Non–Vitamin K Antagonist Oral Anticoagulants
for Stroke Prevention in Asian Patients
With Nonvalvular Atrial Fibrillation
Meta-Analysis
Kang-Ling Wang, MD; Gregory Y.H. Lip, MD; Shing-Jong Lin, MD, PhD; Chern-En Chiang, MD, PhD
Downloaded from http://ahajournals.org by on December 15, 2021
Background and Purpose—The use of vitamin K antagonists (VKAs), the cornerstone treatment for stroke prevention in
patients with atrial fibrillation, is limited by the perceived risk of serious bleeding in Asia. Non-VKA oral anticoagulants
(NOACs) are safer alternatives. Here, we evaluate performance differences of NOACs between Asians and non-Asians.
Methods—We compared efficacy and safety of NOACs between patients enrolled in Asian and non-Asian countries using
aggregative data from phase III clinical trials. The odds ratios (ORs [95% confidence interval]) were calculated by a
random effects model.
Results—Comparing with VKAs, standard-dose NOACs reduced stroke or systemic embolism (OR=0.65 [0.52–0.83]
versus 0.85 [0.77–0.93], P interaction= 0.045) more in Asians than in non-Asians and were safer in Asians than in nonAsians about major bleeding (OR=0.57 [0.44–0.74] versus 0.89 [0.76–1.04], P interaction=0.004), hemorrhagic stroke
(OR=0.32 [0.19–0.52] versus 0.56 [0.44–0.70], P interaction=0.046) in particular, whereas gastrointestinal bleeding was
significantly increased in non-Asians (OR=0.79 [0.48–1.32] versus 1.44 [1.12–1.85], P interaction=0.041). Generally,
low-dose NOACs were safer than VKAs without heterogeneity in efficacy and safety between Asians and non-Asians,
except for ischemic stroke, major, and gastrointestinal bleeding.
Conclusions—Our findings suggest that standard-dose NOACs were more effective and safer in Asians than in
non-Asians, whereas low-dose NOACs performed similarly in both populations. (Stroke. 2015;46:2555-2561.
DOI: 10.1161/STROKEAHA.115.009947.)
Key Words: anticoagulants ◼ atrial fibrillation ◼ hemorrhage ◼ stroke
S
phase III clinical trials.7–10 The availability of NOACs is of
paramount importance to Asian patients who are prone to
bleeding, including devastating ICH with or without VKAs.2,11
The observations from the Japanese Rivaroxaban Once Daily
Oral Direct Factor Xa Inhibition Compared With Vitamin K
Antagonism for Prevention of Stroke and Embolism Trial in
Atrial Fibrillation (J-ROCKET AF) might even imply that different dosing strategies should be applied according to ethnicities, weight, and renal function.12 Several prior observations
suggest that NOACs were more preferentially indicated for
stroke prevention in Asian patients with AF than VKAs.4,6,13
Although each trial was powered to address primary efficacy and safety outcomes of the overall patients who have
been enrolled, the benefit and risk profiles of NOACs in
Asian patients need proper description given the fact that the
troke prevention with vitamin K antagonists (VKAs) is
essential in the management of atrial fibrillation (AF).1
However, it has been generally perceived that Asian patients
are naturally more sensitive to VKAs and have unacceptably
higher rates of intracranial hemorrhage (ICH) even when international normalized ratio is ideally maintained.2 Consequently,
VKAs have been largely underused or underdosed in Asian
patients.3 Despite the average time in therapeutic range with
VKAs was lower in Asian patients than that in non-Asian
patients in clinical trials,4,5 the rates of major bleeding (ICH in
particular) were significantly higher in Asian patients.4,6
The development of non-VKA oral anticoagulants
(NOACs) has changed the landscape of stroke prevention in
patients with AF, with 4 agents available namely dabigatran,
rivaroxaban, apixaban, and edoxaban being tested in large
Received May 1, 2015; final revision received June 9, 2013; accepted June 23, 2015.
