Keywords venous thromboembolism - vitamin K antagonists - direct oral anticoagulants - on-treatment
comparative effectiveness - anticoagulation
Introduction
Anticoagulation (AC) is the mainstay of venous thromboembolism (VTE) treatment, with
only select cases receiving thrombolytic or other reperfusion therapies. For many
years, AC treatment consisted of a parenteral anticoagulant (such as heparin), overlapped
with and followed by a vitamin K antagonist (VKA), such as warfarin. The introduction
of direct oral anticoagulants (DOACs) provided a safe and effective alternative to
this conventional treatment.[1 ]
[2 ]
[3 ]
[4 ]
[5 ] The changing landscape of VTE treatment requires observational studies to assess
the comparative effectiveness of DOACs and VKAs in the global community setting. The
Global Anticoagulant Registry in the FIELD – Venous Thromboembolism (GARFIELD-VTE),
a prospective, multicenter, non-interventional, observational study of patients treated
for acute VTE,[6 ] provides a framework for such a comparative effectiveness study.
Previous analyses of data from GARFIELD-VTE highlighted the high uptake of DOACs as
an alternative AC treatment.[7 ] Patients were separated into five AC groups; those receiving parenteral AC alone,
parenteral AC with a transition to VKAs, VKAs only, parenteral AC with a transition
to DOACs, and DOACs only. We previously compared the effectiveness of VKAs and DOACs
in an intention-to-treat (ITT) analysis, comparing the clinical outcomes of patients
receiving these anticoagulants, with or without parenteral AC bridging.[8 ]
ITT analysis avoids the bias associated with the non-random loss of participants.
However, patients remain in the treatment group they received at baseline, regardless
of whether they discontinued, crossed over to the other treatment(s) being studied,
or adhered to the treatment over the course of follow-up. In contrast, on-treatment
analysis is restricted to the period of follow-up during which a patient is on their
assigned treatment.
On-treatment analysis is imperative in observational studies, because the duration
and choice of AC are at the investigators' discretion and may change over time. We
have seen that the length of time on treatment does vary compared to other indications,
such as atrial fibrillation, where patients are on chronic use of drug indefinitely.
CONSORT guidelines suggest that investigators should report both ITT and on-treatment
analyses because “when both analyses provide identical conclusions, the confidence
level of the investigator for the study results is augmented.”[9 ] This on-treatment analysis leads to essentially the same conclusions as our ITT
analysis, thereby increasing the robustness of our previous results with the advantage
that the same data base was used. Following the rules of good statistical practice
for clinical research, refined methods were used for these analyses as described in
the part of statistics. Available factors that are associated with the initial treatment
decision, duration of treatment, and early discontinuation of treatment are considered
in the modeling process.
The aim of this study was to compare the effectiveness of DOACs and VKAs (with or
without parenteral AC bridging) on 12-month outcomes in VTE patients taking into account
changes in treatment over time. Additional analyses focused on special patient populations
with active cancer or renal insufficiency.
Methods
Study Design and Participants
A detailed description of the rationale and design of GARFIELD-VTE has been published
previously.[6 ] The registry enrolled patients (≥18 years) between May 2014 and January 2017, diagnosed
and treated across a range of care settings from 418 sites in 28 countries worldwide.
The aim of the registry was to record local treatment practices; therefore, no specific
treatments or procedures were mandated by the study protocol. Eligible patients were
required to have an objective diagnosis of VTE (excluding superficial vein thrombosis)
within 30 days of entry into the registry. Patients with recurrent VTE must have completed
treatment for the previous event. Patients were excluded if long-term follow-up was
not planned, or if they were participating in other studies that dictated visits,
diagnostic procedures, or treatments.
Selection of Study Sites
The national coordinating investigator identified the care settings they believed
most accurately represented the management of VTE patients in their country. The contract
research organization provided a list of sites that reflected these care settings,
before contacting a random sample of sites for each care setting from the list. Sites
that agreed to participate were recruited after a qualification telephone call. The
investigator was required to complete a program providing guidance on patient screening,
enrollment, and follow-up in the registry.
