'per patient year' question

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Daniel758

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As far as stats, they aren’t cumulative like that. I’ve been event free for 32 years on warfarin. There is still a 2% chance this year of an event just like there was the first year I received my valve. But that’s a 2% chance among all patients, not me individually.
Yes, your chance this year is still 2% but your chance of having had a bleeding event over the last 32 years was around 48%. Essentially a coin flip and you did well.

Over the next 32 years, your chance of having a bleeding event is also 48%. I wish you luck once again on that coin flip.

Note: 1-(probability of not having an event ^32) is 48%

If they were cumulative, our friend @dick0236 would be having adverse events annually right now (55 years on warfarin) at a 110% chance! He’s at the same 2% risk.
No, Dick's chance of encountering a bleeding event over 55 years was around 67%, not 110%.

Note: The percentage will never go over 100% (and it's not linear). Look up Limit Theory in any first year Calculus book for why this is.

Think if it this way. X% of people die in car accidents annually. Now that you’ve been driving 30 plus years, do you feel like any time now you’re going to die when you get in a car?
Again, no. See above.

Superman, you're a reasonable guy, can you not see that this is a perfect example of why it's not a good idea for you guys to give out medical advice on this forum?

What you believed and offered as fact actually isn't fact.

What other "facts" are you guys giving out that aren't facts either? And how would you know?

Don't you think telling this guy that his chance of a bleeding event (significant or not) over a 30 year period is 2% when in fact the probability is actually 45% could make a difference in his decision making?


Side Note:

Could the probability of bleeding events over time and the consequences for their patients actually be a reason why a surgeon's preference may lean towards tissue and why the industry is trying to develop longer lasting tissue valves or mechanical valves that don't require warfarin?

Could it be possible that medical decisions by cardiac surgeons who have devoted their lives to extending the lives of people like us are not just based on some "surgeons trying to get repeat customers/greedy valve maker's churning profits, etc." conspiracy theory but on actual information/knowledge that they have and that you (and dare I say Pellicle) don't?
 

pellicle

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and … almond milk. (Ducks. Runs for cover at the suggestion of using Almond “milk”)
totally nothing wrong there dude, I personally prefer the Chinese brand ... Udder Li Almond milk

1668484017522.png


its 100% organic and vegan

1668483456992.png

But
 
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Superman

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Superman, you're a reasonable guy, can you not see that this is a perfect example of why it's not a good idea for you guys to give out medical advice on this forum?
You’re reading me wrong. I was saying if this misconception (odds increasing every year) were true, then….

But it isn’t true. This year, like any other year, it remains roughly a 2% chance (assuming that statistic is accurate). Of course I don’t think anyone has a 110% chance of a negative event.

I don’t disagree with the statistics as you say them and I don’t see how they disagree with any point that I’ve made. I also don’t see where I gave any medical advice beyond what you did (aiming to clear up a statistical misunderstanding) so get off your high horse please. Your incessant beating of that drum is more than obnoxious at this point.
 
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JW1970

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Thanks for the numbers, not far away from my first figures really and unsurprisingly they prove how important INR management is, in an theroretical world anyway.

To counter these figures, does anybody know stroke or bleed risk in patients with bio valves who are not taking warfarin? Would be interesting to plug these figures in also.

John.
 

Superman

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And/or even general population risk of clots or bleeds regardless of valve. It’s really the increase in risk that we should be concerned with.

I also think it would be helpful to know exactly what an incident or negative event consists of for studies like this. Is it only something that is worse than dealing with a failing valve again and perhaps having another open heart surgery (or TAVR if one is fortunate to have that option)? Or is it a trip to the doctor to resolve an inconvenience? A person going to the doctor to resolve blood in their urine is very different from a 2% chance of a permanently disabling stroke or hemorrhaging to death.

And as you wisely bring up, the general population isn’t exactly at 0 risk either. In the end it often just boils down the the sleep at night test. Am I more comfortable with the risk of managing my condition via daily medication and monitoring? Or via future intervention when / if needed?
 
