MI mortality rates drop, but non-STEMI incidence increases

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While long-term mortality rates have dropped for both STEMI and non-STEMI patients, only the incidence rate of STEMI has decreased compared with non-STEMI, calling into question preventive measures aimed at non-acute cases, according to a five-year analysis of acute MI trends published in the January issue of the American Journal of Medicine.

“The acute coronary syndrome model espoused by the American College of Cardiology places unstable angina, non-ST-segment elevation MI (NSTEMI) and ST-segment elevation MI (STEMI) at increasingly severe points along a disease continuum,” the authors wrote.

Because few trials or communities have assessed the trends of incidence rates, treatments and prognosis of STEMI or non-STEMI patients, David D. McManus, MD, of the University of Massachusetts Medical School in Worcester, Mass., and colleagues reviewed the medical records of 5,383 patients in Worcester, Mass., who were hospitalized for either STEMI or NSTEMI between 1997 and 2005 to examine the recent trends and death rates of acute MI in Massachusetts.

Patients with STEMI were more likely to be male, younger and less likely to have a history of comorbidities when compared with patients with NSTEMI.

McManus and colleagues found that the incidence rates of STEMI decreased from 121 per 100,000 to 77 per 100,000, while the incidence rates of NSTEMI increased from 126 per 100,000 to 132 per 100,000.  And while the rates of in-hospital and 30-day case-fatality remained stable for both groups of patients, the rates of one-year post discharge death decreased within the five-year study period.

The number of STEMI and NSTEMI patients receiving ACE inhibitors/ARBs, aspirin and beta-blockers differed during the study. Those rates were 62 percent versus 56 percent, 94 percent versus 90 percent and 90 percent versus 84 percent, respectively.

In addition, the rates of patients undergoing cardiac catheterization, PCI and thrombolytic therapy differed between STEMI and NSTEMI patients. These rates were 65 percent versus 43 percent (cardiac cath), 46 percent versus 23 percent (PCI) and 26 percent versus 1 percent (thrombolytic therapy), respectively.

“Improved coronary risk factor awareness and treatment practices may have contributed to the decreases in the incidence of STEMI observed in the present study,” the researchers wrote. “That a similar decrease was not observed in the incidence of NSTEMI may reflect a greater benefit of primary prevention measures for those at risk for STEMI.”

In addition, the researchers said that the increase in diabetes and obesity may have played a part in the development of NSTEMI. The authors said that the decrease in patients’ hospitalizations for STEMI may be due to the fact that fewer patients are being electrocardiographically diagnosed with acute MI. In fact, Framingham investigators reported a 50 percent decrease in these diagnosed cases over a 40-year period.

“Incidence rates of NSTEMI increased slightly during this period, likely as a result of high-sensitivity biomarker introduction,” the authors noted. “Encouraging trends were noted in the post-discharge death rates for both STEMI and NSTEMI at one year, suggesting that acute myocardial infarction treatment practices have likely improved the long-term outlook for all patients hospitalized with acute myocardial infarction.

“Increased attention needs to be directed to secondary prevention practices in the hospital and post-discharge management of patients hospitalized with NSTEMI because the proportion of NSTEMI patients receiving effective cardiac therapies lags behind those with STEMI,” the authors concluded.