Outpatient visits for angina have decreased considerably since the mid-1990s, according to a study published online Jan. 14 in Circulation: Cardiovascular Quality and Outcomes, but it is not yet clear what specific factors played a role in this trend.

Investigators from the Centers for Disease Control and Prevention’s Division for Heart Disease and Stroke Prevention in Atlanta analyzed data from visits to physician offices and outpatient departments across the U.S. between 1995 and 2010. They used data from the National Ambulatory Medical Care Survey and the National Hospital Ambulatory Medical Care Survey.

Between 1995 and 1998, there were an average of 3.6 million outpatient visits every year for angina among adults. Between 2007 and 2010, the number decreased to an average of 2.3 million visits each year. Visit rates per 100,000 declined 1,856 between 1995 and 1998 to 902.3 between 2003 and 2006. The rate slightly increased to 982.8 per 100,000 between 2007 and 2010.

While the number of echocardiograms during angina visits remained relatively stable over time (ranging from 25 percent to 33 percent), stress testing nearly doubled from 7 percent to 13 percent. Referrals to another clinician, a hospital or an emergency room ranged from 8 percent to 15 percent.

“Possible explanations for this decline include a true declining prevalence of angina, based on improvements in heart disease risk factors over time; and a move to better understand the causes of angina, a better ability to do so, and ICD-9-CM coding guidelines designed to better reflect these changing physician practices,” wrote the authors, led by Julie C. Will, PhD, MPH.