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Abstract

What is known and Objective:

Oral anticoagulants are essential drugs for the prevention of thromboembolic events in patients with atrial fibrillation (AF). Anticoagulants are, however, commonly withheld due to a perceived risk of severe adverse events. The underutilization of anticoagulants in patients with AF has been demonstrated internationally, but to date, there are limited data available in the Australian context. The aim of this study was to determine the utilization patterns of anticoagulants (including novel oral anticoagulants) with respect to stroke and bleeding risk among patients with AF within the community.

Methods:

We performed a nonexperimental, retrospective analysis designed to evaluate antithrombotic usage for AF in Australia. The utilization of antithrombotic therapy and the appropriateness of therapy were determined based on CHADS2, CHA2DS2-VASc and HAS-BLED risk stratification schemes. The presence of documented contraindications was used to determine the appropriateness of antithrombotic therapy.

What is new and Conclusion:

Anticoagulants were overutilized in patients at low risk of stroke and underutilized in patients at higher risk of stroke. As the HAS-BLED score increased, the likelihood of patients receiving an anticoagulant decreased regardless of CHADS₂ or CHA₂DS₂-VASc scores.

Keywords

anticoagulants stroke thrombosis prophylaxis

What Is Known and Objective

Atrial fibrillation (AF) is the most common sustained cardiac rhythm disorder and the most common cause of stroke in the elderly. Atrial fibrillation becomes more prevalent with aging and will be more prevalent in the future in our communities due to the increase in the aging population.¹ Anticoagulants are the most effective drugs in reducing the stroke risk of patients with AF.² Despite the clear benefits, they are often underused, and as patients become older, they become less likely to receive anticoagulants.^3

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Underutilization of anticoagulants is attributed to a range of factors, including overestimation of bleeding risk (a serious adverse effect of anticoagulants), experience of adverse events, the inconvenience of international normalized ratio (INR) monitoring in the case of warfarin, poor patient compliance, and fear of bleeding.⁴

Several small studies have been conducted in Australia, investigating the utilization of antithrombotic therapy in older people with AF. Like similar international studies, they have found underutilization of antithrombotics in high-risk patients and overutilization in low-risk patients.^3,4 These studies have also been largely restricted to hospital patient populations, and the findings may not be generalizable to the wider community. We aimed to investigate the utilization pattern of antithrombotics (including novel anticoagulants) in older people with AF in Australia who reside in the community.

Methods

We performed a nonexperimental, retrospective study to investigate antithrombotic usage patterns for Australians with AF who had recently undergone a home medicines review (HMR). HMR is a service provided by an accredited pharmacist following referral from a general practitioner (GP). It involves a patient interview, generation of a report to the GP, and development of a collaborative medication management plan. Patients qualify for a HMR if they take ≥5 medications or take medications with narrow therapeutic indexes.⁷

Data were obtained from Medscope, the leading provider of clinical decision support for pharmacists conducting medication reviews. Using this software, pharmacists enter patient details, including diagnostic information, the medication history, and clinical laboratory data. This information was provided in a deidentified form to the research team for the purposes of this study. At the time of the study, the database contained information from approximately 40 000 HMRs and residential medication management reviews (RMMRs) conducted between January 2008 and June 2012 throughout Australia. All HMRs involving patients >18 years and with a diagnosis of AF were extracted totaling 3125 cases. At the time of the study, dabigatran and rivaroxaban were approved in Australia for use in AF, although they were not subsidized by the government.