Ethics Statement
The registry is conducted in accordance with the Declaration of Helsinki and guidelines
from the International Conference on Harmonization on Good Clinical Practice and Good
Pharmaco-epidemiological Practice, and adheres to all applicable national laws and
regulations. Independent ethics committees for each participating country and the
hospital-based institutional review boards approved the design of the registry. All
patients provided written informed consent to participate and confidentiality and
anonymity are maintained.
Data Collection
Patient data relevant to VTE were collected through a review of clinical records and
patient notes. Data were captured using an electronic case report form designed by
eClinicalHealth Services, Stirling, United Kingdom, and submitted electronically via
a secure website to the registry-coordinating center at the Thrombosis Research Institute,
London, United Kingdom, which was responsible for checking the completeness and accuracy
of data collected from medical records. The GARFIELD-VTE protocol requires that 10%
of all electronic case report forms are monitored against source documentation, that
there is an electronic audit trail for all data modifications, and that critical variables
are subjected to additional audit. The data were extracted from the study database
on October 14th , 2020.
Outcomes
The primary clinical outcomes were all-cause mortality, recurrent VTE, and major bleeding.
Recurrent VTE was defined as a symptomatic event objectively confirmed by compression
ultrasonography, contrast venography, computed tomography (CT) scan or magnetic resonance
venography for deep vein thrombosis (DVT), and ventilation/perfusion scan, spiral
CT scan, chest CT pulmonary angiography, or magnetic resonance angiography for PE.
Major bleeding was defined according to the International Society on Thrombosis and
Haemostasis criteria.[10 ] Non-major bleeding was defined as any overt bleeding not meeting the criteria for
major bleeding. The rates of cancer, non-hemorrhagic stroke/transient ischemic attack,
and myocardial infarction were also recorded. Additionally, information was collected
regarding the cause of death and site of bleeding.
Patients were characterized as having active cancer if they were diagnosed and/or
receiving treatment for their cancer during the window of ≤90 days before VTE diagnosis
and up to 30 days after VTE diagnosis. Patients were defined as having a history of
cancer if the cancer went into remission and the patient was not receiving any cancer
treatment >90 days before the diagnosis of VTE. Cancer events that were diagnosed
more than 30 days after the VTE diagnosis date were considered as cancer outcomes.
Renal insufficiency was defined as stage III-V chronic kidney disease (moderate, severe,
and kidney failure) in patients with a glomerular filtration rate of <60 mL/min/1.73
m2 calculated with equation from Modification of Diet in Renal Disease (MDRD) study.[11 ]
Statistical Analysis
This study evaluates the comparative effectiveness of DOACs and VKAs with or without
pretreatment with parenteral anticoagulants in VTE patients. Patients were excluded
if they received parenteral AC alone, thrombolysis, or surgical or mechanical interventions.
Patients are right censored when the treatment is completed or permanently discontinued.
(OAC has been discontinued for more than 7 days. Discontinuations for less time are
considered temporary discontinuations). This analysis used the “on treatment” or “per
protocol” concept.[12 ] The effects of VKAs and DOACs were evaluated with marginal structural models using
inverse probability weights (IPWs) adjusting for baseline characteristics, possible
confounding by major bleeding events, and for informative censoring due to the effect
of major bleeding on dropout. Baseline variables for the adjustment included: age,
gender, ethnicity, body mass index (BMI), previous aspirin usage, VTE type (DVT alone,
pulmonary embolism [PE] alone, DVT and PE), site of DVT (upper limb, lower limb, caval
vein inferior or superior), care setting, physician specialty, treatment funding source,
country, creatinine clearance, active cancer, recent bleeding or anemia, pregnancy,
family history of VTE, history of cancer, known thrombophilia, prior VTE episodes,
and renal insufficiency. Missing values for the adjustment were imputed using the
Multivariable Imputation by Chained Equations (MICE) method.[13 ] Missing data were reported but not included in percentage calculations. Events were
counted if they occurred within 365 days of the initial VTE diagnosis. Only the first
occurrence of each event was considered.
