Letâ€™s get off cell biology and back to something I really know.
Atrial fibrillation, AF ablation and blood thinners.
There was an important study published today in the Journal of the American College of Cardiology concerning the use of the new blood thinner, dabigatran (Pradaxa), around the time of AF ablation. A very concise overview, including a quote from a blogger, can be found on Cardiobrief.
Basically, Dr Nataleâ€™s group reported that patients who underwent AF ablation while taking dabigatran did less well than a group managed in the usual way with warfarin. The most concerning finding was that dabigatran-treated patients had a higher risk of stroke after ablation.
The increased popularity of non-warfarin blood thinners has injected yet another challenge to AF ablation: how best to prevent the most-feared complication of AF ablation, stroke.
Before there were alternatives to warfarin, AF ablation-ists all had a plan for protecting the 50 or so scabs in the left atrium from forming clots and then stroke. This is the issue with ablation; to electrically wall off areas of the atria, we make burns. Burns must heal, and healing means scabs are exposed to blood.
Most AF centers ablate AF without interrupting warfarin. (Notably, this protocol originated from Nataleâ€™s group.) Other centers favor bridging with IV heparin or subcutaneous low-molecular weight heparin. The point was: we all had a protocol that worked.
Now, the new blood thinners have jostled the AF ablation world. AF patients get started on dabigatran, and most recently, rivaroxaban and soon, apixaban. These drugs are blood thinners; they have solid evidence to support their efficacy, safety and perhaps superiority to warfarin in AF. Butâ€¦there are important issues pertaining to AF ablation.
One is the issue of adequate blood thinning in the weeks before the procedure. With warfarin-treated patients, we can check a weekly INR test to confirm that the drug has indeed thinned the blood. The doctor doing the burns knows the status of the blood. With the new blood thinners, however, this confirmation isnâ€™t possible. Only the patient knows. Some AF doctors arenâ€™t comfortable with trusting that their patients have taken the pills exactly as directed. This uncertainty leads these doctors to recommend a trans-esophageal echo (TEE) before the ablation. I hate this idea because it means doing another procedureâ€”one that entails sticking a thick probe down the throat and esophagusâ€”before the ablation. One that wasnâ€™t needed with the warfarin protocol.
Another procedure-related issue with the new blood thinners stems from their lack of an antidote. If the heart is perforated during the procedure, bleeding in the chest could be worse. Moreover, how does one get catheters out of the leg veins while the blood is fully thinned on dabigatran? These concerns have been answered with warfarin. Good studies and years of experience have taught us that ablating with warfarin is both safe and effective.
Finally, many experts posit that the increase in procedure-related strokes with dabigatran described in Dr Nataleâ€™s study occurred because of a short window after ablation where the blood was not thin. Maybe. But maybe it was just chance? Or maybe the patients missed some doses?
Enough about the minutia.
What are the larger messages of this seemingly focused issue?
Let me offer three that I find compelling:
- Non-warfarin blood thinners are marketed as simpler and easier to use than warfarin. Maybe so in patients with AF that never need anything done to them. In the other 90%, the situation is different. These agentsâ€™ lack of an antidote, un-measurability of effect and dependency on patient compliance belie the notion that they are simple. In other words, the real world use of these drugs looks a little tricky.
- Secondly. Is it bad that I like the idea that experts donâ€™t know what to recommend for peri-procedural blood thinners? In an editorial accompanying Dr Nataleâ€™s study, Dr Bradley Knight proposed 7 possible regimens. If there are 7 possibilities, this means no expert consensus or mandates are likely to emerge in the near-term. We doctors must think and judge. Thank goodness for that. Love judgment.
- Finally, concerning my quote on Cardiobrief. The issue of protecting AF patients from stroke is our most pressing concern, whether it is around the time of ablation or not. I like simple. For now, in patients that I feel sure are taking dabigatran correctly, or in those at low risk of procedural stroke, I donâ€™t feel that a 290 patient study with only 3 events in the dabigatran arm should close the book on non-warfarin blood thinners around the time of ablation.
Before concluding, a comment on rivaroxaban: I know of no data on using rivaroxaban in the peri-ablation period. Since the prevailing thoughts of most AF doctors (rightly or wrongly) are that once-daily rivaroxaban isnâ€™t quite ideal, Iâ€™d be very uneasy about burning the left atrium with only rivaroxaban therapy. (Please note: these thoughts represent pure blogger speculation.)
Hope this helps.
Thanks to my friend and ace heart news journalist, Larry Husten (@Cardiobrief) for the prominent mention.