Data extracted from Medscope included a summary of patient demographic information, current medications, current diagnoses, and relevant pathology data (including INR, serum creatinine, and estimated glomerular filtration rate [eGFR]). The Charlson original comorbidity index (CCI) was calculated based on the presence of 17 specific comorbidities. We calculated the CCI by adding scores assigned to each diagnosis.⁸ The CHADS2 (congestive heart failure, hypertension, age ≥75 years, diabetes,previous Stroke/TIA/TE), CHA2 DS2 -VASc (congestive heart failure, hypertension, age 75 ≥years; double score, diabetes mellitus), previous stroke/TIA/TE; double score, vascular disease, age 65 to 74 years, sex class; female),⁹ and HAS-BLED (hypertension, abnormal renal/liver function, stroke history, bleeding history or predisposition to bleeding, labile INR defined as unstable/high INRs as recorded in the medical record of our patients, patients >65 years of age, drugs predisposing patient to bleeding nonsteroidal anti-inflammatory drugs or alcohol use (>8 drinks per week)) risk stratification schemes were used to determine stroke and bleeding risk.^10,11

For the purposes of our analysis, a CHADS₂ score of 0 indicated that no antithrombotic was needed, a score of 1 was indication for an anticoagulant or an antiplatelet medication, and a score ≥2 indicated that an anticoagulant should be used unless contraindicated. Although the CHA₂DS₂-VASc score was not in widespread use for the entire duration of the study, it was calculated for the purposes of our analysis. A score of 0 warranted no therapy and a score ≥1 warranted an anticoagulant. These recommendations were based on guidelines published at the time of the study by the American College of Chest Physicians, the American Heart Association, the European Society of Cardiology, and the Scottish Intercollegiate Guidelines Network.^2,12
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The following were considered contraindications to warfarin or antiplatelet therapy: liver dysfunction, dementia, labile INR, bleeding risk, bleeding disorder, and alcohol misuse. Peptic ulcer disease was not included as a contraindication, as the database did not specify whether the disease was currently active or not. Risk of falls was not included as a contraindication to antithrombotic therapy, as some may argue that it is not a valid contraindication and is also difficult to assess through retrospective data.^2,15

Dabigatran was considered contraindicated in the presence of a prosthetic heart valve or if the patient had a <30 mL/min. The usual dose of dabigatran is 150 mg twice a day. As the drug is renally cleared, the dose should be reduced to 110 mg daily in patients with an eGFR of 30 to 50mL/min and in patients >75years of age.^16,17

Data were analyzed using SPSS version 20 (IBM).¹⁸ An unpaired t test was used to compare means for continuous variables between groups. In the comparison of more than 2 groups of normally distributed data, the analysis of variance was used to test whether the groups showed an overall significant difference. In case of an overall difference, Fisher PLSD post hoc test was used for a pairwise comparison of the individual groups. For testing whether 2 categorical variables were independent or related, the chi-square test or Fisher exact test was used. A P value of <.05 was considered statistically significant. The study received ethical approval from the Human Research Ethics Committee (University of Tasmania).

Results

The patient characteristics of the population are illustrated in Table 1. A total of 3125 patients had received an HMR. The mean age was 78.6 ± 8.8 years, and 51.4% (1605 of 3125) were female. Only 5.7% (179 of 3125) had a CHADS₂ score of 0, 22.8% (714 of 3125) had score of 1, and a CHADS₂ score of ≥2 was seen in 71.5% (2259 of 3125) of patients. A HAS-BLED score of ≥3 was observed in 10% of patients. Of those patients receiving an anticoagulant, 67.4% (1025 of 1520) were male and 61.6% (988 of 1605) were female (P <.001). Contraindications to antithrombotic therapy were documented in only 7.5% (235 of 3125) of the population.

Table 1.

Characteristics of the Study Sample.

