Cardiac risk: Theme con variations
Stefan N. Willich, MD, MPH Berlin, Germany
Sudden cardiac death is a major threat of our times,
afflicting at least 300,000 individuals each year in the
United States alone.
Approximately 25% of all patients
with acute coronary syndromes die within the first
hour after onset of the event.
Because of this cata-
strophic time sequence, the most promising strategy
in reducing sudden cardiac death is to improve pre-
vention. The triggering mechanisms of sudden cardiac
death are, however, not sufficiently identified, and
effective means of specific prevention remain poorly
developed. Several previous studies have demonstrated
a marked circadian pattern in the onset of sudden
cardiac death with a primary peak during the morning
hours and a trough during the night. These observations
have challenged the view that the onset of sudden
cardiac death is a “random” event in patients with
coronary artery disease and suggest that endogenous
rhythms or activity of the subjects as well as external
factors may play an important role in triggering this
There has been only sparse and inconclusive
data on weekly and seasonal variation of sudden cardiac
death partly because of the lack of adequate databases
and the difficulties in confirming diagnosis.
The study by Peckova et al
in this issue of the Journal
(see page 512) adds important new dimensions to the
evolving field of temporal patterns in sudden cardiac
death. The analyses of weekly and seasonal variation
in the incidence of sudden cardiac death are based on
the unique database from the Seattle emergency ser-
vices. Seattle has an excellent system of prospectively
documenting cases of cardiac arrest including electro-
cardiographic registration and determination of under-
lying cause from field reports with subsequent review
by trained nurses. Cardiac arrests occurred significantly
more frequently on Mondays compared with other
days of the week and in the winter months from
December through March compared with the summer
months. The data are convincing because of the
applied methods, including a population-based
approach, standardized diagnosis confirmation, and
statistical robustness. Furthermore the weekly and
seasonal pattern of the Seattle data is very similar
compared with preliminary analyses of 24,000 patients
with sudden death in the Berlin emergency care system.
This study has important implications regarding the
triggering pathophysiologic mechanisms of the disease
and perhaps improving its prevention. The authors put
forward the hypothesis that physical and emotional
burden as well as environmental influences are
responsible for the observed patterns. Physical activity,
bouts of anger, and other external factors have been
reported as triggers of nonfatal myocardial infarction,
and such activities occur probably more frequently on
Mondays when people return to work compared with
other days of the week. The triggers of sudden cardiac
death are more difficult to determine but could probably
be studied with firsthand data from successfully
resuscitated victims of sudden cardiac death or infor-
mation from bystanders of the events. Alternatively,
patients with implantable cardioverter defibrillators
may be used as a model to study possible triggering
events preceding shock release. Those studies have
not been published, to our knowledge.
The hypothesis of the authors would be strengthened
by looking at weekly patterns of sudden cardiac death
in societies with different days of rest because the
respective subsequent workday would be expected to
be associated with an increased risk. The authors also
speculate on possible physical and emotional reasons
for the seasonal variation of sudden cardiac death. In
addition, climatic factors may play a role. Days of
marked temperature deviation from the average have
been reported to coincide with increased death rate.
The occurrence of blizzards has also been observed to
be associated with an increased cardiac mortality rate.
A recent study demonstrated an increased blood vis-
cosity (a risk factor of cardiovascular disease) during
episodes of air pollution,
which may also occur more
frequently during the winter months.
Further population-based investigation is needed on
the role of underlying and possible contributing fac-
tors (including meteorologic variables and environ-
From the Institute of Social Medicine and Epidemiology, Charité Hospital, Humboldt
University of Berlin, Germany.
Reprint requests: Stefan N. Willich, MD, Institute for Social Medicine and Epidemiol-
ogy, Charité Hospital, 10098 Berlin, Germany.
Am Heart J 1999;137:384-5.
0002-8703/99/$8.00 + 0 4/1/93411
See related article on page 512.