D W Lowdon, J R Harper, N D Gillespie
Section of Ageing and Health, Department of Medicine, Ninewells Hospital and Medical School, Dundee
Correspondence to: DW Lowdon, Specialist Registrar, Department of Ageing and Health, Department of Medicine, Ninewells Hospital, Dundee DD1 9SY. E-mail: Douglas.Lowdon@tpct.scot.nhs.uk
SMJ 2004 49(4): 148-150
Background: Non-valvular atrial fibrillation (NVAF) is more common in elderly people, and is one of the most powerful independent risk factors predisposing to stroke. This risk increases with age. Despite evidence that full dose anticoagulation reduces this risk, and Scottish Intercollegiate Guidelines, warfarin is still being under prescribed, especially in elderly individuals. Objectives: To audit warfarin prescribing in elderly hospital patients with NVAF, and assess whether audit feedback and evidence based guidelines improved warfarin usage. Methods: Discharge summaries and medical notes were reviewed, and warfarin prescribing identified, for all patients with NVAF discharged from the Medicine for the Elderly Department between January 2001 and December 2002. This was done before (16 months) and after (7 months) audit results were presented at a departmental meeting, and evidence based guidelines were produced. Results: Warfarin prescribing significantly increased from 38/121 (31.4%) prior to audit feedback and the introduction of guidelines to 30/55 (54.5%), Chi2–test, p<0.01. Conclusions: Older patients with NVAF were under prescribed warfarin. Audit feedback and the introduction of evidence based guidelines significantly increased anticoagulation usage.
Key words: Warfarin; atrial fibrillation; elderly; stroke prevention; guidelines; audit.
The prevalence of atrial fibrillation increases with age, with 10% of over 80 year olds being affected.1 NVAF increases stroke risk four to seven fold.2 Stroke risk increases further in the presence of other risk factors; previous ischaemic cerebral event, hypertension, diabetes, heart failure and age.3,4 Meta-analysis shows that warfarin reduces stroke risk by 62%, whilst aspirin, reduces risk by 22%. Balanced against this is the two fold increased risk of bleeding.5 This risk appears to be greatest in patients over age 75 years.
Despite the benefits, only 25% of patients with NVAF are anticoagulated.6 Patients at the greatest risk, elderly individuals, are four times less likely to receive warfarin therapy than their younger counterparts.7 Recent SIGN antithrombotic guidelines state that elderly patients have a stroke risk of at least three per cent per year, and if another stroke risk factor is present this risk rises to 5-12%. Warfarin thromboprophylaxis was recommended for both groups.8 The objective of this study was to audit anticoagulation prescribing to older inpatients with NVAF in our Elderly Medicine Unit, and assess whether audit feedback and the introduction of these evidence based guidelines improved warfarin usage.
Consecutive patients discharged from the Elderly Medicine Unit from January 2001 to April 2002 with a diagnosis of NVAF were identified. Antithrombotic status and contraindications were identified from review of the medical notes. Risk factors were identified to stratify individual’s stroke risk. Audit results were presented at a departmental meeting. Guidelines were subsequently introduced and a repeat audit was undertaken between May and December 2002.
The incidence of NVAF was similar in both audits, with 9.0% (121/1342) of patients in the original audit and 8.3% (55/660) of patients in the repeat audit being identified. The prevalence of each of the stroke risk factors was high in both audits. Consequently most patients were stratified as being at high stroke risk, with over 75% of patients audited having at least one other stroke risk factor (Table I). At audit one 38/121 (31.4%) of at risk individuals were anticoagulated. When patients with contraindications were excluded, this figure rose to 38/87 (43.7%). Individuals who were at high stroke risk were more likely to be anticoagulated than those at moderate risk, with 36/69 (52.2%) of appropriate patients receiving warfarin. After the feedback of audit results and the introduction of guidelines the proportion of eligible, at risk individuals who were prescribed warfarin increased significantly (p<0.001) to 30/33 (90.9%). Of this group, high-risk individuals were again more likely to be anticoagulated, with 27/29 (93.1%) receiving warfarin (Table II).
Most individuals in this study had a stroke risk of between 5-12% per annum. At risk elderly patients with NVAF were still not being anticoagulated, with only 43.7% of eligible patients receiving warfarin. There may be several reasons why these elderly patients were not prescribed warfarin. It is not known whether warfarin therapy is as effective at reducing strokes in every day practise as it was in the trial setting, although two prospective studies suggest that warfarin efficacy is similar.9,10 Effectiveness in very old patients was not proven by the pooled analysis data,11 with the mean age being only 69 years, and hence doctors may be reluctant to prescribe warfarin to this group. An observational study however, with a mean age of 84 years, showed a 76% stroke reduction in warfarin users compared to aspirin.12 Concerns regarding the increased bleeding risk associated with warfarin is undoubtedly another factor.5 Patients at risk of falling are commonly not prescribed warfarin, but there is no evidence to suggest that this group of patients would not benefit from anticoagulant therapy. A review analysis looking at the preferred form of thromboprophylaxis in this group concluded that the choice of therapy depended on stroke risk irrespective of falls risk.13 A review of studies looking at doctors’ use of warfarin in NVAF identified lack of awareness of current evidence and guidelines as a significant reason for under-prescribing.14 Following audit feedback and the implementation of thromboprophylaxis guidelines, we showed that antithrombotic prescribing can be significantly improved, with 91% of appropriate patients being anticoagulated. High-risk individuals were more likely to be prescribed warfarin as proven by the fact 93% of these patients were anticoagulated compared with 75% of those at moderate risk.
The fact that INR control was not assessed is a criticism of this study. It is well recognised that this is a powerful determinant of stroke risk,15 indeed many of our warfarinised patients may have had INRs of 1.5 or less, potentially negating the beneficial effects.16 The other concern is obviously over-anticoagulation, and again as this was not assessed we do not know how beneficial warfarin therapy will be for our patients, as we may unnecessarily be putting them at risk of severe bleeding complications. Our simple study closes the audit loop by demonstrating improved clinical practice in a field of preventative medicine which, despite trial data and evidence based guidelines, remains relatively neglected by doctors.
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