		HMR
Total		3125
Age, years	Mean	78.6 (8.8)
	<65	218 (6.9)
	65-74	656 (20.9)
	75-84	1403 (44.8)
	>85	848 (27.1)
Gender	Male	1520 (48.6)
Gender	Female	1605 (51.4)
CHADS₂ score	0	179 (5.7)
	1	714 (22.8)
	≥2	2259 (71.5)
CHA₂DS₂-VASc	0	21 (0.7)
CHA₂DS₂-VASc	≥1	3131 (99.3)
HAS-BLED	0	81 (2.6)
	1	1361 (43.6)
	2	1369 (43.8)
	≥3	314 (10)
Thromboembolic risk factors	Previous stroke, TIA, or TE	528 (16.9)
	Hypertension	2027 (64.9)
	Diabetes mellitus	965 (30.9)
	CHF	742 (23.7)
	Vascular disease, PAD, and aortic plaque	410 (13.1)
Bleeding risk factors	Systolic BP >160	112 (3.6)
	Abnormal kidney function	40 (1.3)
	Liver dysfunction	0
	Bleeding history	34 (1.1)
	Labile INR	11 (0.4)
	Falls risk	133 (4.3)
	Dementia	78 (2.5)
	Peptic ulcer disease	87 (2.8)

Abbreviations: HMR, Home medicines review; CHADS₂, congestive heart failure, hypertension, Age ≥75 years, diabetes, previous Stroke; CHA₂DS₂-VASc, congestive heart failure, hypertension, age ≥75 years; double score, diabetes mellitus, previous stroke/TIA; double score, vascular disease, age 65 to 74 years, sex class; female; TIA, transient ischemic attack; TE, thromboembolism; CHF, congestive heart failure; PAD, peripheral artery disease; BP, blood pressure; INR, international normalized ratio.

Although more than 90.0% of cases analyzed had at least one additional risk factor for stroke, only 67.1% of eligible cases (CHADS₂ score ≥2) received an anticoagulant when one was indicated.

The recommended antithrombotic therapy according to stroke risk for patients without a documented contraindication compared to their current therapy is shown in Tables 2 and 3. Antiplatelet medications were used in 26.5% (543 of 2048) of cases with 6.3% (130 of 2048) not receiving any antithrombotic medication when one was indicated based on CHADS₂ score (CHADS₂ score ≥2). An anticoagulant was being taken by 65.6% (1870 of 2851) of patients who were eligible for an anticoagulant based on the CHA₂DS₂-VASc score (CHA₂DS₂-VASc score ≥1). When an anticoagulant was recommended, 27.7% (790 of 2851) received an antiplatelet agent and 6.7% (191 of 2851) received no antithrombotic therapy. In contrast, 35.9% (14 of 39) of patients in whom no treatment was indicated (CHA₂DS₂-VASc score of 0) received an anticoagulant.

Table 2.

CHADS₂ Risk Category Versus Treatment Observed.^a

		CHADS₂ Risk Classes
		CHADS₂ Score ≥ 2		CHADS₂ Score = 1		CHADS₂ Score = 0		Total		P Value
Actual antithrombotic therapy received	Anticoagulant	1375/2048	(67.1)	415/667	(62.2)	94/175	(53.7)	1884/2890	(65.2)	<.001
	Antiplatelet only	543/2048	(26.5)	207/667	(31)	58/175	(33.1)	808/2890	(28)	.022
	Any antithrombotic	1918/2048	(93.7)	622/667	(93.3)	152/175	(86.9)	2692/2890	(93.1)	0.003
	Nothing	130/2048	(6.3)	45/667	(6.7)	23/175	(13.)1	198/2890	(6.9)	.003

Abbreviation: CHADS₂, congestive heart failure, hypertension, Age ≥75 years, diabetes, previous Stroke.

^aThe anticoagulant group consisted of cases receiving warfarin or dabigatran. This included combinations of an anticoagulant with an antiplatelet. The antiplatelet group consisted of cases receiving aspirin, clopidogrel, dipyridamole, prasugrel, or ticegrelor, either alone or in combination with each other but not in combination with an anticoagulant.

Table 3.

