Seasonal pattern of acute myocardial infarction in the National Registry of Myocardial Infarction.
ABSTRACT The purpose of this study was to determine whether the rate of hospital admission for acute myocardial infarction (AMI) varies seasonally in a large, prospective U.S. registry.
Identification of specific patterns in the timing of the onset of AMI is of importance because it implies that there are triggers external to the atherosclerotic plaque. Using death certificate data, most investigators have noted a seasonal pattern to the death rate from AMI. However, it is unclear whether this observation is due to variation in the prevalence of AMI or to other factors that may alter the likelihood of a fatal outcome.
We examined the seasonal mean number of cases of AMI (adjusted for the length of days in each season) that were submitted to the National Registry of Myocardial Infarction (NRMI) by 138 high volume core hospitals over a 3-year period (December 21, 1990 through December 20, 1993) during which the number of hospitals participating in the Registry was stable. Data were analyzed using general linear modeling and analysis of variance.
High volume core hospitals reported 83,541 cases of AMI to the Registry during the study period. Approximately 10% more such cases were entered into the Registry in winter or spring than in summer (p < 0.05). The same trends were seen in both northern and southern states, men and women, patients < 70 versus > or = 70 years of age and those with Q wave versus non-Q wave AMI.
We conclude that there is a seasonal pattern to the reporting rate of cases of AMI in the NRMI. This observation further supports the hypothesis that acute cardiovascular events may be triggered by events that are external to the atherosclerotic plaque.
- SourceAvailable from: Barbara Forey[Show abstract] [Hide abstract]
ABSTRACT: We update an earlier review of smoking bans and heart disease, restricting attention to admissions for acute myocardial infarction. Forty-five studies are considered. New features of our update include consideration of non-linear trends in the underlying rate, a modified trend adjustment method where there are multiple time periods post-ban, comparison of estimates based on changes in rates and numbers of cases, and comparison of effect estimates according to post-ban changes in smoking restrictiveness. Using a consistent approach to derive ban effect estimates, taking account of linear time trends and control data, the reduction in risk following a ban was estimated as 4.2% (95% confidence interval 1.8 to 6.5%). Excluding regional estimates where national estimates are available, and studies where trend adjustment was not possible, the estimate reduced to 2.6% (1.1 to 4.0%). Estimates were little affected by non-linear trend adjustment, where possible, or by basing estimates on changes in rates. Ban effect estimates tended to be greater in smaller studies, and studies with greater post-ban changes in smoking restrictiveness. Though the findings suggest a true effect of smoking bans, uncertainties remain, due to the weakness of much of the evidence, the small estimated effect, and various possibilities of bias.Regulatory Toxicology and Pharmacology 01/2014; · 2.13 Impact Factor
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ABSTRACT: Seasonal variation in admissions and mortality due to acute myocardial infarction has been observed in different countries. Since there are scarce reports about this variation in Iran, this study was carried out to determine the existence of seasonal rhythms in hospital admissions for acute myocardial infarction, and in mortality due to acute myocardial infarction (AMI) in elderly patients in Isfahan city.ARYA atherosclerosis. 01/2014; 10(1):46-54.
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ABSTRACT: Christensen et al question whether our recent study regarding seasonal variance to the occurrence of venous thrombotic events, and its conclusion, is valid [1,2]. We appreciate the authors' concern and would like to commend the authors' way of discussing our findings by contrasting these to findings from Denmark on seasonal variance and venous thrombosis risk. We studied 5,343 patients with thrombosis from Milan, Leiden and Tromsø, spanning a nearly 3000 km long north-south axis over Europe, and found a 2.3% lower incidence in Spring than in Summer. Christensen at al included 152,548 patients from Denmark, and found an incidence rate ratio of Winter over Summer of 1.19. We offer four points with which to contend Christensen claims on the origin of our different findings, and their clinical relevance. © 2013 International Society on Thrombosis and Haemostasis.Journal of Thrombosis and Haemostasis 03/2013; 11(3). · 6.08 Impact Factor
Seasonal Pattern of Acute Myocardial Infarction in the National
Registry of Myocardial Infarction
JOSEPH P. ORNATO, MD, FACC, MARY ANN PEBERDY, MD, FACC, NISHA C. CHANDRA, MD,*
DAVID E. BUSH, MD,* FOR THE PARTICIPANTS IN THE NATIONAL REGISTRY OF MYOCARDIAL INFARCTION†
Richmond, Virginia and Baltimore, Maryland
Objectives. The purpose of this study was to determine whether
the rate of hospital admission for acute myocardial infarction
(AMI) varies seasonally in a large, prospective U.S. registry.
