While coronary stents have proved effective in restoring blood flow in heart-attack patients, research shows they are no better than medicine, exercise and dietary restrictions in preventing heart attacks in elective patients whose heart disease is deemed stable. When doctors opt for stents, they prop open coronary arteries in a procedure called Percutaneous Coronary Intervention, or PCI. More than 90 percent of PCIs include stenting. To show where the use of stents is high, Bloomberg News ranked regional health-care markets by three measures: the number of PCI procedures for every 1,000 Medicare enrollees; how often they are performed for every 1,000 angiography scans of coronary arteries; and the number per 1,000 cases of diagnosed ischemia — or reduced cardiac blood flow. More procedures in each case may indicate locales where doctors are more inclined to use stents.