From the General Clinical Research Center (K.-L.W., C.-E.C.), Department of Medical Research (K.-L.W., S.-J.L., C.-E.C.), and Division of Cardiology
(K.-L.W., S.-J.L., C.-E.C.), Taipei Veterans General Hospital, Taipei, Taiwan; School of Medicine, National Yang-Ming University, Taipei, Taiwan (K.L.W., S.-J.L., C.-E.C.); University of Birmingham, Centre for Cardiovascular Sciences, City Hospital, Birmingham, United Kingdom (G.Y.H.L.); and
Aalborg Thrombosis Research Unit, Department of Clinical Medicine, Aalborg University, Aalborg, Denmark (G.Y.H.L.).
The online-only Data Supplement is available with this article at http://stroke.ahajournals.org/lookup/suppl/doi:10.1161/STROKEAHA.
115.009947/-/DC1.
Correspondence to Chern-En Chiang, MD, PhD, General Clinical Research Center, Taipei Veterans General Hospital, Taipei, Taiwan. E-mail cechiang@
vghtpe.gov.tw
© 2015 The Authors. Stroke is published on behalf of the American Heart Association, Inc., by Wolters Kluwer. This is an open access article under
the terms of the Creative Commons Attribution Non-Commercial-NoDervis License, which permits use, distribution, and reproduction in any medium,
provided that the original work is properly cited, the use is noncommercial, and no modifications or adaptations are made.
Stroke is available at http://stroke.ahajournals.org
DOI: 10.1161/STROKEAHA.115.009947
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burden of AF and its associated complications is substantially
higher in Asia than in the rest of the world because Asia is
the most populated region and has fast-growing aging societies.14,15 Since nonwhite ethnicities, particularly Asians, are a
major factor attributable to ICH in anticoagulated patients,16–18
more Asian patients would have been deemed ineligible for
treatment because of higher risk of bleeding.19 However, prior
analyses of the individual approved NOACs were underpowered to show quantitative differences in various outcomes
between Asian and non-Asian patients.20–23
In this meta-analysis, we aimed to assess the differences in
efficacy and safety outcomes of NOACs in Asian patients compared with non-Asian patients that have not been addressed in
previously published meta-analyses.24–27 Thus, these data are
new and important for patients, physicians, and other healthcare professionals in this region.
Methods
Data Sources and Searches
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We searched PubMed database (from January 2009 to July 2014),
clinical trial registries, and relevant conference proceedings using
the terms AF, warfarin, apixaban, dabigatran, edoxaban, rivaroxaban,
and stroke. Ximelagatran was excluded from the search because it
has been withdrawn from the market. No language restriction was
imposed. The reference lists of published meta-analyses were also
reviewed.
We consider randomized controlled trials comparing NOACs
with VKAs in patients with nonvalvular AF. Trials were eligible for
inclusion if they (1) involved >500 patients with nonvalvular AF; (2)
reported both long-term efficacy and safety outcomes in Asian patients; and (3) had follow-up ≥1 year.
Data Extraction
All efficacy and safety outcomes were extracted. The efficacy outcomes include the composite of stroke or systemic embolism, ischemic stroke, myocardial infarction, and death from any cause; the
safety outcomes were major bleeding, ICH, hemorrhagic stroke, and
gastrointestinal bleeding. Definitions of those outcomes were the
same across all trials, with the exception for major bleeding where
the trial-specific definitions were adopted. In addition, gastrointestinal bleeding has not been universally reported in Asian patients. Data
were used from the intention-to-treat populations for evaluating the
efficacy outcomes except for J-ROCKET AF, which was primarily
designed for evaluating safety outcomes. The differences in efficacy
and safety outcomes of NOACs compared with VKAs among Asian
and non-Asian patients were the interest of this meta-analysis.
Definition of Asian Patients
Because the individual patient-level data were not available, we could
not ascertain the ethnicity of each patient enrolled in the trials. We
therefore assumed that residence reported in the trials is a surrogate
for ethnicity.