Poisson regression was used to estimate unadjusted incidence rates (expressed per
100 person-years) and corresponding 95% confidence intervals (CI) by treatment for
the clinical outcomes. Time-to-event analyses of outcomes were performed with IPWs
time-varying Cox proportional hazards models. Variance of model coefficients was estimated
using the Huber Sandwich Estimator.[14 ] The relationship between treatment groups was reported with hazard ratios (HRs)
and their corresponding 95% CIs. All analyses are hypothesis generating and not conclusive
in nature. Statistical analyses were conducted using R statistical software version
3.5.1.[15 ]
Results
Patient Enrolment
Of the 11,840 VTE patients invited to enter the registry, 10,868 (91.8%) were enrolled.
Of these, 184 patients were excluded because VTE was not objectively confirmed. Of
the 10,684 patients eligible for this analysis, 8,034 were treated with oral anticoagulants
with or without parenteral bridging; 4,991 (62.1%) received a DOAC and 3,043 (37.9%)
received a VKA. [Fig 1 ] illustrates the treatment pattern over 12-months follow-up. The median follow-up
time was comparable for both treatment groups; VKA: 355 days (interquartile range
[IQR]: 176–365) versus DOAC: 344 days (IQR: 141.5–365).
Fig. 1 Treatment patterns over 12-months follow-up. No OAC includes end of study from death,
termination of treatment or loss to follow-up. DOAC, direct oral anticoagulant; OAC,
oral anticoagulant; VKA, vitamin-K antagonist.
Baseline Characteristics
Baseline characteristics are provided in [Table 1 ]. The median age of patients receiving DOACs or VKAs was similar, 60 years (IQR:47–72)
and 59 years (IQR:44–71), respectively, and a similar proportion were female (48.4
vs. 48.7%, respectively). DOACs were less frequently prescribed to Black patients
than VKAs (1.7 vs. 10.7%), whereas Caucasian patients more frequently received DOACs
(76.3 vs. 64.2%).
Table 1
Baseline characteristics
Variable
VKA (N = 3,043)
DOAC (N = 4,991)
Male, n (%)
1,560 (51.3)
2,576 (51.6)
Age, median (IQR)
59.0 (44.3, 70.7)
60.4 (46.7, 71.8)
Age groups, n (%)
< 50
1,026 (33.7)
1,530 (30.7)
50–65
890 (29.2)
1,469 (29.4)
65–75
612 (20.1)
1,076 (21.6)
75–85
400 (13.1)
733 (14.7)
> 85
115 (3.8)
183 (3.7)
Ethnicity, n (%)
Asian
438 (14.9)
793 (17.1)
Black
315 (10.7)
78 (1.7)
Caucasian
1,882 (64.2)
3,536 (76.3)
Other
297 (10.1)
229 (4.9)
Missing
111
355
BMI, median (IQR)
27.9 (24.3, 32.1)
27.5 (24.3, 31.6)
BMI categories
Underweight (<18.5)
62 (2.3)
69 (1.5)
Normal (18.5–24.9)
756 (27.8)
1,296 (29.0)
Overweight (25–29.9)
911 (33.5)
1,639 (36.7)
Obese (≥30)
992 (36.5)
1,468 (32.8)
Missing
322
519
Creatinine clearance, mL/min, median (IQR)
93.7 (64.1, 127.3)
94.8 (68.1, 123.8)
Creatinine clearance, mL/min, n (%)
I – Normal (≥90)
840 (32.7)
1,288 (30.6)
II – Mild (60–89)
1,053 (41.0)
2,072 (49.3)
III – Moderate (30–59)
499 (19.4)
746 (17.7)
IV – Severe (15–29)
79 (3.1)
48 (1.1)
V – Failure (<15)
97 (3.8)
49 (1.2)
Missing
475
788
Smoking status, n (%)
Never
1,775 (59.9)
2,930 (61.5)
Ex-smoker
687 (23.2)
1,039 (21.8)
Current smoker
499 (16.9)
798 (16.7)
Missing
82
224
Care setting, n (%)
Hospital
2,230 (73.3)
3,474 (69.6)
Outpatient setting
813 (26.7)
1,517 (30.4)
Abbreviations: BMI, body mass index; DOAC, direct oral anticoagulants; IQR, interquartile
range; VKA, vitamin K antagonists.
