Eyeing heart a new way offers hope to stroke victims
By Paul Mayne
March 13, 2014
An inexpensive tool for assessing arteries inside the head may detect a potentially dangerous hole within the heart of some patients with an unexplained stroke, according to a Western researcher.
And those findings may offer new life to thousands worldwide.
Beyond its traditional use exploring the brain, transcranial Doppler equipment can also differentiate the risk of future stroke, related to the severity of the heart defect, according to Dr. David Spence, director of the Stroke Prevention & Atherosclerosis Research Centre at the Robarts Research Institute. (As a bonus, the Doppler costs about one-fifth that of a echocardiogram machine, currently used to explored the heart.)
“It hasn’t been used that widely; I don’t know why. More stroke centres should be doing transcranial Doppler,” said Spence, a Neurology and Clinical Pharmacology professor at the Schulich School of Medicine & Dentistry. “It may be largely that the test that is usually used, involving an ultrasound machine looking at the heart, is done by cardiologists, whereas Dopplers are more of a neurology thing.
“I think it should change because what we’ve shown is the transcranial Doppler is significantly better, both in diagnosing and in predicting which patients are at high risk.”
He presented his research at the 2014 American Stroke Association’s International Stroke Conference this past month in San Diego.
Previous research showed 25 per cent of the population, and a higher percentage of patients who have had unexplained strokes, have what is called a patent foramen ovale (PFO), which occurs when an opening between two heart chambers fails to close at birth.
Many people never have symptoms, Spence said. However, such a hole (or shunt) can allow blood clots that form in a vein to escape from the right side to the left side of the heart. From there, the clot enters the arteries to the brain and causes a stroke – or what is called a paradoxical embolism.
Echocardiography failed to find the PFO in more than 15 per cent of the 340 patients in the study with the defect.
“Surprisingly, some of those shunts were quite large,” said Spence, with about one-quarter of the missed defects being in the three highest grades of severity, according to a five-grade measure.
Accurately detecting PFOs, and knowing its grade, helps doctors decide whether a stroke was due to a paradoxical embolism. Other clues related to the patient’s stroke are also helpful, including shortness of breath at stroke onset; sitting for a long time, such as on an airplane; waking up with a stroke; and having a history of migraine, sleep apnea or varicose veins.
“For people who have had a recent small stroke, their risk is highest soon after the event,” Spence said. “In order to do the best job we can trying to prevent a recurring stroke, we need to find out what was the cause of the initial stroke.”
Diagnosing the underlying cause is essential to choosing the right medicine to help prevent future strokes. Spence added anticoagulant drugs are three times more effective than another commonly used class of drugs in preventing the type of stroke that can be caused by a clot passing through a PFO.
The study’s findings may also be important in understanding which patients with PFO might benefit from closing the hole surgically or with a catheter-deployed device.
“Patching the hole sounds like a good idea, but there could be complications. Research studies, so far, haven’t really shown it makes a significant difference,” Spence said.
PFO is present in about one-quarter of the population but accounts for only about 5.5 per cent of strokes caused by paradoxical embolism. This suggests the defect isn’t a problem in about 80 per cent of patients with it.
“That’s why these clinical clues are so important,” he said.
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