Atrial Fibrillation
Table 2: Antithrombotic Therapy Underuse in Patients with Atrial Fibrillation95–98,107
Reference
Steger et al., 200495
Glazer et al., 200796
Study Population Number of Use of Oral Patients
AF + stroke, Austria
Newly detected AF, US
Overall: 992 − AF: 304
AF: 33 No AF: 688 − Overall: 581 Overall: 45
High risk: 444 High risk: 48 Intermediate Intermediate risk: 33 risk: 42
Low risk: 34 Low risk: 95
Rosenman et al., New onset AF 200997
and/or flutter (eligible for VKA), US
Nieuwlaat et al., AF patients at 200798
Gallagher et al., Chronic AF in 2008107
Overall: 3,634 Overall: 61
high risk for stroke, Europe
Overall: 41,910 Overall: 35 primary care, UK AF = atrial fibrillation; VKA = vitamin K antagonists.
were tested as continuous point scales, CHA2DS2-VASc had unusually high c-statistics when applied using the traditional
categories of low- (CHADS2 score of 0), intermediate- (CHADS2 score of 1–2) and high-risk groups (CHADS2 score of ≥3), which suggests that the new scheme provides improvements in predicting stroke risk
over the CHADS2 scheme. The annual rate of thromboembolism including peripheral artery embolism, ischaemic stroke and
pulmonary embolism in the CHA2DS2-VASc low risk group was 0.78 per 100 person years, compared with 1.67 per 100 person years in
the CHADS2 low risk group.
Only 8.7 % of the study population met the low risk CHA2DS2-VASc criteria, compared with 22.3 % when using the CHADS2 criteria (see Figure 1).58
This finding is similar to other assessments, including
a UK study in which only 8.6 % of patients with AF in general practice were considered low risk by CHA2DS2-VASc.59
In the Danish study, the
CHA2DS2-VASc scheme performed better than CHADS2 in predicting patients at high risk; 80 % of the patients were considered high risk
using CHA2DS2-VASc, however fewer than half would have met high-risk criteria if CHADS2 were used.58
The study also found that the rate for patients in the intermediate risk group was 4.75 with
CHADS2 compared with 2.01 with CHA2DS2-VASc. Thus, the newer stratification methods such as CHA2DS2-VASc appear to offer improved risk stratification, reduce the number of people classified
into the intermediate-risk group, which is the category that can cause ambiguity regarding whether to treat with warfarin or aspirin.50,55 Moreover, a recent study assessed the risk of stroke according to specific risk stratification schemes, in a cohort of 662 elderly AF
patients treated with warfarin. The results indicated that the CHADS2 and CHA2DS2-VASc schemes had the best c-statistics (0.717 and 0.724, respectively) for predicting the residual thromboembolic risk
despite warfarin treatment and that other risk schemes had some limitations in this setting.55
Other Risk Factors, Risk Modifiers and the Role of Biomarkers
In addition to the risk factors included in current risk stratification schemes, several other risk factors have been recognised. These
190
In preliminary results presented at the American Heart Association Scientific Sessions 2010 of the Asymptomatic atrial fibrillation and stroke evaluation in pacemaker patients and the atrial fibrillation reduction atrial pacing trial (ASSERT), episodes of device-detected atrial tachycardia greater than six minutes were found in 261 of 2,580 pacemaker patients, with hypertension but no history of AF over almost three years of follow-up. These arrhythmias were associated with a 2.5-fold increase in risk of ischaemic stroke and
systemic embolism. Among the patients with a CHADS2 score of ≥2, device-detected ATs increased the absolute risk of stroke to 2.1 % per year. Among pacemaker patients without any prior history of atrial arrhythmias, 35 % of all strokes and systemic emboli were preceded by device-detected ATs.63,64
A study contributing further information comparing the duration of AF with the risk of stroke found that in patients without atrial arrhythmias, the risk of stroke was 1.2 % per year. If at least five minutes of atrial arrhythmias were detected, the event rate remained low at 1.7 % per year. If 24 hours or more of atrial arrhythmias were detected, the event rate was 4 % per year.
However, by adding the patient’s CHADS2 score to the duration of atrial arrhythmia, groups at low risk (0.8 % per year) and at high risk (5 % per year) for thromboembolic events could be better identified.62
This is still an uncertain area, however there are several EUROPEAN CARDIOLOGY Overall: 3,329 Overall: 45 Anticoagulant (%)
Chronic kidney disease is a major cardiovascular risk factor, which is particularly common among elderly people. 61
However, whether it
The presence of proteinuria has also been shown to reflect an increased thromboembolic risk in patients with normal or moderately impaired renal function.61
does in fact independently raise the risk for ischaemic stroke is poorly understood. Among 13,535 adults with AF, chronic kidney disease raised the risk of thromboembolism in AF independently of other known risk factors.61
include a family history of stroke,60 the presence of chronic kidney
disease, atrial high-rate episodes (AHRE) and atrial tachyarrhythmia (AT)/AF burden.61–65
The duration of AF was previously not considered as a risk factor for stroke in AF patients due to the ambiguity of clinical symptoms.65 However, the diagnostic features of atrial-based pacemakers are now sufficiently advanced to supply information on the presence and duration of atrial arrhythmias.65
Three key studies have assessed
the consequences related to these arrhythmias. In a study to evaluate the relationship between daily AT burden from implantable device diagnostics and stroke risk (The relationship between daily atrial tachyarrhythmia burden from implantable device diagnostics and stroke risk [TRENDS]), the overall rate of ischaemic events was low in this cohort of more than 2,400 patients (1.3 % per year). Patients with atrial rate >175 bpm, lasting >20 seconds, for <5.5 hours on a single day during a 30-day period experienced a clinical thromboembolism rate of 1.1 % per year, while the event rate among those with a high AT/AF burden was 2.4 % per year. After statistical adjustment for stroke risk factors and antithrombotic therapy, a high AT/AF burden <5.5 hours per day over 30 days was associated with a risk of thromboembolism similar to that of patients entirely free of AT/AF, while the risk doubled among patients with AT/AF during >5.5 hours per day. However, compared with zero burden, the difference in HR for the groups with low and high AT/AF burdens was not statistically significant.65
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