Bridging Anti-coagulation is Dead! Long Live Bridging Anti-coagulation!

I am interrupting my current obsession with Top 5 lists  to bring you this important announcement: Peri-operative anti-coagulation, (also known as bridging anti-coagulation) is done! Is it time to stick a fork in it?

Right now you’re probably wondering, what the heck I’m talking about, and why you should consider it important. Currently hundreds of thousands of people throughout the country are on the oral blood thinner coumadin (also known as warfarin) to prevent a blood clot. For those who are on it long term, having a procedure can be problematic, as stopping the drug can increase the risk of blood clots, while continuation of the drug increases the risk of bleeding with surgery. Thus many patients undergo a process known as “bridging” wherein the coumadin is stopped  several days before the surgery, and a short acting injectable blood thinner is substituted so that the blood thinning effect of coumadin has time to wane before the surgery. This practice has been perpetuated without very clear evidence that it decreases the risk of blood clots or bleeding, and without much certainty about which people on coumadin need to be “bridged”. Recently, researchers sought to shed some light on this question by pooling together data from several smaller studies looking at patients who underwent bridging  to determine what the various risks and benefits of bridging might be.  The study  “Periprocedural Heparin Bridging in Patients Receiving Vitamin K Antagonists” was published  in the Journal Circulation and has received much attention, as it should have as it was co-authored by my former mentor (shout out Dr. Kaatz!) but also since it is the first large scale study of its kind.

The venerable clotblog described the study as “another nail in the coffin” of the concept of anticoagulation bridging. The twitterverse has since tweeted and re-tweeted the results  citing the up to 5 fold increased risk of bleeding with bridging therapy without a  significant reduction in clot risk.

So does this study truly represent another nail in the coffin of the practice of anti-coagulation bridging? The question of whether people on anti-coagulation should receive bridging with enoxaparin or other agents is a difficult one. It’s also a question of great relevance, given the huge burden of atrial fibrillation, which makes up the lion’s share of people on anti-coagulation. However there are a number of reasons why the findings in this study should not necessarily change how clinicians practice, all of which were pointed out by the authors.

First, as we now know, drawing conclusions from data gained by looking through retrospectacles can be dangerous. A metanalysis of such restropective data is no different. The study gleaned data from 34 different studies, only one included randomized data, the rest were of the observational type.  Of the studies that were used in the analysis, the authors state: “study quality was generally poor”.

Second, not all of the anti-coagulation was the same. Some people who received bridging anti-coagulation were on prophylactic doses, while some were on full dose, whereas others were on an intermediate dose. The data does not tell us who had what and how much. Rather  everybody who got any anti-coagulation were lumped into the “received bridging anti-coagulation” group.

Another problem is that the indications for  anti-coagulation were varied  There are  different indications for blood thinners, and while they may all be treated with the same class of medication, they are very different diseases. The patient with atrial fibrillation is very different from the patient with pulmonary embolism. While we do know that 22% of the enrolled patients had venous thromboembolic disease (such as DVT and pulmonary embolism), and we know that their rate of recurrence was similar to no anti-coagulation, we don’t know how many were being treated with bridging therapy and what the exact indications were. There can be vast differences in people with the same disease, for example a person with a DVT 6 days ago is a very different case from the same person who had a DVT 6 months ago. This is the kind of information that we would like to have, but it’s not available.

Lastly, the main caveat in the study goes back to the fact that the underlying data was of an observational nature, leading to bias. The patients were not randomized, so those patients who were receiving anti-coagulation were likely given it because they were thought to be at higher risk. Thus to truly answer the question of who to bridge and how to do it, we will need to wait for results of the BRIDGE  and PERIOP-2 studies, which will hopefully give us randomized controlled trial data to answer these questions. Until then, when it comes to peri-operative anti-coagulation, I would listen to what the ACCP (American College of Chest Physicians) advises in these situations; the best course is an ” individualized approach to determining the need for bridging anti-coagulation based on the patient’s estimated thrombo-embolic risk and peri-procedural bleeding risk”

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