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tommyboy14

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Hi John,

Short Answer: There have been two randomised control studies that randomised patients into a mechanical Bjork-Shiley and bio valve. If you look at these trials, the risk of stroke, endocardities etc is the same across valves. Mech valves in these trial had a roughly 2% chance of bleed per year. Bio valves had a 1% change of bleeding per patient year. It is important to note that these studies were done on the Bjork-Shiley valve. The mechanical valves we receive today are one generation up from that valve, so risk of complications likely lower than reported in these trials.

Long Answer:

1) The Edinburgh study,
which randomly assigned either a bio procine valve and Bjork-shiley mech valve:

From the abstract of the paper: Major bleeding was more common in Bjork-Shiley patients (40.7 (5.4)% v 27.9 (8.4)% after 20 years, p = 0.008), but there was no significant difference in major embolism or endocarditis.

2) the US veterans hospital trial:


From the abstract of the paper: Bleeding occurred more frequently in patients with mechanical valve. There were no statistically significant differences for other complications, including thromboembolism and all valve-related complications between the two randomized groups.

They have this chart

1668515845269.png
 

tom in MO

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I was told by my cardio and surgeon that my mech. valve would last until I died of something else. That's all the statistics I need. I did however check the FDA records for my St. Jude and there was only 1 reported failure in the valve's history. That's a direct cause and effect of having my valve implanted.

I looked into the statistics of mechanical valves and adverse events and found out that if the patient or deceased is on warfarin that anything that can be ascribed to warfarin is. There is never any follow-up to see if warfarin caused the problem or if it was a comorbidity. Only 4% of hospital deaths are autopsied. It might not be possible to know, but this is important since about 25% of all tissue valve recipients wind up on warfarin for other reasons (e.g. afib). Some of these reasons can be related to the tissue valve implantation, but nobody really knows or cares to find out.

In the real world you have a 100% chance of being dead if you suffer the human condition, even Jesus died.
 

Mister_James

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The answer is:

1 minus the probability of the event NOT happening

(1-(.98^30))100= 45% over 30 years at 2% per year.

So a little less than half of people receiving a mechanical valve should be expected to encounter a “stroke or bleed” event at some point over a 30 year period.

If the risk of stroke or bleed is lowered to 1% the answer would be roughly 26%, much better and why it’s important to keep your INR in range.

Note: Your probability of having an “event” is not 50-50 on the specific year 35, your probability of having an “event” is 50-50 by the time you reach year 35.

The longer the time period, the higher the probability that the event will happen within that time period.
I don't know if this is quite right.
If 100 patients are tracked for 3 years that is 300 patient years. If 10 have strokes, 300/10 = 1 stroke every 30 patient years.
In this bunch there is well coagulated patients and people who are not, people who monitor diligently and those who don't. The average population risk does not translate evenly across the patients.
 

Daniel758

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You’re reading me wrong. I was saying if this misconception (odds increasing every year) were true, then….

But it isn’t true. This year, like any other year, it remains roughly a 2% chance (assuming that statistic is accurate). Of course I don’t think anyone has a 110% chance of a negative event.

I don’t disagree with the statistics as you say them and I don’t see how they disagree with any point that I’ve made. I also don’t see where I gave any medical advice beyond what you did (aiming to clear up a statistical misunderstanding) so get off your high horse please. Your incessant beating of that drum is more than obnoxious at this point.
You may be reading the original poster wrong.

The original poster was asking what his risk was over a 30 year period based on a risk of 2% per year, not simply for year 1 or any specific individual year within the 30 year period.

Your answer of 2% was incorrect and bad information if the poster was to rely on this information to make his valve decision.

(Again, the odds for the individual year doesn't increase but as the number of years increases, the probability of an event occurring in the total number of years does increase.

That's how the probability of 2% the first year increases to 45% by year 30 and grows higher with each year after.)

Have a good day.
 

pellicle

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Ok, I wanted to report an error in the post I made here in this thread in this post:
The excel formula is basically chances =A2^B2
this is inadequately phrased as this is the formula for calculating the repeating nature of independent probability events.

So, if cell A2 contains the probability and B2 contains the years this is correct, but my wording would imply to someone other than me (in a hurry) that the following table was of that formula. This is not what was in that table. The table was assembled to show in tabular form that probability play out in a sort of simple data model (which I hoped would be easier to see than just a result).

