A recently published study purports to show that the incidence of acute myocardial infarction (AMI) in the US has decreased over the nine-year period between 1999 and 2008. As reported in the June 10, 2010 issue of the New England Journal of Medicine, Dr. Robert Yeh of Mass. General Hospital and Harvard and colleagues from Kaiser Permanente and the University of California, San Francisco analyzed data from the Kaiser Permanente Northern California integrated healthcare delivery system, which cares for more than three million people and is believed to be broadly representative of local and statewide populations. The Permanente Medical Group is the largest medical group in the country.
If, as the authors believe, this trend is applicable to the general, non-California US population, it is good news and continues the overall favorable trend in heart-disease-related deaths. However, the increasing rates of obesity and diabetes remain worrisome, leading to a general concern by researchers that heart-disease-related deaths may level off or possibly increase over the near term future.
The researchers identified 46,086 hospitalizations for MI during 18,691,131 person-years of follow-up from 1999 to 2008. The age- and sex-adjusted incidence of MI increased from 274 cases per 100,000 person-years in 1999 to 287 cases per 100,000 person years in 2000, but then it decreased each year thereafter, to 208 cases per 100,000 person-years in 2008, representing a 24% relative decrease over the whole study period.
The age- and sex-adjusted incidence of STEMI decreased by 62% throughout the study period (from 133 cases per 100,000 person-years in 1999 to 50 cases per 100,000 person-years in 2008) , whereas the incidence of non-STEMI increased from 155 cases per 100,000 persons in 1999 to 202 cases per 100,000 persons in 2004, before decreasing thereafter.
The rate of 30-day mortality after MI decreased from 10.0% in 1999 to 7.8% in 2008. This was driven by significantly lower death rate among patients with non-STEMI, whereas mortality did not change significantly among patients with STEMI. Asked why there appeared to be a much larger decrease in STEMI than in non-STEMI over the nine-year period, senior author Dr. Alan Go remarked that this may be due to increased sensitivity for diagnosing non-STEMI with the introduction of troponin tests.
The decrease in the overall cardiovascular death rate is generally attributed to decreases in smoking rates, decreasing levels of both cholesterol and hypertension through aggressive pharmacologic intervention. Other researchers have pointed out that mortality rates in lower socioeconomic areas have not decreased at the same rate, and increasing levels of diabetes and obesity among this population is a real issue. Identification and treatment of heart disease continues to improve. It appears that the public health elements of heart disease focused on education, prevention, screening and early detection, need to catch up.
As always, CFA invites your comments. For further information, refer to: Yeh FW, Sidney S, Chandra M, et al. Population Trends in the Incidence and Outcomes of Acute Myocardial Infarction, New England Journal of Medicine 2010; 362: 2155-65.