Preventing AF-related stroke 2
Stroke is the most important complication of AF and even those receiving rhythm control strategies are still at risk. It is very important to understand your risk of stroke and to discuss it with your doctor as the effects are often life-long, not only you, but also for your family and friends.
The prevention of stroke is managed using medications that are often referred to as 'blood thinners' even though they don't technically thin the blood.
Platelets are small cells that circulate in the blood to help prevent bleeding. When you are injured they become activated and stick together to form a plug at the site of injury. Antiplatelets block the mechanism by which these cells attach to one another to prevent a clot forming and are sometimes given to those that are at low risk of stroke. However, AF-related clots are formed by a different mechanism where blood flow stagnates in the heart, activating clotting factors. Because these clots do not involve platelets, the usefulness of antiplatelet therapy in AF is limited.
These are highly effective medications for preventing AF-related stroke as they block the mechanisms by which clots are formed. There are different types of anticoagulants, vitamin K antagonists and novel oral anticoagulants (also known as direct oral anticoagulants and non-vitamin K antagonists).
Vitamin K antagonists – also known as VKAs, are very effective with long-term use, preventing 67% of AF-related strokes. 30 However, despite their effectiveness VKAs have significant drawbacks:
- The therapeutic range (the amount needed to achieve the desired therapeutic effect versus the amount that causes severe side effects) is very narrow. This means that you will have to visit the hospital regularly to make sure that you are receiving the right amount.
- VKAs are highly susceptible to different foods and, in some cases, the therapeutic benefits can be greatly reduced in a single meal.
- VKAs are also associated with unwanted drug-drug interactions that have to be carefully monitored.
Novel oral anticoagulants - these fall into two classes: factor Xa (factor 10a) inhibitors and direct thrombin inhibitors. Both have been shown to be as effective as VKAs, but with better safety profiles. 28
Factor Xa inhibitors – factor Xa is a protein that is integral to the formation of a blood clot. Unlike VKAs, which require close monitoring due to their high susceptibility to unwanted drug-drug and food interactions, factor Xa inhibitors are associated with fewer drug-drug and food interactions. This means that their anticoagulation properties are more predictable and therefore a person’s coagulation time does not need close monitoring. 28 Some of the novel oral anticoagulants can come with an increased pill burden (the number of pills a person needs to take each day), however, there are factor Xa inhibitors that only need to be taken once a day, that can help to reduce this burden. 29,30
Direct thrombin inhibitors – thrombin is a protein that is integral to the coagulation process. These agents are associated with fewer drug-drug and food interactions than VKAs and also do not require close coagulation monitoring. 28 However, as with factor X inhibitors, direct thrombin inhibitors can be associated with increased pill burdens. 31