Protocol for Relative Hydrodynamic Assessment of Tri-leaflet Polymer Valves

Summary

There has been renewed interest in developing polymer valves. Here, the objectives are to demonstrate the feasibility of modifying a commercial pulse duplicator to accommodate tri-leaflet geometries and to define a protocol to present polymer valve hydrodynamic data in comparison to native and prosthetic valve data collected under near-identical conditions.

Abstract

Limitations of currently available prosthetic valves, xenografts, and homografts have prompted a recent resurgence of developments in the area of tri-leaflet polymer valve prostheses. However, identification of a protocol for initial assessment of polymer valve hydrodynamic functionality is paramount during the early stages of the design process. Traditional in vitro pulse duplicator systems are not configured to accommodate flexible tri-leaflet materials; in addition, assessment of polymer valve functionality needs to be made in a relative context to native and prosthetic heart valves under identical test conditions so that variability in measurements from different instruments can be avoided. Accordingly, we conducted hydrodynamic assessment of i) native (n = 4, mean diameter, D = 20 mm), ii) bi-leaflet mechanical (n= 2, D = 23 mm) and iii) polymer valves (n = 5, D = 22 mm) via the use of a commercially available pulse duplicator system (ViVitro Labs Inc, Victoria, BC) that was modified to accommodate tri-leaflet valve geometries. Tri-leaflet silicone valves developed at the University of Florida comprised the polymer valve group. A mixture in the ratio of 35:65 glycerin to water was used to mimic blood physical properties. Instantaneous flow rate was measured at the interface of the left ventricle and aortic units while pressure was recorded at the ventricular and aortic positions. Bi-leaflet and native valve data from the literature was used to validate flow and pressure readings. The following hydrodynamic metrics were reported: forward flow pressure drop, aortic root mean square forward flow rate, aortic closing, leakage and regurgitant volume, transaortic closing, leakage, and total energy losses. Representative results indicated that hydrodynamic metrics from the three valve groups could be successfully obtained by incorporating a custom-built assembly into a commercially available pulse duplicator system and subsequently, objectively compared to provide insights on functional aspects of polymer valve design.

Introduction

Heart valve disease often results from degenerative valve calcification¹, rheumatic fever², endocarditis^3,4 or congenital birth defects. When valve damage occurs, causing stenosis and/or regurgitation valve prolapse and cannot be surgically repaired, the native valve is usually replaced by a prosthetic valve. Currently available options include mechanical valves (cage-ball valves, tilting disk valves, etc.), homograft, and bioprosthetic valves (porcine and bovine valves). Mechanical valves are often recommended for younger patients based on their durability; however the patient is required to remain on anticoagulant therapy to....

Protocol

1. Preparation

1. Design and fabricate an assembly to accommodate a tri-leaflet valve geometry. This will at minimum include a valve holder to suture-in the valve leaflets and a tube to house the valve holder and surrounding accessories to secure the assembly onto the pulse duplicator system. In our case, we utilized a commercially available pulse duplicator system available from ViVitro Labs Inc. (Victoria, BC). Valve holder design as well as pre and post assembly configurations are depicted in Figure 1.
2. The entire loop will need to be primed prior to usage. This involves two steps: i) cleansing of the entire loop system using soap....

Results

Representative flow and pressure waveforms are shown in Figures 3, 4 and 5. The plots were averaged over the sample size of valves tested for each group, which was, n = 5, 4, and 2 valves for polymer, native porcine and bi-leaflet groups, respectively. The mean hydrodynamic metrics and the standard error of the mean for these sample sizes are presented in Table 1.

Discussion

In this study, we have demonstrated the utility of modifying a commercially available pulsatile duplicator unit to accommodate tri-leaflet valve geometries so that hydrodynamic testing of polymer and native porcine valves can be performed. Specifically in our case, the system modified was a ViVitro left heart and systemic simulator system (Figure 1a) controlled via the ViViTest data acquisition system (ViVitro Systems, Inc, Victoria, BC, Canada). However, the system is not unlike several in vitro

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Pump	ViVitro Labs		http://vivitrolabs.com/products/superpump/
Flow Meter and Probe	Carolina Medical	Model 501D	http://www.carolinamedicalelectronics.com/documents/FM501.pdf
Pressure Transducer	ViVitro Labs	HCM018
ViVitro Pressure Measuring Assembly	ViVitro Labs	6186
Valve holder	WB Engineering		Designed by Florida International University. Manufactured by WB Engineering
Pulse Duplicator	ViVitro Labs	PD2010	http://vivitrolabs.com/wp-content/uploads/Pulse-Duplicator-Accessories1.pdf
Pulse Duplicator Data Acquisition and Control System, including ViViTest Software	ViVitro Labs	PDA2010	http://vivitrolabs.com/products/software-daq
Porcine Hearts and Native Aortic Valves	Mary's Ranch Inc
Bi-leaflet Mechanical Valves	Saint Jude Medical		http://www.sjm.com/
High Vacuum Grease	Dow Corning Corporation		http://www1.dowcorning.com/DataFiles/090007b281afed0e.pdf
Glycerin	McMaster-Carr	3190K293	99% Natural 5 gal
Phosphate Buffered Saline (PBS)	Fisher Scientific	MT21031CV	100 ml/heart
Antimycotic/Antibiotic Solution	Fisher Scientific	SV3007901	1 ml in 100 ml of PBS/heart; 20 ml for ViVitro System
NaCl	Sigma-Aldrich	S3014-500G	9 g/L of deionized water
Deionized Water	EMD Millipore Chemicals		Millipore Deionized Purification System. 1.3 L for ViVitro System, 200 ml for heart valve dissection process