Combined MRI and echocardiography improves stroke diagnosis
14 March 2007
Using both MRI and echocardiography to image the heart greatly improves
the ability of physicians to identify the cause of stroke, especially
cardioembolic strokes, the worst type. These strokes have a worse prognosis,
producing larger, more disabling strokes that are more likely to recur
compared to other types. The technique could revolutionise patient care.
MRI of he heart. Credit: Society of
Based on a new study, researchers urge more comprehensive imaging for
patients presenting to hospitals with stroke symptoms. Using both MRI and
echocardiography to image the heart greatly enhances the detection of the
cause and selection of the best treatment of cardioembolic strokes, the
“meanest” type of stroke.
A cardioembolic stroke occurs when a thrombus (clot) dislodges from the
heart, travels through the cardiovascular system and lodges in the brain,
first cutting off the blood supply and then often causing a hemorrhagic
bleed — a double whammy of both types of stroke, ischemic first and then
The study found that MRI detected nearly twice as many sources of stroke
in the heart than echocardiogram alone. It also showed the ability of MRI to
reveal more heart disease conditions that contribute to clot formation in
the first place. Echocardiography, however, was strong in the detection of
heart valve lesions.
Combined, these imaging systems can more clearly identify underlying
causes of future stroke, helping doctors decide the best initial therapy and
the best treatment to prevent a secondary stroke. The research was presented
today at the Society of Interventional Radiology’s 32nd Annual Scientific
"This can revolutionize patient care because we can detect the underlying
cause of the stroke and prevent it from occurring again,” says lead author
John Sheehan, M.D., an interventional radiologist at Northwestern University
and Northwestern Memorial Hospital. “A potential cardiac source should be
considered in all patients presenting with ischemic strokes. All stroke
patients should routinely have an MRI and ultrasound of their heart, in
addition to having their brain and carotids imaged with CT and MRI. It’s
nice to be on the front end of a stroke – able to stop it, than on the back
end, figuring out how to deal with its damage.”
Stroke teams generally consist of emergency room physicians,
neurologists, and interventional radiologists. Interventional radiologists
are a critical part of the stroke team because they can diagnose and treat
ischemic stroke with clot-busting drugs, or open a blocked carotid artery
nonsurgically. They are also actively involved in creating more stroke teams
across the country.
Cardioembolic strokes, which account for 20 percent of embolic strokes,
have a worse prognosis, producing larger, more disabling strokes that are
more likely to recur compared to other types of stroke. Blood clots can be
treated with drugs before they can leave the heart, in conjunction with
treating identified heart conditions, to prevent another life-threatening
stroke. In the United States stroke is the leading cause of adult disability
and the third leading cause of death; only heart disease and cancer cause
more deaths annually.
In the study, of the 93 patients who had an MRI and echocardiogram of
their heart after a stroke, MRI detected nearly twice as many potential
causes of stroke originating from the heart compared to echocardiography.
MRI also detected significant heart conditions that predispose a patient to
stroke in 30 percent of patients compared to echocardiography. These
additional findings included acute myocardial infarction, myocardial
scarring, and left ventricular aneurysms. Echocardiography was, however,
more sensitive to detecting potential embolic lesions on prosthetic cardiac
valves and strokes related to a hole in the heart. (Abstract 132 can be
found at http://www.SIRmeeting.org)
“By using cardiac MRI and echocardiography to assess stroke patients, we
have two sets of eyes: two ways to see what is causing the stroke to provide
the best immediate care, and two ways to see what problems lie ahead for
this patient that we could prevent with better long-term care,” Sheehan
added. “The earlier we can detect underlying cardiac problems, the more
quickly we can intervene to prevent future strokes. One stroke is more than
enough. The chances of experiencing another stroke can be dramatically
reduced by taking appropriate actions.”
Definition of “stroke” and “cardioembolic stroke”
A stroke occurs when the blood supply to a part of the brain is
interrupted or severely reduced, depriving brain tissue of oxygen and
nutrients. Within a few minutes, brain cells begin to die; as a result,
abilities controlled by that area of the brain are lost. These abilities can
include speech, movement, vision and memory.
There are two basic types of stroke: ischemic (blockage of an artery) or
hemorrhagic (rupture of an artery). About 80 percent of strokes are ischemic
strokes. They occur when blood clots, plaque or vegetation block arteries to
the brain and result in damage. Ischemic strokes are either embolic or
Typically in an embolic stroke, a blood clot forms somewhere in the body,
usually the heart, and travels through the blood stream to the brain. Once
in the brain, the clot will continue traveling until it lodges in a small
blood vessel blocking blood flow beyond that point, resulting in a stroke.
This type of blood clot is called an embolus.
A cardioembolic stroke occurs when the embolus has traveled from the
heart. About 1 in 4 ischemic strokes are cardioembolic. The annual incidence
of cardioembolic strokes in the U.S. is estimated at approximately 125,000
cases. These strokes can not be considered a single disease process as there
are many different types of cardiac disorders that lead to cardioembolic
stroke, each with unique clinical features, risks of initial and recurrent
stroke, and optimal therapy.
Causes of cardioembolic stroke
A variety of heart diseases can predispose patients to the formation of
clots within the heart, including atrial fibrillation, a recent heart
attack, dilated cardiomyopathy (stretching and poor pumping action of the
heart chambers), and diseases of the heart valves. These abnormalities can
cause blood flow to slow down in parts of the heart; whenever blood slows,
it tends to clot. In order to prevent these clots from forming, doctors put
patients on medications that help reduce their occurrence. Specific cardiac
risk factors include atrial fibrillation, acute myocardial infarction, left
ventricular aneurysms, prosthetic heart valves and rheumatic heart disease.
Atrial fibrillation (AF) is the most common heart condition that causes
stroke. AF is caused when the two upper chambers of the heart (atria) beat
rapidly and unpredictably. This causes the atrial walls to wriggle without
contracting. Blood flow tends to slow down in this non-beating chamber,
allowing clots to form. AF increases stroke risk up to six times. About 15
percent of all people who have a stroke have AF.
Diagnosis of cardioembolic stroke
Traditionally, an echocardiogram is used to evaluate the heart in stroke
victims. Echocardiograms use ultrasound to look inside the heart for clots
and other potential causes of cardioembolic stroke.
Recently, magnetic resonance imaging (MRI) has emerged as a noninvasive
imaging technique that can provide additional and complementary information
to that obtained by echocardiography. MRI uses harmless magnetic fields that
are used to take detailed pictures of the heart. It generates
three-dimensional views of the heart, as well as surrounding organs, to
create a larger diagnostic window into the patient’s health.
The combination of MRI and echocardiography of the heart provides the
optimal imaging assessment of stroke patients, leading to improved detection
of not only the potential source of the stroke, but the underlying cause.