Lewis D. Harrison

Assessment of Minimally Invasive Device That Provides Simultaneous Adjustable Cardiac Support and Active Synchronous Assist in an Acute Heart Failure Model

One of the major maladaptive changes after a major heart attack or cardiac event is an initial decline in pumping capacity of the heart leading to activation of a variety of compensatory mechanisms, and subsequently a phenomenon known as cardiac or left ventricular remodeling, i.e., a geometrical change in the architecture of the left ventricle. Evidence suggests that the local mechanical environment governs remodeling processes. Thus, in order to control two important mechanical parameters, cardiac size and cardiac output, we have developed a minimally invasive direct cardiac contact device capable of providing two actions simultaneously: (1) adjustable cardiac support to modulate cardiac size and (2) synchronous active assist to modulate cardiac output. As a means of enabling experiments to determine the role of these mechanical parameters in reverse remodeling or ventricular recovery, the device was further designed to (1) be deployed via minimally invasive surgical procedures, (2) allow uninhibited motion of the heart, (3) remain in place about the heart via an intrinsic pneumatic attachment, and (4) provide direct cardiac compression without aberrantly inverting the curvature of the heart. These actions and features are mapped to particular design solutions and assessed in an acute implantation in an ovine model of acute heart failure (esmolol overdose). The passive support component was used to effectively shift the EDPVR leftward, i.e., counter to the effects of disease. The active assist component was used to effectively decompress the constrained heart and restore lost cardiac output and stroke work in the esmolol failure model. It is expected that such a device will provide better control of the mechanical environment and thereby provide cardiac surgeons a broader range of therapeutic options and unique intervention possibilities.

Development of a Non-Blood Contacting Cardiac Assist and Support Device: An In Vivo Proof of Concept Study

One of the maladaptive changes following a heart attack is an initial decline in pumping capacity, which leads to activation of compensatory mechanisms, and subsequently, a phenomenon known as cardiac or left ventricular remodeling. Evidence suggests that mechanical cues are critical in the progression of congestive heart failure. In order to mediate two important mechanical parameters, cardiac size and cardiac output, we have developed a direct cardiac contact device capable of two actions: (1) adjustable cardiac support to modulate cardiac size and (2) synchronous active assist to modulate cardiac output. In addition, the device was designed to (1) remain in place about the heart without tethering, (2) allow free normal motion of the heart, and (3) provide assist via direct cardiac compression without abnormally inverting the curvature of the heart. The actions and features described above were mapped to particular design solutions and assessed in an acute implantation in an ovine model of acute heart failure (esmolol overdose). A balloon catheter was inflated in the vena cava to reduce preload and determine the end-diastolic pressure-volume relationship with and without passive support. A Millar PV Loop catheter was inserted in the left ventricle to acquire pressure-volume data throughout the experiments. Fluoroscopic imaging was used to investigate effects on cardiac motion. Implementation of the adjustable passive support function of the device successfully modulated the end-diastolic pressure-volume relationship toward normal. The active assist function successfully restored cardiac output and stroke work to healthy baseline levels in the esmolol induced failure model. The device remained in place throughout the experiment and when de-activated, did not inhibit cardiac motion. In this in vivo proof of concept study, we have demonstrated that a single device can be used to provide both passive constraint/support and active assist. Such a device may allow for controlled, disease specific, flexible intervention. Ultimately, it is hypothesized that the combination of support and assist could be used to facilitate cardiac rehabilitation therapy. The principles guiding this approach involve simply creating the conditions under which natural growth and remodeling processes are guided in a therapeutic manner. For example, the passive support function could be incrementally adjusted to gradually reduce the size of the dilated myocardium, while the active assist function can be implemented as necessary to maintain cardiac output and decompress the heart.