All key factors typical of those with silent stroke are also linked to 10-year risk of having a clinical stroke.
A recent study found that about 10 percent of the apparently healthy middle-aged participants with no symptoms of stroke were injured from "silent strokes," researchers report in Stroke,* a journal of the American Heart Association.
Silent cerebral infarction (SCI), or "silent stroke," is a brain injury likely caused by a blood clot interrupting blood flow in the brain. It's a risk factor for future strokes and a sign of progressive brain damage that may result in long-term dementia.
"The findings reinforce the need for early detection and treatment of cardiovascular risk factors in midlife," said Sudha Seshadri, MD, co-author of the study and associate professor of neurology at Boston University School of Medicine. "This is especially true since SCIs have been associated with an increased risk of incident stroke and cognitive impairment."
MRIs of 2,000 People Examined
Researchers evaluated magnetic resonance imaging (MRI) from about 2,000 people, average age 62, who are part of the Framingham Offspring Study (children of participants in the original Framingham Heart Study, begun in 1948). The offspring have undergone clinical examinations every four to eight years.
Among patients who displayed no symptoms of stroke, 10.7 percent had SCIs on routine brain MRI, researchers said.
Previous estimates of SCIs ranged from 5.8 percent to 17.7 percent depending on age, ethnicity and other issues.
Of those in the study with SCIs, 84 percent had a single lesion.
Framingham 10-Year Stroke Risk Profile
The study is the first to correlate the total score of the Framingham Stroke Risk Profile to prevalence of SCI. The risk profile estimates the 10-year probability of having a stroke. The factors in the profile are:
Systolic blood pressure [peak pressure in the arteries, expressed “over” diastolic pressure – the lowest pressure]
Left ventricular hypertrophy [increased heart muscle mass that doesn’t increase pumping ability, as it would in an athlete, but instead accumulates scar tissue]
And atrial fibrillation (AF) [irregular heartbeat].
All These Factors Increase Silent Stroke Risk Too
All the components of the Framingham Stroke Risk Profile were positively associated with an increased prevalence of SCI. For the first time, researchers found a significant correlation between atrial fibrillation and silent cerebral infarction. Atrial fibrillation is the most common form of heart arrhythmia, or irregular heartbeat in people older than 65. "In our data, AF increased the risk of prevalent SCI more than two-fold," Seshadri said. Hypertension and systolic blood pressure were also associated with an increased prevalence of SCI.
Risk factors for stroke are also risk factors for atrial fibrillation. Hypertension and other factors that make it more likely individuals will experience AF also predispose those people to clinical stroke and probably to SCI. Atrial fibrillation, therefore, may be a simultaneous outcome rather than a cause of SCI, researchers said.
The observational data could not indicate if screening for and appropriately treating AF would reduce the population burden of silent stroke, researchers said.
The study also found that high systolic blood pressure, hypertension and elevated levels of blood homocysteine, a sulfur-containing amino acid found in the blood, were other risk factors commonly associated with stroke that also raised participants' chances of having SCI. Hypertension consistently has been implicated as a risk factor of SCI.
Impact of Risk Factors Not Age or Gender Linked
Neither age nor gender significantly changed the effect of any of the risk factors on SCI. Researchers' ability to generalize findings for other ethnic groups is limited because participants in the Framingham study are mostly of European descent.
"The significant relationship between hypertension, elevated serum homocysteine, carotid artery disease and prevalent SCI underscores the importance of current guidelines for the early diagnosis and prevention of hypertension and atherosclerosis and their risk factors," Seshadri said.
The National Heart, Lung, and Blood Institute, the National Institute on Aging and the National Institute of Neurological Disorders and Stroke funded the study.
* Source: “Prevalence and Correlates of Silent Cerebral Infarcts in the Framingham Offspring Study,” Stroke, June 26, 2008, by Das RR, Seshadri S, et al.
Note: For more information on stroke and stroke warning signs, visit the American Stroke Association Web site.