Warfarin anticoagulation: What you need to know
—— For every patient after prosthetic heart valve replacement Han Qingqi, Department of Thoracic Surgery, Shanghai Changhai Hospital
Department of Thoracic Surgery, Shanghai Changhai Hospital
Institute of Thoracic Surgery of the Chinese People’s Liberation Army
Shanghai Adult Cardiovascular Disease Clinical Medical Center
Han Qingqi
Prosthetic heart valve replacement is one of the most important methods of surgical treatment for heart valve diseases. Currently, there are two main types of prosthetic heart valves in the world: biological valves and mechanical valves. Generally, after biologic valve replacement, if there is no atrial fibrillation, only Warfarin anticoagulation therapy is required for 3-6 months, while mechanical valves require lifelong Warfarin anticoagulation therapy. China is the world’s largest country with the largest number of patients with rheumatic heart valve disease in the world. Rheumatic heart valve disease typically develops in middle age, and given the longevity of the biologic valve, the vast majority of patients require replacement of the mechanical valve. In this way, Warfarin anticoagulation is an issue that every postoperative patient must face, and must face carefully! The consequences of improper anticoagulation can be very serious. However, you do not have to worry, as 99% of patients are safe as long as you follow the professional instructions.
If you happen to be a patient with a mechanical valve replacement, please read about Warfarin anticoagulation: what you need to know?
About Coagulation
Coagulation is a very important self-repair mechanism that has been built up over the course of biological evolution on Earth. It is no exaggeration to say that without coagulation, human beings would not exist today. Under normal conditions, blood flows within the blood vessels without bleeding or clotting. Once the blood leaves the cardiovascular system, or a foreign body enters the interior of the cardiovascular system, coagulation is rapidly activated as a physiological response for the body to protect itself. The most typical example, when we accidentally cut the skin, as long as it is not a major vascular injury, even if we do not deal with him, there will soon be a blood scab formed locally, and the bleeding will stop. This is the coagulation function is protecting us, if there is no coagulation function, or coagulation function problems, it will bleed more than one, the consequences are unimaginable. Today, human beings have evolved to the point where coagulation is quite complex, at the cellular level, such as platelets; at the protein level, such as coagulation factors, of which there are more than a dozen in the human body, which form an intricate network; and at the genetic level, such as certain genetic diseases, of which hemophilia is a good example. The study of coagulation itself has become an important discipline that the general public does not need to know in such detail.
About Warfarin anticoagulation
Sometimes for certain preventive or therapeutic purposes, we wish to weaken the coagulation function, and this is when anticoagulant drugs are used. Anticoagulation therapy is the use of such drugs to affect the coagulation function of the body. After prosthetic valve replacement, it is equivalent to having a foreign body (prosthetic valve) inside the cardiovascular system, and our normal coagulation function is rapidly activated, which makes it easy to form a thrombus around the prosthetic valve. The thrombus can affect the function of the prosthetic valve locally, and even cause the leaflet of the prosthetic valve to not open, i.e., the valve is stuck, which is very dangerous; when the prosthetic thrombus is dislodged, it can go to all parts of the body with the blood flow, causing embolism of important organs, such as brain embolism, which is also very dangerous. Therefore, after prosthetic valve replacement, we must provide anticoagulation therapy.
Now clinically, for patients with prosthetic mechanical valve replacement are generally anticoagulated with Warfarin, which has proven to be effective and safe, but requires patients to closely monitor the intensity and fineness of anticoagulation according to certain requirements. Adjust the dosage of Warfarin.
Warfarin is an oral anticoagulant of the coumarin class, which exerts its anticoagulant effect by inhibiting the synthesis of coagulation factors II, VII, IX and X by vitamin K in liver cells. Did you know? Warfarin was originally developed as a rat drug, and its anticoagulant effect was not discovered until much later.
Warfarin is widely used in clinical practice, not only for the prevention of thromboembolic complications after prosthetic valve replacement, but also for the prevention and treatment of other thromboembolic diseases, such as the prevention and treatment of deep vein thrombosis in the lower extremities, the prevention of ischemic stroke in patients with atrial fibrillation, the treatment of thromboembolic vasculitis, the prevention of pulmonary embolism in patients with pulmonary hypertension, and the reduction of major surgical procedures, such as thromboembolic complications after artificial joint replacement, etc.
Warfarin is also very simple to use and is usually taken orally only once a day (preferably at regular intervals to facilitate the stabilization of blood levels)
Clinical anticoagulation therapy must be moderate. Excessive anticoagulation often causes bleeding, which can be very serious if internal bleeding occurs; insufficient anticoagulation is ineffective and cannot prevent thromboembolic complications. Therefore, we need to find the balance point of anticoagulation therapy.
About the monitoring and management of Warfarin anticoagulation
After oral anticoagulation therapy with Warfarin, the effect of anticoagulation and dose adjustment are mainly reflected by measuring the international normalized ratio (INR) of prothrombin time (PT) and PT is a unit of time, usually expressed in seconds (s), which is generally around 11s-15s in normal subjects. Due to differences in all instruments and testing reagents, PT results in the same person can sometimes be biased. For this reason, INR is now used internationally as an indicator for anticoagulation monitoring in Warfarin, and INR is a ratio and therefore has no units. It is independent of instruments and reagents and is universal worldwide.
The safe therapeutic window of Warfarin is reflected by the range of INR values. The safe range of INR is different between different ethnic groups, with blacks and whites being significantly higher than yellow. For us Chinese, the INR safety window for Warfarin therapy is 2.0 to 3.0 for the current standard bileaflet mechanical flap (for patients with a biologic flap with atrial fibrillation this standard can also be referenced).
Unlike other drugs, Warfarin is not administered at a single dose for life, but requires phased dose adjustment. If the dose is too high, there is a risk of intentional bleeding, and if it is too low, the anticoagulant effect will not be achieved. To be safe and effective, treatment must reach the “anticoagulant balance point”. This requires a certain frequency of PT and INR testing to adjust the dose of Warfarin.
How often should we test PT and INR? Based on European and American guidelines and Chinese physical characteristics, we recommend that the frequency of INR testing be as follows.
Clinical situation
INR testing frequency
Start of treatment to reach INR within safe treatment window
1 time/1-2 days
Within 4 weeks thereafter
2 times/week
INR continues to stabilize
1 time/2-4 weeks
Warfarin INR dose adjustment
Need to re-monitor INR
In case of dietary changes, combination of medications (especially herbs), smoking cessation, surgery, etc., or unexpectedly large fluctuations in INR
Re-monitoring of INR is required
If the INR is below the safe therapeutic window, generally increase the dose by 10-20% of the original dose, or 1/8-1/4 tablet at a time, until the safe therapeutic window is reached.
If your INR is steadily controlled within the range recommended by your doctor, the risk of unexpected bleeding is very small. Some common bleeds include unexplained bleeding from the gums, nosebleeds, bruising or purple spots on the skin, black stools or blood in the urine. In the most severe cases, intracranial bleeding requires emergency treatment.
If the INR value exceeds the safe treatment window, professional guidance is usually required. The principles are as follows.
Clinical situation
Frequency of INR testing
INR < 5< span=""> and no significant bleeding or risk of bleeding
1 discontinuation and dose reduction from the next
5