Data Synthesis and Analysis
Primary Analysis
Two doses of dabigatran and edoxaban were tested in the Randomized
Evaluation of Long-Term Anticoagulation Therapy (RE-LY) and the
Effective Anticoagulation With Factor Xa Next Generation in Atrial
Fibrillation–Thrombolysis in Myocardial Infarction 48 (ENGAGE
AF-TIMI 48), respectively, and the low dose of rivaroxaban was compared with VKAs in J-ROCKET AF. Instead of combining data from
different doses into one meta-analysis, which merges the therapeutic
implications of different doses that might have diverse risk-benefit
profiles, we conducted 2 separate meta-analyses. The meta-analysis for standard-dose NOACs included data of dabigatran 150 mg,
edoxaban 60 mg, rivaroxaban 20 mg, and apixaban 5 mg. The metaanalysis for low-dose NOACs included data of dabigatran 110 mg,
edoxaban 30 mg, and rivaroxaban 15 mg.
Sensitivity Analysis
Data of Asian patients have not been homogenously published in detail. In the prior subanalyses reporting efficacy/safety among Asian
and non-Asian patients, there were 5, 1, and 3 Asian countries included as non-Asian countries in the Rivaroxaban Once Daily Oral
Direct Factor Xa Inhibition Compared with Vitamin K Antagonism
for Prevention of Stroke and Embolism Trial in Atrial Fibrillation
(ROCKET AF),21 the Apixaban for Reduction in Stroke and Other
Thromboembolic Events in Atrial Fibrillation (ARISTOTLE),22 and
ENGAGE AF-TIMI 48,23 respectively. In addition, patients enrolled
in Asian countries might not necessarily be ethnically Asian, vice
versa. To mitigate the confounding of such heterogeneous data, we
performed 3 sensitivity analyses by (1) examining data of 3 factor Xa
inhibitors, and using (2) ethnicity-level, and (3) region-level information available from regulatory agencies. The outcome data used for
sensitivity analyses were limited. Therefore, we could only investigate the composite of stroke or systemic embolism and major bleeding with respect to standard-dose NOACs compared with VKAs.
The odds ratio (OR) and associated 95% confidence interval (CI)
were calculated for each outcome and trial separately and for the pooled
results that were compared with DerSimonian and Laird random effects
model. Heterogeneity between trials was assessed using the Cochran
Q statistic and I2 test. Interaction between Asian and non-Asian patients about therapeutic outcomes of NOACs compared with VKAs
was systematically tested. Statistical analysis was performed using
Comprehensive Meta-Analysis software, version 2 (Biostat Inc, NJ).
Results
Of the 78 studies identified from the literature search, 73
were excluded because of reports of the trial design, subgroup
analyses without data of Asian patients, short follow-up, and
limited patient numbers (Figure I in the online-only Data
Supplement). The characteristics of the trials and treatment
included in this meta-analysis are shown in Table I in the
online-only Data Supplement. The 5 included studies namely
RE-LY, ROCKET AF, J-ROCKET AF, ARISTOTLE, and
ENGAGE AF-TIMI 48 comprised 8928 Asian patients (5250
with NOACs and 3678 with VKAs) and 64 033 non-Asian
patients (37 800 with NOACs and 26 233 with VKAs).
Standard-Dose NOACs Versus VKAs
The comparative efficacy of standard-dose NOACs and VKAs is
presented in Figure 1. Standard-dose NOACs significantly reduced
the composite of stroke or systemic embolism both in Asian and
non-Asian patients (OR, 0.65; 95% CI, 0.52–0.83; P<0.001 for
Asian patients; OR, 0.85; 95% CI, 0.77–0.93; P<0.001 for nonAsian patients). The reduction was more prominent in Asian
patients than in non-Asian patients (P interaction=0.045). The
effect of standard-dose NOACs on ischemic stroke and myocardial infarction was comparable with VKAs in both Asian and
non-Asian patients (P interaction=0.673 and 0.977, respectively).
