DL Murdoch, K O’Neill+, J Jackson, A McMahon#, A Rumley*, I Wallace+, GDO Lowe*, RC Tait*
Department of Cardiology, Southern General Hospital, Glasgow: *Departments of Haematology and Vascular Medicine, Glasgow Royal Infirmary: +Glasgow Primary Care NHS Trust: #Robertson Centre for Biostatistics, University of Glasgow
Correspondence to: DL Murdoch, Department of Cardiology, Southern General Hospital, Glasgow, G51 4TF, Scotland Email: david.murdoch@sgh.scot.nhs.uk
SMJ 2005 50(4): 166-169
Abstract
Background and Aims: We wanted to determine the prevalence of atrial fibrillation (AF) in a community based cross sectional study in greater Glasgow and how current anti-thrombotic management compares to published guidelines. Methods: 1466 patients with AF were identified in General Practices in our community and 1008 consented to take part. Their demographic details and medical history were recorded. Results: 1466 patients (mean age 73.4; 55% female) with AF were identified, in our community, giving a prevalence of 1%. 53% of patients were on warfarin therapy. Of those not receiving warfarin, only one third had a putative contra-indication. The proportion of AF patients on warfarin increased with increasing stroke risk, and over the period of the study. Conclusions: Prevalence of AF was in keeping with previous estimates. The proportion of patients with AF receiving warfarin therapy appears to be increasing. In the moderate risk group, there was a tendency to use more warfarin in the younger age groups compared to the elderly. It was in the moderate and low risk groups that there was still evidence of deviation from published guidelines.
Introduction
Atrial fibrillation (AF) is the most common sustained arrhythmia encountered in clinical practice and, in patients with non-valvular atrial-fibrillation, increases the risk of stroke by three to seven-fold.1-4 Approximately 1% of the adult population is known to have AF with the prevalence rising to over 10% in the over 85 year olds.5 Anti-thrombotic therapy reduces the risk of stroke although aspirin is less effective than warfarin (20% risk reduction vs. 68%).4 Although there has been a pronounced increase in the percentage of patients with AF prescribed oral anticoagulants or aspirin5 it is clear from previous studies that a significant number of patients with AF with additional risk factors for ischaemic stroke, and no contraindications for anticoagulation are not being treated with anticoagulants.6,7
The reasons for this are not clear. Despite a prospective cohort study showing that the rates of stroke and major haemorrhage after anti-coagulation in clinical practice were comparable to those obtained from pooled data from randomised controlled trials for patients with AF at high risk of stroke,8 there has been uncertainty about the value of long term anti-coagulation compared to anti-platelet therapy because of the heterogeneity of the trials and the limited data in the elderly.9 Only small numbers of elderly patients were included in the randomized trials and there is evidence that patients over the age of 75 have a significantly increased risk of major haemorrhage with anticoagulation.10
In actual clinical practice, patients are older and have more co-morbid conditions compared to trial participants. However, although the rates of stroke and major bleedings in patient with AF on warfarin appear to be similar to trial patients, the risk of minor bleeding is higher and they may require more intensive monitoring.11
The aims of this study were to determine the current prevalence in a sample of the local population of Glasgow and assess whether the publication of Scottish national (SIGN) guidelines in 1999 may have influenced the use of anticoagulation in this condition.12
Methods
Individuals in the community with AF were identified by searching diagnostic (atrial fibrillation) and prescription (digoxin) databases from 36 participating general practices in the Glasgow area between October 1999 and March 2001. Medical records for the patients identified were then reviewed for evidence of ECG-documented AF. Thus, from a general practice population base of 186,030 we identified 1466 patients with a confirmed diagnosis of AF.
Limited data (age, gender and use of warfarin) were available on this prevalence cohort. However all 1466, except those with a life expectancy of less than three months or significant dementia (such that they could not reliably provide informed consent) were invited to participate in a prospective observational study approved by the local community ethics committee. Those who consented (n=1008, 69%) formed the ‘study cohort’ for which more detailed information was recorded. This included demographic data, medications and medical history with specific emphasis on known risk factors for stroke and putative risk factors of haemorrhagic complications of antithrombotic therapy.
Results
Population opulation pr prevalence evalence of AF A total of 1466 patients (mean age 73.4y; 54.8% female) with documented AF were identified, giving a population prevalence of 0.79% (or 0.99% of adults, >17y of age) (Table I).
Prevalence was higher in the older age groups and almost half (48%) of AF cases were older than 75y. There was a higher prevalence among females (0.86% v. 0.72%) largely due to the great excess of females in the older age groups.
Anti-thrombotic therapy
Of the 1466 patients identified, 53% were receiving oral anticoagulant therapy (warfarin), but fewer of the elderly (age> 85y, 19%; 75-84y, 53%; 45-74y, 70-80%), as seen in Figure 1. Analysis of clinical information available on the ‘study cohort’ of 1008 AF patients consenting to followup, revealed a slightly younger age (mean 71.7y) and higher use of warfarin (Table II) which correlated inversely with year of diagnosis of AF (Table III). Chronic persistent AF was more prevalent than paroxysmal AF (80% v. 20%).
Antithrombotic therapy according to stroke risk
Traditional risk factors for AF-related stroke were common in the study group (Table IV). In particular, there was a high prevalence of ischaemic heart disease (44%; angina, myocardial infarction or coronary artery bypass graft) and cerebrovascular disease (29%).
