Risk of Thrombosis For Mechanical Aortic Valves Managed Without Anticoagulation (Noncompliance).

Patients with mechanical heart valves are routinely treated with life long anticoagulation.  with warfarin (Coumadin) therapy.  Why are mechanical aortic (and mitral) heart valves managed with anticoagulation?  For the same reason atrial fibrillation is treated  with this vitamin K antagonist.  Blood is thinned  to reduce the risk of clot formation on the metallic foreign body and subsequent  risk for systemic embolization.  In other words, anticoagulation is used to prevent stroke and other complications of peripheral emboli.  What is the risk of systemic clot embolization  in patients with a  mechanical heart valve? Here are the numbers for the incidence of major embolism
  • Coumarin therapy:  1 per 100 patient-years.
  • With antiplatelet therapy:  2.2 per 100 patient-years.
  • No antithrombotic therapy: 4 per 100 patient-years.
  • Patients with mitral valve are double the risk than patients with aortic valves.
  • Tilting disc valves and bileaflet valves showed a lower incidence of major embolism than caged ball valves.
  • Some medical societies recommend all patients with a mechanical heart valve should also take 75-100 mg of aspirin per day, unless contraindicated.  
  • An incidence of major bleeding was found in patients treated with coumarin derivatives of 1.4 per 100 patient-years.
Coumadin is a nasty drug that can be very difficult to manage.  The Joint Commission has safety standards for anticoagulation managment in the hospital.  That does not mean they can dictate how physicians order warfarin, but maybe they should.

As a hospitalist, I see an incredible clinical variation in anticoagulation management.     Failure to adequately dose Coumadin correctly can lead to dangerous supratherapeutic parameters.And when that point has arrived, I may be forced to place subclavian central lines in fully anticoagulated patients.  Interestingly enough, none of my central lines in these folks have ever had procedural related bleeding.  That is because they are in  hypovolemic shock.

In my opinion, physicians are often either too lazy, to ignorant or to arrogant to appropriately manage warfarin therapy in the safest possible way.   I don't blame them.  The drug is difficult to predict and has so many confounding clinical variables that standardizing its management is the only way to safely administer it across populations of hospital patients who's drug profile and nutritional status change on a day to day basis.  Doctors who think they are smarter than  Coumadin are a danger to patient health. Don't touch me or my family.  I would choose a pharmacist driven warfarin management protocol over a physician directed concept of a care plan every day of the week.

With the dangers of Coumadin readily established, I must also point out the dangers of bridging anticoagulation using heparin or Lovenox.  Since warfarin often takes up to five days or more for the coagulation cascade to be adequately suppressed, physicians will bridge with these other drugs while waiting for the INR of Coumadin therapy to reach therapeutic goal. 

Unfortunately, even these drugs come with potentially devastating and life threatening complications, including severe bleeding and shock  (I particularly see a fair amount of retroperitoneal bleeding from Lovenox therapy) as well as H.I.T. positive antibody related thrombosis.  Does the risk of heparin or Lovenox bridging outweigh the risk of thrombosis from not providing bridging and allowing the INR to rise over several days in the post operative period in patients with mechanical heart valves?

The ACC/AHA, in their published 2008 guidelines gave guidance for bridging anticoagulation management in patients with mechanical heart valves in the perioperative period.   Their recommendations are pretty aggressive.   In high risk patients, they recommend restarting warfarin and bridging heparin as soon after surgery as bleeding stability permits (Class I Recommendation).  They define high risk as a patient with a mechanical mitral valve or any mechanical aortic valve patient with at least one risk factor (atrial fibrillation, previous thromboembolism, left ventricular dysfunction, a hypercoagulable state, older generation thrombogenic valves, a mechanical tricuspid valve, or multiple valves.)

This recommendation seems a bit counter intuitive to me.  Why?  The stated incidence ofthrombosis for mechanical aortic valves is 4 per 100 patient-years.  That's a pretty low daily risk of thromboembolism. Based on my decade of hospitalist clinical experience, I get a clinical sense that my short term risk  of complications from bridging heparin is greater than the daily risk of no bridging with anticoagulation.

You won't find many doctors or patients these days willing to test the limits of avoiding anticoagulation with mechanical valves.  We have been scared into anticoagulation submission, driven by fear and aggressive Society guidelines that leaves little room for clinical interpretation. I have difficulty understanding how a thrombosis incidence of 4 per 100 patient-years off all therapy translates into such an aggressive clinical standard for perioperative bridging. 

I recently hit  non compliant research jackpot that provides insight into real life experience that would  never get past today's strict ethical standards.  He was a 52  year old Hispanic roofer who decided two years prior to stop taking his warfarin for his mechanical aortic valve.    It was too much of a hassle getting his blood drawn and avoiding his favorite foods. Oh yeah, and the falls off the ladder kept giving him bruises.   To his credit, two years and four falls later he was doing just fine. Would you stop taking your Coumadin and play Russian roulette with your heart valve?  Some folks do, like Mr Hispanic Ladder Guy do and they they apparently do just fine.

While only an N=1 case report, it makes one pause about how aggressive our recommendations really are for perioperative anticoagulation management in mechanical valves and whether those recommendations reduce thrombosis from the valve at the expense of complications from bridging therapy on a short term and long term basis   Is any of this research looking at the big picture?

What's the benefit of a 3% yearly reduction in stroke if you increase your risk of having a major bleeding complication by 5%?   Would you rather die from a stroke or an intracranial hemorrhage?  Pick your poison.  Hosptialists will take care of you either way.  Although, to some degree, membership in the patient noncompliance club may have its benefits.    If you're on Coumadin or warfarin, here are some resources you might find helpful:

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