Family Practice Advance Access originally published online on October 1, 2004
Family Practice 2004 21(6):612-616; doi:10.1093/fampra/cmh606
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Family Practice Vol. 21, No. 6 © Oxford University Press 2004, all rights reserved.
Anticoagulant treatment of patients with chronic atrial fibrillation in primary health care in Sweden—a retrospective study of incidence and quality in a registered population
a Department of Clinical Sciences, Center of Family Medicine, Karolinska Institute, Stockholm and b Department of Surgery, Institute of Surgical Sciences, Göteborg University, Göteborg, Sweden
Correspondence to Gunnar Nilsson, MD, PhD, Department of Clinical Sciences, Center of Family Medicine, Karolinska Institute, Alfred Nobels allé 12, SE-141 83 Huddinge, Sweden; Email: gunnar.nilsson{at}nlpo.sll.se
Received 10 May 2004; Accepted 20 July 2004.
Nilsson GH, Björholt I and Krakau I. Anticoagulant treatment of patients with chronic atrial fibrillation in primary health care in Sweden—a retrospective study of incidence and quality in a registered population. Family Practice 2004; 21: 612–616.
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Abstract |
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Background. The number of patients receiving anticoagulant treatment is increasing. Chronic atrial fibrillation is the most common treatment diagnosis. The literature indicates a variable level of treatment control. Estimates of time within the therapeutic range have been recommended as a measurement of quality. Electronic patient records are providing clinical data that are useful for audits concerning anticoagulant treatment in real-life practice.
Objective. Our aim was to assess warfarin treatment for chronic atrial fibrillation in primary health care with regard to prevalence, incidence and quality.
Methods. A 2 year retrospective study was carried out of electronic patient records up to April 2002 in primary health care in Stockholm, including 12 primary health care centres with a registered population of 203 407. Main outcome measures were the number of new patients on wafarin treatment for chronic atrial fibrillation, and time within the therapeutic prothrombin range in the first 90 days of treatment using a linear interpolation method.
Results. In total, 827 patients were on warfarin treatment for chronic atrial fibrillation, giving a prevalence of 0.41%. Of these, 144 patients (study group) started treatment with warfarin for chronic atrial fibrillation during the study period, giving a yearly incidence of 0.07%. Their mean age was 73.1 years and 61.1% were men. There were 1721 prothrombin monitoring episodes registered in the first 90 days of treatment, on average once a week per patient. The average proportion of time within the therapeutic range was 54.1% (95% confidence interval (CI) 50.1–58.1), and the proportion of therapeutic tests was 50.2% (95% CI 47.8–52.6).
Conclusions. During the first, second and third months of warfarin treatment for chronic atrial fibrillation, patients were outside the therapeutic range time nearly half the time. There was a gender difference favouring men regarding initiation of treatment.
Keywords. Anticoagulant treatment, atrial fibrillation, incidence, primary health care, quality assurance.
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Introduction |
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Oral anticoagulant drugs, i.e. vitamin K antagonists, have been shown in well-designed clinical trials to have antithrombotic effectiveness in a variety of disorders and conditions. They are medically and economically justified in the prevention of embolic stroke in patients with chronic atrial fibrillation (CAF).1,2
Warfarin is the standard anticoagulant drug used in Sweden. It is an efficacious anticoagulant, but it has a narrow therapeutic range. A prothrombin time (PT) corresponding to the International Normalized Ratio (INR) target of 2.5 (range 2–3) is recommended for most indications. The anticoagulant response to warfarin is influenced by many drug interactions and it is also affected by genetic and significant environmental variability. A large number of studies have demonstrated that the risk of bleeding complications during treatment with warfarin increases drastically with an INR above the target value, and that the antithrombotic effectiveness disappears with low INR values.3,4 There is a relationship between the effectiveness of warfarin and the proportion of INR values within the therapeutic range, and this has therefore been used as a surrogate measure of anticoagulant treatment quality. The time within the therapeutic range has been recommended as a more accurate measurement of quality, but is rarely used.
The number of anticoagulant-treated patients is increasing,5,6 and comprises 
0.9% of the population of Sweden7, although this figure was 0.4% in an earlier study.8 Several studies indicate that CAF is the most common treatment diagnosis,9,10 and the prevalence of patients treated for CAF has been reported to be 0.3–0.4%.9,11 The number of serious complications is increasing by 3–4% yearly,12 and half of these are seen during the first 3 months of treatment,13 i.e during initiation of therapy. Monitoring is frequently managed by GPs,7 and there is ongoing discussion concerning whether levels of efficiency and safety can be kept as high in primary health care (PHC) as at special anticoagulation clinics.
