Norm,
Pem, you're asking smart questions, and I'm guessing that you're already starting to find some answers, searching here and elsewhere. Reops for mech-valve people are hardly ever for valve failure per se. Other things do sometimes need surgery even if the valve is "permanent", or growths (pannus or veg from Endocarditis) can "jam" an intact valve. Those complications are much rarer than a tissue valve reaching its natural demise, so the longer-term re-op comparison is quite asymmetrical, in favor of the mechs. OTOH, the mech-valves' greater thrombogenesis and the bleeding risks from the lifelong ACT that's applied to counter that thrombogenesis, bring risks of mortality and morbidity that are roughly comparable to those of re-ops, at least in patients older than ~60-ish.
Thanks for your thoughtful reply! This position seems consistent with the "party line": that survivability is equivalent for tissue and mechanical valves when you exclude non-valve-related issues and consider both reop risk and ACT risks. However, I recently wrote to a well-respected German surgeon to ask about stentless valves, and in the discussion he mentioned that all things considered, mechanical valves have a survivability advantage over tissue valves. That was the first I had heard anyone suggest that.
This paper seems to provide a nice model for analyzing (in actuarial fashion) the comparative risks (both in terms of morbidity and mortality) of the valve types:
http://circ.ahajournals.org/cgi/reprint/117/2/253.pdf
One finding in this paper that seems to favor tissue valves is markedly lower morbidity. Also, something I didn't realize is that when a mechanical valve fails, it is often an emergent situation with significantly higher operative risk than an elective reop for a tissue valve. But since such a situation is so unlikely for a mech valve, the overall risk over time is mitigated.
The newer studies on tissue valves are showing longer lives, but we naturally only have good stats on valves that have been in use for decades, not today's "third generation" or "state of the art" valves. You haven't mentioned your age, and that's the biggest "independent variable" in determining the likely longevity (or "time to structural deterioration") of a tissue valve. Not only are younger people more likely to live longer than (say) a 15-year tissue valve, but they are also less likely to have a tissue valve last 15 years, for reasons that are only dimly understood. The profession is reasonably convinced that the reason is NOT the greater activity level of younger folk -- as if the valve "wears out" after a given number of beats -- but the dominant "consensus" opinions are vague. Of course, if they were less vague, they would point to effective ways to defeat that mechanism, and we apparently haven't found those yet.
Based on what little I know, I agree that tissue valve failure is probably not related to heart rate. Younger people, especially more active people, tend to have a lower heart rate while sedentary (and higher stroke volume), so more active people probably have over the course of years fewer heart beats than inactive or older people. However, active folks might produce (during activity) higher pressure gradients and so forth that result in increased turbulence and calcification. Just speculating of course. You probably know more than I do about this.
My own well-established valve has been studied by my own well-established cardiac-care team, in an article entitled "Hancock II Bioprosthesis for Aortic Valve Replacement: The Gold Standard of Bioprosthetic Valves Durability?" by Tirone E. David, MD, Susan Armstrong, MS, Manjula Maganti, MS, in Ann Thorac Surg 2010;90:775-781, abstract at ats.ctsnetjournals.org/cgi/content/abstract/90/3/775? . Only the abstract is free online, alas, though I've got a fax copy and have typed some key passages into posts here and there on this site. They say "Gold Standard of Bioprosthetic Valves Durability" because the 10-, 15-, and 20-year durability of this pig valve seems to exceed that of the Carpentier-Edwards Perimount (cow-pericardium) valve in all the age groups reported in the published studies. (Some earlier studies suggested that "cow" valves outlasted "pig" valves. I'm not clear whether that was wrong or whether something important changed, but I find the discussion in this article convincing that it's not true now -- at least for THIS pig valve, installed in THIS center.)
I guess you are a celebrity of sorts
These findings help me reconcile the fact that everyone else seems to be saying cow valves are better but my local surgeon says it's inconclusive and that he never makes clinical decisions on the basis of pig vs cow. Incidentally, if was surprised to discover that the valves used for percutaneous insertion (valve-in-valve by catheter) tend to be made from equine (horse) tissue.
My local surgeon had allowed me to choose between tissue and mechanical valve but reserves the choice of valve within those categories if I opt for a tissue valve. In other words, he will not permit me to choose the particular tissue valve, he would make that call operatively based on what he sees. I can see the rationale for this, but I wonder if it is common practice. Do most people choose their particular tissue valve or is it chosen for them? I imagine there are aspects of making this decision that are highly idiosyncratic to experience, comfort-level, patient, valve morphology, and subtle differences among tissue valve options that would suggest allowing the surgeon to make that call during the procedure.
Newer designs may well do even better, but there's no proof yet -- such is the nature of hindsight! E.g., the ATF horse-pericardium valve seems very attractive to me in a number of ways, but I think it hardly has a 5-year record "on the track".
The "market share", esp. in North America, has apparently been shifting rapidly from mech valves toward tissue valves, and the patient age where the inflection point comes has been shifting younger. Whether that primarily reflects the influence of (1) rational thought, (2) irrational patient choices, (3) surgeons' (and institutions') desire for long-term job security, or something else, is a matter of debate here and elsewhere.
Just as the tissue-valve durability studies may not reflect today's state-of-the-art, the best-documented numbers on re-op success and on Warfarin risks, have probably both been overtaken by improving reality. Many centers now do a LOT of re-ops, and their reported results are quite comparable to those (also fast improving) of first-time ops. And improving management of ACT levels -- especially with home INR testing -- has presumably significantly decreased the "twin risks" of thrombosis and bleeding on the mech-valve side.
I think I read at least one of the papers from which that notion originated (that reops have the same risk level as first time ops). But at a close reading what I gathered is that the risk is the same after you factor out all non-valve-related comorbities. But the fact remains that people are more likely to have other diseases as they age that could impact surgical risk of reop, so while it may be technically true that the reop risk is equivalent to first time op, I don't think there's practical value in that notion unless you think you are in the subpopulation that is less prone to age-related disease. If one assumes that one is average in their risk for age-related disease, then to me it makes sense to consider that the reop will likely be riskier. On the other hand, knowing this might induce someone with a tissue valve to do more preventive medicine in general with a high rate of return on investment. What do you think on this?
And then there are the personal values, weights, and preferences that get layered onto the uncertain facts!!
Re: your last question: A-fib is depressingly common after any OHS, certainly including HVR. I haven't heard that it's more common after re-ops, but that doesn't mean it isn't. Post-op Magnesium supplementation decreases the frequency significantly according to one study I've seen, but only from way too high to still too high.
Yesterday I went to my first real cardio rehab session, with hours of "meet the team" talking, as well as a mile of track-walking. The staff cardiologist told us that the approach with serious post-op A-Fib is shifting from "cure it" to "manage it" (mostly with beta-blockers and ACT). E.g., he asked for a show of hands for how many of us (~50?) cardio rehab subjects had gotten cardioversion to cure our A-Fib. Five guys put up their hands. Then he asked "And how many of you had your A-Fib return, after the cardioversion?" and FOUR of those FIVE guys stuck their hands back up! Then he asked the FIFTH guy when he had his cardioversion. "November," he said. "You're still young," the Cardiologist told him!!
Well-taken. At least in your informal study the incidence was about 10% compared to the 30% incidence of Afib I read about in a formal study.
Anyway, thanks a lot for all the helpful information. I'm digging hard and fast to learn what I can, but I am humbled and grateful for the experiential wisdom and perseverance of the folks represented on this site. Please let me know if you think I'm way off base with anything or have anything else to add.
