The Vitality™ Heart Valve System

The VXi Exchangeable Valve System brings together the safety and longevity of time-proven surgical valves, with the least invasive access of the new wave of transcatheter valves. The VXi Vitality™ is based on the off-patent design principles of the industry leading Edwards Perimount™ valve which has demonstrated 18-year durability in some patients.

The Vitality™, however, is a two-part valve. The healed-in support frame of the valve remains in the heart, while the worn-out leaflet set can be quickly exchanged without open-heart surgery or cardiopulmonary bypass. The new leaflet set then provides the same years of service life as the original with no reduction in valve function.

The VALVEXCHANGE™ procedure can be done without open chest surgery or cardiopulmonary bypass. It can be done transapically, through a small incision between the ribs and a small hole in the apex of the heart, both of which heal readily. Minimally Invasive Surgery (MIS) is now performed routinely at many surgical centers. With the VALVEXCHANGE™ technology, off-pump MIS techniques can be applied to both the initial implant and subsequent exchanges later in life.

Unlike transcatheter valves, the advanced VALVEXCHANGE™ approach is without compromise. It offers minimally invasive, off-pump approach for the implant of a highly durable, long-lasting tissue valve, and exchangeable leaflets. Please see the Patient Dilemma Section for the compromises between Mechanical Valves, Tissue Valves and Transcatheter valves. TOP

The Exchangeable Tissue Valve

The design of the VXi Vitality™ exchangeable tissue valve grows out of the proven design features of the bovine pericardial heart valve – the Edwards Perimount™ valve. This valve is now off-patent, and the design features that give it its 18-year durability can now be implemented in the next generation of tissue valves. Visually, the Edwards Perimount™ and the VXi Vitality™ are nearly identical.

The main difference between the two valves is beneath the skin. In the Perimount™ valve, the frame that holds the leaflets is permanently connected to the base of the valve – to the sewing cuff. In the Vitality™, the frame is snapped onto the base and held securely by clips hidden within the stent posts. The system is designed to be released only by a specialized tool. Schematically, the components of the system are shown below.

The collapsible frame contains leaflets, made from chemically preserved bovine pericardium, that can be delivered in a collapsed state, expanded and seated in the permanent docking station, then re-collapsed later when replacement is required. The exchangeable components collapse into a size small enough to be inserted and removed through an incision in the heart, without requiring the patient to be placed on cardiopulmonary bypass. TOP

Valve Delivery and Exchange System:

The VALVEXCHANGE procedure is designed to be performed using a range of approaches, from open surgical to minimally invasive, to off-pump transapical, depending on the clinical indication of the patient and physician recommendation. The exchange tools are scalable between surgical and transapical approaches, and robust enough to extract the leaflet set regardless of the degree of fibrotic overgrowth. Schematically, the exchange tools are shown below.

The VALVEXCHANGE system has three tools that work in concert with each other. These are (i) valve stabilizer, (ii) valve removal tool, and (iii) valve insertion tool. All three tools nest within each other coaxially so that once one tool is aligned to the stent posts, all others become aligned also. The valve stabilizer grabs onto the docking station and the extraction tool grabs onto the exchangeable leaflet set. Relative force is then applied between the two tools to pull the leaflet set off the docking station. This relative force is applied by way of a handle, much like bicycle brake calipers squeeze the wheel without actually pushing left or right. In the a similar way, the exchange tool set applies a relative force between the two valve components, shielding the heart from any direct pulling or pushing. An animation of this, as applied to a transapical exchange system, can be viewed here. TOP

Transapical Implant and Exchange:

Our advanced, Second Generation product, the Vanguard ™ is currently in development. This valve offers not only a transapical exchange, but also the transapical implant of the original docking station. Unlike transcatheter valves, which suffer from geometrical instability and leaflet wrinkling as demonstrated in a clinical study, the VXi transapically-implanted docking station adheres to the three time-proven principles of good valve design:

(i) Flexible stent posts to cushion the closing leaflets
(ii) Central gap to accommodate leaflet extension
(iii) Absolute geometrical precision of 120 leaflet degree symmetry

This is because the VXi Vanguard™ is not fabricated from a compliant metal mesh, like most transcatheter valves. The docking station of the Vanguard™ is fabricated from a solid, yet collapsible, metal ring with far greater radial stiffness. Incorporated into the solid metal ring are the same three stent posts and clips of our surgically implantable docking station. These stent posts ensure that point (i) above is achieved and the metal ring ensures points (ii) Central Gap and (iii) 120 degree symmetry are maintained. The design of the Vanguard™ thus provides the geometrical precision that long-lived pericardial valves require. It is also repositionable during the implant procedure for precision placement.