Lets look at a dice roll. Lets say a 1 is an "event" (as per an INR related event). We know that we have a 1 in 6 probability of a 1 on a roll. If we roll again we know that we will also have a 1 in 6 probability ... and so on
this is 1/6 x 1/6 x 1/6 ...

We use a term in maths called an Exponent to represent repeating calculations like that and so we could write
1668548048743.png

so that would be 0.1666... probability of a 6 ... which is a much higher probability than the 2% (which would be 2 divided by 100 or 0.02)

For convenience (and being too lazy to write it out, unable to find my own and of the view you can google it if you want) I submit this rather clear description of why we take the inverse of that here:

Chance of anything bad happening in 1 year = .02, chance of anything bad not happening in 1 year is 1 - .02 = .98. Total is always 1.

Let's say we are dealing with n years.

Chance that nothing bad happens during n years + Chance that something bad happens (in 1 or more years) = 1. There is no other possibility.

It is easy to calculate that "Chance that nothing bad happens during n years" is .98 multiplied n times = (.98) ^n.
So chance that something bad happens in n years = 1 - (.98) ^ n .
So it will move towards 1 (it means 100%), but it will never be greater that or equal to 1.

It is like throwing coins multiple times. Chance that you get head in atleast one of the try increases with each trial. But still there is a small chance that you will get all the tails and no head.
(*thanks to @rakesh1167)

So with that clarification my points should be clearer now.

Again if anyone wants to discuss this (who didn't fail high school probability and statistics ... 🤔 or if you did and want to work the problem) please follow up (quoting so I know of it) with questions or corrections. Anyone who I'm not blocking (due to say, an established history of being strongly with the dark side of the sect of kunnttedness within the Dark Side of the Force) that is ... because if I'm blocking you I just won't see it when you reply or even quote me.

Best Wishes

PS: for those students who really want to get stuck into it I recommend a more full answer (to my and Rakeshs simplification) can be found here

and as I confessed right up that I did "probability for chemists" not "pure probability" my calculation nomenclature is probably outdated

Happy reading
 
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pellicle

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Dear @JW1970
as you know there are some (rather strange) politics going on here and a particular member who has an axe to grind. I hope that you would see these things and make whatever informed decision that you see best. Its sad that this individual harps on about supporting people but 1) has no experience with this 2) has a false impression of his own choice and I supsect 3) has problems facing truth there.

The thing which has been left out of this decision is best found in that study, and that is the key definition of "an event"

An Event does not have to be a serious event (although some were).

What isn't discussed (meaning its outside the scope of that paper) is the issue of how the events were handled and if people then went on with life.

There is no certainty that you won't have events with a Tissue prosthesis either and (perhaps worse) there is an increasing possibility that you'll go on to be on warfarin even if you choose a tissue prosthetic.

The reality is fundamentally this:
  • there are no perfect solutions
  • each solution has a different set of issues which accompany it
  • at your age a reoperation is very likely and while TAVR may be on the table, you would want to make very sure that the "camp site" will be available after you've hiked 15 years to get there.
  • its true that mechanical valve as a choice requires the patient to be actively interested in the management of their choice. Being from the UK that sort of thing is far more available to you than it is to many of the American posters on this site.
So yes its a tough decision and only you can make it. All we can do is provide you with information to make the decision which you feel best suits you.

Feel free to keep asking questions

Best Wishes
 

Nick Drew

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ON-X fitted in June this year and managing warfarin at home (UK) apart from hearing the valve ticking which i have got used to i have not had any great problems so far. Did drink a bit but cut down and enjoying a wine or beer at the weekend but found my capacity to drink greatly reduced INR is ok and not hindering life so far
 

Superman

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That's how the probability of 2% the first year increases to 45% by year 30 and grows higher with each year after.)
That statement still reads wrong. Assuming the risk is 2%, by year 30 the probability is still 2% in that coming year.

The probability that something might have happened over the prior 30 years is 45%. But it’s not 45% in year 30 if you happened to have no issues in the prior years. And it’s not 0% either if you’ve already had one. It’s still 2%.

