Thanks so during the days of no protection the chances are that slim basically.
Yes, the odds are in that range.
There are many people who mistakenly believe that a dip below their target INR will guarantee an immediate (or at least a fairly quick) stroke.
I have researched this topic extensively in the 18 months or so since I had my mitral valve replaced, and the reputable scholarly studies I could find simply do not bear this out.
The 10% per year risk in the absence of any anticoagulation therapy (ACT) that I quoted came from this article:
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Oral anticoagulant treatment in patients with mechanical heart valves: how to reduce the risk of thromboembolic and bleeding complications.
Cannegieter SC, Torn M, Rosendaal FR.
Journal of Internal Medicine, 1999 Apr
The risk of thrombus formation on the valve and subsequent
embolism
without any antithrombotic treatment
averages about 10% per year
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The paper I referenced previously in the earlier post, and the ones referenced below are in that same ballpark range. If you search the literature, you will find risk values which vary over the years, mainly as valve design has improved.
But, to give a few references:
----------------------------------------------------
1. PROSTHETIC HEART VALVES
The New England Journal of Medicine
Volume 335 Number 6 1996
WANPEN VONGPATANASIN , M.D.,
L. DAVID HILLIS, M.D.,
AND
RICHARD A. LANGE, M.D.
In patients with mechanical valves, the incidence
of major embolization (resulting in death or a persistent
neurologic deficit) is roughly
4 percent per
patient-year in the absence of antithrombotic therapy,
2 percent per patient-year with antiplatelet therapy,
and
1 percent per patient-year with warfarin
therapy, with the majority of embolizations manifesting
as cerebrovascular events.
The risk of embolization is increased with mitral-valve prostheses,
caged-ball valves, and multiple prosthetic valves.
--------------------------------------------------------
2. Caring for patients
with prosthetic heart valves
CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 69 • NUMBER 1 JANUARY 2002
Patients with mechanical valves are routinely treated with
anticoagulants because
without this therapy,
they have a lifetime risk of thromboembolism
that may be as high as 34%
[my note: at 10% per year, a lifetime risk of 34% equates to an average patient lifetime of about 4 years post valve implantation. At an assumed 4% per year risk, it equates to a 10 year post-valve implantation lifetime.]
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3.
Oral anticoagulant therapy in patients with mechanical heart valve
and intracranial haemorrhage
In the absence of antithrombotic treatment,
patients with mechanical heart valves are exposed to a
very high thromboembolic risk: the cumulative
incidence of
valve thrombosis, major and minor embolism in patients with a
bileaflet valve ranges
between 8.6 and 22% per year
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4. Thromboembolic and Bleeding Complications
in Patients With Mechanical Heart Valve Prostheses
S C Cannegieter, F R Rosendaal and E Briët
Circulation Vol 89, No 2 February 1994
We found an incidence of
major embolism in the absence of antithrombotic therapy of 4 per
100 patient-years. With antiplatelet therapy this risk was 2.2
per 100 patient-years, and
with cumarin therapy it was reduced
to 1 per 100 patient-years. This risk varied with the type and
the site of the prosthesis. A prosthesis in mitral position
increased the risk almost twice as compared with the aortic
position. Tilting disc valves and bileaflet valves showed a lower
incidence of major embolism than caged ball valves.
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I'll try to add links and possibly more references if time and the impending hurricane permit.
Please keep in mind that I am not a doctor, and I'm not offering medical advice, but, my personal research on the topic indicated that while the ACT is important to reduce the risk of stroke, which would otherwise have a higher risk of occurrence at lower INR values, you are not guaranteed certain death or stroke immediately upon going below your target INR range. Neither are you guaranteed absolute freedom from stroke if you stay within your INR range.
Of course, this is of little consolation if you happen to be among the 2 or 3 percent who do have a stroke when you get below target INR for a short while, but many of those might have equally been among the unfortunate few who would have had the same stroke had they been optimally anti-coagulated.
