Aren’t large orifices (like other valves offer) best for the patient?
No, it’s counter intuitive but bigger is not always better. It’s true that the larger the valve is, the less resistance there is to flow, but this mainly applies to smaller hearts. At physiological flow rates, the benefit rapidly diminishes beyond a certain size and is overshadowed by the increasing mechanical stresses, backflow, closing impact, wear and blood damage. On-X LTI carefully considered the orifice area of each valve size and determined that with On-X valve’s efficient flow, the 25 mm size is the “optimum orifice size” to maximize patient benefit and minimize risk. The hemodynamic performance of the On-X valve is second to none. Not only did MCRI resist the temptation to make the valves unnecessarily large, they also designed them with features like “soft landing” to minimize stresses in all sizes.
If the flared inlet is as important as you say, why don’t other companies use it?
That’s a good question. One obstacle for the competition is that it would be very difficult to manufacture a flared valve like the On-X valve because of the brittleness of silicon-alloyed carbon. On-X carbon was the key to the manufacturability of the On-X valve design. Second, prior to the On-X valve there were no successful flared valves to emulate. Most current bileaflet valves emulate the St. Jude valve because it was the first successful bileaflet valve and the market leader. Future valves, we feel, will emulate the hemodynamic features of the On-X valve, including its very effective inlet flare.
Your valve has new features, but what really distinguishes your valve from the rest?
Our valve design includes several inspired innovations that we proudly present. But regardless of how many improvements or differences we tout, it is the clinical performance—how it performs in the body—that truly distinguishes one valve from another. On-X clinical results are excellent so far, perhaps the best of any mechanical valve. Over time, the results should improve even more since greater long-term experience typically reduces complication rates. Additionally, over the years the On-X valve’s generous length will be quietly preventing the performance degradation caused by tissue impingement and overgrowth that can be experienced with short valves.
Why isn’t your valve available at my hospital?
Acceptance of a new medical product can be slow until its benefits are widely known. On-X LTI is working hard to make it known that the On-X valve is not just another mechanical valve but is operating at a new performance level. We are making progress in that regard and we feel our valve will eventually be available at your hospital. When the awareness of the valve reaches the patient level, and patients begin requesting On-X valves by name, we will have succeeded.
Other companies mention the goal of mechanical valves without anticoagulant therapy. Is that really a possibility?
The durability of mechanical valves makes them very attractive, but anticoagulation therapy is their unwelcome companion. It’s understandable that all mechanical valve manufacturers, including On-X LTI, wish that it could be avoided. But thrombosis (clotting) remains the number one concern. On-X LTI has taken significant measures to alleviate the known causes of thrombosis i.e., surface roughness, cavitation, turbulence, stagnation and silicon carbide. The full degree to which we have succeeded cannot be known immediately because any attempt to reduce or eliminate anticoagulants puts a patient at potential risk. Therefore, On-X LTI cannot recommend a change of anticoagulation therapy policy from prior mechanical valves.
In a large population of recipients, however, a certain percentage of patients do not follow their anticoagulant program. Evaluation of these patients offers a glimpse at the potential of the valve. Preliminary evidence strongly suggests that the On-X recipients fare better with sub-optimal therapy than recipients of other mechanical valves. Only time and extended research will prove whether or not the On-X valve truly tolerates reduced anticoagulant therapy.
Are tissue valves better than mechanical valves?
Compared to contemporary mechanical valves, tissue valves produce fewer bleeding problems with reduced anticoagulation therapy. But tissue valves are prone to fatigue failure and begin to deteriorate in six to nine years. About half have failed after approximately thirteen years. When that happens, recipients face another serious surgery at a current cost of about $60,000. Mechanical valve recipients need not be concerned about valve failure but must adhere to a more rigorous anticoagulation therapy. Manufacturers are working to minimize the shortcomings of both valve types, with On-X LTI and On-X leading the way for mechanical valves.
Can a mechanical valve fail, and if so, how?
The beauty of a mechanical valve is that it never wears out. There have been, however, extremely rare instances of component breakage that causes failure. Knowing this, On-X LTI has taken every precaution to reduce the possibility of such occurrences, and none have been experienced. Another possible cause of valve failure arises from tissue that overgrows the valve and interferes with its function. The On-X valve’s extended length provides a reassuring barrier to such overgrowth—more protection than any other valve can offer.
Your valve is longer than the others I’ve looked at. Why?
Intuitively, a short valve might seem better because the flow path through it is shorter. In reality, more length is required to organize the flow to a non-turbulent state, which actually reduces flow resistance and increases flow volume through the valve. That’s just one way the length of the On-X valve works better for the patient. The extra length serves other important functions as well. The valve’s leaflets are able to close to more of a “V” profile which means they don’t travel so far and fast to close. This reduces the volume of reverse flow. The length also provides extra protection from tissue overgrowth into the valve, which could interfere with the valve’s function. So there are very good reasons for making the valve longer. In fact, the On-X valve’s length is about the same length as that of the natural valve.
So your carbon doesn’t have silicon. Why is that so important?
Purity and strength are undeniable advantages that we discuss throughout this site. But people outside the valve industry probably can’t fully appreciate how much more it means to us. First of all, we couldn’t have made the On-X valve with traditional carbon. The silicon makes it too weak and brittle. In addition to our pure non-thrombogenic surfaces, On-X carbon technology lets us “coat to size” creating a smooth contoured surface that does not require grinding. Additionally, On-X carbon is a “green” product. Our new processes are so clean that we can operate our factory in an office building. By eliminating the corrosive chemicals necessary for alloying the carbon and neutralizing waste we’ve reduced industrial impact on the environment. The On-X processes increase reliability and improve the workplace. On-X carbon is beneficial in every aspect.
I’m convinced your valve is the best, but my doctor uses a different valve. What should I do?
People are most comfortable with what they are familiar with and that’s especially true when the stakes are high, as they are in this case. Although our valve is relatively new in the marketplace, acceptance is steadily growing. Encourage your physician to investigate the benefits of the On-X valves. We’re confident that once they are familiar with the valve it will become their valve of choice.