It’s also interesting that the thread is drifting a bit now to defining events and comparing them to events with the general population. As we all know, stats don’t generally live on an island.

As an example. Once about 16 years ago or so, I did go to urgent care with brown urine. Blood in urine was the cause of the discoloration. My INR had gotten way high. This was prior to home testing. Bringing my INR down was the fix and fairly easy. The fact that I went to urgent care probably puts me in the category of a negative event. But I would take that negative event over another heart surgery any day. Personally, I saw it as a minor inconvenience. So much so that (as you can see from my previous posts) I still essentially consider myself event free.
 

pellicle

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Good morning fellow Gang Member
(lets leave Chuck as the leader, cos I'm sure not gonna wrestle him for leadership)

That statement still reads wrong. Assuming the risk is 2%, by year 30 the probability is still 2% in that coming year.
well I'm sure that the one-eye'd wink meant that he was signalling his being disingenuous for the sake of his personal amusement, this .-) normally means the poster you are talking to is one eyed (and that whole kingdom of the blind thing) or is implying you are.

However the points I'm wanting to make are:
  1. genuine engagement
  2. due dilligence
This guy shows neither and indeed worse, shows a reaction of upping the game to get him to win. Its all about him (or why else would you not discuss things openly and genuinely on a thread that a newbie has started seeking advice). If this guy genuinely believed his normal position of "don't trust some random guy on the internet" (but listen to me) then he'd shut up and say "ask your doctor".

The fact is that the person asked here and the other fact is some of us do know. Further the fact is that (if the guy was genuine the internet has many resources for maths and these are well written
Eg

The guy could then check that his method was correct and engage in genuine discussion, perhaps citing a few references. Do we see that? No we don't. We instead see personal attacks, contradictions to arguments (dismissal of them) and smug delivery of strawman arguments. All the hall marks of some other personality characteristic.

I'm not sure how old your kids are but I'm pretty sure that if they approached maths the way this guy is that their teacher would say "sorry, but that's not correct and you can't justify it" and they'd have to go about learning what is correct. Unlike "faith" there is a correct in maths.

Lastly engaging with this guy from this direction is doing exactly what he wants. You'll play by the rules, he wont.

This guy just wrote a submission about providing support for both sides of the room. Is he doing that or is he just appealing to words that will mean something to a genuine person but not him.

Here we see he's not actually doing anything genuinely.

I believe that the problem is he is butthurt about his valve choice and is gradually seeing that what he thinks he heard the surgeon tell him (that your valve will last 2 to 3 times longer than previous tissue valves) may not be true. I understood that he's written here that "people shouldn't talk about these things because it triggers him" ... suggesting that nobody after me deserves supportive and open discussion because "I made a call that I'm not going to convince myself was right"

This if fundamentally the hallmark of an idiot, which is not to say someone is stupid, or unintelligent, it is rather something different. Let me quote from Matthew B Crawfords great book on the value of work:

{referencing Zen and the Art of Motorcycle Maintenance}
Pirsig’s mechanic is, in the original sense of the term, an idiot. Indeed, he exemplifies the truth about idiocy, which is that it is at once an ethical and a cognitive failure. The Greek idios means “private,” and an idiōtēs means a private person, as opposed to a person in their public role—for example, that of motorcycle mechanic.
Pirsig’s mechanic is idiotic because he fails to grasp his public role, which entails, or should, a relation of active concern to others, and to the machine. He is not involved. It is not his problem. Because he is an idiot.
This still comes across in the related English words “idiomatic” and “idiosyncratic,” which similarly suggest self-enclosure. For example, when a foreigner asks him for directions, the idiot will reply idiomatically, rather than refer to a shared coordinate system. He also lacks the attentive openness that seeks things out in the shared world, as when Pirsig’s mechanic “barely listened to the piston slap before saying, ‘Oh yeah. Tappets.’”
At bottom, the idiot is a solipsist

You can't teach an idiot to not be an idiot.