[Table 2 ] summarizes all risk factors present in both patient groups. Patients receiving VKAs
were more likely to have had acute medical illness (7.2 vs. 4.3%), or have been hospitalized
within the 3 months preceding VTE diagnosis (12.1 vs. 9.7%) than those receiving DOACs.
Chronic heart failure and a recent bleed or anemia were also more common in patients
receiving VKAs (4.3 vs. 2.4% and 4.2 vs. 2.1%, respectively).
Table 2
VTE risk factors present within the 3 mo preceding VTE diagnosis
Risk factor, n (%)
VKA (N = 3,043)
DOAC (N = 4,991)
Acute medical illness[a ]
218 (7.2)
214 (4.3)
Hospitalization[a ]
367 (12.1)
483 (9.7)
Long-haul travelling[a ]
168 (5.5)
286 (5.7)
Surgery[a ]
345 (11.3)
617 (12.4)
Trauma of the lower limb[a ]
212 (7.0)
443 (8.9)
Active cancer
144 (4.7)
264 (5.3)
Pregnancy
55 (1.8)
31 (0.6)
Recent bleed or anemia
129 (4.2)
106 (2.1)
Chronic heart failure
132 (4.3)
121 (2.4)
Chronic immobilization
183 (6.0)
206 (4.1)
Family history of VTE
192 (6.3)
354 (7.1)
History of cancer
285 (9.4)
493 (9.9)
Hormone replacement therapy (females)
46 (1.5)
82 (1.6)
Known thrombophilia
85 (2.8)
144 (2.9)
Oral contraception (females)
143 (4.7)
316 (6.3)
Prior episode of DVT and/or PE
514 (16.9)
795 (15.9)
Renal insufficiency
179 (5.9)
107 (2.1)
Abbreviations: DOAC, direct oral anticoagulant; DVT, deep vein thrombosis; VKA, vitamin
K antagonist; VTE, venous thromboembolism.
a Provoking factors.
Patients with PE ± DVT were as likely to receive a DOAC or a VKA (40.3 vs. 36.9%),
as those with DVT alone (59.7 vs. 63.1%). Of those with lower limb DVT, patients with
isolated distal DVT were more likely to receive a DOAC than a VKA (38.8 vs. 29.5%),
whereas patients with proximal (±distal) DVT were more likely to receive a VKA (70.5
vs. 61.2%) ([Table 3 ]).
Table 3
VTE characteristics
Variable, n (%)
VKA (N = 3,043)
DOAC (N = 4,991)
VTE type
DVT
1,920 (63.1)
2,978 (59.7)
PE
740 (24.3)
1,127 (22.6)
DVT and PE
383 (12.6)
886 (17.8)
Site of DVT
Upper limb
86 (3.7)
180 (4.7)
Lower limb
2,184 (95.1)
3,630 (93.9)
Caval vein (inferior)
15 (0.7)
32 (0.8)
Caval vein (superior)
12 (0.5)
22 (0.6)
Type of lower limb DVT
Distal
638 (29.5)
1,394 (38.8)
Proximal
956 (44.2)
1,143 (31.8)
Proximal & distal
570 (26.3)
1,057 (29.4)
Missing
879
1,397
Type of PE
Main
308 (27.6)
560 (28.1)
Lobar
360 (32.3)
571 (28.6)
Segmental
338 (30.3)
677 (34.0)
Sub-segmental
109 (9.8)
186 (9.3)
Missing
1,928
2,997
Abbreviations: DOAC, direct oral anticoagulants; DVT, deep vein thrombosis; PE, pulmonary
embolism; VKA, vitamin K antagonist; VTE, venous thromboembolism.
Patients enrolled from vascular medicine practices were more likely to receive a DOAC
than a VKA (49.4 vs. 39.8%), whereas those enrolled from internal medicine practices
were more likely to receive a VKA (51.1 vs. 37.3%). Patients enrolled in Europe were
more likely to receive DOACs than a VKA (60.5 vs. 52.9%), whereas the opposite was
true in patients enrolled in the Middle East and South Africa (6.6 vs. 19.5%). A breakdown
of the number of patients from each country receiving DOACs or VKAs is provided in
[Supplementary Table S1 ].
