Since the invention of prosthetic heart valves, surgeons and patients of less than 65 years face a major dilemma, having to choose between:
Current mechanical valves are made with very strong materials and are designed to last a lifetime.
However, they elicit blood coagulation response, which can result in the formation of blood clots that may break free and travel to the brain, heart or lungs, causing complications, including stroke.
Due to this inherent risk, patients who receive a traditional mechanical valve must take anticoagulant medication (warfarin) that reduces the risk of blood clots formation around their replaced valve(*), every day for the rest of their lives. Unfortunately, this preventive therapy requires very strict monitoring and exposes patients to disastrous bleeding accidents.
Several studies conducted on patients less than 65 years of age who had undergone a mechanical valve replacement showed that in a 10-year period 1% / patient-years will develop thrombosis or bleeding events9. A mechanical valve placed in mitral position almost double this risk as compared with the aortic position14. These complications are even more frequent when this treatment is not properly followed, which is typically the case in emerging economies.
Anticoagulation therapy (warfarin) required with current mechanical valves. Read more...
Although warfarin anticoagulant is one of the most frequently prescribed drugs in developed countries, it remains a palliative, dangerous and constraining medication for patients:
In order to prevent blood from clotting around current mechanical valves, warfarin anticoagulant medication must be taken every day and be associated with a close monitoring for the rest of the patient’s life. Regular blood test must be performed about once a month in specialized clinics to compute the international normalized ratio (or INR, a system used to report the ability of the blood to clot) and to ensure that the patient is always taking the correct dosage.
Self-testing kits are also available, allowing home INR testing and monitoring. Results are sent to the doctor who follows the patient and anticoagulation dosage could then be adjusted through a phone call. However, self-testing does not replace the need for regular follow-up visits with the patient’s doctor.
Life‐threatening bleeding risk
According to the Wall Street Journal 8/16/07, “warfarin is the second-most-likely drug, after insulin, to send Americans to the emergency room.”
Anticoagulation therapy with warfarin required with current mechanical valves exposes patients to disastrous bleeding accidents. The risk of severe bleeding events is small but definite and potentially fatal. Several studies have reported significant long-term risk of anticoagulation-related major bleeding after mechanical valve replacement14. A recent study conducted in adults less than 65 years old who had undergone elective isolated mechanical aortic valve replacement has shown that anticoagulation-associated major hemorrhage after mechanical AVR was 1% / patient-year at 10 years9. This study also indicates that survival rates of these patients were lower than those of a population of the same age. These complications tend to increase with the age of the patients and are even more frequent when this treatment is not properly followed.
Although self-managed anticoagulation may reduce bleeding complications by optimizing INR control, warfarin remains a palliative treatment that carries an inherent risk of major bleeding. Moreover, while tolerated in patients in developed countries, anticoagulation therapy seems less suitable in emerging countries, where this treatment is often difficult to follow properly. At the same time, hopes put in more effective and less dangerous anticoagulant therapies were deceptive and clinical tests abandoned16.
Diet and activity constraints
Anticoagulation therapy entails constraints on the patient’s diet. Numerous over-the-counter medications, foods and alcohol may pose risks for patients taking warfarin anticoagulant medication.
Patients with prothrombin time greater than the therapeutic range should also avoid contact sports or activities such as skiing, that risk blunt trauma, which can be dangerous.
Lastly, before medical or dental procedures, the anticoagulant treatment should be temporarily interrupted, which is a difficult issue to manage.
Not suitable for women of childbearing age and for patients with certain medical conditions
Women who are pregnant or who may become pregnant should avoid anticoagulation medication as it may cause the fetus to develop abnormally.
Anticoagulation therapy could also not be suitable for patients who have a history of bleeding ulcers, high blood pressure, diabetes, kidney or liver disease, stroke or alcohol abuse.
Tissue valves (also called bioprosthetic valves) are made with animal tissue like porcine, bovine or equine, which undergo several chemical procedures in order to make them suitable for implantation in the human heart.
With their tri-leaflets design that mimics a native valve in form and in function, they avoid the inherent life-threatening obstructive thrombosis of mechanical heart valves and thus liberate patients from the need for lifelong anticoagulation therapy.
However, tissue valves are prone to premature structural deterioration. Their lifetimes may vary from patient to patient but various independent clinical studies indicate that tissue valves typically last 10–15 years in adult patients13, and even lower in children and young adults13, 21, 47 and in the mitral position39.
Therefore, tissue valves carry an inherent risk of reoperation for removal and re-replacement of the valve. Moreover, before complete prosthetic failure is identified and re-replacement is recommended, patients may be exposed during months or years to a significant malfunction of their tissue valve, which could induce adverse cumulative hemodynamic effects12.
Tissue valves limited durability. Read more...
- Important efforts have been invested since the1980s to increase tissue valves’ longevity. Results seem to be modest because of strong mechanical barriers and biologic fundamentals(*), notably immunological because of chronic rejection of animal tissues as recently discovered in young patients48, 49, 50, 51, 52, 53, 54.
- For operable patients less than 75 years of age, traditional open-heart surgery with tissue valve replacement remains the gold standard. Since 2004, a less invasive procedure (called TAVI or TAVR) is offered to inoperable patients over 75 years old suffering from aortic valve stenosis, and often with multiple severe concomitant diseases.
- A third of these patients were not treated because they were considered either too old or frail to tolerate an operation. For these patients the placement of a tissue valve based on catheter technology through a peripheral artery may relieve symptoms without major surgery.
- The life expectancy of a tissue valve placed with this new catheter technology remains uncertain and would be at best similar to that of conventional surgical tissue valves56. The use of this procedure on patients under 75 years of age, whose life expectancy is not compromised, is also not supported by currently available evidence13, 19, 23, 24, 56.
- Most importantly, a study dated August 2012 from the U.S. Department of Health25 encourages systematic testing for preemptive treatment earlier in the disease course, which could save thousands of lives and could easily be done today at a low cost55.
- Preemptive treatment would also reduce the need for later stage procedures and their economic burden for health insurance companies. The placement of a tissue valve based on catheter technology requires indeed a sophisticated and costly organization with multidisciplinary teams.