Applications of the visible heart for cardiac valve repair and replacement devices.

Abstract

The Visible Heart® methodologies utilize an isolated heart apparatus for the investigation of large mammalian hearts, such as human, swine, canine, or sheep. In vitro, the hearts are perfused with a clear buffer, allowing for real-time, intracardiac imaging of a beating heart. These methodologies have been developed, enhanced, and employed at the University of Minnesota for over ten years, with the general methods having been previously described. The primary focus of earlier studies was on lead implantation and assessments of functional anatomy. My work was to investigate how this unique experimental setup could be optimized to better understand valve function. In addition, I designed subsequent experiments as a means to better design products for the repair and/or replacement of pathological cardiac valves. In order to achieve my desired thesis goal, it was paramount to gain a thorough understanding of cardiac anatomy. As such, a review of the four main cardiac valves is provided in Chapter 1. The goal of this chapter is to familiarize the reader with current nomenclature of the cardiac valves as well as the important anatomical features associated with each. In Chapter 2, the capabilities and limitations of the Visible Heart®, in its current state, are discussed in context of the design process for cardiac valve repair and/or replacement products. To this end, the following areas are identified as applications for the Visible Heart® that can aid valve repair and replacement: (1) Functional Anatomy, (2) Device Delivery and Device/Tissue Interactions, (3) Chronic Model Development and Acute Valve Assessment, (4) Acute Assessment of Surgical Repairs, (5) Pre-clinical Human Heart In Vitro Testing, and (6) Early Prototype Testing for Designers. Chapters 3-7 provide detailed examples of employing Visible Heart® methodologies as they relate to each of these areas. The functional anatomy affecting two percutaneous mitral valve repair procedures is discussed in Chapters 3 and 4. Chapter 5 investigates the delivery and device/tissue interactions of a transcatheter pulmonary valve. A chronic animal model of dilated cardiomyopathy was developed in which mitral regurgitation due to ventricular remodeling was observed after several weeks of pacing; this model is now available within the Visible Heart® for acute assessment of devices seeking to treat this valve pathology (Chapter 6). Chapter 7 then looks at the acute assessment of the "edge-to-edge" mitral valve repair technique following induced P2 prolapse and provides control data for any device seeking to mimic this repair procedure percutaneously. Perfusion-fixed human specimens were utilized in Chapters 3 and 4, and a reanimated human heart was utilized for in vitro testing in Chapter 5. Finally, many early prototypes have been studied and tested in our laboratories using the Visible Heart® methods, but it is beyond the scope of this thesis to discuss the details of these studies. This work has advanced our understanding of the capabilities and limitations of a large mammalian, isolated heart preparation as it relates to the design processes for valve replacement and/or repair devices. This work is not an exhaustive list, but rather the beginning of many potential studies that will now be better designed based upon the capabilities and limitations I have identified. Additionally, the Visible Heart® is a dynamic system that will continue to advance and add capabilities, which will only serve to make it more important in the field of valve assessment.