While it is said that a stroke patient should be administered treatment within three hours of the onset of symptoms, an American study suggests that a clot-busting drug may extend this time period up to nine or more hours.
Published in the online edition of Radiology, the study report says that the drug may be beneficial for some patients who suffer a stroke as a result of a blockage in an artery in the brain.
"Stroke is the third leading cause of death in the US. Every hour that we can add to the treatment window would allow vastly more stroke patients to be treated with potentially life-saving therapy," said the study's lead author, Dr. William A. Copen, Director of Advanced Magnetic Resonance Neuroimaging at Massachusetts General Hospital (MGH) in Boston.
The most common type of stroke is called ischemic stroke, which occurs when a blood clot blocks a blood vessel supplying blood to the brain.
Some ischemic strokes can be treated with clot-busting therapy using tissue plasminogen activator (t-PA), which helps dissolve the blockage. However, the window of opportunity to safely administer the medication is generally considered to be just three hours.
Fewer than seven percent of patients receive the drug because most of the patients fail to get to the hospital to be diagnosed and treated within that time frame.
During the current study, the research group analysed the test results of 109 ischemic stroke patients at MGH.
They have revealed that the testing methods included two different MRI scanning techniques: perfusion MRI, which measures blood flow in the brain and diffusion MRI, which measures the movement of water molecules in tissue.
"Comparing the lesions that we see in these two MR images reveals which areas of the brain are threatened by a lack of blood flow, but could still be salvageable. A mismatch between the lesions suggests that a patient might still benefit from thrombolytic therapy," Dr. Copen said.
The researchers observed that most patients with blockage in a proximal artery, close to the base of the brain, continued to demonstrate a diffusion-perfusion mismatch between nine and 24 hours after the onset of their strokes.
"Patients who have a mismatch have been successfully treated up to nine hours after stroke onset, which is already much longer than the guidelines allow. Our findings suggest a need for a clinical trial to measure the effectiveness of thrombolytic therapy more than nine hours after the onset of an ischemic stroke, Dr. Copen said.