The second study, known as CLOSE and led by Dr. Jean-Louis Mas, a professor of neurology at Paris Descartes University, compared closure to aspirin therapy. No strokes occurred among the 238 patients in the closure group, but 14 of the 235 controls had a stroke (P<0.001). Dr. Mas said in an email that the data "confirm the direct responsibility of the patent foramen ovale in the occurrence of cerebral infarction in patients with no other identifiable cause—and provides a clear therapeutic response to a frequent and serious medical problem." In about 30 percent to 40 percent of ischemic strokes, the cause is not known and is classified as “cryptogenic stroke.” "In previous studies, the definition of cryptogenic stroke was less stringent," Dr. Mas said. He stressed that a comprehensive workup is needed "to rule out other potential causes of stroke." Regarding the Gore REDUCE study, coauthor Dr. Scott Kasner of the University of Pennsylvania told Reuters Health by email that his group saw a 49 percent reduction in new brain infarctions. "We believe we were able to enroll patients whose stroke was most likely due to the PFO, and therefore closure of the PFO would most likely be beneficial," he said. "The PFO is most likely the cause of the stroke in patients who are younger and have few traditional risk factors for stroke, such as hypertension, diabetes, and smoking," he said. "This is critical, since PFO is a relatively common finding (25 percent of the population), and it is only worth closing if it was the probable cause of the stroke. We also used the Gore devices that have a favorable safety profile and a low risk of erosions." Dr. Saver said, "All of the five trials actually provide consistent findings. All showed fewer strokes numerically in the device group than the treatment group. The statistical strength of the findings is greater in the current three trials for several reasons, including larger study sizes; use of better devices than in the first trial; more-stringent selection of patients with definite strokes and no other source found; and different rates of use of antiplatelet agents versus anticoagulant agents in the medical, non-device arms (anticoagulants appear likely better than antiplatelet agents)." "Both of the treatment options to prevent recurrent stroke, placement of a closure device or use of medication alone, work pretty well; but for patients matching the trial populations, treatment with a closure device works a bit better and will often be a preferred strategy," Dr. Saver said.