Stroke is common, and frequently fatal or disabling.1,2 In Australia, stroke is the second leading contributor to disease burden after ischaemic heart disease.3
Stroke occurs most commonly in patients with known risk factors. It has been estimated that the proportion attributable to these factors is as high as 80%,4 implying that stroke is largely a preventable disease. However, as various preventive therapies are now widely employed, it is uncertain whether these estimates still apply.
The effects of ischaemic stroke (the most common kind) can potentially be minimised with thrombolysis.5 However, thrombolysis rates in Australia are around 3%,6 and treatment rates, even at centres of excellence, struggle to exceed 10%.7 There is therefore scope for reducing the effects of stroke by expanding thrombolysis.
We performed an observational stroke unit-based study with retrospective assessment of prestroke therapies. Eligibility for thrombolysis was determined at or shortly after admission.
The Royal Adelaide Hospital serves a local population within metropolitan Adelaide, and is also a tertiary referral centre for adjacent rural areas. Its stroke unit admits all patients with a diagnosis of acute stroke regardless of age or severity, except those requiring neurosurgical intervention (subarachnoid haemorrhage and some with intracerebral haemorrhage) and those transferred from high-level residential care. The study was approved by the Royal Adelaide Hospital Research Ethics Committee.
We calculated percentage stroke preventability using a previously published method,8 assuming a multiplicative scale for relative risk reductions of underutilised therapies:
Factors assessed included untreated or suboptimally treated hypertension,9 untreated or suboptimally treated atrial fibrillation,10 indications for statin11 or antiplatelet therapy but no treatment,12 inappropriate hormone replacement therapy,13 untreated “normal” post-stroke blood pressure,14 untreated symptomatic carotid disease,15 smoking,16 and subtherapeutic warfarinisation,17 (Box 1). Only risk factors with strong data from randomised controlled trial (RCT) meta-analyses or large RCTs were included, except for smoking,16 which has robust population relative risk data, and for suboptimal anticoagulation, which cannot feasibly be assessed in an RCT but clearly increases stroke risk.17,18 Studies on the effect of smoking and hypertension on stroke risk have not always reliably distinguished ischaemic and haemorrhagic stroke, and hence the impact of these factors on the preventability of ischaemic and haemorrhagic stroke was not differentially weighted.
Efficacy of hypertension management was assessed by comparing the last two prestroke systolic blood pressure readings with national guidelines.19 Undertreated hypertension was identified where both readings were more than 10 mmHg above those recommended in guidelines, and grossly undertreated hypertension was identified where both were more than 20 mmHg above. Only systolic pressure was considered.20 Adequacy of anticoagulation for atrial fibrillation was assessed by comparison with national guidelines,21 and hypercholesterolaemia with Pharmaceutical Benefits Scheme guidelines applicable in 2006. Hormone replacement therapy was designated inappropriate unless a patient had significant menopausal symptoms refractory to other therapies. Inadequate warfarininsation was defined as subtherapeutic admission and preadmission international normalised ratio (INR) readings or, in the case of periprocedural stroke, a failure to follow national guidelines.22 All smoking-associated strokes were deemed potentially preventable.
Potential prevention of disability from stroke by thrombolysis was assessed by comparing actual versus potential thrombolysis cases (ie, patients with ischaemic stroke potentially able to reach hospital within 120 minutes of stroke onset with no contraindications). A number needed to treat (NNT) of 8 (95% CI, 5.3–15.3) was derived from a recent meta-analysis,5 being the number needed to render one patient who had had a stroke minimally symptomatic or asymptomatic (a modified Rankin score of ≤ 1).
Categorical variables potentially influencing stroke preventability were assessed by the χ2 test with two-tailed P values. Variables prospectively hypothesised to be associated with stroke preventability were being male, social isolation, rural address, non-English-speaking background and older age. A post-hoc analysis was conducted of the association between hypertension targets not being reached and whether those targets were standard (140/90 mmHg) or lower (130/85 mmHg or less). Relative risks and 95% CIs were calculated. Analyses were performed with GraphPad Prism, version 5.00 for Windows (GraphPad Software, San Diego, Calif, USA).
During the study period, 306 patients were admitted to the stroke unit; 43 had a diagnosis other than stroke. Four patients did not or could not consent to inclusion in the study, leaving a total of 259 patients who had had a stroke.
Demographic data, risk factor prevalence and therapies, and stroke characteristics are shown in Box 2. Almost all patients identified a treating doctor. Stroke type and mortality, median ages and sex distribution did not differ from recent Australian population-based studies.2,23 Over 70% of patients were being treated with at least one preventive therapy. The most common previously identified risk factor was hypertension. Most patients with hypertension were being treated, many with polytherapy.
Overall, 135 patients (52%) had at least one suboptimally modified risk factor (Box 3), and 10% had two or more. In these patients, average stroke preventability was 52%. Therefore, overall, 70 out of 259 strokes (27%) were preventable.
At least two recent blood pressure measurements had been recorded for 95% of patients; a quarter were not within the target range. Patients were more likely to have had inadequately controlled hypertension if their target systolic pressure was 130 mmHg or less (patients with diabetes, young-onset hypertension and renal disease;19 relative risk, 4.27; 95% CI, 2.58–7.05; P < 0.001).
