The severity of incident MIs has dropped significantly in the US over
a 15-year period, a new analysis of the Atherosclerosis Risk in
Communities Study (ARIC) has shown [1]. This has likely contributed
to a decline in populationwide death rates for coronary heart disease
(CHD), say Dr Merle Myerson (St Luke's Roosevelt Hospital, New York,
NY) and colleagues in their report published online January 19, 2009
in Circulation.

"Our severity indicators all seemed to indicate that MIs were less
severe, the cardiac enzymes did not go as high, and there were fewer
Q waves on ECG. This is very good, because if people have less severe
heart attacks, the chances are less that they'll die," Myerson told
heartwire.

"Although this study was not particularly designed to tell us exactly
why heart attacks are less severe, it certainly appears that better
in-hospital care and better prevention beforehand may have played a
role," she added. One thing that has not improved, however, is the
time it takes people to get to the hospital. "We were surprised to
find this, because efforts have been made through public-education
programs. But we didn't see any improvement, and this is in agreement
with several other studies," she noted.

Consistent Picture Showing Clear Decline in MI Severity

The new study by Myerson et al extends previous findings from ARIC,
an ongoing epidemiologic trial that includes data from four areas--
Forsythe County, NC, including Winston-Salem; Washington County, MD,
including Hagerstown; and the suburbs of Minneapolis, MN and Jackson,
MS.

In the previous analysis, focusing on 1987 to 1994, researchers found
a decrease in many but not all indicators of severity. This new study
includes an extra eight years of data, covering 10 285 patients, ages
35 to 74, who were discharged from the hospital diagnosed with a
definite or probable first-time heart attack from January 1, 1987
through December 31, 2002.

"We wanted to explore why mortality from CHD has declined, to see
whether we can discover what's working and what's not working,"
Myerson explained to heartwire. The new findings show a more
consistent picture, with a clear decline in severity of heart
attacks, she says.

MI classification was assigned according to an algorithm consisting
of chest pain, ECG evidence, and cardiac biomarkers. The number of MI
cases with major ECG abnormalities declined as shown by a 1.9%/year
decline (p=0.002) in the proportion of those with initial ST-segment
elevation, a 3.9%/year drop (p<0.001) in those with subsequent Q
waves, and a 4.5%/year reduction (p<0.001) in those with any major Q
wave. Maximum creatinine kinase and creatinine kinase-MB values also
fell (by 5.2% and 7.6%; p<0.001 and p<0.001 per year, respectively),
although in later years maximum troponin I values remained stable.

But the percentage of patients who arrived at the hospital less than
two hours after symptom onset remained unchanged over the course of
the study, at approximately 33%.

Study Findings Generalizable

Myerson says one of the key strengths of ARIC is its
generalizability.

"We had four geographic areas--including urban, rural, and suburban--
and we have men and women and blacks and whites in this study," she
says. "And while we certainly can't say we captured everybody in this
country, the beauty and strength of the ARIC study is that we can
say, 'Hey, we're finding it in each of these populations.' "

The results likely indicate that risk factors, such as blood pressure
and cholesterol, are being better controlled, says Myerson, and that
when people do get to the hospital there has been an improvement in
care there. "Attributing the reduction in severity to specific causes
will be an important next step, so that effective strategies can be
reinforced and public-health policies can be better directed," she
concludes.


Myerson M, Coady S, Taylor H, et al. Declining severity of myocardial
infarction from 1987 to 2002. The Atherosclerosis Risk in Communities
(ARIC) Study. Circulation 2009; 119:503-514. Abstract