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Research Papers

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

[+] Author and Article Information
Michael R. Moreno

Department of Biomedical Engineering,  Texas A&M University, College Station, TX 77843-3120; CorInnova Incorporated, College Station, TX 77845michael.moreno@tamu.edu

Saurabh Biswas

Department of Biomedical Engineering,  Texas A&M University, College Station, TX 77843-3120

Lewis D. Harrison, Guilluame Pernelle

 CorInnova Incorporated, College Station, TX 77845

Matthew W. Miller, Theresa W. Fossum

 Texas A&M Institute for Preclinical Studies, Texas A&M University, College Station, TX 77843; Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Texas A&M University, College Station, TX 77943-4474

David A. Nelson

 Texas A&M Institute for Preclinical Studies, Texas A&M University, College Station, TX 77843

John C. Criscione

Department of Biomedical Engineering,  Texas A&M University, College Station, TX 77843-3120; CorInnova Incorporated, College Station, TX 77845

J. Med. Devices 5(4), 041008 (Nov 28, 2011) (9 pages) doi:10.1115/1.4004652 History: Received January 29, 2011; Revised July 09, 2011; Published November 28, 2011; Online November 28, 2011

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.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Normal, null, and inverted curvature in apex-to-base, radial plane (long axis). Direct cardiac compression devices designed to invert the curvature of the heart to increase ejection fraction are inducing aberrant strain patterns that are not likely conducive to restorative remodeling processes and/or cardiac rehabilitation.

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Figure 2

(Left) Illustration depicting the geometry and orientation of the Nitinol scaffold. (Right) Illustration of the device cross-section revealing the inner passive component, the outer active component and the location of the Nitinol scaffold between these two components.

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Figure 3

As the inner passive component bladder is filled with saline via a subcutaneous injection port it conforms to the shape of the heart and can therefore be used to fit the device to the heart and/or provide adjustable passive support or constraint

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Figure 4

Minimally invasive device delivery using the deployment tube and pericardial stabilization system with guidewires to ensure proper device placement

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Figure 5

(Top) LV volume during transition from no assist to 20 mmHg of assist. Note that though the end-diastolic volume (EDV) decreased with assist, the reduction in end-systolic volume (ESV) was greater; thus the stroke volume is actually increased. (Bottom) Device pressure during transition from no assist to 20 mmHg of active assist. Note that the device pressure goes from 0 mmHg during systole (before device activation) to 20 mmHg during systole (following device activation). The end-diastolic pressure (EDP) in the device is constant at 15 mmHg before assist begins and falls to 10 mmHg after assist starts.

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Figure 6

PV loops of the left ventricle were acquired during vena cava occlusion. Two cases were investigated, (1) no passive support, i.e., no saline in the passive component and (2) passive support with 40ml saline in the passive component of the device. As the preload is gradually reduced by slowly occluding the vena cava, the pressure-volume relationship is altered. The end-diastolic data points for each case are plotted. The resulting curve is the EDPVR. Note that support shifts the EDPVR to the left, which could be beneficial as disease tends to shift the EDPVR to the right.

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Figure 7

PV loops of the left ventricle for the esmolol induced failure state with 0 mmHg active assist transitioned to 20 mmHg active assist. The improved stroke work is evident in the increase in area.

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Figure 8

Comparison of the healthy, Esmolol failure, and assisted failure cases. Notice the significant improvement in CO and doubling of SW for the esmolol induced failure state when active assist of 20 mmHg is applied. As illustrated, CO and SW can be returned to healthy levels with assist.

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Figure 9

Dark regions near the heart wall correspond with the contrast filled inner passive component of the device. When activated, air fills the outer active component, which compresses the inner passive component of the device. Fluid in the passive component is displaced and pressure is applied uniformly to the heart.

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Figure 10

Deployed device with saline filled inner passive chambers conforming to the heart. Contrast was injected into the passive chambers for visual confirmation of placement and action.

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Figure 11

Gross pathological examination of device within pericardial sac: Pictures of device within the pericardial sac following acute, terminal study in a normal sheep are shown with the sac closed (left) and open (right) to reveal the device around the heart

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Figure 12

Pressure-volume loops of left ventricle prior to device deployment and after deployment. Stroke work and cardiac output were not significantly affected.

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Figure 13

The fluoroscopic images were not sufficient for quantitative analysis of cardiac curvature, though qualitative analysis revealed no substantial evidence of device induced curvature inversion

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Figure 14

(Left) The chambers of the device are designed such that the cavity takes on a cuplike shape when activated. This prevents device induced curvature inversion and also allows the heart to be held in place in the device via an intrinsic pneumatic attachment. (Right) As illustrated in this simple contour drawing of the Anstadt cup (see Anstadt 2009), conventional direct cardiac compression devices are designed to invert the curvature of the heart. Inversion of wall coverage is likely to lead to increased ejection fraction; yet such wall motion is abnormal or aberrant.

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