CHA₂DS₂-VASc Risk Category Versus Treatment Received.^a

		CHA₂DS₂-VASc Risk Classes
		CHA₂DS₂-VASc Score ≥1		CHA₂DS₂-VASc Score = 0		Total		P Value
	Anticoagulant	1870/2851	(65.6)	14/39	(35.9)	1884/2890	(65.2)	<.001
Actual antithrombotic therapy received	Antiplatelet only	790/2851	(27.7)	18/39	(46.2)	808/2890	(28)	.011
	Any Antithrombotic	2660/2851	(93.3)	32/39	(82.1)	2692/2890	(93.1)	.015
	Nothing	191/2851	(6.7)	7/39	(17.9)	198/2890	(6.9)	.015

Abbreviation: CHA₂DS₂-VASc, congestive heart failure, hypertension, age ≥75 years; double score, diabetes mellitus, previous stroke/TIA; double score, vascular disease, age 65 to 74 years, sex class; female.

^aThe anticoagulant group consisted of cases receiving warfarin or dabigatran. This included combinations of an anticoagulant with an antiplatelet. The antiplatelet-only group consisted of cases receiving aspirin, clopidogrel, dipyridamole, prasugrel, or ticegrelor, either alone or in combination with each other but not in combination with an anticoagulant.

Table 4 shows the anticoagulant usage noted within the sample with respect to CHADS₂ and HAS-BLED scores. Utilization of anticoagulants dropped by 39.7% when HAS-BLED score increased from 1 to 2 (P <.001) in those at high risk of stroke (CHADS₂ score ≥2).

Table 4.

The Use of Anticoagulants in Relation to CHADS₂ Score and HAS-BLED Score.^a

	HAS-BLED Score	Observed Cases Receiving an Anticoagulant
CHADS₂ score 0	0	13/18 (72.2)
	1	60/90 (66.7)
	2	17/60 (28.3)
CHADS₂ score 1	0	26/32 (81.2)
	1	262/313 (83.7)
	2	87/262 (33.2)
	≥3	4/13 (30.8)
CHADS₂ score ≥2	0	22/28 (78.6)
	1	759/849 (89.4)
	2	439/883 (49.7)
	≥3	68/187 (36.4)

Abbreviation: CHADS₂, congestive heart failure, hypertension, Age ≥75 years, diabetes, previous Stroke.

^aOnly cases with no contraindication to any antithrombotic therapy were included in this table.

Of the 178 cases receiving dabigatran, 2.2% (n = 3) were receiving a high dose of dabigatran when a low dose was indicated, and 2.3% (n = 4) were receiving a low dose of dabigatran (110 mg twice daily) when the drug was contraindicated. An abnormally low dose of 75 mg twice daily was noted in 3.4% (n = 6) of cases; a reduced dose was indicated in only half of these cases.

Discussion

The risk factors for stroke and bleeding have considerable overlap, and patients with high CHADS₂ scores typically have an elevated risk of bleeding as measured by the HAS-BLED score. Despite this, available data still suggest that in the majority of patients, the net benefit favors anticoagulation to reduce the stroke risk rather than no antithrombotic to prevent bleeding¹⁹; thus, those who will gain the most benefit from anticoagulants are typically less likely to receive them. This pattern was prominent in this study and is well supported by findings within other studies.²⁰

In contrast to the issue of underutilization of anticoagulant in high-risk patients, it was demonstrated in this study that anticoagulants in low-risk patients were overutilized. This issue is also illustrated in other international studies with little conclusion as to the underlying reasons. The findings suggest that anticoagulants are administered simply because the patients have AF, and it may also be that in patients with a low stroke risk and low bleeding risk, clinicians feel more at ease prescribing anticoagulant as there is less chance of fatal side effects.²⁰ In addition to this, there are discrepancies across major international guideline recommendations when patients have an intermediate risk of stroke (CHADS₂ score of 1 or a CHA₂DS₂-VASc score of 1).^2,14,21,22 These discrepancies create further confusion, and clearly, there is a need to focus on interventions to address both the over- and the underuse of anticoagulants, not just the underuse.