All-cause mortality was significantly lower in both with standarddose NOACs than with VKAs (OR, 0.80; 95% CI, 0.65–0.98;
P=0.030 for Asian patients; OR, 0.91; 95% CI, 0.86–0.97;
P=0.003 for non-Asian patients; P interaction=0.219).
Figure 2 shows the preferential benefit of standard-dose
NOACs in safety outcomes in Asian patients. Standard-dose
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NOACs in Asians
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Figure 1. Efficacy outcomes of stroke or systemic embolism (A), ischemic stroke (B), myocardial infarction (C), and all-cause mortality (D) for the
standard-dose non–vitamin K antagonist (VKA) oral anticoagulants (NOACs) vs VKAs. CI indicates confidence interval; and OR, odds ratio.
NOACs reduced major bleeding more in Asian than in nonAsian patients (OR, 0.57; 95% CI, 0.44–0.74; P<0.001 for
Asian patients; OR, 0.89; 95% CI, 0.76–1.04; P=0.143 for
non-Asian patients; P interaction=0.004). ICH was significantly reduced in both with standard-dose NOACs (OR, 0.33;
95% CI, 0.22–0.50; P<0.001 for Asian patients; OR, 0.52;
95% CI, 0.42–0.64; P<0.001 for non-Asian patients; P interaction=0.059). Standard-dose NOACs had a substantial reduction in hemorrhagic stroke, which was more notable in Asian
than in non-Asian patients (OR, 0.32; 95% CI, 0.19–0.52;
P<0.001 for Asian patients; OR, 0.56; 95% CI, 0.44–0.70;
P<0.001 for non-Asian patients; P interaction=0.046) compared with VKAs. Moreover, standard-dose NOACs increased
the risk of gastrointestinal bleeding in non-Asian patients but
not in Asian patients (OR, 1.44; 95% CI, 1.12–1.85; P=0.005
for non-Asian patients; OR, 0.79; 95% CI, 0.48–1.32; P=0.378
for Asian patients; P interaction=0.041).
on stroke or systemic embolism and ischemic stroke both in
Asian and non-Asian patients (P interaction=0.353 and 0.504,
respectively). With regard to myocardial infarction, nonAsian patients had more events with low-dose NOACs than
with VKAs (OR, 1.28; 95% CI, 1.06–1.55; P=0.010), whereas
the effect of low-dose NOACs seemed to be similar to VKAs
in Asian patients (OR, 0.92; 95% CI, 0.48–1.79; P=0.816);
however, there was no statistic heterogeneity (P interaction=0.352). Low-dose NOACs were associated with a significant reduction in all-cause mortality in non-Asian patients and
a trend for a reduction in Asian patients (P interaction=0.934).
The safety outcomes of low-dose NOACs are presented
in Figure 4. Low-dose NOACs reduced major bleeding, ICH,
and hemorrhagic stroke in both Asian and non-Asian patients
(P interaction=0.579, 0.661, and 0.944, respectively). There
was no difference in gastrointestinal bleeding in Asians and
non-Asians (P interaction=0.460).
Low-Dose NOACs Versus VKAs
Sensitivity Analysis
The comparative efficacy of low-dose NOACs and VKAs
with regard to the various efficacy outcomes is presented in
Figure 3. Low-dose NOACs had similar efficacy to VKAs
The sensitivity analysis undertaken using factor Xa inhibitor
trials showed parallel results to the primary analyses except for
stroke or systemic embolism (Table II in the online-only Data
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Figure 2. Safety outcomes of major bleeding (A), intracranial hemorrhage (B), hemorrhagic stroke (C), and gastrointestinal bleeding (D) for the
standard-dose non–vitamin K antagonist (VKA) oral anticoagulants (NOACs) vs VKAs. CI indicates confidence interval; and OR, odds ratio.
