The heart is a powerful muscle that has 4 chambers. There is a right atrium, a left atrium, a right ventricle, and a left ventricle. Normally, each of these chambers contracts to pump blood effectively. The right atrium contracts to pump blood into the right ventricle, and the left atrium contracts to pump blood into the left ventricle.
Atrial fibrillation and the need for anticoagulation:
In atrial fibrillation, the right and left atria do not contract. Instead, they merely quiver or “fibrillate.” Due to the lack of contraction, blood does not move effectively. Generally speaking, blood that does not move will form a clot. The process of forming a blood clot is called “coagulation.”
Therefore, patients with atrial fibrillation have a high risk of forming clots in the atria of their hearts. If pieces of these clots break off, they can exit the heart and enter the blood vessels of the body. If a blood clot enters the blood vessels of the brain, then it can cause a stroke. This is one of the most dreaded complications of atrial fibrillation.
To prevent strokes, patients with atrial fibrillation are often prescribed blood thinners, or “anticoagulants.” One of the most common anticoagulants is warfarin, also known by its brand name, Coumadin.
The practice of “bridging” anticoagulation around surgery:
However, many patients have to stop taking warfarin in order to have surgery due to the risk of bleeding. Most commonly, doctors tell their patients to stop taking warfarin for 5 days leading up the surgery, and then to restart warfarin 5 to 10 days after the surgery.
What do patients do for those 10 to 15 days without anticoagulation? Wouldn’t this put them at risk for a stroke?
In order to prevent a stroke in the days immediately leading up to and following a surgery, many doctors choose to put their patients on a fast-acting anticoagulant such as dalteparin or enoxaparin. These fast-acting anticoagulants are part of a large class of medications called “low-molecular-weight heparins” or simply “LMWH.” This practice of temporarily switching from warfarin to LMWH and back to warfarin is called “bridging.”
But does bridging actually help patients? Theoretically it should, but there have been no studies to give evidence one way or the other. Until now, that is.
The BRIDGE trial:
Recently, a large-scale study called the BRIDGE trial was published in the New England Journal of Medicine. There were 1884 patients with atrial fibrillation who take warfarin and had to stop warfarin due to upcoming surgery. These patients were randomly assigned to receive either LMWH or to receive a placebo during the 10 to 15 day period that warfarin was stopped around the surgery.
What happened? Researchers followed these patients for 30 days. The risk of stroke was the same for patients who received LMWH or placebo. However, the risk of major bleeding was higher for patients who got LMWH (3.2% risk) compared to placebo (1.3% risk). Overall, there was no difference in mortality between the groups of patients.
What does this mean?
The BRIDGE trial provides evidence that the practice of bridging does not benefit patients who have a low-to-intermediate risk of forming blood clots. Based on this study, it seems reasonable for doctors to choose to merely stop all anticoagulation in anticipation of surgery, as opposed to using LMWH.
There are 2 important limitations to this study that I would like to highlight:
(1) This study did not include many patients with high risk for blood clots (risk based on factors like age, blood pressure, diabetes, etc.). Fortunately, another study is on its way to answer that question! Read about it here: http://www.clinicaltrials.gov/ct2/show/NCT00432796
(2) This study only examined patients taking warfarin. Many patients with atrial fibrillation take newer anticoagulants such as dabigatran, rivaroxaban, or apixaban instead of warfarin. It is not clear whether this study applies to these patients.
Take care! And keep staying informed!