This study found that as the HAS-BLED score increased, utilization of anticoagulants in eligible cases declined regardless of CHADS₂ scores. This finding is supported by outcomes within the ORBIT-AF registry (Outcomes Registry for Better Informed Treatment of Atrial Fibrillation)²⁰ and is likely to be due to the fear of life-threatening bleeding as the major adverse effects of anticoagulants. Some physicians view cognition, frailty, and risk of falls as all associated with increased risk of bleeding, despite the lack of evidence supporting these factors as contraindications to anticoagulation. While there was no way of measuring frailty in this study, risk of falls was however documented in the database and was not found to have a significant effect on the use of anticoagulants. It is possible that in a select few eligible high-risk patients (no contraindications to antithrombotic therapy and CHADS₂ ≥2), risk of falls may have been the reason the therapy was being withheld, particularly when taking previous studies into account.²³

Unlike warfarin, the new oral anticoagulants do not require INR monitoring, dose adjustment, and have fewer drug and food interactions. For these reasons, they may be viewed as more suitable for the older population.¹¹ Despite this, dosing inconsistencies were noted among the population in accordance with other studies,²⁴ which suggest that more caution is needed in the initial dosing of dabigatran.

The levels of utilization of anticoagulants in AF and the issues associated in this study are comparable to international findings.^4,25,26 Multiple studies discuss poor alignment between physician recommendation and current guidelines.^4,25
–27 Several interventions have been conducted nationally and internationally aiming to improve the use of oral anticoagulants in AF, these interventions have been relatively small scale and heavily resourced, limiting their capacity to be replicated on a larger scale. The interventions included audit feedback after access to locally produced guidelines, introduction of evidence-based guidelines, and computer software to support clinical decision-making.^28

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The selection of a single set of guidelines to be adopted has been shown in Scotland and in a small Australian study to improve treatment rates; this may be effective on a large scale^28,29 and may aid the situation in Australia mainly because local guidelines are also lacking.

This study is the largest and the most recent investigation of antithrombotic utilization in patients with AF in Australia and is the only study containing data on dabigatran. It provides a valuable illustration of potential areas of concern surrounding the management of AF in Australia. Results are similar to frequently cited international findings.^{4,25
–27,32} Inadequate thromboprophylaxis in patients with AF is a global occurrence, and “implementation of educational initiatives and feedback mechanisms”³³ are required on a global scale.

The accuracy of our results may be limited by the retrospective nature of the study, as we relied on the documentation of both AF and antithrombotic medications. Home medicines reviews potentially target patients with complex needs; consequently, our study cohort may not be representative of the wider community. As such, lower rates of medication use may have been observed in our study compared to those demonstrated in the community. Conversely, our findings may overstate medication use in the community, since the diligence of GPs who refer their patients for HMRs may also be reflected in the provision of greater support regarding medication prescription and adherence, and the presence of narrow therapeutic index medicines, such as anticoagulants, are a trigger for HMR referral.

What Is New and Conclusion

This study outlines key issues in the prescribing patterns of anticoagulants in Australians with AF. Anticoagulants were overutilized in patients at low risk of stroke and underutilized in patients at higher risk of stroke. As HAS-BLED score increased, the likelihood of patients receiving an anticoagulant decreased regardless of CHADS₂ or CHA₂DS₂-VASc scores. The findings are comparable to international trends.

Footnotes

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article. In the past 5 years, L Bereznicki has received speaker fees/honorarium from Boehringer Ingelheim and was a member of the Pradaxa Advisory Board (Boehringer Ingelheim) in Australia in 2015. He has also received consultancy research funding from Aspen Pharmacare within the past 5 years.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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The Utilization of Antithrombotic Therapy in Older Australians With Atrial Fibrillation

Abstract

What is known and Objective:

Methods:

What is new and Conclusion:

Keywords

What Is Known and Objective

Methods

Results

Discussion

What Is New and Conclusion

Footnotes

Declaration of Conflicting Interests

Funding

References