It has become generally accepted practice to treat new-onset atrial fibrillation and atrial flutter with electrical cardioversion in the acute setting – provided the known onset of atrial fibrillation is less than 48 hours. Beyond that, caution tends to be advised – whether through use of transesophageal echocardiography to rule out left atrial thrombus, or through pre- and post-procedural anticoagulation.
However, this data from a research letter in JAMA suggests – possibly we ought to be even more cautious regarding time-of-onset.
This is a re-analysis of FinCV, a 7 year trial registry of cardioversion for atrial fibrillation from Finland. The study cohort is comprised of 2,481 patients undergoing 5,116 electrical cardioversions, all without peri-procedural anticoagulation for symptom onset <48 hours. Outcomes were gathered from vital records review, evaluating for cerebrovascular thrombotic complications within 30 days.
Of these patients undergoing cardioversion, there were 38 definite thrombotic complications. 30 of these 38 occurred in patients whose symptom onset was >12 hours. There were few apparent pro-thrombotic differences between groups, and thus, the authors very reasonably conclude – we should be cautious regarding cardioversion after 12 hours. Other predisposing factors in their multivariate analysis include female sex, heart failure, and diabetes – but increasing length of time showed the strongest association.
The 12-48 hour window in this study still only represented a 1.1% risk for 30-day thromboembolism, compared to the ~2% risk after 48 hours. However, it still exceeds the ~0.3% risk of thromboembolism with peri-procedural anticoagulation. There are other risks associated with anticoagulation, but it is reasonable to suggest the management strategy is no longer as clear-cut around 48 hours.
“Time to Cardioversion for Acute Atrial Fibrillation and Thromboembolic Complications”
http://www.ncbi.nlm.nih.gov/pubmed/25117135
Very interesting topic and highly relevant to our practice in the ED. Certainly will keep this in mind for future conversations about risk of cardioversion without anti-coagulation. Would be interested to know how this stacks up with similar registry data in those who go peri-procedural anticoagulation and risk of bleeding.
Bleeding risk can be individualized, although most data is "bleeds per person-years", and geared towards long-term anticoagulation, e.g., HAS-BLED:
http://www.mdcalc.com/has-bled-score-for-major-bleeding-risk/
This is an observational study designed to find out the incidence of thromboembolic events following cardioversion. It can not be used to alter treatments or suggest treatment strategies. It can potentially be used as a baseline to compare with the results of alternative treatments.
In a nutshell-
a) what would have been the thromboembolism rate if they did not cardiovert the patients?
b) I have not seen the whole paper so maybe they did put a definition, but how do they define a stroke?
c) what would have been the complication rate if they anticoagulated the pt? I.e. how many patients had a CLINICALLY SIGNIFICANT event and again what would it have been if the treatment was different?
You are correct in your assessment of an observational registry study in the hierarchy of evidence. That said, many treatment strategies in medicine are glommed together from various levels of evidence (and eminence). This sort of finding is hypothesis-generating for further study, but it's also not unreasonable to think about the various alternative risks for patients greater than 12 hours out. I think we'll see a more nuanced approach to individualizing treatment based on some of these data.