Aswan Heart Centre Science & Practice Series - Volume 2011, Issue 1

Background: Achieving competence in transoesophageal echocardiography (TOE) requires a clear understanding of cardiac anatomy as well as an ability to correlate two-dimensional (2D) echocardiographic images with the three-dimensional (3D) structures which they represent. Training in the technique is a long process, which may also be hampered by insufficient access to teaching in the clinical environment. These challenges would be met by a simulator which demonstrates detailed cardiac anatomy with a previously unavailable degree of accuracy.

Methods: A TOE simulator system was created by collaboration with a wide range of clinical specialists and a post-production company skilled in the generation of computer graphics and special effects for the film industry. The core of the system is an animated, accurate and detailed virtual heart. Echocardiographic simulation was developed to provide a real-time display of ultrasound images alongside the 3D anatomical correlate of the imaging plane.

Results: A freely interactive animated model of the heart was created as the basis for ultrasound simulation. Creation of a mannequin simulator which drives the software allowed reproduction of the practical experience of the TOE procedure.

Conclusions: Partnership with groups with a wide diversity of skills can result in a simulator teaching tool of high fidelity.

Transcatheter aortic valve implantation (T-AVI) has shown good results in high-risk patients with severe aortic stenosis. Throughout the whole process of T-AVI, different imaging modalities are indispensable. Preoperatively, multislice computed tomography, angiography and transesophageal echo (TEE) are utilized for patient selection, valve selection, approach selection and the planning of implant placement. Intraoperatively, angiography and TEE are used for controlling placement of the guidewire and valve positioning. Quality control and follow-up require TEE imaging and can require additional CT or angiography studies. In the first half of this paper, we discuss the applicability of different imaging modalities for T-AVI in the light of the current best practice.

In the second half of this paper, we present an overview on research projects in medical engineering which aim at development of image-based methods for increasing patient safety during T-AVI. Template-based implantation planning, as it is applied in dental, orthopedic and other surgical disciplines, is proposed as an aid during implant selection in order to help reduce the incidence of complications such as atrioventricular node block and paravalvular leaks. Current research tries to apply state-of-the-art engineering techniques, such as computational fluid dynamics to optimize valve selection and positioning. For intraoperative assistance during valve positioning, real-time image processing methods are proposed to track target landmarks and the stented valve.

Aortic valve stenosis is the most common form of acquired valvular disease, with a prevalence of 1% to 2% in people over the age of 65 years. Untreated, the presence of severe symptoms is associated with a life expectancy of less than 5 years. Relatively little is known about the role of the cells within the valve or the regulatory pathways that are involved in the onset and progression of the disease. The aim of this article is to review the role played by valve interstitial and endothelial cells and highlight the role of pathways and individual mediators that have been implicated in playing a role in the disease process. This includes mediators that regulate pro- and anti-calcification mechanisms. The clinical significance of calcium within the valve is discussed, as are the therapeutic opportunities that may allow for development of a medical therapy for aortic stenosis. Understanding the molecular and cellular mechanism of valve calcification will allow development of alternative therapies to surgical replacement of the valve and improve prognosis of patients with aortic stenosis.

Clinical echocardiography began as a one-dimensional (1D) technique using initially the A-mode (Amplitude mode) and then the M-mode (time-motion mode) with dedicated investigators exploring the potential applications. The development of two-dimensional (2D) echocardiography expanded the applications and resulted in more widespread applications of the technique. In order to overcome the problem of examining three dimensional (3D) structures, such as the heart with its intricate anatomy, several windows for 2D imaging have been developed. This approach requires a mental reconstruction of the intracardiac anatomy based on multiple 2D imaging planes. A need to define the mitral valve anatomy as related to emerging valve repair techniques resulted in development of systematic transesophageal multiplane images [1,2]. These have permitted accurate assessment of the valve pathology based on mental reconstruction of 3D anatomy with varying success [3]. Even when successful, this approach does not lend itself to easy communication with the surgeon, depending on his/her familiarity with echocardiographic imaging planes. The advent of 3D echocardiography promises to permit more consistent and accurate evaluation of the valvular and other cardiac structures and provide for more effective communication between the echocardiographer and the surgeon.

Prosthesis-patient mismatch (PPM) is present when the effective orifice area of the inserted prosthetic valve is too small in relation to body size. Its main hemodynamic consequence is to generate higher than expected gradients through normally functioning prosthetic valves. The purpose of this review is to present an update on the present state of knowledge with regards to diagnosis, prognosis and prevention of PPM. PPM is a frequent occurrence (20%–70% of aortic valve replacements) that has been shown to be associated with worse hemodynamics, less regression of left ventricular hypertrophy, more cardiac events, and lower survival. Moreover, as opposed to most other risk factors, PPM can largely be prevented by using a prospective strategy at the time of operation.