The literature indicates a variable level of control in real-life settings, with levels within therapeutic ranges 44–83% of the time.10,14–16 Experiences from studies in Swedish populations conducted in different settings show similar results, with levels within therapeutic ranges in 58–71% of cases.9,17,18 Although various studies have attempted to document the effectiveness of warfarin treatment in real-life practice,19 this is a difficult issue to study directly, as relevant outcomes generally cannot be determined reliably in a retrospective observational study. Few studies have attempted to document anticoagulation management in a representative sample of clinics.
Patients on warfarin treatment in Stockholm are now almost universally managed in PHC. The procedure for patients undergoing INR monitoring generally includes a blood sample at the PHC centre, and the same day or the next day the patient receives a dosage schedule and a time for the next test from the GP, either on a dosage chart or by telephone. Electronic patient records (EPRs) are used currently by almost all GPs in the area, providing us with clinical data that are useful for research.
The objective of this study was to assess prevalence, incidence and quality of treatment during the initiation phase of warfarin therapy for CAF in a PHC setting.
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Methods |
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Selection of PHC centres
We invited 12 PHC centres to participate and all agreed. In order to compensate for local variations regarding the population and the quality of data in the EPRs, the selection of centres included at least two from each of the five different health care districts in Stockholm County, at least two from each of the five main EPR systems in the area, and considerations given to our knowledge of the population in the area. The EPRs included the entire medical record, and no paper records were used. In each PHC centre, one GP was appointed as investigator. The total registered population (calculated from a population registry maintained for each GP) of the participating GPs comprised 203 407 individuals at the end of the study period.
Selection of patients
The initial selection criterion was all patients over 18 years of age on warfarin treatment during the 24 month study period (May 2000–April 2002). This was further specified as patients who were monitored with INR values and whose daily dosages of warfarin were ordered by a GP at the PHC centre. The EPR systems were searched for INR through their statistical modules in primary data retrieval. The investigator thereafter manually reviewed all these EPRs. Patients who had started treatment during the study period with CAF as the only treatment diagnosis, or as one of several treatment diagnoses, were included (study group), and they were subjected to a more detailed follow-up of PT monitoring. The initiation period was defined as the first 90 days of treatment. The follow-up started with the first day of treatment and continued until the last day of the period or the date of discontinuation.
Data collection
For the selected patients (as described above), information was collected concerning age, gender, duration and type of CAF (e.g. constant or intermittent), start date for treatment, other chronic diseases to be considered when prescribing warfarin, medication and attempts at cardioversion. Data from each monitoring episode (i.e. where PT was monitored and dosages given) included date, INR value, previous dosage, following dosage and discontinuation. The monitoring of anticoagulant treatment was performed using INR values, and the standard range was from 2.1 up to 3.0 INR, which is the target interval commonly used in the Stockholm area. Patients with values below this range have a subtherapeutic value, and those with values above the range have a supertherapeutic value.
Statistical analysis
The data were analysed using the SAS® software program. The time spent in the INR target range was estimated using linear interpolation,20 which assumes that the INR between two consecutive measurements varies linearly. The chi-square test was used to test the distribution of cross-classified nominal variables. Ninety-five percent confidence intervals (CIs) were used.
Ethical considerations
This study was approved by the regional ethics committee at Karolinska Institutet.
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Results |
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Background data, prevalence and incidence
There were 827 patients on warfarin treatment for CAF, giving a prevalence of 0.41% in the population. There were 144 patients who started warfarin treatment for CAF at the participating PHC centres, giving an incidence of 0.07% (0.06% for women and 0.08% for men). Their mean age was 73 years, 61% were men, and 70% were
70 years of age.
Clinical background
CAF was noted as being constant for 95 (66.0%) of the patients, intermittent for 21 (14.6%) and information was not available for 28 (19.4%). Forty-five (31.3%) patients had undergone an earlier attempt at cardioversion. Mean time since first being diagnosed with CAF was 3.2 years.
Almost two-thirds (63.2%) of the patients had one or more chronic diseases in addition to CAF. Hypertension was most frequent and was noted in 23.6%, followed by chronic heart failure in 20.8%, ischaemic heart disease in 13.9% and diabetes in 7.6%. Approximately 85% were taking one or more medications on a continuous basis.
Initiated treatment
Data on a total of 1721 PT monitoring episodes were collected. The PT value was monitored on average 12.0 times per patient. The individual range for INR values was 2.1–3.0 for 141 of the patients, while three patients had a narrower or lower range.