Clinical Outcomes
After 12 months follow-up, the unadjusted rate of all-cause mortality was lower in
patients receiving DOACs than in those receiving VKAs (2.61 [2.12–3.20] per 100 person-years
vs. 5.69 [4.76–6.79] per 100 person-years). The rate of recurrent VTE was similar
in patients receiving DOACs and VKAs (2.97 [2.44–3.61] per 100 person-years vs. 4.32
[3.52–5.30] per 100 person-years, respectively). The rate of major bleeding was also
comparable (DOAC: 1.69 [1.30–2.18] per 100 person-years vs. VKA: 2.35 [1.78 − 3.10]
per 100 person-years) ([Table 4 ]). The unadjusted survival curves for all-cause mortality, recurrent VTE, and major
bleeding are provided in [Figs. 2A ], [B ], and [C ], respectively.
Fig. 2 Kaplan-Meier curves for (A) all-cause mortality, (B) recurrent VTE, and (C) major bleeding. The number of patients at risk at each time point is shown below
each curve.
Table 4
12 Month unadjusted event rates. event rates are shown per 100 person-years
Outcome
VKA (N = 3,043)
DOAC (N = 4,991)
Number of events
Rate (95% CI)
Number of events
Rate (95% CI)
All-cause mortality
122
5.69 (4.76 − 6.79)
90
2.61 (2.12 − 3.20)
Recurrent VTE
91
4.32 (3.52 − 5.30)
101
2.97 (2.44 − 3.61)
Major bleeding
50
2.35 (1.78 − 3.10)
58
1.69 (1.30 − 2.18)
Any bleeding
258
12.65 (11.20 − 14.29)
395
12.02 (10.89 − 13.26)
Myocardial infarction
12
0.56 (0.32 − 0.99)
15
0.44 (0.26 − 0.72)
Stroke/TIA
8
0.37 (0.19–0.75)
21
0.61 (0.40 − 0.93)
Abbreviations: TIA, transient ischemic attack; VTE, venous thromboembolism.
After adjustment, the rate of all-cause mortality remained lower in patients receiving
DOACs than in those receiving VKAs (HR: 0.58; 95% CI: 0.42–0.79, p = 0.001). The risk of recurrent VTE was comparable with DOACs and VKAs (HR: 0.74;
95% CI: 0.55–1.01), p = 0.06. The rates of major bleeding were similar in patients receiving DOACs and
VKAs (HR: 0.76; 95% CI: 0.47–1.24, p = 0.270) as were the rates of myocardial infarction and stroke ([Fig 3 ]). Patients receiving DOACs were less likely to die from VTE complications than those
receiving VKAs (2.2 vs. 4.9%), but were more likely to have cancer-related deaths
(45.6 vs. 34.4%). They were also less likely to have a fatal bleed than those receiving
VKAs (0.0 vs. 4.9% of all deaths) ([Table 5 ]). The site of recurrent DVT did not differ between treatment groups, however, the
burden of PE seemed to be lower in the DOAC group. The main and lobar pulmonary branches
were affected in 74.2% of the patients treated with VKAs versus 43.3% in the DOAC
group ([Supplementary Table S2 ]). The most common sites of major bleeding in patients receiving DOACs and VKAs were
the upper gastrointestinal tract (15.5 and 10.0%), lower gastrointestinal tract (19.0
and 22.0%), and uterus (17.2 and 12.0%) ([Supplementary Table S3 ]).
Table 5
Cause of death
Cause of death, n (%)
VKA (N = 122)
DOAC (N = 90)
VTE
6 (4.9)
2 (2.2)
Stroke
2 (1.6)
1 (1.1)
Cardiac
10 (8.2)
11 (12.2)
Cancer-related
42 (34.4)
41 (45.6)
Bleed
6 (4.9)
0 (0.0)
Other
31 (25.4)
14 (15.6)
Unknown
25 (20.5)
21 (23.3)
Abbreviation: VTE, venous thromboembolism.