Potential contra-indications to warfarin therapy (previous haemorrhage, history of falls, alcohol excess, uncontrolled hypertension, likely non-compliance and use of non-steroidal anti-inflammatory medication) were identified in 20.4%. These latter factors appeared to influence choice of antithrombotic therapy, since 85% of those receiving warfarin had no identifiable contra-indication while of those not on warfarin, 22% had one relative contra-indication and 8%> two contra-indications. However, 65% of those not receiving warfarin (22.5% of all AF patients) had risk factors for stroke but no apparent contra-indication to warfarin. Details of antithrombotic therapy according to overall stroke risk is shown in Table V.
Discussion
The results of our study suggest that the prevalence of AF in the community has probably not changed over time. There is a high prevalence among women but this is mainly due to the great excess of females in the older age-groups.
Previous studies have reported an increasing prevalence of AF in the community from 1.1% in 1994 to 1.3% in 19986 but there may be other explanations for this including greater awareness of the arrhythmia leading to increased diagnosis as well as an absolute increase in prevalence. There does appear to be an increase in hospitalisation and morbidity and mortality associated with AF13 and there may be several factors other than a true increase in the prevalence of arrhythmia in the community to account for this such as a lower threshold for admission, co-morbidities and even changes in coding practice.
The percentage of AF patients in this population on warfarin (53%) was higher than in previous UK studies, where the percentage prescribed warfarin varied between 23% and 36%.5, 14, 15 Indeed, a previous study in Glasgow in the early 1990s found only 20% patients with a prior diagnosis of AF receiving warfarin.16
One question which this study sought to answer was whether guidelines had affected practice. The Scottish Intercollegiate Guideline Network (SIGN) Guidelines on Anti-thrombotic therapy were published in 1999.12 Our results suggest that medical practice was changing before then with an increasing number of patients being prescribed warfarin from the mid 1990s onwards (after publication of the pooled data from trials in 19944), although there was further improvement after 1999.
Despite this encouraging trend, there were patients who were eligible for warfarin but who were not receiving it at the time of the study (22.5% of eligible patients in the study group). Conversely there were patients who had putative contra-indications for anticoagulation who were still receiving warfarin - but these were mainly patients with high or very high stroke risk.
This study has also identified problems with the risk benefit decision regarding warfarin therapy in the low risk patients. There is also evidence of the persisting dilemma of anticoagulation in elderly patients with AF. These patients tend to fall in to the highest risk groups for stroke but, because of more frequent putative contraindications to warfarin, the proportion receiving warfarin was less than in other age groups. Overall, 325 patients, at moderate, high or very high risk of stroke, were not on warfarin and, of these, only 100 had putative contraindications to warfarin therapy. In other words, 225 patients not on warfarin had no obvious contraindication to warfarin therapy.
Only about 75% of patients have the diagnosis of AF actually recorded in the casesheet.15 Screening for digoxin prescription detects about 50% of patients with AF16 so a combination of methods was used to increase sensitivity. We believe the methods used in searching for AF in our Glasgow practices would not have omitted an important number of cases of undiagnosed AF.
Our community has a high prevalence of cardiovascular disease and social deprivation which was reflected in the current study group with over 40% of AF participants having a history of IHD or hypertension and nearly 30% with a history of cerebrovascular disease. Consequently, the majority of AF patients had additional risk factors for AF-related stroke and as a result there were few low risk patients (<5%). Reassuringly, the vast majority of very high risk patients were on oral anticoagulant therapy as were the majority of high risk patients. In the moderate-risk group there was a tendency to use more warfarin in the younger age-groups (<65y; 72% v. 47%). Similarly, in the lowest risk category (<65y with lone AF), where there is no benefit of warfarin over aspirin, 40% were receiving warfarin.
Doctors in general, in contrast to patients, seem to be more concerned with the bleeding risks of warfarin rather than risk of stroke associated with AF.18,19 This concern may be misplaced since there is conflicting evidence for the anticipated poorer anticoagulant control and higher bleeding risk in elderly AF patients.10, 20 Furthermore, there is now evidence that warfarin not only reduces the incidence of stroke in AF but also reduces stroke morbidity and mortality.21 Thus, older patients with AF who have higher risk of stroke will have most to gain by treatment with warfarin. However, this study supports the suggestion that doctors are overestimating the risk of AF in younger patients and underestimating the risk in older patients and are still not adhering closely to national guidelines. An additional factor, limiting the use of warfarin in the elderly, may be the logistical difficulties associated with provision of an accessible anticoagulation monitoring service for those less mobile elderly patients. However, this problem may be obviated by development of mobile anti-coagulation nurse services, and newer oral anticoagulants which do not require regular coagulation monitoring.22
Conclusions
The prevalence of AF recorded in the above study is in keeping with historical estimates suggesting there is no real increase in this condition. However, after publication of pooled data from relevant randomised trials in 1994, followed by national guidelines in the late 1990s, there appears to have been a gradual increase in the percentage of patients receiving warfarin. Nevertheless, there remains a significant proportion of around 20% of patients, particularly over the age of 75y, who may be eligible for warfarin, but not yet receiving it.
ACKNOWLEDGEMENT: We thank all participating General Practices. Funding:This work was supported by a grant (K/MRS/50/C2715) from the Chief Scientist Office, Scottish Executive Health Department.
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