But while that
number may sound concerning, it marks an improvement over
estimates from earlier studies, according to a report in a
recent issue of the American Journal of Cardiology.
It is possible,
the study authors explain, that greater public awareness of
heart attack symptoms and more-sensitive cardiac tests have
led to fewer unrecognized heart attacks in recent years.
Although most heart
attacks involve chest pain or discomfort, some occur without
these symptoms. In addition, milder chest discomfort and other
heart attack symptoms such as dizziness or shortness of breath
may not readily signal a heart attack to the patient, or even
in the US and elsewhere has suggested that anywhere from 20%
to 40% of heart attacks may go undetected. But these estimates
are based on patients who had heart attacks prior to the late
1980s, according to the authors of the new report, led by
Lori L. Boland of the University of Minnesota in Minneapolis.
Boland's team analyzed
data on more than 12,800 men and women who had participated
in a national study of cardiovascular health between 1987
and 1998. Participants were between the ages of 45 and 65,
and free of coronary artery disease at the study's start.
They were followed for 10 years, on average.
found that, based on periodic electrocardiograms taken as
part of the study, 20% of the 500 heart attacks participants
suffered went unrecognized. African Americans had a slightly
higher percentage of undetected heart attacks than whites
did -- 23%, compared with 19%.
Despite the commonness
of undetected heart attacks among these patients, Boland and
her colleagues point out that the percentage is "slightly
lower than previous estimates from other populations."
Although they don't
know for sure, the authors note that it's "plausible"
that in the 1990s, Americans became more likely to seek medical
care for possible heart attack symptoms. In addition, they
write, recent advances in detection, such as cardiac enzyme
tests, may have allowed doctors to spot more cases of mild
Journal of Cardiology 2002;90:927-931