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Non-vitamin K antagonist oral anticoagulants (NOACs) have been quickly incorporated into practice in the 6 years since becoming available for stroke prevention in patients with non-valvular atrial fibrillation (Afib) -- overtaking other antithrombotics for usage worldwide -- a registry study found.

Since dabigatran (Pradaxa) became the first NOAC available in 2010, almost half of newly diagnosed Afib participants in the Global Registry on Long-Term Oral Antithrombotic Treatment in Patients with Atrial Fibrillation (GLORIA-AF) registry received NOACs (47.6%); another 32.3% got vitamin K antagonists (VKAs; warfarin); 12.% got aspirin and/or another antiplatelet; and 7.8% received no antithrombotics at all.

These figures make for a stark contrast to the pre-NOAC era, during which the percentages of patients on aspirin, VKAs, and other antiplatelets were 41.7%, 32.8%, and 3.4%, respectively. Additionally, one-fifth of the population received no antithrombotic therapy back then, according to , of Leiden University Medical Center in the Netherlands, and colleagues in their study in the .

"Perhaps the more important and disturbing finding is that nearly 20% of Afib patients are not on appropriate stroke preventive therapy," commented , of the University of California, San Francisco, in Fresno, and , of the National Heart, Lung, and Blood Institute in Bethesda, Md., writing in an .

Even after accounting for patients at high risk of bleeding, "at least 10% of the eligible patients are either on no therapy or on inferior therapies such as aspirin.

"Some readers that take the 'glass half-full' point-of-view may be encouraged by the findings of the GLORIA-AF phase II registry and argue that 80% coverage is a marked improvement from what has been reported so far. And herein comes the word of caution in interpreting these results: the reported high percentage of oral anticoagulant use is not consistent across the board," Deedwania and Acharya wrote, citing the lower rates of adoption observed in the GARFIELD-AF and PINNACLE registries.

GLORIA-AF was an international registry spanning five continents in which 15,641 patients were enrolled within 3 months of Afib diagnosis (2011-2014); ultimately, 15,092 were eligible (45.5% women, median age of 71).

The study population was characterized by a high stroke risk: most had a CHA₂DS₂-VASc score of 2 or greater (86.1%), with the rest presenting with a score of 1.

In Europe, the rates of prescribing NOACs, warfarin, and antiplatelets were 52.3%, 37.8%, and 6.0%. No antithrombotics were given to 3.8%

North America had a similar rate of NOAC use (52.1%), although warfarin was less commonly given (26.2%) and more people received no antithrombotic treatment (7.5%). Another 14.0% of patients were on other antiplatelets.

NOACs were least popular in Asia, where about a quarter of the study population each got them (27.2%), warfarin (27.5%), other antiplatelets (25.0%), or none of these options (19.8%).

"There are some indications within the registry that are concerning," according to the editorial. "For example, sites from Africa are reported to have an 87.4% compliance rate with oral anticoagulant prescription (compared with 78.3% in North America) with only 1.5% of eligible patients not on any therapy (7.5% in North America).

"This incongruently superior compliance with an expensive therapy in a low-resource setting suggests selection bias and requires further explanation."

Deedwania and Acharya also noted that the study cohort was not comparable to Afib patients in general due to the over-representation of paroxysmal Afib. In addition, participating sites were not required to use screening logs in their directions to enroll consecutive patients, leaving room for selection bias.

It would also be incorrect to directly compare the NOAC and pre-NOAC periods using the current data: "There was minimal, if any, overlap between patient populations represented in phase I and phase II studies," the editorialists said.

"Whereas the current phase II registry reports data predominantly from Europe (47.1%) and North America (22.5%), 67.1% of the patients enrolled in the phase I cohort were from China. In fact, no centers from North America were represented in the phase I cohort. Thus, any comparison of oral anticoagulant use between the two phases may represent geographical rather than temporal variation.

"Let us not be lulled into a false sense of security," Deedwania and Acharya said. "More representative data are needed to get realistic estimates of where we stand in terms of oral anticoagulant use for stroke prevention in Afib."

"Meanwhile, from the information we have, it is apparent that much ground needs to be covered before all eligible patients with Afib, especially those at high risk of stroke, receive appropriate guideline-directed anticoagulant therapy."

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