Data Shed Light on Acute MI Mortality Trends Over Time

October 2009

Improved Prognosis Associated With Acute Mi Likely Reflects Advances In Medical Care And Greater Use Of Evidence-Based Cardiac Therapies.



By Elizabeth Mechcatie
Elsevier Global Medical News


Two retrospective studies reveal trends in acute myocardial infarction and mortality associated with cardiogenic shock in hospitalized patients.


One study compared incidence and survival rates of initial acute myocardial infarction (AMI) diagnosed either by ECG or by serum biomarkers, in 9,824 men and women aged 40-89 years, in the Framingham Heart Study between 1960 and 1999. Of the 941 first AMIs documented during this time, 639 (68%) were diagnosed with an ECG and 302 (32%) were diagnosed with a biomarker.


During this time, there was a 50% drop in the rates of AMI diagnosed with ECGs. But the rates of AMI diagnosed with biomarker measurements increased by about twofold, "offering a possible explanation for apparently steady national rates of overall AMI in the face of improvements in primary prevention," the authors concluded (Circulation 2009;119:1203-10).


Significant reductions in AMIs diagnosed by ECGs were noted among men aged 50-59 years, men aged 70-79 years, and women aged 70-79 years. Statistically significant increases in AMIs diagnosed with biomarkers were seen among men aged 50-59 and 70-79, and among women aged 70-79. Changes among AMIs in both categories were "largely flat" for those aged 60-69, they said.


"The advent of increasingly sensitive biomarkers for AMI has substantially influenced AMI detection rates in the United States over the past several decades," concluded the authors, led by Dr. Nisha I. Parikh of the National Heart, Lung, and Blood Institute's Framingham (Mass.) Heart Study, and Beth Israel Deaconess Medical Center, Boston. "National MI trend data may be biased by a diagnostic drift resulting from the advent of diagnostic biomarker tests for AMI," they said, adding that this "may explain the paradoxical stability of AMI rates in the United States despite concomitant improvements in CHD risk factors."


In addition, 30-day, 1-year, and 5- year AMI case fatality rates dropped by 60% between 1960 and 1990, a highly statistically significant effect, with parallel declines observed for both AMIs diagnosed with ECG and those diagnosed with biomarkers.


"The marked improvements in the short- and long-term prognosis associated with AMI likely reflect advances in medical care and greater use of evidence-based cardiac therapies," Robert J. Goldberg, Ph.D., professor of medicine and epidemiology at the University of Massachusetts, Worcester, wrote in an editorial (Circulation 2009;119:1189-91).


Dr. Goldberg was the lead author of the second study, which analyzed trends in hospital mortality from cardiogenic shock complicating AMI--the most common cause of death in hospitals associated with AMI--among patients enrolled in the Worcester (Mass.) Heart Attack study.


Of the more than 13,000 people hospitalized with an AMI in the Worcester metropolitan area during 15 annual periods between 1975 and 2005, 6.6% developed cardiogenic shock. The incidence of cardiogenic shock associated with AMI was relatively stable between 1975 and the late 1980s, at an average 7.5%. Subsequently, the incidence was inconsistent until 1990, when the rate dropped to 4.8%, and reached a low of 4.1% in 2003.


This lower incidence of cardiogenic shock is "all the more impressive" considering that the patient population has gotten much older and diabetes, heart failure, and other serious comorbidities have become more common, noted Dr. Goldberg and his associates (Circulation 2009;119:1211-9).


About 65% of those who developed cardiogenic shock died in the hospital, compared with 11% of those who did not develop cardiogenic shock, a significant increased risk of death during hospitalization. Over the 30-year period, the risk of dying in the hospital was nearly 18 times as great among those who developed cardiogenic shock than among those who did not. In patients hospitalized during 2003 and 2005, the mortality risk among those with cardiogenic shock remained high, although the absolute risk was lower: 12.5 times as great as those who did not develop cardiogenic shock.


Short-term death rates dropped significantly during the period studied: In 1975 and 1978, 76% of patients who developed cardiogenic shock and 16.5% of those who did not died in the hospital. But in 2003 and 2005, 45% of those who developed cardiogenic shock died while in the hospital, compared with 7% of those who did not. In 2003 and 2005, hospital mortality associated with cardiogenic shock increased with older age, from nearly 36% in patients aged 65-74 years, to 57% in those aged 75-84 years, and almost 65% in those aged 85 years and older.


At baseline, those who developed cardiogenic shock were more likely to have certain demographic and clinical characteristics, including having a do-not-resuscitate order; and having a history of diabetes, heart failure, or MI. Those who developed cardiogenic shock also were significantly older and were likely to be female, and were more likely to present with dyspnea, and to develop a Q-wave MI while hospitalized.


Noting that the rate of cardiogenic shock after AMI remains relatively high, despite apparent drops over the past 30 years, the authors wrote, "it remains to be seen whether current efforts aimed at reducing the extent of prehospital delay and door-to-balloon times may lead to further declines in the incidence" and fatality rates.


None of the other authors of the two studies had conflicts of interest to report. Both studies were supported by the National Institutes of Health/National Heart, Lung, and Blood Institute.

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