5/18/99
MEDIA CONTACT: Ruthann Richter () or M.A. Malone () or call 723-6911
FOR COMMENT: Michael Dake, MD, (650) 725-5202, or Craig Miller, MD, (650) 725-3826
PHOTOGRAPHY: Black and white photos showing an aortic dissection before and after stent-graft treatment are available through Walter Hangad () or call (650) 723-7897
STANFORD - Probably the most devastating condition that can affect the aorta, the main line from the heart, is a problem known as an aortic dissection, a tear in the inner lining of the aorta that unzips the vessel and allows blood to spill down a second channel. Even with current surgical interventions, patients with aortic dissections often die of multiple complications.
But in a new study, Stanford researchers say patients with a type of dissection known as Stanford Type B (in which the tear is located in the descending aorta) can be effectively treated with a device known as a stent-graft. The device, a stainless steel wire mesh tube with a polyester cover, is shuttled to the site of the tear to cover the damaged area from the inside and restore normal blood flow. Sixteen out of 19 patients who were fitted with experimental stent-grafts at Stanford and at Mie University in Japan recovered from the dissection and have returned to their normal daily routines, said Michael Dake, MD, Stanford associate professor of radiology and medicine (pulmonary) and lead author of the report.
"In principle, this is a potential new treatment for patients with acute Type B dissections, especially for patients with complications that involve multiple organ systems," Dake said. "It is a less invasive alternative for patients who have no surgical option."
Doctors have spent nearly four decades looking for an alternative to major surgery in patients with aortic dissections involving the descending thoracic aorta, said Craig Miller, MD, Stanford professor of cardiovascular surgery and a co-author on the report.
"We were able to avoid a major operation in 18 of these 19 people, and the results were quite respectable, considering how sick they were. So it is really a landmark advance," Miller said.
The report on the new treatment is scheduled for publication in the May 20 issue of the New England Journal of Medicine.
As many as 5,000 Americans each year are plagued by aortic dissections, which tend to mimic other ailments and can be very difficult to diagnose, said Dake, who is also chief of cardiovascular and interventional radiology at Stanford.
"Although it's not a common problem, it's a high-profile disease, dramatic and life-threatening," Dake said.
As many as 35 percent of patients with a dissection involving the ascending aorta die in the hospital because the condition has gone unrecognized, he said. Without treatment, between 60 and 70 percent of patients die within a week, according to published figures.
A dissection can occur either in the ascending aorta, which is contiguous to the heart and directs blood supply to the head and arms, or in the descending aorta, which carries blood into the abdomen and pelvis. A tear in the ascending aorta, known as a Type A dissection, is typically treated with a surgical procedure in which a tube of polyester graft material is stitched to the arterial wall to replace the damaged segment. The mortality rate among patients who undergo this surgical repair is about 10 to 15 percent in medical centers with special expertise and extensive experience in thoracic aortic surgery, such as Stanford, Miller said.
Patients who have a rip in the descending aorta, known as a Type B dissection, are most often treated with drugs to keep their blood pressure in check, Dake said. Still, about 20 percent of these patients die as a result of complications, and others subsequently need an operation due to aneurysm development.
In 1996, the Stanford researchers began testing the stent-grafts for aortic dissections where the tear was in the descending aorta as a possible alternative treatment that would be less invasive than traditional open surgery and improve patients' odds of survival. In 1992, Dake and his colleagues began placing similar stent-grafts in patients with thoracic aortic aneurysms, a life-threatening balloon-like enlargement of the vessel, and found the device to be a safe and effective form of therapy for this condition.
The tubular device, which was designed at Stanford, can vary in diameter, length and design, depending on each patient's particular problem, Dake said. During the dissection procedure, the stent-graft is collapsed inside a catheter, which is threaded from the patient's groin to the area of damage in the aorta. Once in place, the stent-graft is released as the catheter is withdrawn. The device then expands to fill the vessel, effectively covering the hole, Dake said. Once this is accomplished, the extra channel disappears and normal blood flow returns. The entire procedure takes just an hour-and-a-half, he said.
Between October 1996 and October 1998, 10 patients with acute aortic dissections were fitted with stent-grafts at Stanford, while another nine patients received the device in Japan under the direction of Noriyuki Kato, MD, and his team at Mie University. Kato had been a research associate in interventional radiology at Stanford and brought the technology back to his home country, Dake said. Four of the patients in the study had a Type A dissection in which the ascending aorta had become secondarily involved, while the remaining 15 had Type B disease involving the descending portion of the vessel. The average age of the patients was 53.
Of the 19 patients in the study, three died within a month of treatment, the researchers reported. Dake said the three patients had extensive multi-organ compromise before the procedure, and stent-graft placement was unable to save them. The other patients have done well and have returned to their jobs and regular routines, he said.
Dake said the stent-grafts not only appear to have an advantage over traditional surgery but in certain situations also could be a promising option for Type B patients without complications who are typically treated with high blood pressure medication alone. In many of these patients, the new channel that forms as a result of the initial tear in the aorta becomes enlarged and prone to rupture over time, he said.
"For patients treated medically, in the long term you may have results with the stent-graft that are superior to pharmacologic therapy," he said.
It will still require five or 10 years of follow-up before doctors will know whether the stent-graft can eliminate the possibility that the vessel will develop an aneurysm that could rupture, Miller noted.
The stent-grafts used in the study are a first generation device, still relatively crude in design, Dake said. But he noted that these initial experiments already have spawned more sophisticated, refined commercial stent-graft devices. Ultimately, this form of treatment could become the standard of care, he said.
"With the ideal stent-graft, we expect this will be a paradigm shift in how we treat acute Type B aortic dissections," Dake said.
In addition to Miller, Dake's Stanford colleagues in the study are R. Scott Mitchell, MD, associate professor of cardiovascular surgery; Charles P. Semba, MD, assistant professor of radiology; and Mahmood K. Razavi, MD, assistant professor of radiology. Kato's colleagues in Japan include Takatsugu Shimono, MD; Tadanori Hirano, MD; Kan Takeda, MD; and Isao Yada, MD.
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