Risk Factors

Abnormal Blood Pressure

High Blood Pressure (Hypertension). High blood pressure (known medically as hypertension ) contributes to 70% of all strokes. Researchers have estimated that controlling blood pressure can prevent nearly 40% of strokes.

Two numbers are used to describe blood pressure phases and may affect stroke risk separately:

• The systolic pressure (the higher and first number) is measured as the heart contracts to pump out the blood. Evidence suggests that elevated systolic pressure poses a significant danger for heart and stroke emergencies when diastolic is normal, a condition called isolated systolic hypertension. The wider the spread between the systolic and diastolic measurements, the greater the danger.
• The diastolic pressure (the lower and second number) is measured as the heart relaxes to allow blood to refill the heart between beats. Abnormally higher diastolic pressure is a strong predictor of heart attack and stroke in most people with hypertension.
• Stroke from Low Blood Pressure (Hypotension). Uncommonly, blood pressure that is too low can reduce oxygen supply to the brain and cause a stroke. This can occur from a heart attack, a major bleeding episode, an overwhelming infection, or rarely, from surgical anesthesia or from overtreatment of high blood pressure.

Click the icon to see an image of the risks of untreated hypertension.

Heart Abnormalities Causing Traveling Blood Clots (Embolisms)

Atrial Fibrillation. About one in six strokes are due to atrial fibrillation. This is a heart rhythm disorder in which the atria (the upper chambers in the heart) beat very quickly and nonrhythmically. The blood pools instead of being pumped out, increasing the risk for formation of blood clots that break loose and travel toward the brain. Atrial fibrillation poses a six-fold increased risk for stroke and may also pose a higher risk for complications after a stroke.

Atrial fibrillation is uncommon in people under 60 years old, but about 6% of adults over age 80 have this heart rhythm disorder. In this patient group, the risk for stroke may be higher or lower with the presence of other risk factors, including having heart failure, high blood pressure, diabetes, and a previous history of stroke, TIA, or rheumatic heart disease. More women than men have AF, but risk for stroke is higher in women with this condition than in men.