Supplement). Additional analyses using data available from the
regulatory agency indicated the qualitatively similar results to
our primary analyses that standard-dose NOACs significantly
reduced stroke or systemic embolism and major bleeding to a
greater degree in Asian than in non-Asian patients (Figures II
and III in the online-only Data Supplement).
Discussion
Our study is the first meta-analysis of large phase III clinical trials that compared NOACs with VKAs in Asian and
non-Asian patients with regard to both efficacy and safety
outcomes. This analysis included >8000 Asian patients; the
responses to NOACs were qualitatively similar between Asian
and non-Asian patients with quantitatively greater benefits in
Asian patients. Our data suggest that both standard-dose and
low-dose NOACs are preferentially indicated in Asian patients
for the prevention of AF-associated stroke rather than VKAs.
Previous meta-analyses consistently showed that standarddose NOACs were more effective than VKAs on the reduction
of stroke or systemic embolism.24–27 In our analysis, standarddose NOACs were more effective than VKAs in both Asian
and non-Asian patients, but NOACs fared even better in Asian
patients. In addition, standard-dose NOACs were more effective on the reduction of hemorrhagic stroke in Asian than in
non-Asian patients, which is most likely attributed to a higher
bleeding risk with VKAs in Asian patients.
The major criticism of standard-dose NOACs, which has
been consistently shown in previous meta-analyses, was that
they were less effective on the reduction of major bleeding.25–27
In our analysis, however, standard-dose NOACs were still effective in Asian patients, compared with VKAs. In non-Asian
patients, the beneficial effect on major bleeding was marginal.
It is possible that NOACs are more effective in Asian patients
than in non-Asian patients because the risk of major bleeding in
Asian with VKAs is generally higher than in non-Asian patients
even though more Asian patients had international normalized
ratio <2.0 and less Asian patients had international normalized
ratio >3.0.4 The absolute risk of major bleeding with NOACs
was numerically lower in Asian than in non-Asian patients (the
annual risk was 2.17% versus 3.52%, 3.44% versus 3.60%, and
2.02% versus 2.15%, with dabigatran 150 mg, rivaroxaban 20
mg, and apixaban 5 mg, respectively). Therefore, the absolute
risk reduction in major bleeding by standard-dose NOACs was
generally greater in Asian than in non-Asian patients.20–23
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Figure 3. Efficacy outcomes of stroke or systemic embolism (A), ischemic stroke (B), myocardial infarction (C), and all-cause mortality (D) for
the low-dose non–vitamin K antagonist (VKA) oral anticoagulants (NOACs) vs VKAs. CI indicates confidence interval; and OR, odds ratio.
Another important criticism of standard-dose NOACs is an
increase in risk of gastrointestinal bleeding.25–28 We found that
the increased risk of gastrointestinal bleeding was only significant in non-Asian patients. Indeed, the numbers for gastrointestinal bleeding in Asian patients were not reported either in
ROCKET AF or in ARISTOTLE, but the risk of gastrointestinal
bleeding was numerically higher in overall patients with rivaroxaban than with VKAs (3.15% versus 2.16%) in ROCKET
AF.8 The risk of digestive tract bleeding was numerically similar
in overall patients with apixaban versus VKAs (0.78% versus
0.88%).29 Unlike other bleeding events, gastrointestinal bleeding with VKAs was similar in Asian and in non-Asian patients
(1.41% versus 1.01% and 1.11% versus 1.24% for Asian patients
versus non-Asian patients in RE-LY and ENGAGE AF-TIMI
48, respectively). Concomitant antiplatelet therapy is an independent predictor for gastrointestinal bleeding.28,30,31 In RE-LY,
the concomitant use of aspirin was more common and the use of
proton pump inhibitors was less common in Asian than in nonAsian patients, but gastrointestinal bleeding was not increased
by dabigatran 150 mg.20 Our findings may suggest that standarddose NOACs should not be avoided in Asian patients simply on
the basis of the risk of gastrointestinal bleeding.