Of the 1721 episodes, 18 had incomplete data. For the remaining 1703 episodes, the average proportion of patient time with therapeutic PT values was 54.1% (Table 1). The proportion of time spent with supertherapeutic and subtherapeutic PT values was 13.1 and 32.8%, respectively. The proportion of monitoring episodes with therapeutic PT values was 50.2%. A value with a high bleeding risk (INR > 6.0) was found in three episodes. The mean ordered dosage was 11.3 (CI 10.5–12.2) mg per week. Minor bleeding complications were found in three patients (2.1%) and no thromboembolic events were registered. A short discontinuation of treatment was registered for 16 patients.
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Discussion |
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In this study, we investigated warfarin treatment for CAF in PHC with regard to occurrence and quality. We found that patients were outside the therapeutic range almost half the time during the first 90 days of treatment. The amount of time within the therapeutic range did, however, seem to improve from the first month to the third month. There was a gender difference favouring men in the initiation of treatment. We also found that it was feasible to study warfarin treatment for CAF by reusing information in EPRs from everyday clinical practice.
The prevalence of warfarin treatment for CAF has differed somewhat in studies performed in recent years. Our figure corresponds well to other studies with prevalence figures from 0.3 to 0.4%.7,9,11 However, most studies are not based on PHC with a registered population, a representative sample of patients and records from everyday clinical practice, which is an advantage of our study. Incidence has received little attention, and there is no recent study with which to compare our findings. The incidence of warfarin treatment in our study (0.07%) is surprisingly low considering the increased number of CAF patients in the past decade. This suggests that there may be an under-diagnosis of CAF in our study, as well as under-treatment with warfarin.
Regarding the INR values, our figures on monitoring episodes within the therapeutic range are numerically lower than in a recent study in the area, where 65% of the INR values were within the therapeutic range.9 However, that study included patients receiving treatment irrespective of the date treatment was started, while our study was confined to the initiation phase. Another important factor is the therapeutic range. In a study using a 2.0–4.0 INR range, 80% of the values were therapeutic.8 This complicates the comparison between studies, and makes the use of INR values within the therapeutic range problematic. However, estimates of time within the therapeutic range have been recommended as a more accurate measurement of quality. We have taken this into consideration and it is an advantage of our study.
Our rate for minor bleeding complications was 2.1% in a 90 day period; this is in line with a recent study in the area,9 but is low compared with figures reported by special anticoagulation clinics.4 However, our figure is likely to be low due to under-reporting, and a more comprehensive evaluation of the rate of complications with warfarin treatment in PHC would require more patients or a longer observation time than in this study.
The number of patients on warfarin treatment and their frequent health care contacts in PHC have received little attention. An increasing number of patients are already being referred to PHC in the Stockholm area, as has been suggested.12 The high frequency of testing when starting treatment is underlined in our study. This is going to require an organized approach to anticoagulant management including computer dosing systems and improved systems for follow-up.5
The major limitation is the lack of power to study the clinical implications regarding the effectiveness and safety of the results concerning time within and outside the therapeutic range. Furthermore, the study is local and, although we tried to compensate for local variations, conclusions about PHC in general must be drawn with caution. The validity of data in EPRs can also be questioned, particularity regarding the detection of adverse events, where our figures are likely to be underestimates. There is no reason to believe that patients on warfarin treatment were missed, as all patients receiving treatment (as defined above) at the PHC centres are registered under PT values in the laboratory module of the record systems. However, there are probably a few patients on warfarin treatment who have never been in contact with a GP, and the incidence and prevalence figures may have been underestimated.
Conclusions
The incidence and prevalence of warfarin treatment for CAF do not seem to be increasing in PHC in Stockholm. During the initiation phase of treatment, patients are outside the therapeutic range for almost half of the time, and the clinical implications of this should be subjected to further research. There is a gender difference favouring men in the initiation of treatment. Given the frequent monitoring episodes and the level of therapeutic control, warfarin treatment for CAF entails a considerable workload, both for patients and for those providing care, and there is a clear need for an organized approach to its management.
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Declaration |
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Funding: This study was supported by grants from the Stockholm County Council and AstraZeneca Sverige AB.
Ethical approval: Karolinska Institute (02-270).
Conflicts of interest: I.B. was employed by AstraZeneca Sverige AB when the study was undertaken.
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Acknowledgments |
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We thank all the GPs who participated in the study: Evy Adler, Kjell Andersson, Lena Andersson-Pommerlau, Peter Homann, Åke Johansson, Inger Larsbrink, Roland Morgell, Ulla Nordström, Samuel Sultani, Eva Toth-Pal, Rikard Viberg and Jan-Olov Östling.
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