Warfarin treatment and risk of stroke among primary care patients with atrial fibrillation

Figures & data

Table 1. Data on subjects aged 45 + years with a diagnosis of AF in primary care from 1 January 2001 to 31 December 2007, and patients with an IS.

	All (n = 11,517)		With IS (n = 1465)
	Women	Men	Women	Men
	n = 5248	n = 6269	n = 768	n = 697
Age (years), mean (SD)	76.9 (9.3)	71.8 (10.2)	79.0 (8.0)	74.7 (8.8)
Age group (years)	n (%)	n (%)	n (%)	n (%)
45–54	105 (2.0)	363 (5.8)	6 (0.8)	17 (2.4)
55–64	499 (9.5)	1184 (18.9)	43 (5.6)	79 (11.3)
65–74	1199 (22.9)	1951 (31.1)	137 (17.8)	213 (30.6)
75–84	2343 (44.7)	2162 (34.5)	381 (49.6)	298 (42.8)
85+	1102 (21.0)	609 (9.7)	201 (26.2)	90 (12.9)
Neighbourhood SES
High	1810 (34.5)	2508 (40.0)	265 (34.5)	281 (40.3)
Middle	2508 (49.2)	2866 (45.7)	396 (51.6)	318 (45.6)
Low	858 (16.4)	895 (14.3)	107 (13.9)	98 (14.1)
Marital status
Married	1552 (29.7)	3705 (60.1)	188 (24.6)	405 (58.3)
Unmarried	374 (7.2)	606 (9.7)	50 (6.5)	53 (7.6)
Divorced	739 (14.2)	942 (15.1)	91 (11.9)	96 (13.8)
Widowed	2558 (49.0)	956 (15.2)	435 (56.9)	141 (20.3)
Educational level
Compulsory school	2407 (52.2)	2340 (39.4)	372 (57.2)	251 (38.1)
Secondary school	1527 (33.1)	2234 (37.6)	200 (30.8)	266 (40.4)
College/university	680 (14.7)	1369 (23.0)	78 (12.0)	142 (21.6)
AF-related disease
Hypertension	2553 (48.7)	2591 (41.3)	387 (50.4)	324 (46.5)
Coronary heart disease	1098 (20.9)	1260 (20.1)	155 (20.2)	157 (22.5)
Congestive heart failure	1084 (20.7)	1082 (17.3)	157 (20.4)	121 (17.4)
Diabetes mellitus	1021 (19.5)	1231 (19.6)	134 (17.5)	181 (26.0)
Drugs
Ever-present warfarin	2461 (46.9)	3485 (55.6)	354 (46.1)	397 (57.0)
Warfarin ITT	2310 (44.0)	3306 (52.7)	236 (30.7)	251 (36.0)
Warfarin PP	1768 (33.7)	2508 (40.0)	160 (20.8)	148 (21.2)

SES denotes “socio-economic status”.

ITT denotes “intention-to-treat”: prescription before the years of first stroke, or present among subjects not experiencing a stroke.

PP denotes “per-protocol” (“PP”): prescription the year before and the year of first stroke, or present among subjects not experiencing a stroke if present at least during three years, of at least 50% of actual years after first recorded year of AF, or during both 2006 and 2007.

Table 2. Patients with atrial fibrillation in primary care: all women and men, and women and men without persistent warfarin treatment (“per protocol” warfarin treatment), respectively, divided into patients without or with first hospital-admitted IS, during 2001–2010 by scores on CHA₂DS₂-VASc, with number of patients (percentage).