Fig. 3 Adjusted hazard ratios between DOAC and VKA (reference) treatment groups. Values
<1 favor DOAC treatment over VKA because they are indicative of a reduction in the
hazard rate. [* ] HRs were adjusted for major bleeding and dropout at follow-up in addition to the
following baseline characteristics: age, gender, ethnicity, BMI, previous aspirin
usage, VTE type (DVT alone, PE alone, DVT, and PE), site of DVT (upper limb, lower
limb, caval vein inferior or superior), care setting, physician specialty, treatment
funding source, country, creatinine clearance, active cancer, recent bleeding or anemia,
pregnancy or postpartum, family history of VTE, history of cancer, known thrombophilia,
prior VTE episodes, and renal insufficiency. DOAC, Direct oral anticoagulants; DVT,
deep vein thrombosis; PE, pulmonary embolism.
In patients with renal insufficiency, the unadjusted rate of all-cause mortality was
lower in patients receiving DOACs than in those receiving VKAs (4.70 [3.25–6.81] per
100 person-years vs. 9.97 [7.51–13.23] per 100 person-years). The rates of recurrent
VTE and major bleeding were comparable between treatment groups ([Table 6 ]). In patients with concomitant active cancer, the rate of all-cause mortality was
lower in those treated with DOACs than in those treated with VKAs (26.52 [19.37–36.29]
per 100 person-years vs. 52.51 [37.33–73.86] per 100 person-years). The rate of recurrent
VTE was also lower in cancer patients receiving DOACs than in those receiving VKAs
(3.40 [1.42–8.18] per 100 person-years vs. 17.93 [9.93–32.38] per 100 person-years).
The rates of major bleeding were comparable between treatment groups ([Table 7 ]).
Table 6
12 Month unadjusted event rates in VTE patients with renal insufficiency
Outcome
VKA (N = 675)
DOAC (N = 843)
Number of events
Rate (95% CI)
Number of events
Rate (95% CI)
All-cause mortality
48
9.97 (7.51–13.23)
28
4.70 (3.25–6.81)
Recurrent VTE
28
5.96 (4.11–8.63)
16
2.73 (1.67–4.46)
Major bleeding
18
3.79 (2.39–6.01)
17
2.87 (1.79–4.62)
Any bleeding
65
14.18 (11.12–18.09)
89
15.92 (12.93–19.59)
Myocardial infarction
6
1.25 (0.56–2.79)
3
0.50 (0.16–1.57)
Stroke/TIA
5
1.04 (0.43–2.50)
2
0.34 (0.08–1.34)
Abbreviations: TIA, transient ischemic attack; VTE, venous thromboembolism.
Table 7
12 month unadjusted event rates in VTE patients with active cancer
Outcome
VKA (N = 144)
DOAC (N = 264)
Number of events
Rate (95% CI)
Number of events
Rate (95% CI)
All-cause mortality
33
52.51 (37.33 − 73.86)
39
26.52 (19.37 − 26.29)
Recurrent VTE
11
17.93 (9.93 − 32.38)
5
3.40 (1.42 − 8.18)
Major bleeding
7
11.24 (5.36 − 23.58)
6
4.10 (1.84 − 9.12)
Any bleeding
17
28.05 (17.44 − 45.13)
26
18.59 (12.66 − 27.30)
Myocardial infarction
2
3.18 (0.80 − 12.73)
0
N/A
Stroke/TIA
0
N/A
2
1.36 (0.34 − 5.44)
Abbreviations: TIA, transient ischemic attack; VTE, venous thromboembolism.
Time on Treatment
When comparing the median (Q1,Q3) time in days that patients were on treatment, patients
that were treated with VKA were on treatment for longer than those treated with DOAC:
355.0 (176.0, 365.0) versus 344 (141.5, 365.0) ([Table 8 ]). It should also be noted that patient follow-up was stopped at the time the treatment
ended so the time of follow-up is identical to the time on treatment.
