As the only multi-center, prospective, randomized trial comparing endovascular coiling of ruptured brain aneurysms to neurosurgical clipping, ISAT demonstrated that in patients equally suited for either treatment, coiling provides better outcomes in terms of survival free of disability at one year.

When a brain aneurysm ruptures, blood flows into the space surrounding the brain (the subarachnoid space), resulting in a subarachnoid hemorrhage, the deadliest form of stroke. In the United States it is estimated that as many as 18 million people will develop a brain aneurysm during their lifetime. Every year it is estimated that more than 30,000 people suffer from ruptured brain aneurysms. Ten to 15 percent of these patients will die before reaching the hospital. More than 50 percent will die within the first 30 days after rupture. Of those who survive, approximately half suffer some permanent neurological deficit.1

Health care analysts suggest that as many as 75 percent of patients with brain aneurysms in the United States are currently treated by neurosurgical clipping, which involves performing a craniotomy (removing a section of the skull) and placing a surgical clip at the neck of the aneurysm. Endovascular treatment, which was introduced in the early 1990s, involves insertion of a catheter into the femoral artery in the patient's leg and navigating it through the vascular system under X-ray guidance, into the head and into the aneurysm. Tiny platinum coils are then threaded through the catheter and deployed into the aneurysm, obstructing blood flow into the aneurysm and preventing further damage.

"This study was designed to provide results that will help guide physician practice," said Richard Kerr, M.D., Neurosurgical Principal Investigator of ISAT and a consultant neurosurgeon with the Department of Neurosurgery at the Radcliffe Infirmary in Oxford, England. "Patients had to be suitable for both treatments to be included in the trial and once in the trial, patients were systematically randomized so that the two treatment arms were comparable in terms of age, gender, patient condition and aneurysm location. For patients with ruptured brain aneurysms suitable for both treatments, endovascular coiling is significantly more likely to leave patients alive and free of disability. However, as in any study, long-term follow-up will be essential to evaluate the substantial early advantage of endovascular coil treatment."

"There has been a critical need for high-quality evidence comparing surgical and endovascular treatment of ruptured brain aneurysms," said Andrew Molyneux, M.D., Neurointerventional Principal Investigator of ISAT and a consultant neuroradiologist with the Department of Neuroradiology at the Radcliffe Infirmary. "The ISAT addressed this need, and the results suggest that patients should be informed of the option and evaluated for endovascular treatment first, and if that approach is not appropriate, then surgery should be considered."

Funded by the Medical Research Council of Great Britain in 1997, ISAT systematically compared endovascular coiling to neurosurgical clipping. Forty-three neurosurgical centers in Europe, North America and Australia participated, enrolling patients who were deemed suitable for either treatment.

The study's primary objective was to determine whether endovascular coiling reduces the number of patients with poor outcomes compared to neurosurgical clipping. Following a planned interim review by the Data Monitoring Committee, the Trial Steering Committee halted the trial on May 2 because the difference in outcomes between the two procedures was so great that it was no longer deemed ethical to randomize patients to neurosurgical clipping.

"This landmark trial clearly demonstrates that all patients with ruptured brain aneurysms should be thoroughly evaluated for endovascular coiling," said Jim Feenstra, President of Boston Scientific's Target division. "Although Boston Scientific has helped to introduce endovascular coiling to more than 300 major medical centers in the United States, less than 25 percent of ruptured brain aneurysm patients are admitted to hospitals where endovascular coiling is available. The ISAT findings suggest that when medically possible, all ruptured brain aneurysm patients should be transferred to -- and treated primarily at -- hospitals that provide both therapeutic options."

Target is a leading developer of less-invasive medical technologies for endovascular neurosurgery and interventional neuroradiology. It manufactures coils, guidewires and catheters used to treat brain aneurysms. All of the endovascular patients in the study with one-year follow-up were treated using Target's GDC™ coil.

"This study provides compelling evidence that patients with ruptured brain aneurysms should be considered for treatment at hospitals that have an endovascular capability and also should receive an initial consultation by an endovascular physician," said Randall Higashida, M.D., President of the American Society of Interventional and Therapeutic Neuroradiology.

"The ISAT results come at a time when less-invasive technology has improved significantly," added Charles Strother, M.D., Vice President and President-elect of the American Society for Neuroradiology. "Physicians can now identify brain aneurysms using completely non-invasive diagnostic imaging technologies and provide treatment in the form of less-invasive coiling. The combined benefits to patients and the healthcare system are tremendous."

While today's Lancet article on ISAT reflects survival and disability data, additional data on cost effectiveness, quality of life, angiographic findings and rebleed rates are still being collected and analyzed for release in 2003. In order to continue evaluating the long-term follow-up data, the Medical Research Council of Great Britain has granted funding for ISAT through 2007.

(1) Malisch and Duckwiler, "What you should know about aneurysms: A patient's guide to endovascular therapy." July 1998

Boston Scientific (NYSE: BSX) is a worldwide developer, manufacturer and marketer of medical devices whose products are used in a broad range of interventional medical specialties.

This press release contains forward-looking statements. The Company wishes to caution the reader of this press release that actual results may differ from those discussed in the forward-looking statements and may be adversely affected by, among other things, risks associated with clinical trials, the regulatory approval process, reimbursement policies, competitive offerings, physician preference, intellectual property, commercialization of new technologies and other factors described in the Company's filings with the Securities and Exchange Commission.