Patients and physicians will have two options – surgical or transapical implant. Surgical implant (the Vitality™) enables the greatest effective orifice area and best hemodynamics. As with current technologies, transapical implant (the Vanguard™) does not enable excision of the calcified native leaflets and may thus result is a slightly smaller valve size. However, it avoids the open-chest approach to valve implantation which some patients may perfer. Both approaches offer the same long-lived bioprosthetic valve leaflets with the option for transapical, off-pump leaflet exchange and renewal. TOP

The Apical Introducer:

It is well known that prolonged time on cardiopulmonary bypass can lead to neurological deficit, and “cross-clamping” the aorta can liberate atheroma. It is the risk of these complications that have encouraged the development of “off-pump” surgical techniques. Transcatheter valve implantation is an emerging solution. Transcatheter valves, however, have durability limitations, caused largely by the need for collapse into a tight bundle for delivery via catheter. Delivery via the femoral artery also risks liberating atheroma and sometimes simply cannot be done due to torturous femoral arteries. Because of that, a larger proportion of transcatheter valves are delivered through the apex of the heart. Currently the technology used for transapical delivery is a larger version of the conventional catheter introducer/dilator. Images of conventional catheter introducers are shown at right. Typically, a wire is first pushed through the heart. A plastic dilator with a conical tip is then passed over the wire. Multiple dilators are switched in and out until the hole in the ventricle is large enough for the transcatheter valve to pass through. To close the hole, the standard approach is to place a “purse string” suture around the hole (see image right). When the suture is pulled tight, the tissue wrinkles up and closes the hole.

This approach is not optimal with respect to the heart. Making the hole the first time tears the heart muscle. In some patients with diseased hearts, these tears are difficult to close and propagate along natural cleavage planes within the heart. Closure with the purse string is also not ideal because a healthy heart is a thick, contracting muscule (see image right) that does not pucker up like cloth or thin tissue when the purse-string closure method is used. Insertion of transcatheter valves and closure of the heart in this way has led to the occasional rupture of the ventricle and bleed-out.

VXi has solved these problems with the Guiraudon Universal Cardiac Introducer (GUCI™) and is developing its use for transapical valve implant and exchange procedures (see image right). Like catheter-based approaches, it is less invasive, can be done on the beating heart but with the advantage of using rigid tools that give the surgeon direct tactile feedback. More importantly, the GUCI™ protects the heart from stretching and risk of tearing because it does not require dilation of the muscle tissue to obtain access.

Making a linear cut in the heart muscle and closing with suture, like done for skin incision (image right) is also not a good idea for heart muscle. Heart muscle is more friable and tears along natural cleavage planes. If a slit is made in the myocardium, like is typically done to the skin, it begins to tear away from the edge of the incision. It is well-known that to avoid crack propagation in most materials, the end of the crack is drilled out (see image right). This blunts the crack point, distributes the stresses over a larger area and stops the crack from growing. We use a similar strategy to safely access the interior of the heart. Instead of making a linear slit, a circular cutter is used to create a round access port. The GUCI™ is first sutured onto the heart by way of a “sewing cuff-like” ring. This is done by using deep interrupted sutures (see image right), or by way of the “G-Clip™” that is currently in development. A coring device is then inserted through the GUCI™ and an access port is then cut through the myocardium. The sewing cuff acts as a stress relief and the circular hole prevents crack propagation and tearing. Use of the GUCI™ thus protects the integrity of the heart muscle and avoids the tearing of the heart muscle that is required when the standard catheter introducer/dilator is used. After the procedure, the GUCI™ is folded over, cut and sutured to the myocardium without pulling on any of the original sutures out of the cuff. The hole that was cut in the muscle tissue remains protected by the GUCI™ until it heals and fills with scar tissue. The next time the valve is exchanged, the same scar tissues can be cored out.

The GUCI™ allows the passage of larger devices and tools in and out of the heart because it solves the hemostasis problem with a simple pinch of the flexible introducer – the GUCI™ does not need any internal check valves. Because it has a quick disconnect fitting, large tools and objects can be “back loaded” into the GUCI™ without having to pass them through the narrow seal of the tool adaptor. The GUCI™ is thus a combination introducer/closure device for more effective and safer access that conventional introducers that dilate, and purse-string closure that risks tearing..

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