Therapies for AF-related stroke prevention
Though warfarin is commonly used, non-vitamin K antagonist oral anticoagulants are increasingly a better option.
BY: Eleanor Yap
Throughout the world, cardiovascular diseases account for one-third of deaths or nearly 18 million. Mirroring the global burden, heart diseases and stroke are significant causes of death and disability in Asia. Specifically, in Singapore, stroke is the fourth leading cause of death, and the largest cause of long-term physical disability. With a rapidly ageing population, the burden of stroke is expected to increase, further posing challenges to the healthcare system as well as society.
Atrial Fibrillation (AF), a heart condition characterised by irregular heartbeats, increases the risk of stroke by five-fold. AF-related strokes are also more severe, causing disability in over 50 percent of patients and generally worse outcomes compared to strokes due to other causes. The prevalence of AF is estimated to increase also as the population ages. By 2050, Asia will have 72 million AF patients, and 2.9 million among them will suffer from AF-associated stroke.
The good news is an AF-related stroke can be prevented. However, there are challenges in the use of conventional therapies such as warfarin in AF stroke prevention due to “suboptimal control” and the risk of warfarin-induced bleeding in the brain is higher among Asians. The new class of therapies such as non-vitamin K antagonist oral anticoagulants (NOACs) matches warfarin in stroke prevention, but is easier to administer and significantly reduces the risk of life-threatening bleeding in the brain. These agents may provide an alternative to warfarin in Asian patients.
Ageless Online speaks to Adjunct Associate Professor Ching Chi Keong, senior consultant, Department of Cardiology and director of Cardiac Electrophysiology and Pacing, National Heart Centre Singapore, about warfarin and NOACs:
AF-related stroke will likely increase as the population ages. What other factors also play into this increase?
The main factor is age. However, AF-related stroke may be seen in other conditions such as hypertension, diabetes, existing heart disease, abnormal valves that interfere with heart function, obesity, sleep apnoea, etc. Interplay with all these factors can increase the risk of AF.
Can you explain warfarin’s “suboptimal control”?
The therapies for AF-related stroke prevention include restoration of normal rhythm, to control heart rate while in AF and to reduce risk of strokes related to AF.
What warfarin does is it opposes Vitamin K in the body and serves as a blood thinner. It starts working two to three days after a patient takes it. Also, each patient has a unique dosage and it is about the doctor and patient finding that sweet dosage. It is also fastidious in that it has food interactions. For instance, if a patient takes foods containing lots of Vitamin K, it can interrupt the efficacy of warfarin in the body.
Besides that, it also has significant interactions with other drugs such as gastric drugs and even antibiotics, where these drugs may affect the anticoagulant effect of warfarin in the body. Furthermore, the effects of warfarin are measured by a blood test – if it reads too low, it then means the patient is not protected sufficiently from stroke. If the test indicates a high ratio, the patient runs a risk of internal bleeding. Most serious is bleeding in brain where surgery might be necessary and that occurs in one percent in the controlled trials.
How does NOACs compare?
NOACs are effective three to five hours after oral intake. They also have little interactions, although they may interact with blood thinners. They have little food interactions and their effects are more predictable than warfarin. There is also no need to measure how thin the patient’s blood is like warfarin. The risk of internal bleeding is half that of warfarin and trials of NOACs showed that they are as good as warfarin in reducing AF-related strokes. They are generally safer for patients.
Also, with NOACs, once the patient is stable, he will only need to take a blood test every six to 12 months. In patients on warfarin, they may need to take weekly blood tests when they are started on warfarin. Once their international normalised ratio (INR), a test of blood clotting, readings are stable, patients will take an INR test every two to three months.
Why are doctors still prescribing warfarin with this kind of risk?
Many are, mainly because it is cheap and affordable. (WRITER’S NOTE: Warfarin costs S$0.12 per tab, while Rivaroxaban, a NOAC, costs S$3.08 per tab.)
If a patient is taking warfarin, he must watch his food as well as the drugs he takes and inform his doctor. He must also do regular blood checks for monitoring.
Are there certain patients who shouldn’t take any of these preventive therapies including NOACs?
Yes, those who have advanced kidney disease, moderate mitral stenosis or a mechanical heart valve.
How many NOACs are there available in Singapore?
There are three – Rivaroxaban (introduced in March 2012), Dabigatran (introduced in March 2011) and Apixaban (introduced in September 2013).