Three hospitals have consistently outpaced all others in Maryland in the use of stents to treat heart patients, according to data obtained by The Baltimore Sun, raising questions as state regulators examine whether the expensive procedure is performed unnecessarily by some doctors.

St. Joseph Medical Center in Towson became the subject of a state investigation earlier this year after it notified 585 patients that they might have received unneeded stents to prop open their arteries. The new data, from the Health Services Cost Review Commission, shows that Union Memorial Hospital in Baltimore and Washington Adventist Hospital in Takoma Park are also likely to be subject to review.

Each of the three hospitals exceeded the state's average rate of placing a stent after diagnosis by 20 percent to 30 percent over the past five years. Combined, they placed more than half the stents given to all patients in Maryland.

St. Joseph led Maryland hospitals in both the number of stents placed and the percentage of patients treated with stents after being diagnosed, the data indicates. Stents and related heart procedures generated an average of $81 million in annual charges for St. Joseph over that five-year period. Dr. Mark Midei, who ran the cardiac catheterization lab at St. Joseph until last year, lost his privileges to practice medicine there amid accusations that he had implanted unneeded stents. Since then, St. Joseph is on track to post roughly $55 million in stent-related charges.

The Sun obtained the data through a request under Maryland's public information law. State health officials are using the same information to direct a multi-agency investigation into potentially uncalled-for medical procedures, and have said they are focusing on doctors and facilities with the highest performance rates. State officials plan to complete their review by the fall.

Regulators and area cardiologists caution that high rates of stent placement are not necessarily indicative of overuse, because all three of the top hospitals have cardiac centers that see many of the state's toughest cases and get referrals from other hospitals.

"Based on a cursory review of the data, some may conclude that higher ratios of stents to [diagnostic procedures] may be indicative of unnecessary utilization," Robert Murray, executive director of the commission, wrote in a letter to The Sun. "However, this may well not be the case."

Officials at the three hospitals replied in a similar vein.

"High intervention ratios may need to be evaluated, but no conclusions should be drawn without patient-specific data," St. Joseph said in a statement.

"Cardiologists from around the region refer their most difficult patient cases to our experts," Union Memorial spokeswoman Debra Schindler said in a statement. "This means that our institution regularly treats patients above the average both in terms of volume and severity of their condition."

St. Joseph officials noted a "definable decrease" in the hospital's rate of stent placements since Midei stopped practicing there in May 2009. Union Memorial has also seen a decrease over the past year, bringing stent-placement rates at the competing Baltimore-area hospitals much closer to the state average.

Cardiac catheterization, in which a device is threaded into a patient's arteries to explore blockage, is a $500 million annual business for Maryland hospitals. They performed an average of more than 38,000 procedures in each of the past five years. Stents, mesh tubes that are placed in arteries to treat blockages found during catheterization, were used an average of 13,400 times a year, the state data shows.

At its peak in 2006, St. Joseph placed 3,690 stents, billing an average of more than $14,000 per procedure, records show. Stent use has declined nationwide since about 2007, when results of a large clinical trial showed that treatment with medicine is less dangerous and equally effective for many patients.

Unwarranted treatments are a growing concern throughout the U.S. health care industry, and the federal government estimates that as much as 30 percent of Medicare's $500 billion budget is wasted on them.

President Barack Obama recently called for increased "scrutiny of physicians in high-risk areas or those that order a high volume of high-risk services," according to a White House fact sheet. And several federal investigations are focusing specifically on stent placement, including in Maryland and the District of Columbia.

The state's investigation was spurred by allegations against Midei, who ran the cardiac catheterization program at St. Joseph until the hospital, acting on a patient complaint, reviewed two years' worth of his records and determined that he had placed stents that might not have been necessary in 585 patients. The Maryland Board of Physicians conducted a review and has filed administrative charges to strip the Towson cardiologist of his medical license.

Midei has denied the allegations, and supporters suggest that he is being framed by a vengeful colleague.

When St. Joseph hired Midei in early 2008, the move scuttled a $25 million deal that his former employer, MidAtlantic Cardiovascular Associates, had struck to merge with MedStar Health, the parent company of Union Memorial. At the time, MidAtlantic's CEO told Midei that he would "destroy him personally and professionally," according to court records.

As cardiology business at St. Joseph declined since 2006, it picked up at Union Memorial. Between them, the two hospitals have accounted for more than $760 million in billings for cardiac catheterization and stent procedures since 2005.