Here is a link to some of my thoughts on mechanical valve selection from a previous post. The first part discusses some issues I had with valve marketing that we have already beaten to a pulp so feel free to disregard that. The rest of the message offers my thoughts on undergoing a mechanical valve replacement.
http://www.valvereplacement.com/forums/showthread.php?p=332857#post332857
On a previous thread, I had intended to respond to dtread?s entry on how he went about selecting his mechanical valve. Given the activity and discussion on this thread, let me pick it up here.
Earlier in this thread,
AlCapshaw2 opined,
?To my mind, the BIG feature of the On-X Valves are that they have a greatly reduced propensity for clot formation, even with NO anti-coagulation as demonstrated by the African study where many patients were non-compliant in taking their Coumadin / Warfarin. This bodes well for those times when one may need to go OFF anti-coagulation for other invasive procedures / surgeries.?
Given what I believe is a lack of good science that exists in support of his opinion, I feel the need to offer up my thoughts on valve data. Forgive my long winded message. It is not an easy subject to condense to sound bites.
In medical science, a blinded randomized prospective trial is the Holy Grail for determining whether one product or procedure is better than another. As an example, if you wanted to determine if one valve was better than another, you would find a good surgeon and have him/her implant 500 valves. Before each case, they would flip a coin to determine whether the patient gets Brand A or Brand B and then they would follow those patients for an extended period of time to determine complication rates and outcomes. This eliminates most, but not all of the variables that can affect the outcome of the study and it would provide a conclusion with a strong statistical and scientific basis.
With regards to mechanical heart valves, these types of studies almost never exist. They are very expensive to conduct and take very long periods of time to accumulate enough data to be significant. However, if you were a valve manufacturer and had a valve that you really believed was superior to SJM for example, wouldn?t it make sense to fund a randomized study? Put your valve against SJM head to head and in a few years you would have great scientific data that unequivocally showed your valve was superior. Simple. So why don?t the manufacturers do it? Because they know that after spending lots of time and money on a study like that, at best it will show their valve as equivalent to the others. They know that good science will show all the mechanical valves to be comparable in performance. The link below is to a paper that has been posted before in the forum. It talks about valve studies and is a good reference for valve selection with regards to mechanical vs tissue and touches on studies and evidence. Note that they don?t discuss the brands of mechanical valve at all.
http://http://circ.ahajournals.org/cgi/content/full/117/2/253
In the absence of randomized studies, what happens? Individual medical centers collect data on their patients, sometimes pool it into a multicenter study and publish retrospective reviews of their experience. This is valuable, but it has significant limitations. Many variables enter into the information that is collected. The patient demographics of one center can vary widely from another center. The manner in which one center conducts follow up or the way they categorize complications can vary vs. another center. One may have older, sicker patients. There are all kinds of variables which makes comparing one center?s experience to another?s more of an apples to oranges comparison. For example, if one were to go back and look at a variety of studies on the SJM valve which has been the subject of over a thousand published papers, you would find a wide variance in the rate of thromboembolic complications even though the valve is the constant.
What does the valve company do? Their marketing departments slave over the data and find a way to ?cherry pick? it. Since the studies have variable results, they take the data from their best studies and compare it to the competitor?s less favorable studies. They do this particularly with complications such as thromboembolism and bleeding among others. They also do this with hemodynamic comparisons which can be highly variable. It is not good science, it is just marketing. I won?t spend the time getting into specifics that I have seen on websites or in advertising, but if you really want to get into that, send me a private email.
I will admit that years ago when I first started seeing On-X data, it was intriguing, although sometimes under the category of ?too good to be true?. I agree with surgeons who believe that all of the bileaflet mechanical valves are now so good that patient related factors are more of a determinant in outcomes than the mechanical valve itself. AlCapshaw2's opinion that the On-X has a greatly reduced propensity for clot formation rings very hollow when there isn?t a great propensity for clot formation in today?s mechanical valves to begin with.
And yet, at least on these forums, On-X is given a free pass when it comes to branding it as ?aspirin only? ?low dose? or ?reduced complication rates?. Please show me good science. Some point to Australian experience with no anticoagulation. Where is that published? Others point to African experience. Actually it is South African experience. I could look up the paper, but all I have to remember about it is that in the disclosure, it was noted that the principal author, a Dr. Williams I believe, is married to a woman who is the principal On-X sales distributor for South Africa. No potential for bias there??
On-X is not without some decent studies. One is titled:
Single-Center Experience with the On-X Prosthetic Heart Valve between 1996 and 2005 and the authors were Tossios, Reber, Oustria, Holland-Letz, Germing, Buchwald, and Laczkovicz from the University of Bochum, Bochum, Germany. At 10 year?s, it has reached a benchmark. Laczkovicz implanted the first On-X valve in the world if I have my facts straight so you know they feel good about the valve and the company. I would guess that they have as much if not more experience with the On-X valve than anybody in the world. With all of this experience and good will behind them, here are a couple of things they had to say:
"In the present study the linearized incidence rate of thromboembolic events of 1.49% per pt-yr for AVR and 1.61% per pt-yr for MVR was low but above all, in this series not superior to previously reported rates for other bileaflet valves. New generation bileaflet valves such as Sorin Bicarbon and ATS valves, demonstrated lower rates of thromboembolic events despite a reduced level of anticoagulation.?
And for all of you who are promoting low dose anticoagulation, this item:
?Inadequate or stopped anticoagulation, or low levels of anticoagulation, also rendered patients with an On-X valve prone to thromboembolic complications.?
Conclusion: After almost one decade of clinical experience in a single center, the On-X valve continues to be reliable and effective.
What else can one conclude? It is a good valve, but nothing extraordinary.
There is also a very critical point to note here about alleged aspirin only studies in Europe. I do recall an aspirin only study that was reported on at a surgical meeting a couple of years ago. If it was going well, don?t you suspect you would be hearing biannual if not quarterly updates? In spite of no updates, talk still persists on this forum about aspirin only regimens with On-X. The lead investigator on the aspirin only study was Axel Laczkovicz of Bochum, Germany, the first implanter of an On-X valve, loyal supporter, and an author of the paper we just talked about. And what did that paper say?
?Inadequate or stopped anticoagulation, or low levels of anticoagulation, also rendered patients with an On-X valve prone to thromboembolic complications.?
Short of On-X issuing a press release stating that the aspirin only study was stopped because of unacceptable complication rates, I don?t think the above could make it any clearer that you need to anticoagulate On-X just like the rest of the mechanicals. Heck, ATS has far longer experience with low dose anticoagulation than just about anybody. Bicarbon isn?t available in the US and there are SJM accounts as well as CarboMedics I would guess who have run their noncomplicated aortic valve patients at a INR low target below 2.0 for years. At home monitoring and stable maintenance of INR has been shown to be the key to lowering complications related to anticoagulation.
I am not here to disparage On-X. It is a good valve. Just not better based on the science that I have seen. Promoting it as such on this forum should not go unchallenged.
I will catch up on some other points as time allows.
The information above represents the opinions of the author who is not a medical professional.
Mr. Magoo