So fundamentally (in my view) this guy is going to go on about this as there is an inner conflict occuring in him where parts of him are tapping him on the shoulder saying "hey, mate ... this isn't right" while other parts of him recoil from that because it implies "I made a mistake, I shouldn't have just sat like a sack and listened to my Dr's solo opinion."

There are members here who've recently had (say) an On-X valve and now see that perhaps a StJude would be a small margin better. However do they deny that? Nope, they fess it up and act like an Honest Man. I'm the same, I have an ATS valve yet have gone on record as say things like "that while each mech valve is more or less the same I'd advise people to have a good look at the St Jude" as not only does it meet its claims in situ, but has a huge track record to back it up. To me that's what an Honest Mand does.

This guy isn't acting like an Honest Man he's acting like a disingenuous idiot.

So my advice is to simply correct what disinformation this guy spreads and politely allow him then to continue spreading disinformation to satisfy his ego.

Lastly I'm writing this publically to you @Superman rather than going "covert" to prevent people from getting their ego dented, because I believe that this is a point about honesty.

Best Wishes
 
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tom in MO

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...You can't teach an idiot to not be an idiot....This guy isn't acting like an Honest Man he's acting like a disingenuous idiot.
It's not appropriate on a forum such as this to call Daniel758 dishonest and a disingenuous idiot. It'd be nice if you'd reign it in every so often.

A person can be wrong but honestly believe they are correct, this is not being dishonest.

Not sure what you mean by idiot, but Daniel758 does not seem to be a "a person of low intelligence" or "a stupid person". Lots of people with very high intelligence and multiple advanced degrees have trouble with the correct application of statistical theory and calculations. For example, virtually nobody on this forum reports the assumptions behind the statistics they present....that's probably because they don't know them since researchers sometimes are not up front about assumptions due unintended bias.
 

dick0236

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I've hesitated in answering this post since I am very old and have not studied Calculus since my college days 60 years ago. I'll provide another sampling of one.......me.

At 31 I had an Aortic valve replacement with a Starr-Edwards "ball-in-cage" mechanical vale.......the only mechanical or tissue valve available in 1967. My surgeon told me I would not live to 40 without a valve replacement.

He told me this mechanical valve was designed and tested to last 50 years which, at the time, was longer than my normal life expectancy (73). I really thought the valve would last about 20 years and then I would die. My mechanical valve has now lasted over 56 years with no end in sight.

I first learned I would be on warfarin for life during my exit interview from the hospital post op.
After all these years on warfarin I have had only one event (stroke). That was 7 years after my surgery when patients (maybe doctors as well) did not fully understand warfarin management. My stroke was probably 75% my fault for not taking my pill as prescribed and 25% my docs fault since they had no good way of measuring/monitoring proper clotting time for artificial valves. That stroke was a bitter pill for me to swallow .......but it did teach me to be more aware of the importance of correctly managing warfarin. It has now been 48 years since that one and only event because I am now fully aware of the importance of my involvement in INR management.......and it DOES NOTtake a rocket scientist to manage the drug warfarin.

To you folks who are now facing valve choice, I have only one piece of advice. Do YOUR homework and be sure you understand all of the current and FUTURE ramifications of living with your choice.
 

pellicle

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That was 7 years after my surgery when patients (maybe doctors as well) did not fully understand warfarin management.
when I was being discharged in 2011 I was advised to look for blood in my urine and in my stools. I looked at them for a while and was asked if I had any questions (my face must have shown my question).

Yes (I said), what does blood look like in my stools?
there was a silence and then the nurse answered "you'll know it when you see it".
Ok (I asked), but do I get up and check before I wipe my arse? Because usually toilet paper covers it.
They didn't have a good answer for that. Great!

I'm not sure if I worked it out over time because I've never seen it ...

So I never asked about in my urine (or the other questions I had).
 

Superman

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So I never asked about in my urine (or the other questions I had).
Depends on the issue. If it’s red (or pink) it’s fresh and probably some kind of wound that’s bleeding. My issue was internal. Don’t know exactly where the blood was coming from, but urine was more of a brown, which I was told meant the blood was older. Not from any currently bleeding place close to the exit. But when you google brown urine, you can come up with some ideas that give you a good scare.
 

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