How does elevated blood pressure increase the risk of stroke?

Elevated Blood Pressure and Stroke Risk

Hypertension is the single most important modifiable risk factor for both cerebral infarction and intracerebral hemorrhage, with a continuous, consistent relationship between blood pressure and stroke risk that is independent of other risk factors. 1

Pathophysiological Relationship Between Hypertension and Stroke

• The relationship between blood pressure and stroke risk is direct - the higher the blood pressure, the greater the stroke risk, beginning from levels as low as 115/75 mmHg 1
• Hypertension contributes to stroke through multiple mechanisms:
  • Accelerated atherosclerosis in cerebral vessels 1
  • Damage to small penetrating arteries in the brain 1
  • Increased risk of both ischemic stroke and hemorrhagic stroke 1, 2
• In Asian populations, a 10 mmHg increase in systolic blood pressure increases risk of hemorrhagic stroke by 72%, compared to 49% in Western populations 1

Epidemiology and Impact

• Hypertension affects at least 65 million persons in the United States and is a major risk factor for both cerebral infarction and intracerebral hemorrhage 1
• More than two-thirds of persons over 65 years of age are hypertensive 1
• The Framingham Study found that individuals who are normotensive at 55 years of age have a 90% lifetime risk for developing hypertension 1
• Despite the efficacy of antihypertensive therapy, only 70% of Americans with hypertension are aware they have the condition, 60% are being treated, and only 34% are controlled to <140/90 mmHg 1

Benefits of Blood Pressure Control

• Antihypertensive therapy is associated with a 35% to 44% reduction in the incidence of stroke 1
• A meta-analysis of 18 long-term randomized trials found that both β-blocker therapy (RR 0.71; 95% CI 0.59 to 0.86) and treatment with diuretics (RR 0.49; 95% CI 0.39 to 0.62) were effective in preventing stroke 1
• FDA-approved antihypertensive medications specifically note that "lowering blood pressure reduces the risk of fatal and nonfatal cardiovascular events, primarily strokes and myocardial infarctions" 3, 4, 5
• The largest and most consistent cardiovascular outcome benefit of blood pressure reduction has been a reduction in the risk of stroke 3, 4, 5

Treatment Recommendations

Classification and Treatment Targets

• The JNC 7 classification system defines:

  • Normal: <120/80 mmHg
  • Prehypertension: 120-139/80-89 mmHg
  • Stage 1 hypertension: 140-159/90-99 mmHg
  • Stage 2 hypertension: ≥160/≥100 mmHg 1

• The American Heart Association recommends controlling blood pressure to <120/80 mmHg with medication and lifestyle changes to reduce stroke risk 6

Pharmacological Treatment

• For Stage 1 hypertension: Thiazide-type diuretics for most patients; may consider ACEIs, ARBs, β-blockers, calcium channel blockers, or combination 1
• For Stage 2 hypertension: Two-drug combination for most patients (usually thiazide-type diuretic and ACEI or ARB or β-blocker or calcium channel blocker) 1
• Losartan is specifically indicated to reduce the risk of stroke in patients with hypertension and left ventricular hypertrophy 3
• All effective antihypertensive agents appear to have similar efficacy in reducing stroke risk when they effectively lower blood pressure 2

Lifestyle Modifications

• Lifestyle modifications are recommended for all patients and include:
  • Weight reduction if overweight
  • Limitation of alcohol intake
  • Increased aerobic physical activity (30-45 minutes daily)
  • Reduction of sodium intake (<2.34 g)
  • Maintenance of adequate dietary potassium (>120 mmol/d)
  • Smoking cessation
  • DASH diet (rich in fruits, vegetables, and low-fat dairy products and reduced in saturated and total fat) 1, 6

Special Considerations

• Patients with existing cardiovascular disease have a significantly increased risk of first stroke compared to those without (RR 1.73 for men; RR 1.55 for women) 1
• In patients with prehypertension (120-139/80-89 mmHg), antihypertensive treatment appears to reduce the risk of stroke 1
• For secondary prevention in patients who have already had a stroke, optimal blood pressure range appears to be 120-140/80-90 mmHg 7
• Acute management of blood pressure during stroke requires different approaches for ischemic vs. hemorrhagic stroke 8

Common Pitfalls to Avoid

• Failure to diagnose and adequately treat hypertension, particularly in minority populations and the elderly 1
• Inconsistent medication adherence can increase stroke risk, with up to 40% of stroke patients not taking medications as prescribed 6
• Simply providing health information without behavioral interventions is ineffective; structured programs that use behavior change theory with ongoing support are recommended 6
• Addressing only one risk factor rather than multiple risk factors simultaneously (hypertension, diabetes, smoking, etc.) 6
• Waiting for symptoms to appear before treating hypertension - hypertension is typically asymptomatic until end-organ damage occurs 1