Table 8
Follow-up time by treatment
Follow-up (days)
VKA (N = 3,043)
DOAC (N = 4,991)
Total (N = 8,034)
Mean (SD)
257.4 (122.7)
252.7 (123.9)
254.5 (123.4)
Median (Q1,Q3)
355.0 (176.0, 365.0)
344.0 (141.5, 365.0)
346.0 (157.0, 365.0)
Min–Max
1.0–365.0
1.0–365.0
1.0–365.0
Missing
0
0
0
Abbreviations: DOAC, direct oral anticoagulants; VKA, vitamin K antagonist.
Discussion
Garfield-VTE was launched shortly after the clinical introduction of DOACs. Differences
in ethnicity and geography were observed between the two oral AC groups. Geographical
differences observed between treatment patterns with DOACs or VKAs may reflect the
availability or approval status for DOACs in the respective countries worldwide. These
differences may also represent inherent global health inequities and reimbursement
differences for DOACs versus VKAs.
This on-treatment comparative effectiveness analysis of VKAs and DOACs demonstrates
that the risk of all-cause mortality in VTE patients is more than one-third lower
with DOACs than with VKAs. Both fatal bleeds and VTE-related deaths were reduced in
patients receiving DOACs. Our findings of significant reduction in VTE-related deaths
in the DOAC group are consistent with the findings of Mai et al, who performed a meta-analysis
of randomized clinical trials (RCTs) evaluating the effect of extended AC as secondary
prevention for VTE compared with placebo. The authors found that DOACs were associated
with a reduction in overall (risk ratio [RR], 0.48; 95% CI, 0.27–0.86; p = 0.01) and VTE-related (RR, 0.36; 95% CI, 0.15–0.89; p = 0.03) mortality, whereas VKAs were not.[16 ] This meta-analysis also described that VKAs and DOACs similarly prevented recurrent
VTE,[16 ] which we can confirm through our real-world observations, i.e. the risk of recurrent
VTE, as well as arterial events such as myocardial infarction and stroke, was not
significantly different between treatment groups in GARFIELD-VTE. Regarding arterial
events, however, it must be noted that the event rates in both groups are very low
and unlike venous events, these arterial events are based on clinical information
provided by the investigator and rather than objectively proven diagnoses. In contrast
to Mai et al[16 ] we could not confirm a general reduction of bleeding (both major and overall) in
favor of DOACs. However, our findings of reduced fatal bleedings in the DOAC group
should be reemphasized.
The RCTs of apixaban, dabigatran, edoxaban, and rivaroxaban showed comparable rates
of all-cause mortality between DOACs and VKAs.[1 ]
[2 ]
[3 ]
[4 ] Our results of reduced mortality are in agreement with the non-interventional XALIA
study programme that showed a significant reduction in mortality with rivaroxaban
compared with conventional AC treatment.[17 ] Indeed, due to the early clinical availability of rivaroxaban worldwide, approximately
80% of patients receiving a DOAC were prescribed rivaroxaban in GARFIELD-VTE.[7 ] The mortality results of our comparative effectiveness analyses also concur with
a recent meta-analysis of real-world studies comparing effectiveness and safety of
the DOACs rivaroxaban and apixaban with standard of care in patients with VTE. The
authors showed that in real-world practice, rivaroxaban and apixaban were associated
with a lower risk of recurrent VTE and major bleeding events compared with standard
of care and a survival benefit in patients treated with rivaroxaban was also observed.[18 ] Our findings are also in agreement with those of the START2-Register, which showed
significantly reduced mortality in elderly VTE patients receiving DOACs compared with
VKAs. However, the average age was significantly higher in that registry than in patients
in GARFIELD-VTE.[19 ]
The results of this on-treatment analysis are in agreement with our previous ITT analysis,
which, after adjustment, estimated a 27% reduction in the risk of all-cause mortality
with DOACs compared with VKAs.[8 ] We now report a 42% reduction in this study, using marginal structural models to
control for time-varying confounding. This finding suggests that the benefits of DOACs
over VKAs for VTE treatment may be greater than initially thought. Indeed, ITT analysis
typically underestimates the superiority effect of a treatment.[20 ] On-treatment analyses are most informative in observational studies, because the
choice and duration of AC are not dictated by a protocol, but are decided individually
by the investigator and the patient.[21 ] This on-treatment analysis shows that the reduction in the risk of all-cause mortality
remains after accounting for changes in the anticoagulant received or delivered, treatment
non-adherence, or medically indicated discontinuation.
