FIMH09  Keynotes lectures abstracts

Robert Howe, Director of Harvard Biorobotics Laboratory

Harvard School of Engineering and Applied Sciences, Cambridge, MA 02138, USA

Web : http://people.seas.harvard.edu/~howe/

Title : "Fixing the Beating Heart : Ultrasound Guidance for Robotic Intracardiac Surgery"

Abstract

To treat defects within the heart, surgeons currently use stopped-heart techniques. These procedures are highly invasive and incur a significant risk of neurological impairment. We are developing methods for performing surgery within the heart while it is beating. New real-time 3-D ultrasound imaging allows visualization through the opaque blood pool, but this imaging modality poses difficult image processing challenges, including poor resolution, acoustic artifacts, and data rates of 30 to 40 million voxels per second. To track instruments within the heart we have developed a Radon transform-based algorithm. Implementation using a graphics processor unit (GPU) enables real-time processing of the ultrasound data stream. For manipulation of rapidly moving cardiac tissue we have created a fast robotic device that can track the tissue based on ultrasound image features. This allows the surgeon to interact with the heart as if it was stationary. Our in vitro studies show that this approach enhances dexterity and lowers applied forces. To complete integration of ultrasound imaging with the robotic device we have developed a predictive controller that compensates for the imaging and image processing delays to ensure good tracking performance. We will present applications of this technology in atrial septal defect closure and mitral valve annuloplasty procedures, demonstrating the potential for improved patient outcomes.

Andrew D. McCulloch, Director of Cardiac Mechanics Research Group

University of California San Diego, La Jolla, CA 92093-0412, USA

Web: http://cmrg.ucsd.edu/

Title : "Multi-scale modeling of excitation-contraction coupling in the normal and failing heart"

Abstract

The excitation-contraction coupling properties of cardiac myocytes isolated from different regions of the mammalian ventricular walls vary considerably, but their effects on integrated ventricular electromechanical function is poorly understood. We developed a detailed model of excitation-contraction coupling model with region-dependent parameters for epicardial, mid-myocardial and endocardial myocytes. Incorporating these cell models into three-dimensional models of ventricular action potential propagation, we gained new insights into the mechanisms of arrhythmia formation due to mutations in genes associated with the LQT1 and LQT3 variants of long-QT syndrome.

Next we incorporated the cell models into fully coupled finite element models of ventricular electromechanics coupled to a close-loop lumped parameter model of the circulation. Comparing this model with one in which heterogeneous myocyte parameters were assigned randomly throughout the mesh while preserving the total amount of each cell subtype, we observed similar transmural patterns of fiber and cross-fiber strains at end systole, but major differences in fiber strain distributions at earlier times during systole. Hemodynamic function, including peak left ventricular pressure, maximum rate of left ventricular pressure development, and stroke volume were largely unchanged between in the models.

We also modeled ventricular electromechanics in the dyssynchronous failing dog heart and examined the relative roles of dilation, negative inotropy, negative lusitropy and electrical dyssynchrony on global and regional function. The analysis suggested that there is significant interactions between dilation and dyssynchrony especially on regional mechanics.

Finally, we present initial findings on a preliminary clinical study to test the ability of such multi-scale models of electromechanics in the failing heart to predict clinical outcomes of cardiac resynchronization therapy in patients with congestive heart failure. New methods for patient-specific cardic modeling will be presented.

Supported by : NIH, NSF, UC Discovery, Medtronic

Terry Peters, Scientist

Robarts Research Institute, Ontario N6A 5K8 , USA

Web :  http://www.imaging.robarts.ca/~tpeters/

Title : "Virtual Environments to Guide Cardiac Interventions"

Abstract

Minimally invasive beating heart intracardiac surgery is an area of research with many unique challenges. Surgical targets are in constant motion in a blood-filled environment that prevents direct line-of-sight guidance. To compensate for the lack of direct vision, surgeons need reliable information regarding the surgical targets and surrounding anatomy to enable tool manipulation during therapy delivery.

We have developed a novel method for approaching multiple targets inside the beating heart, and describe our procedure for accessing them under virtual-reality (VR)-assisted image guidance. The surgical platform integrates real-time ultrasound imaging with virtual models of the surgical instruments, along with virtual cardiac anatomy acquired from pre-operative images.

Dynamic, pre-operative, subject-specific cardiac models can predict the location of anatomical features of interest and surgical targets throughout the cardiac cycle, and provide the surgeon with anatomical context –“the bigger picture” of the surgical field - not intuitively displayed via real-time ultrasound. Moreover, an intra-operatively-suitable registration technique is used to merge the pre- and intra-operative data. This approach employs easily identifiable features from both datasets, does not significantly lengthen the procedure, and provides a desired alignment (within 5 mm) of the pre-operative models and intra-operative ultrasound data in the region of interest.

We conducted extensive in vitro studies aimed at assessing the operator’s ability to accurately navigate tracked surgical instruments to dynamic intracardiac targets under augmented reality guidance, via both trans-mural access and transluminal “therapy delivery”. Augmented reality-guided assisted therapy led to significantly more accurate targeting (1.2 mm) compared to ultrasound image guidance alone (>10 mm), accompanied by a reduction of procedure time by half. Moreover, we have performed preliminary in vivo acute studies on porcine models, and demonstrated successful prosthesis positioning for beating-heart septal defect repair and mitral valve implantation via direct surgical access, using the navigation facilities provided by our augmented reality environment.

While still in their infancy, these results demonstrate the promise of ultrasound-enhanced model-guided environments for minimally-invasive cardiac therapy, whether it is delivered by a catheter introduced into the vascular system, or via a cannula inserted through the heart wall.