Cynthia Leibson and her colleagues at the Mayo Clinic in Rochester, Minn., and the University of British Columbia in Vancouver used data from death certificates and pathology reports to assess trends in coronary artery disease among residents of Minnesota's Olmsted County, age 16 through 64, who died of unnatural causes from 1981 to 2004.

Of the 3,237 Olmsted County residents who died, 515 died of unnatural causes. Among those 515, 96 percent were autopsied and 82 percent had grades assigned based on the amount of blockage in several coronary arteries. Grades ranged from zero for no blockage to five for 100 percent blocked.

"Over the full (study) period, 8.2 percent of the 425 individuals had high-grade disease, and 83 percent had evidence of any disease," the authors said in a statement. "High-grade disease was defined as a grade of three or higher in the left main artery or a grade four or higher in any other single artery -- declines in the grade of coronary disease ended after 1995 and possibly reversed after 2000."

The findings are published in the Archives of Internal Medicine.