations confirm the usefulness of our approach and give starting points for new hypotheses and further analyses. Because of its reduced dimensionality, the stent map data is an appropriate input for statistical group evaluation and machine learning methods.

Three-dimensional template-based planning for transapical aortic valve implantation

Despite the lack of randomized trials comparing transapical aortic valve implantation (TA-AVI) with surgical aortic valve replacement, there is consensus that the approach may be advantageous for a high-risk group of patients. Nevertheless, several complications are associated with TA-AVI. Paravalvular leak resulting in aortic insufficiency of grade II or more is reported at a high incidence and promotes left ventricular dysfunction, hemolysis, and endocarditis. The onset of atrioventricular block (AVB) is correlated with the implantation of large-diameter valves in patients with a small annulus diameter. Although some of the reported complications are inherent to the procedure, others may be reduced by careful procedure planning. Three-dimensional template-based planning, as used in dental and orthopedic surgery, is proposed as an intuitive tool for this task. We present an initial retrospective patient trial of a system for 3-dimensional template-based TA-AVI planning.

Workspace definition for Navigated Control Functional Endoscopic Sinus Surgery

For the pre-operative definition of a surgical workspace for Navigated Control® Functional Endoscopic Sinus Surgery (FESS), we developed a semi-automatic image processing system. Based on observations of surgeons using a manual system, we implemented a workflow-based engineering process that led us to the development of a system reducing time and workload spent during the workspace definition. The system uses a feature based on local curvature to align vertices of a polygonal outline along the bone structures defining the cavities of the inner nose. An anisotropic morphologic operator was developed solve problems arising from artifacts from noise and partial volume effects. We used time measurements and NASAs TLX questionnaire to evaluate our system.

Computational Stent Placement in Transcatheter Aortic Valve Implantation

Transcatheter aortic valve implantation (TAVI) is a minimally invasive procedure to treat severe aortic stenosis in patients with a high risk for conventional surgery. In-silico experiments of stent deployment within patient-specific models of the aortic root have created an opportunity to predict stent behavior during the intervention. Current limitations in procedure planning are a primary motivator for these simulations. The virtual stent placement preceding the deployment phase of such experiments has major influence on the outcome of the simulation, but only received little attention in literature up to now. This work presents a methodical approach to patient-specific planning of placement of self-expanding stent models by analyzing experimental outcomes of different sets of boundary conditions constraining the stent. As a results, different paradigms for automated or expert guided stent placement are evaluated, which demonstrate the benefits of virtual stent deployment for intervention planning. To build a predictive planning pipeline for TAVI we use an automatic segmentation of the aorta, aortic root and left ventricle, which is converted to a finite element mesh. The virtual stent is then placed along a guide wire model and deployed at multiple locations around the aortic root. The simulation has been evaluated using pre- and post-interventional CT scans with an average relative circumferential error of 4.0% (±2.5%), which is less than half of the average difference in circumference between individual stent sizes (8.6%). Our methods are therefore enabling patient-specific planning and provide better guidance during the intervention.