Interventional radiology researchers in the U.S. and Germany are building the case for stenting to treat renal artery stenosis, using five years' worth of data that point to high survival rates and improved clinical risk factors. The latest round of studies presented at the Society of Interventional Radiology meeting in Salt Lake City, Utah, showed improved restenosis rates as well.

ASPIRE 2, a multicenter prospective nonrandomized trial, followed 208 patients who were stented between December 1997 and May 1999 after failing percutaneous transluminal renal angioplasty (PTRA). Investigators found that stents improved patients' vascular outcomes over the previous standard, a 40% nine-month restenosis rate. Outcomes remained above that rate for up to two years after stenting.

Stent placement was successful in 99.6% of patients, with a restenosis rate of 17.4% at nine-month follow-up with duplex ultrasound. An acute procedure success-stenosis of less than 30% and a systolic blood pressure gradient of less than 5 mm Hg-was reported in 80.2% of patients. A controlled degree of stenosis (less than 50%) and stable renal vascularization was achieved in 87.7% of patients at two-year follow-up. Adverse cardiac events, the major complication reported, affected 19.7% of patients during the same period.

Results and technical success rates, indicating the stent could be delivered where it was intended, suggest that stenting should be the top invasive approach to renal artery stenosis, said Dr. Rodney D. Raabe, principal investigator for ASPIRE 2 at Sacred Heart Medical Center in Spokane, Washington.

Only 2% of all patients in the study achieved normal blood pressure after stent placement. But 45% kept their blood pressure stable two years after the procedure, a statistically significant finding, according to Raabe.

The ASPIRE 2 trial validated a number of smaller single-institution studies. Preliminary results led the U.S. FDA to approve Palmaz in 2002 as the first stent specifically indicated for renal artery stenosis.

In another study, Dartmouth Medical School investigators retrospectively reviewed 131 patients who had PTRA and stenting between 1992 and 1999. They also found stabilized hypertension and renal function control after the procedure. Patients undergoing PTRA and stenting seemed to carry lower cardiovascular morbidity and mortality risks than patients with similar demographic profiles not undergoing these procedures.

"Our data suggest an improvement in patients' systolic blood pressure over time," said lead author Dr. Robert K. Myers, an interventionalist from Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire. "Fifty-eight percent of the patients in the study had a previous history of cardiovascular disease. We had an 87% survival rate at two years."

The procedure's benefits do have limits. The Dartmouth study found that patients with creatinine levels lower than 3 mg/dL are most likely to have a successful renal function salvage. Hypertensive patients, in contrast, showed varying degrees of improvement. And while some physicians believe a link between intervention and a lower risk of cardiovascular events is possible, this should be validated by case-controlled or prospective randomized studies, Myers said.

Finally, German researchers studied a novel, less invasive technique for stent placement. Investigators assessed 47 patients treated for either severe hypertension or renal insufficiency using a monorail-balloon-stent device. They were able to deploy stents safely using a 5-French guiding sheath with a 100% technical success rate.

These studies help establish the durability of renal artery stenting, said Dr. Timothy W.I. Clark, an assistant professor at the University of Pennsylvania Hospital's vascular and interventional radiology section.

"This is a technical innovation. The device can be threaded through a smaller sheath," he said.