OXVASC

The incidence of new cases of first-ever TIA or stroke can only be reliably assessed in prospective population-based studies (Sudlow and Warlow 1996 Feigin et al. 2003 Rothwell et al. 2004) since hospital-based studies are subject to referral bias (Table 1.4). One of the most comprehensive population-based studies of stroke and TIA incidence is the Oxford Vascular Study, OXVASC, which has near-complete case ascertainment of all patients, irrespective of age, in a population of 91 000 defined by registration with nine general practices in Oxfordshire, UK (Coull et al 2004). This is in contrast to previous studies, such as the MONICA project and the Framingham study, which had an age cut-off at 65 or 75 years or relied on voluntary participation. 

The OXVASC study showed that the annual incidence of stroke in the UK in the first few years of this century, including subarachnoid hemorrhage, was 2.3/1000 and the incidence of TIA was 0.5/1000 (Rothwell et al. 2005), with about a quarter of events occurring in those under the age of 65 and about a half in those above the age of 75 (Fig. 1.1). The incidence of cerebrovascular events in OXVASC was similar to that of acute coronary vascular events in the same population during the same period (Fig. 1.2), with a similar age distribution (Rothwell et al 2005). Incidence rates, however, measure first-ever-in-a-lifetime definite events only and exclude possible, recurrent and suspected events, so do not represent the true burden of a condition. This is especially true for TIA, where a significant proportion of cases referred to a TIA service have alternative, non-vascular... 

Table 1.5. Incidence rates of transient ischemic attack and stroke according to stringency of definition applied and previous cerebrovascular disease measured in OXVASC (2002-2005)...

Table 2.1. Demographics and risk factor prevalence in incident strokes in OXVASC...

OXVASC, Oxford Vascular Study OCSP, Oxford Community Stroke Project Cl, confidence interval. 

Table 8.2. Numbers of patients referred to dedicated TIA clinics" in whom a non-neurovascular diagnosis was eventually made in Oxford Vascular Study (OXVASC 2002-2004) and the Oxford Community Stroke Project (OCSP 1981-1986)...

Fig. 10.1. Numbers of patients referred to the Oxford Vascular Study (OXVASC) between 2002 and 2007 with suspected transient ischemic attack (TIA) or minor stroke showing clinical diagnosis (before imaging) and revised...

Table 10.3. Rates of infarction, primary hemorrhage or hemorrhagic infarction on CT scan among subjects with probable or definite transient ischemic attack or minor stroke in the Oxford Vascular Study (OXVASC)...

In the OXVASC cohort of patients with probable or definite TIA or minor stroke, 699 were imaged with CT. Rates of infarction and hemorrhage detected with CT are listed in Table 10.3. 

Among 334 patients with definite or possible minor stroke in OXVASC in whom hemorrhage could be detected reliably by either CT performed within 10 days or MRI (regardless of delay), primary hemorrhage was detected in 17 (5.1% 95% Cl, 3.2-8.0), and hemorrhagic transformation of an infarct in four (1.2% 95% Cl, 0.5-3.0). 

Comparable risks of stroke after TIA were measured in population-based studies in Oxfordshire, UK (Lovett et al. 2003 Coull et al. 2004). In a cohort of 249 consecutive patients with a TIA ascertained in the Oxford Vascular Study (OXVASC) over a 30-month period, stroke risks at two and seven days were 6.8% (95% confidence interval [Cl], 3.7-10.0) and 12.0% (95% Cl, 8.0-16.1), respectively (Rothwell et al. 2007). Although this cohort was smaller than the Californian cohort, it had the advantages of being population based and, therefore, included patients who were treated as inpatients, as outpatients and managed solely in primary care diagnoses were made by an experienced stoke physician and follow-up was face to face with independent adjudication of outcome events. 

The risk of stroke following minor stroke has not been studied in such depth. However, in a provisional report from the first year of OXVASC, the risk of stroke among 87 patients with minor stroke (defined as a score of < 3 on the National Institutes of Health Stroke Scale (NIHSS)) was 11.5% (95% Cl, 4.8-11.2) at seven days and 18.5% (95% Cl, 10.3-26.7) at 90 days (Coull et al. 2004). Among patients with minor stroke who were referred to the dedicated neurovascular clinic in the EXPRESS study and did not need immediate admission to hospital, the rates of recurrent stroke at 90 days were 10-8% (17/158) in phase 1, without urgent intervention, and 4.0% (5/125) in phase 2, with urgent intervention (Rothwell et al. 2007) (Ch. 20). 

Sources-. Flossman et a . 2006 (OXVASC) Lovett et al. 2003 (OCSP) Petty et al. 2000 (Rochester study) Kolominsky-Rabas et al. 2001 (Erlingen study). 

The Early Use of Existing Preventive Strategies for Stroke (EXPRESS) study aimed to determine the effect of more rapid treatment after TIA and minor stroke in patients who were treated in a specialist neurovascular cUnic (Rothwell et al. 2007) within OXVASC. In a prospective, population-based, sequential comparison study, the effect on the process of care and outcome of either urgent access and immediate treatment in a dedicated neurovascular clinic or an appointment-based access and routine treatment initiated in primary care were compared for all patients with TIA or minor stroke who did not need hospital admission. The primary outcome was the risk of stroke during the 90 days after first seeking medical attention. 

Of the 1278 patients in the OXVASC population who presented with TIA or stroke throughout the study period, 607, predominantly with major stroke, were referred or presented directly to the hospital 620 were referred for outpatient assessment with TIA or minor stroke and 51 were not referred to secondary care. Of all outpatient referrals. 

Because the EXPRESS study was nested within OXVASC (Rothwell et al. 2004b), identical methods of case ascertainment, assessment and follow-up for the entire study population during both phases ensured that there were no temporal changes in referral patterns, patient characteristics or other potential sources of bias. The findings, therefore, strongly suggested that the considerable impact on outcome was a consequence of more rapid assessment and treatment... 

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