An Ex Vivo Porcine Model for Hydrodynamic Testing of Experimental Aortic Valve Procedures and Novel Medical Devices

Summary

We present a method for mounting a porcine aortic valve on a pulse duplicator to test its hydrodynamic properties. This method can be used to determine the change in hydrodynamics after the application of an experimental procedure or novel medical device prior to use in a large animal model.

Abstract

The options for testing new cardiac procedures and investigative medical devices prior to use in an animal model are limited. In this study, we present a method for mounting a porcine aortic valve in a pulse duplicator to evaluate its hydrodynamic properties. These properties can then be evaluated before and after the procedure under investigation is performed and/or the investigative medical device is applied. Securing the inflow segment presents some difficulty owing to the lack of circumferential myocardium in the left ventricular outflow tract. This method addresses that issue by securing the inflow segment using the anterior leaflet of the mitral valve and then suturing the left ventricular free wall around the inflow fixture. The outflow segment is secured simply by inserting the fixture into an incision in the superior aspect of the aortic arch. We found that specimens had significantly different hydrodynamic properties before and after tissue fixation. This finding induced us to use fresh specimens in our testing and should be considered when using this method. In our work, we used this method to test novel intracardiac patch materials for use in the valvular position by performing an aortic valve neocuspidization procedure (Ozaki procedure) on the mounted porcine aortic valves. These valves were tested before and after the procedure to assess the change in hydrodynamic properties in comparison to the native valve. Herein, we report a platform for hydrodynamic testing of experimental aortic valve procedures that enables comparison with the native valve and between different devices and techniques used for the procedure under investigation.

Introduction

Aortic valve disease represents a significant public health burden, particularly aortic stenosis, which affects 9 million people worldwide¹. Strategies to address this disease are currently evolving and include aortic valve repair and aortic valve replacement. In the pediatric population especially, there is a significant incentive to repair rather than replace the valve since currently available prostheses are prone to structural valve degeneration (SVD) and are not growth tolerant, requiring reoperation for re-replacement as the patient grows. Even the Ross procedure, which replaces the diseased aortic valve (AV) with the native pulmonary val....

Protocol

All research was performed in compliance with institutional guidelines for the care of animals.

1. Considerations and preparations for the experiment

1. Utilize a suitable pulse duplicator (PD) for the simulation of cardiac output through the AV. The PD will need to be able to accommodate biological materials and be able to be cleaned.
   1. Utilize PD settings appropriate for testing the AV: 70 mL displacement volume and 70 beats per minute (5 L/min cardiac output), 35% of the cardiac cycle in systole, 100 mmHg mean transvalvular pressure gradient, 120 maximum pressure gradient, and 80 minimum pressure gradi....

Results

The representative data collected from the pulse duplicator includes regurgitation fraction (RF), effective orifice area (EOA), and mean positive pressure difference (PPD). The RF and EOA, in particular, are used in the ISO standards for prosthetic valves (ISO 5840) and will be important to collect if prosthetic valve products are under investigation. The PPD offers information regarding how much pressure is required to open the valve and is commonly referenced when discussing prosthetic valve replacement

Discussion

The method presented here provides a platform for hydrodynamic testing of the AV in order to examine the effect of an experimental procedure or a novel medical device. By mounting the native aortic valve on a pulse duplicator machine, we are able to determine the effect of the experimental procedure on all the hydrodynamic parameters used in the investigation and approval of novel valve prostheses (ISO 5840). This provides an opportunity to fine-tune procedures and prostheses prior to use in a large animal model.

Materials

Name	Company	Catalog Number	Comments
3D Printer	Ultimaker	Ultimaker S5	Used for printing custom fixtures for hydrodynamic testing
Crile-Wood Needle Driver	Emerald Instruments	2.0638.15	Used for suturing ventricle
Debakey Forceps	Jarit	320-110	Used for dissection and sample preparation (can use multiple if working with an assistant)
Ethanol 200 proof	Decon Labs Inc.	DSP-MD.43	Used for fixed tissue storage
Formalin 10%	Epredia	5701	Used for tissue fixation
Gerald Forceps	Jarit	285-126	Used for dissection and sample preparation
Glass jars	QAPPDA	B07QCP54Z3	Used for tissue storage
Glutaraldehyde 25%	Electron Microscopy Sciences	16400	Used for tissue fixation
HEPES 1 M buffer solution	Fisher	BP299-100	Used to make glutaraldehyde 0.6%
Mayo Scissors	Jarit	099-200	Used for cutting suture
Metzenbaum Scissors	Jarit	099-262	Used for dissection and sample preparation
O-ring	Sterling Seal & Supply Inc.	AS568-117	Used as a gasket on the end of the 3D printed fixtures
Polylactic acid resin	Ultimaker	1609	Used for 3D printing fixtures
Polyproplene suture	Covidien	VP-762-X	Used for suturing ventricle, tapered needle
Pulse Duplicator	BDC Laboratories	HDTi-6000	Used for hydrodynamic testing
Silk ties	Covidien	S-193	Used for ligating coronary arteries
Tonsil Clamp	Aesculap	BH957R	Used for coronary artery dissection
Zip ties (6 inch)	Advanced Cable Ties, Inc.	AL-06-18-9-C	Used for securing sample to fixtures, 157.14 mm long (6 inches), 2.5 mm wide
Zip ties (8 inch)	GTSE	GTSE-20025B.1000	Used for securing sample to fixtures, 203 mm long (8 inches), 2.5 mm wide