Use of oral anticoagulants in atrial fibrillation is highly variable and only weakly associated with estimated stroke risk: Cross-sectional population database study

Figures & data

Box 1. Points scored for stroke risk factors under CHADS₂ (14,43) and CHA₂DS₂VASc (43). Under both schemes, the scored points are summed, with 0 = ‘low risk’, 1 = ‘intermediate risk’ and ≥ 2 = ‘high risk’.

	No. of points scored under
Risk factor	CHADS2	CHA2DS2VASc
Congestive heart failure	1	1
Hypertension	1	1
Aged ≥ 75 years	1	2
Diabetes mellitus	1	1
Stroke, TIA or thromboembolic event	2	2
Vascular disease (prior myocardial infarction, peripheral arterial disease or complex aortic plaque on transthoracic echocardiogram^a)	Not included	1
Aged 65–74 years	Not included	1
Sex, female	Not included	1

^aTransoesophageal echocardiogram is not a routine investigation in patients with simple AF in UK primary care, and is not routinely coded in primary care records, so not included.

Table 1. Demographics of 21 096 patients with atrial fibrillation without rheumatic heart disease or valve replacement.

Basic demographics
Male	54.6%
Mean age in years (95% CI)	75.5 (75.3–75.6)
Prevalence of atrial fibrillation by age group (95% CI)
45–54 years	0.3% (0.2 to 0.3)
55–64 years	1.1% (1.0–1.1)
65–74 years	3.5% (3.4–3.6)
75–84 years	7.8% (7.7–8.0)
85 years and over	12.2% (11.9–12.6)
Prevalence of comorbidity in patients with atrial fibrillation
Hypertension	54.7% (54.0–55.3)
Coronary heart disease	38.6% (37.9–39.2)
Heart failure	20.6% (20.0–21.1)
Diabetes	16.5% (16.0–17.0)
Non-haemorrhagic stroke or TIA	13.5% (13.0–14.0)
Peripheral vascular disease	6.6% (6.3–7.0)
Dementia	4.9% (4.6–5.2)
Previous peptic ulcer	10.0% (9.6–10.4)
No. of oral repeat drugs in addition to an oral anticoagulant
Mean (95% CI)	5.6 (5.55–5.63)
Median (Interquartile range)	5 (2–7)

Table 2. Predicted risk category for 21 096 patients with atrial fibrillation without rheumatic heart disease or valve replacement.

	Low risk n (%)	Intermediate risk n (%)	High risk n (%)
CHADS2	3358 (15.9)	6396 (30.3)	11 342 (53.8)
CHA2DS2VASc	1109 (5.3)	2039 (9.7)	17 948 (85.1)

Table 3. Current treatment and ever anticoagulation by risk stratification for 20 443 patients with atrial fibrillation without rheumatic heart disease or valve replacement, and diagnosed for at least 12 weeks.

	All patients	‘Low risk’ as defined by		‘Intermediate risk’ as defined by		‘High risk’ as defined by
	n (%)	CHADS2	CHA2DS2VASc	CHADS2	CHA2DS2VASc	CHADS2	CHA2DS2VASc
	n = 20 443	n = 3218	n = 1061	n = 6163	n = 1955	n = 11 062	n = 17 427
No current antithrombotic treatment	17.8%	27.0%	39.4%	17.5%	23.4%	15.2%	15.8%
Current antiplatelet only^a	38.9%	34.5%	30.0%	39.4%	34.3%	39.9%	39.9%
Current anticoagulant only^b	39.1%	35.2%	28.6%	38.3%	38.2%	39.7%	39.2%
Current anticoagulant plus antiplatelet^c	4.3%	3.3%	2.1%	4.8%	4.1%	5.2%	5.0%
All current anticoagulant^d	43.3%	38.5%	30.6%	43.1%	42.3%	44.9%	44.2%
Anticoagulant ever since diagnosis	58.5%	53.0%	48.4%	57.4%	57.7%	60.8%	59.2%

^a31.9% on aspirin only, 4.2% on dipyridamole or clopidogrel only, 2.8% on aspirin and (clopidogrel or dipyridamole) and 0.02% on all three antiplatelets.

^b0.5% additionally prescribed an antiplatelet drug other than aspirin.

^c0.2% additionally prescribed an antiplatelet drug other than aspirin.

^d0.3% prescribed an oral anticoagulant other than warfarin.

Table 4. Patient and practice variables associated with current prescription of anticoagulation for 20 443 patients with atrial fibrillation without rheumatic heart disease or valve replacement, and diagnosed for at least 12 weeks. Univariable and adjusted odds ratios are estimated in a multilevel model to account for clustering by practice. Adjustment was by variables shown in the table.