In contrast to RCTs, the GARFIELD-VTE registry includes patients with multiple comorbidities,
including renal insufficiency and active cancer, who would have been excluded from
the pivotal trials. We observed that the reduced rate of all-cause mortality with
DOACs compared with VKAs was maintained in these vulnerable sub-groups. The analysis
in VTE patients with active cancer is of particular interest because guidelines for
the treatment of such patients changed during the course of patient follow-up in GARFIELD-VTE.
Parenteral AC was the standard of care at the time of patient recruitment. Guidelines
changed following the publication of the results of randomized trials comparing DOACs
with dalteparin for VTE treatment in patients with active cancer.[22 ]
[23 ]
[24 ] DOACs are now often used instead of parenteral AC, but our subgroup comparison of
DOACs and VKAs demonstrated that oral AC with VKAs would not be a reasonable alternative
for patients with active cancer. When compared with VKAs the rates of recurrent VTE
were lower with DOACs than with VKAs in this patient population.
Although the adjusted HRs for both major and overall bleeding favored DOAC treatment,
differences were not statistically significant. In contrast, a meta-analysis of randomized
controlled trials compared DOACs with VKAs for VTE treatment reported a 40% reduction
in major bleeding with DOACs.[25 ] A potential explanation for this discrepancy is the fact that unlike the randomized
trials, GARFIELD-VTE did not exclude patients at risk for bleeding, such as those
with renal insufficiency or active cancer. A Japanese study that compared DOACs with
VKA in the chronic phase of VTE treatment identified active cancer as an independent
risk factor for major bleeding and recurrent VTE in the VKA group only but not the
DOAC group. They concluded that DOACs appear to be an attractive therapeutic option
for extended treatment of cancer-associated VTE.[26 ] In our analysis, there were no fatal bleeds in patients receiving DOACs, compared
with six fatal bleeds in patients receiving a VKA (4.9% of all VKA-associated deaths).
Our study has limitations. As in any non-randomized study, there may be an imbalance
in non-adjustable confounders which may have an impact on clinical outcome, including
the cost and access to anticoagulants in each country. Furthermore, adjusted analyses
were not carried out for subgroups due to an inadequate number of events. An additional
limitation is the lack of central adjudication of outcome events and missing data,
specifically on the causes of death. Finally, the majority of patients receiving DOACs
within GARFIELD-VTE received rivaroxaban because this was the first DOAC in the market
and the only one available when GARFIELD-VTE was launched. Therefore our results may
not be generalizable to all DOACs.
Conclusion
Our findings add to the growing body of evidence that supports DOACs over VKAs for
VTE treatment because they are associated with reduced all-cause mortality, even in
patients with active cancer or renal impairment. This is in addition to the convenience
of fixed dosing without the need for coagulation monitoring.
What Is Known on This Topic?
Intention-to-treat comparative effectiveness analysis within the GARFIELD-VTE registry
of real-world patients showed that DOACs provide a safe and effective alternative
to VKAs for the treatment of VTE.
Intention-to-treat analysis assesses all enrolled participants according to the treatment
group assigned at baseline. It does not, however, account for patient treatment status
over time (e.g., complete, incomplete, and altered treatment plan).
CONSORT guidelines recommend both intention-to-treat and on-treatment evaluation.
The on-treatment analysis accounts for alterations in treatment choice and plan over
time.
What Does This Paper Add?
This study provides an on-treatment comparative effectiveness analysis of DOACs and
VKAs in VTE patients.
At 12 months, rates of recurrent VTE, major bleeding, and overall bleeding with DOACs
and VKAs are comparable.
All-cause mortality was significantly lower with DOACs than with VKAs. Mortality related
to VTE or bleeding was more likely with VKAs than DOACs.
Unadjusted analyses suggested that VKA patients with active cancer or renal insufficiency
were more likely to die than patients treated with DOAC.