	Women						Men
	All		Without PP-warfarin				All		Without PP-warfarin
	No IS	IS	No IS	IS			No IS	IS	No IS	IS
CHA2DS2-VASc:	n	n (%)	n	n (%)	IR	NNT	n	n (%)	n	n (%)	IR	NNT
0	–	–	–	–	–		720	39 (5.1)	482	34 (6.6)	1.09 (0.78–1.52)	22.1
1	258	21 (7.5)	184	19 (9.4)	1.55 (0.99–2.42)	14.9	1064	81 (7.1)	581	71 (10.9)	1.86 (1.48–2.36)	11.3
2	494	73 (12.9)	309	67 (18.3)	3.20 (2.51–4.06)	6.6	1557	159 (9.3)	888	133 (13.0)	2.52 (2.12–2.98)	10.8
3	1157	191 (14.2)	730	165 (18.4)	3.71 (3.18–4.32)	7.9	1287	194 (13.1)	696	161 (18.8)	3.81 (3.27–4.45)	7.4
4	1419	231 (14.0)	895	206 (18.7)	3.84 (3.35–4.40)	7.1	631	133 (17.4)	354	109 (23.5)	5.27 (4.37–6.36)	6.4
5	814	167 (17.0)	498	143 (22.3)	4.95 (4.20–5.84)	6.8	225	58 (20.5)	131	47 (26.4)	5.96 (4.48–7.94)	6.3
6	266	60 (18.4)	156	52 (25.0)	5.91 (4.51–7.76)	5.5	70	28 (28.6)	36	25 (41.0)	10.70 (7.23–15.84)	3.0
7	57	22 (27.9)	36	16 (30.8)	6.28 (3.85–10.26)	11.7	17	4 (19.1)	9	3 (25.0)	5.66 (1.83–17.65)	N/A
8	14	3 (17.7)	10	2 (16.7)	4.12 (1.03–16.48)	N/A	1	1 (50.0)	0	1 (100.0)	N/A	N/A
9	1	0 (0.0)	1	0 (0.0)	N/A	N/A	–	–	–	–	–
All	4480	768 (14.6)	2810	670 (19.3)	3.89 (3.61–4.20)	7.3	5,572	697 (11.1)	3177	584 (15.5)	2.98 (2.75-3.23)	9.1

IR for IS in patients without PP-warfarin treatment. NNT shown for the prevention of first IS by warfarin treatment during 5.4 years of follow-up.

Values for all patients and for those with no warfarin treatment according to “per protocol”-analysis. IR per 100.

Person-years at risk (95%CI) shown for IS without warfarin treatment.

NNT denotes “numbers needed to treat” during a mean follow-up of 5.4 years.

Table 3. IR and Cox regression for risk of first IS in women and men with atrial fibrillation treated with ITT- or PP-warfarin, versus patients without ITT- or PP-warfarin treatment as referents.

				Warfarin PP HR (95%CI)
	Events/at risk (n, %)	Incidence rate (95%CI)	Warfarin ITT HR (95%CI)	Model 1	Model 2	Model 3
First IS
Women	768/5248 (14.6%)	2.77 (2.58–2.98)	0.66 (0.46–0.97)	0.27 (0.21–0.33)	0.24 (0.17–0.34)	0.25 (0.18–0.36)
Men	697/6269 (11.1%)	2.02 (1.88–2.18)	0.73 (0.55–0.96)	0.27 (0.22–0.33)	0.26 (0.20–0.33)	0.25 (0.19–0.32)

ITT denotes “Intention-to-treat”: prescription before the years of first stroke, or present among subjects not experiencing a stroke.

PP denotes “Per-protocol”: prescription of the year before and the year of first stroke, or present among subjects not experiencing a stroke if present at least during 3 years, of at least 50% of actual years after first recorded year of AF, or during both 2006 and 2007.

IR per 100 person-years at risk.

Model for warfarin ITT (with patients on PP-warfarin treatment excluded): fully adjusted (age, neighbourhood socioeconomic status, educational level, marital status, hypertension, CHD, CHF and diabetes, with interaction term between age and marital status).

Models for warfarin PP: Model 1 age-adjusted, Model 2 also adjusted for socioeconomic factors (neighbourhood socioeconomic status, educational level and marital status), and Model 3 also for co-morbidity (hypertension, CHD, CHF and diabetes).