Variable^a	No. (%) of patients currently anticoagulated	Multilevel univariable odds ratio (95% CI)	Multilevel adjusted odds ratio (95% CI)^b
Patient level variables
Age
< 45 years (n = 273)^c	51 (18.7)	0.21 (0.15–0.28)	0.26 (0.19–0.36)
45–54 years (n = 640)^c	204 (31.9)	0.43 (0.36–0.51)	0.50 (0.41–0.60)
55–64 years (n = 2282)^c	1001 (43.9)	0.70 (0.63–0.77)	0.70 (0.63–0.78)
65–74 years (n = 5265)^c	2750 (52.2)	1	1
75–84 years (n = 7573)^c	3647 (48.2)	0.85 (0.79–0.91)	0.83 (0.77–0.89)
85+ years (n = 4410)^c	1208 (27.4)	0.34 (0.32–0.38)	0.33 (0.30–0.36)
Gender
Male (n = 11 170)	5179 (46.4)	1	1
Female (n = 9273)	3682 (39.7)	0.76 (0.72–0.81)	0.90 (0.85–0.96)
Co-medication
No. of repeat oral drugs	1464 (37.6)	1	1
excluding anticoagulants
0–2 drugs (n = 3892)
3–5 drugs (n = 7804)	3826 (49.0)	1.53 (1.41–1.66)	1.33 (1.21–1.45)
6–8 drugs (n = 5899)	2519 (42.7)	1.17 (1.08–1.28)	0.93 (0.84–1.02)
9–11 drugs (n = 2161)	807 (37.3)	0.93 (0.83–1.04)	0.67 (0.59–0.76)
12+ drugs (n = 687)	245 (35.7)	0.86 (0.72–1.02)	0.55 (0.45–0.66)
AF type
Chronic AF (n = 17 886)	8349 (46.7)	1	1
Paroxysmal AF (n = 2557)	512 (20.0)	0.27 (0.24–0.30)	0.26 (0.23–0.29)
Comorbidity
No diabetes (n = 17 050)	7263 (42.6)	1	1
Diabetes (n = 3393)	1598 (47.1)	1.19 (1.11–1.28)	1.18 (1.08–1.28)
No heart failure (n = 16 194)	6788 (41.9)	1	1
Heart failure (n = 4249)	2073 (48.8)	1.36 (1.27–1.45)	1.45 (1.35–1.57)
No hypertension (n = 9240)	3763 (40.7)	1	1
Hypertension (n = 11 203)	5098 (45.5)	1.23 (1.16–1.30)	1.19 (1.11–1.27)
No stroke/TIA (n = 17 863)	7509 (42.5)	1	1
Stroke/TIA (n = 2760)	1352 (49.0)	1.33 (1.24–1.42)	1.48 (1.35–1.62)
No PVD (n = 19 069)	8295 (43.5)	1	1
PVD (n = 1374)	566 (41.2)	0.94 (0.84–1.05)	0.88 (0.78–0.99)
Relative contra-indications
No dementia (n = 19 437)^d	8717 (44.8)	1	1
Dementia (n = 1006)^d	144 (14.3)	0.21 (0.17–0.25)	0.25 (0.20–0.30)
No history PU (n = 18 384)	8065 (43.9)	1	1
History PU (n = 2059)	796 (38.7)	0.82 (0.75–0.91)	0.79 (0.72–0.88)
Practice level variables
Training status
Not training (n = 10 929)^a	4913 (45.0)	1	1
Training (n = 9218)	3801 (41.2)	0.86 (0.77–0.96)	0.87 (0.78–0.97)
Rurality
Primary city (n = 6955)	2830 (40.7)	1	1
Urban area (n = 6980)	2992 (42.9)	1.09 (0.96–1.24)	1.07 (0.94–1.23)
Accessible (n = 3322)	1534 (46.2)	1.29 (1.11–1.48)	1.20 (1.03–1.40)
Remote (n = 1479)	677 (45.8)	1.21 (1.11–1.48)	1.13 (0.89–1.43)
Very remote (n = 1707)	828 (48.5)	1.40 (1.17–1.69)	1.44 (1.19–1.74)
High risk prescribing rate
Quartile 1 low (n = 6187)	2508 (40.5)	1	1
Quartile 2 (n = 5301)	2276 (42.9)	1.05 (0.92–1.20)	1.01 (0.87–1.17)
Quartile 3 (n = 4896)	2160 (44.1)	1.10 (0.96–1.27)	1.05 (0.90–1.23)
Quartile 4 high (n = 4059)	1917 (47.2)	1.29 (1.12–1.49)	1.25 (1.07–1.45)

^aAdjusted for the confounders shown in the table. Other variables examined but not significantly associated in adjusted model were socioeconomic deprivation (based on the postcode sector of the patient's address (25)), duration of atrial fibrillation, presence of coronary heart disease, practice list size, whether the practice held a standard General Medical Services or a locally varied Personal Medical Services contract, whether the practice dispensed its own prescriptions. AF: atrial fibrillation; TIA: transient ischemic attack; PVD: peripheral vascular disease; PU: peptic ulcer.

^bPractice level data missing for 6 practices and 296 patients.

^cAge in years assessed on 31 March 2007.

^dDementia (defined as either a relevant Read code or prescription of an acetylcholinesterase inhibiting drug that is exclusively used in dementia (26).

Figure 1. Variation between practices in receipt of OAC by individual patients (odds ratio and 95% confidence intervals) after adjustment for patient characteristics. An odds ratio of 1.00 represents the average across all 315 practices.

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