We had hypothesised that the very old were more likely to be treated suboptimally. However, as shown in Box 4, we found the opposite. There was a strong trend for the association of suboptimally managed risk factors with younger age, principally because of the prevalence of smoking and unmet blood pressure targets in this group. Our other hypotheses, that rural address, social isolation, non-English-speaking background and being male might be linked to stroke preventability, were not supported.
Compared with optimal modification of risk factors, fewer strokes were “preventable” with best-practice thrombolysis (Box 5). Roughly a quarter of stroke patients were ineligible for treatment with tissue plasminogen activator because of intracerebral haemorrhage, or were not transferred in time from rural hospitals. Of the remaining 168, 125 had a contraindication to thrombolysis, most commonly because of time-of-onset uncertainty (most often awaking with neurological symptoms) or unavoidable presentation outside the 3-hour window (eg, being found by relatives after a prolonged period). A third of potential thrombolysis (14/42) candidates received treatment. Assuming a number needed to treat of 8,5 disability could potentially have been prevented in four strokes under optimal conditions.
Our study demonstrates the continued high prevalence of suboptimally modified risk factors in a hospital-based cohort of consecutive patients admitted with stroke from 24 January 2006 to 10 January 2007 from whom informed consent could be obtained. Although this was a highly treated population (over 70% were being treated with at least one preventative therapy), over half had at least one suboptimally modified risk factor. According to the assumptions outlined in our methods, over a quarter of strokes were preventable. By comparison, best-practice thrombolysis could have prevented disability in a smaller number of strokes.
Estimates of stroke preventability were conservative, as lifestyle factors contributing independently to stroke risk that cannot be readily quantified were not included (eg, obesity,24 physical inactivity,25 alcohol consumption26 and poor diet24). Furthermore, statin therapy,27 therapeutic anticoagulation18 and angiotensin-converting enzyme inhibition28 not only prevent stroke, but also lessen stroke severity.
Stroke preventability is difficult to define and quantify, and our finding that a quarter of strokes could be prevented is less than the 80% attributable risk cited in the introduction,4 and a recently estimated 80% reduction in recurrence risk with best-practice treatments.8 However, our population was already being treated with a number of preventive therapies, in contrast to patients in both cited articles, in which no therapy, rather than some therapy was assumed. Additionally, one article focused only on secondary prevention, and included dietary and exercise interventions,8 which are not proven on a population basis for primary stroke prevention. Our study identifies and quantifies the risk factors that remain suboptimally managed in an era of widespread medical therapies and declining smoking habits.
We found that the three suboptimally modified risk factors with the greatest impact were smoking, hypertension and atrial fibrillation. This finding is consistent with a recent population-based study of general practice patients,29 and broadly consistent with international data.30 Smoking and suboptimally treated hypertension were more prevalent in younger patients, explaining the higher prevalence of “stroke preventability” in this group. These patients often also had lower blood pressure target values, which could only have been achieved by combination therapy. Hypertension and other risk factors were well managed in older patients, despite the greater prevalence of risk factors, refuting the possibility that therapeutic nihilism or undertreatment among older people may be a significant cause of ischaemic stroke. We did, however, demonstrate a continued reluctance of health practitioners to prescribe warfarin and of patients to take it, also documented elsewhere.31 It is to be hoped that new data confirming the efficacy and safety of warfarin therapy in older people will help allay persisting concerns.32
1 Relative risk reductions from published studies for modification of designated risk factors for stroke
* 95% confidence intervals were not provided in the articles cited. |
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2 Demographic characteristics, prestroke risk factors and therapies, and stroke characteristics and outcomes for 259 patients admitted to Royal Adelaide Hospital stroke unit from 24 January 2006 to 10 January 2007
Median admission National Institutes of Health stroke scale score |
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3 Total strokes preventable by optimal management of each risk factor for 135 patients with one or more risk factors
Abstract
Objective: To identify and quantify current deficiencies in primary and secondary stroke prevention, as well as potential gains from optimal employment of thrombolysis.
Design, participants and setting: Observational study of 259 consecutive patients admitted to a tertiary hospital stroke unit from 24 January 2006 to 10 January 2007, with retrospective assessment of prestroke risk factors and therapies to determine stroke preventability, based on relative risk reductions from published meta-analyses of preventive therapies.
Main outcome measures: Numbers of strokes preventable by optimal risk factor modification and numbers of strokes with preventable disability through optimal thrombolysis; characteristics of patients with preventable strokes; contributions of each risk factor to stroke preventability.
Results: 183 patients had a disabling or fatal stroke; 135 patients had at least one suboptimally managed risk factor. On the basis of prespecified stroke preventability weightings, 70 strokes were preventable. The younger the patient, the more likely that the stroke was potentially preventable (relative risk [RR] for age < 60: ≥ 80 years, 3.10; 95% CI, 1.96–4.92). Smoking, inadequate control of hypertension and suboptimal anticoagulation accounted for nearly 90% of preventable strokes. Patients with target systolic blood pressures of 130 mmHg or lower were more likely to have inadequately controlled hypertension (RR, 4.27; 95% CI, 2.58–7.05). By comparison, disability could have been prevented in four strokes through optimal thrombolysis.
Conclusions: A significant proportion of stroke remains preventable, especially in younger patients, by optimal modification of risk factors, particularly smoking, blood pressure and anticoagulation. Only a small proportion of patients will benefit from best-practice thrombolysis.