Treatment of a “deep vein thrombosis” which is a blood clot in the vein of the leg, arm or lungs has historically involved treatment for three months with a blood thinner. Since recurrence of these types of clots is highest in the first year after treatment, there has been a line of thinking that to prevent such a recurrence certain people should take a daily aspirin or stay on their blood thinner medication beyond the usual 3-6 months of treatment.
Recently, the prevention of a second blood clot episode (secondary prevention) has become a more precise exercise in both decision making and patient safety. The fundamental concept of determining if a blood clot in the vein is “provoked” or “unprovoked” is the first step in this decision process.
A clot that develops after a surgical procedure or from an indwelling catheter placed in a vein falls into the provoked category and three months of a blood thinner is customarily recommended. Blood clot recurrence for these patients is <1%/year since the inciting factor is usually overcome or removed. Other provoked but nonsurgical conditions are pregnancy, trauma, bed rest for more than three days, immobilized limb or prolonged confined-space travel (plane, car, train). Recurrence of a blood clot for this group is 4%/year and more than 3 months of anticoagulation is usually not recommended.
Unprovoked blood clot events are just that. In this group there is no history of immobilization or trauma, no surgery within three months or cancer diagnosis within 5 years. For reasons which are not clear, this group has a blood clot recurrence rate of 10% in the first year and 30% over 5 years. Also unexplained is that over 5 years, males have a 2-3 times higher blood clot recurrence rate than females.
Over the last several years, taking a daily aspirin (81mg) after completing 3-6 months of blood thinner treatment has been recommended to reduce blood clot recurrence rates. This recommendation was seen as a balance between aspirin’s modest ability to prevent a second clot from forming vs. aspirin’s perceived greater safety compared to staying on a blood thinner.
A recent medical study called “Einstein Choice”, published in the New England Journal of Medicine in 2017 convinces me that at least for the unprovoked blood clot group, giving a blood thinner for an additional 12 months with one of the new types of oral blood thinners ( ex. rivaroxaban) is as safe as taking an aspirin yet reduces blood clot recurrence rates by 75% compared to aspirin’s only 20% success. In addition, the dose of blood thinner that accomplished this feat is only half the normal dose.
Thankfully, prevention of blood clot recurrence with the new oral blood thinner medications seems just as safe as taking a daily aspirin and far more effective.