Measures to Prevent Stroke

Summarized by Robert W. Griffith, MD
January 24, 2003 (Reviewed: January 21, 2005)

Introduction

Stroke is a major cause of morbidity and long-term disability, and is the third leading cause of death in developed countries. Different reports in the literature have indicated ways in which stroke can be prevented, and these have been analyzed and summarized by three Canadian physicians in a JAMA article. They searched MEDLINE, the Cochrane Library, and the ACP Journal Club databases, focusing chiefly on papers from 1998 onwards.

Over 350 articles were analyzed, and classified according to the strength of the evidence in favor of a particular preventative intervention. Level 1 was based on evidence from randomized clinical trials, level 2 was data from observational studies (cohort, case-control, and outcome studies), level 3 comprised case-reports, and level 4 represented 'expert opinion'.

Known risk factors for stroke

Using levels 1 and 2 evidence, the authors listed the known modifiable risk factors for stroke. These are given in the table below:

Risk Factor	Prevalence	Relative Risk
Hypertension	25% - 40%	3 - 5
Raised cholesterol level*	6% - 40%	1.8 - 2.6
Smoking	25%	1.5
Physical inactivity	25%	2.7
Obesity	18%	1.8 - 2.4
Carotid stenosis (>50%)	2% - 8%	2
Alcohol > 5 drinks/day	2% - 5%	1.6
Atrial fibrillation	1%	5 - 17

* >240 mg/dL (6.2 mmol/L)

There are also non-modifiable risk factors - increasing age, male sex, nonwhite race, coronary heart disease, congestive heart failure, and a family history of stroke or transient ischemic attacks (TIA).

A history of treated TIAs has been associated with an 11% incidence of stroke, with half of the cases occurring within 2 days of a TIA.

Preventive strategies for primary prevention

Antihypertensive treatment: Lowering blood pressure in hypertensives reduces the relative risk (RR) of stroke - both ischemic and hemorrhagic - by 42%. In elderly patients with isolated systolic hypertension, the RR reduction is 30%. There is a therapeutic effectiveness-outcome relationship; the greater the reduction in blood pressure, the greater the risk reduction. All classes of antihypertensives are effective in this respect.

Treatment of hyperlipidemia: Statin therapy is associated with a RR reduction of stroke of 25%. Other lipid-lowering therapies - resins, fibrates, and diet - have not been shown to be effective in reducing the risk of stroke.

Antithrombotic therapy in atrial fibrillation: The risk of stroke in patients with non-rheumatic atrial fibrillation - paroxysmal or chronic - is about 5% per year. Warfarin is the most efficacious agent in preventing stroke; the associated slight risk of hemorrhage can be greatly reduced in almost every case by careful dosing and lab controls.

Antiplatelet therapy after myocardial infarction: Aspirin lowers the RR of stroke in post-MI subjects by 36%.

Treatment of diabetes: One small study has shown a 44% reduction in the RR of stroke in diabetics who had their blood pressure tightly controlled. Otherwise, level 1 or 2 evidence is lacking for possible valuable effects of tight blood sugar control in diabetics on the risk of stroke. The proven useful effects on microvascular renal disease suggest that such a benefit must exist, though the appropriate studies have not yet been reported.

Stopping smoking, antiplatelet therapy with aspirin, ACE inhibitors: The evidence for these measures is inadequate to be able state unequivocally that prevent stroke (except for the antihypertensive action of ACE inhibitors).

Carotid endarterectomy: In asymptomatic patients with over 50% stenosis, the risk of stroke or death in the immediate peri-operative period was quadrupled, but there was a 30% reduction in the RR of death or stroke in the next 3 years. Obviously more trials need to be done to identify those best suited for this type of intervention.

Strategies for secondary stroke prevention

Around 7% of all patients with a stroke or TIA will have a recurrence every year. Secondary prevention is therefore likely to be much more cost-effective than primary prevention attempts - the RR reductions for each measure remain largely the same, but the absolute RR reductions are clearly much higher. Thus the number needed to treat (NNT) to prevent one stroke a year is in the 1000's for primary prevention measures, and in the 100's for secondary prevention.

The RR reductions for effective antihypertensive treatment in preventing another stroke or TIA is 28%, for statin therapy it's 25%, for adjusted-dose warfarin in atrial fibrillation patients it's 62%, for aspirin it's 28%, and for thienopyridines (clopidrogel or ticlopidine) there is a 13% advantage over and above aspirin. Unlike primary prevention, stopping smoking as a secondary prevention measure carries a RR reduction of 33%. The results for carotid endarterectomy are rather variable from one study to the next, depending on the skill and experience of the surgery team, the age and sex of the patient, systolic blood pressure, and peripheral vascular disease.

Comment

Although not specifically addressed in this analysis of published trials, there is little doubt that the lifestyle changes usually suggested to be 'heart healthy' - appropriate diet, weight control, physical exercise, no smoking, etc. - are highly likely to have a beneficial impact on the risk of stroke. Indeed, we have posted several articles that point in this direct (see links below).

This particular analysis focuses on those steps that have been proven in well-conducted studies to provide a reduction in the risk of having a stroke. All physicians and healthcare professionals should be aware of these measures, and propose them in treating their patients at risk.

Source

• New evidence for stroke prevention. SE. Straus, SR. Majumdar, FA. McAlister, JAMA, 2002, vol. 288, pp. 1388--1395

Related Links
Polyunsaturated Fat May Protect Against Stroke
Survey Data Ties Folate to Reduced Stroke Risk
Potassium May Curb Stroke Risk
Vitamin C Status Linked to Stroke Risk

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