Low-dose NOACs are similarly effective as VKAs in prevention against stroke or systemic embolism for both Asian
and non-Asian patients but might not be as effective for protection against ischemic stroke. They are safer than VKAs
with respect to hemorrhagic stroke, and no difference could
be found between Asian and non-Asian patients. Our analysis
suggests that low-dose NOACs were effective on the reduction of major bleeding and ICH in both Asian and non-Asian
patients, compared with VKAs. Again, no signal of increased
gastrointestinal bleeding was observed. Based on our analysis, low-dose NOACs can be effective and safe alternatives to
VKAs in Asian patients and should be considered in patients
with higher bleeding risk.
Finally, the general mechanisms involved with the differential effects of NOACs compared with VKAs between Asian and
non-Asian patients are yet to be determined. Genetically, Asian
patients are more likely to be VKA sensitive or highly sensitive responders, who seem prone to excessive bleeding.32 Except
for the variations in distributions of genetic polymorphisms for
VKA metabolism,33,34 Asian patients tended to have lower body
weight, smaller proportions of prior myocardial infarction, VKA
experiences, and the concomitant use of gastric antacid drugs,
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Figure 4. Safety outcomes of major bleeding (A), intracranial hemorrhage (B), hemorrhagic stroke (C), and gastrointestinal bleeding (D) for
the low-dose non–vitamin K antagonist (VKA) oral anticoagulants (NOACs) vs VKAs. CI indicates confidence interval; and OR, odds ratio.
and greater proportions of impair renal function, prior stroke,
nonparoxysmal AF, and the use of antiplatelet medications.20–23
Those demographic differences might be clinically relevant factors for anticoagulant treatment other than ethnic per se.
Limitations
Our analysis has several limitations. First, we did not have
individual patient-level data from trials included for this metaanalysis. Without individual patient-level information, some of
the patients enrolled in Asian countries described in our metaanalysis might not be ethnically Asian, and some of the Asian
patients were included in non-Asian populations in the analyses
of clinical trials.21–23 However, the majority of Asian patients
would be enrolled in Asia as, for example, only 11 Asian
patients were recruited at US sites in ARISTOTLE. In addition,
the sensitivity analyses with the available information at ethnic
and regional levels from the regulatory agency showed similar
results to our primary analyses. Second, the benefit of NOACs
in Asian population may be related to genetic polymorphism
for VKA metabolism, and lower body weight and creatinine
clearance. However, relative efficacy of NOACs is consistent
across a broad range of vulnerable patients,27 and a greater
reduction in bleeding risk with NOACs compared with VKAs
was seen across genotypes,32 body weight,7–9 and renal function.7,8 Finally, there was some heterogeneity between included
trials. Therefore, we used a random effects model to account for
heterogeneity within individual trials.
Conclusions
Both standard-dose and low-dose NOACs performed equally
well, or even better, with regard to efficacy and safety in
Asian than in non-Asian patients. Standard-dose NOACs are
preferred over VKAs in Asian patients, whereas low-dose
NOACs are effective and safe alternatives to VKAs.
Sources of Funding
This work was supported, in part, by grants from the Ministry of
Health and Welfare (MOHW104-TDU-B-211-113-003) and from the
Ministry of Science and Technology (102-2628-B-075-004-MY3),
and intramural grants from the Taipei Veterans General Hospital
(V104B-026; V104C-016).
Disclosures
Dr Wang has received honoraria from Bayer and Daiichi-Sankyo.
Dr Lip has served as a consultant for Bayer, Biotronik, BMS/Pfizer,
Wang et al
Boehringer Ingelheim, Daiichi-Sankyo, Medtronic, Merck, Portola,
and Sanofi and has been on the speaker bureau for Bayer, BMS/Pfizer,
Boehringer Ingelheim, Daiichi-Sankyo, and Medtronic. Dr Chiang
has been on the speaker bureau for Bayer, Boehringer Ingelheim, and
Daiichi-Sankyo. Dr Lin reports no conflicts.
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