While hemostasis is necessary for survival, the pathological formation of a blood clot, or thrombosis, poses significant health risks.
The main indications for a patient to receive vitamin K antagonists (VKAs) are the following:
Permanent anticoagulation therapy is justified by an increased risk of thromboembolic complications after replacement of any valve with a mechanical prosthesis.1,2 Most heart valve defects are acquired later in life and are due to degenerative heart valve disease. Heart valve replacement becomes necessary when hereditary or acquired defects severely limit valve function.
Causes of heart valve defects:3
Acquired valvular stenosis may be a consequence of organic changes to the tissue of the valve; insufficiency may be a secondary consequence of ventricle volume load or congestive heart failure.
Today, the indication for operation and/or interventional treatment of the heart valves is considered earlier.4 In Europe, corrective heart valve surgery is performed in approximately 25% of all heart operations: Mechanical heart valves are particularly long-lived, but require that the patient takes life-long oral anticoagulation medication.2 Biological heart valve prostheses have the benefit of not requiring prolonged anticoagulation, but calcify sooner and have to be replaced after 10 to 15 years,5 with an increased risk linked to the second valve replacement surgery.
Anticoagulation
Lifelong oral anticoagulation treatment using a VKA is recommended for all patients with a mechanical valve.6
According to the American College of Chest Physicians (ACCP) guidelines, the following is recommended for patients:7
The American College of Cardiology (ACC)/American Heart Association (AHA)8 provide fairly similar recommendations regarding the use of anticoagulation. However, the target INR should be adapted to patient risk factors and the thrombogenicity of the prothesis.6
Post-operative mortality and morbidity can be improved through individual adjustment of anticoagulation intensity, involvement of the patient, and the use of the international normalized ratio (INR) as a control parameter. Studies such as ESCAT (Early Self Controlled Anticoagulation Trial)9,10 have shown that in cases where patients practice self-management they remain within their optimum therapeutic target range for a higher percentage of time and so significantly reduce the rate of complications. Recent guidelines from the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS) also strongly support INR self-management provided appropriate training and quality control are performed (class I, level B recommendation)6
Non-Vitamin K antagonist oral anticoagulant (NOAC) treatment is contraindicated in patients with a mechanical heart valve.11
Risk factors:
Atrial fibrillation, previous thromboembolism, LV dysfunction, hypercoagulable conditions, older-generation thrombogenic valves, mechanical tricuspid valves, or more than 1 mechanical valve.8
Atrial fibrillation is the most common heart rhythm abnormality that people develop. During AF the heart's two upper chambers (the atria) beat chaotically and irregularly. The condition causes poor blood flow and the development of blood clots within the heart which can subsequently release into the arteries of the brain and cause a stroke. It is primarily a problem of the elderly.
AF is often classified as follows:
Approximately 15%-20% of ischemic strokes occur in patients with atrial fibrillation (AF).12 The risk of stroke in AF patients increases with age, from a 1.5% annual risk in patients aged 50-59 years to 23.5% in those aged 80-89 years.13 Indeed, elderly patients with AF are at the highest risk for stroke and the highest risk for hemorrhage.14 After adjusting for comorbid cardiovascular conditions, AF is associated with a 50% to 90% increase in mortality risk.15 Furthermore, stroke is a leading cause of serious long-term disability.16
AF is the most common arrhythmia worldwide and the estimated global age adjusted prevalence was 0.5% in 2010 - nearly 33.5 million individuals.17 During the last 20 years there has been a 66% increase in hospitalizations due to atrial fibrillation and atrial fibrillation is regarded as one of the major risk factors for thromboembolic-caused stroke.18
Anticoagulation
Five landmark clinical trials - AFASAK, SPAF, BAATAF, CAFA, and SPINAF - have demonstrated the unequivocal benefits of the VKA, warfarin, in preventing stroke among patients with AF. Below 2.0, patients have an increased risk for ischemic stroke, and above 3.0, the risk for intracranial bleeding begins to rise.19-23
This was confirmed recently by the BAFTA study showing that stroke risk is lowered by 64% with warfarin treatment compared to no treatment, and stroke is reduced by 22 % with antiplatelet agents.24 Warfarin was therefore found to be 39% more efficacious than antiplatelet therapy and was appropriate for use in an elderly population.24
Where oral anticoagulation is indicated, a risk stratification (e.g. using the CHA2DS2-VASc score) should performed to estimate the risk of stroke in patients with nonvalvular AF.25 The CHA2DS2-VASc scoring system assigns a score based on the age and sex of a patient as well as the following risk factors for stroke:26
Recent ESC guidelines highly recommend (class I - level A) the CHA2DS2-VASc score for stroke risk prediction in AF patients.27 In general, patients without clinical stroke risk factors do not need antithrombotic therapy, while patients with stroke risk factors (i.e. CHA2DS2-VASc score of 1 or more for men, and 2 or more for women) are likely to benefit from oral anticoagulant therapy.27
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