Background. Identification of specific patterns in the timing of
the onset of AMI is of importance because it implies that there are
triggers external to the atherosclerotic plaque. Using death cer-
tificate data, most investigators have noted a seasonal pattern to
the death rate from AMI. However, it is unclear whether this
observation is due to variation in the prevalence of AMI or to
other factors that may alter the likelihood of a fatal outcome.
Methods. We examined the seasonal mean number of cases of
AMI (adjusted for the length of days in each season) that were
submitted to the National Registry of Myocardial Infarction
(NRMI) by 138 high volume core hospitals over a 3-year period
(December 21, 1990 through December 20, 1993) during which the
number of hospitals participating in the Registry was stable. Data
were analyzed using general linear modeling and analysis of
Results. High volume core hospitals reported 83,541 cases of
AMI to the Registry during the study period. Approximately 10%
more such cases were entered into the Registry in winter or spring
than in summer (p < 0.05). The same trends were seen in both
northern and southern states, men and women, patients <70
?70 years of age and those with Q wave versus non-Q wave
Conclusions. We conclude that there is a seasonal pattern to the
reporting rate of cases of AMI in the NRMI. This observation
further supports the hypothesis that acute cardiovascular events
may be triggered by events that are external to the atherosclerotic
(J Am Coll Cardiol 1996;28:1684–8)
?1996 by the American College of Cardiology
The time of onset of both acute myocardial infarction (AMI)
and cardiac death varies in a circadian pattern, with a peak
from 6 AM to noon and a lower prevalence during the night
(1–6). Variations in platelet aggregability and sympathetic
activity have been proposed to explain the observation, but the
actual mechanism is not completely understood (1–6). Al-
though it is known that short-term climatic changes (e.g., a
heat wave) can influence cardiovascular morbidity and mortal-
ity transiently, investigators throughout the world (7–23) have
reported that there is a seasonal pattern of deaths due to AMI
with more fatal events in winter than in summer. However, it
is unclear whether this observation is due to variation in the
prevalence of AMI or to other factors that may alter the
likelihood of a fatal outcome. The purpose of this study was to
further explore this distinction by determining whether the rate
of hospital admission of patients with AMI varies seasonally in
a large, prospective, United States registry of cases of AMI.
Study inclusion characteristics. The National Registry of
Myocardial Infarction (NRMI) Phase 1 (NRMI-1) was a
nationwide, observational data base containing quantitative
and qualitative information about characteristics, diagnosis,
treatment, clinical course and outcome of patients with AMI.
Patients with a Q wave or non-Q wave AMI and those treated
with a thrombolytic agent or mechanical revascularization
or neither were included in the Registry. A broad range
of community and teaching hospitals from all across the
United States participated voluntarily in this large, industry-
sponsored, observational data base. At the time of this inves-
tigation, 1,073 hospitals participated in NRMI, representing
14.4% of all general medical/surgical hospitals in the United
States. As a group, NRMI-1 hospitals were significantly larger,
more likely to be certified by the Joint Commission on
Accreditation of Health Care Organizations, more likely to be
affiliated with a medical school and to have a residency
teaching program and more likely to have an emergency
department, coronary care unit, cardiac catheterization labo-
ratory and cardiac surgery program than were non-Registry
From the Division of Cardiology, Virginia Commonwealth University–
Medical College of Virginia, Richmond, Virginia; and *Division of Cardiology,
The Johns Hopkins University School of Medicine, Baltimore, Maryland. †The
National Registry of Myocardial Infarction is supported by Genentech, Inc.,
South San Francisco, California. Genentech, Inc. reimburses ClinTrials, Inc. for
the cost of data analysis and biostatistical services.
Manuscript received February 8, 1996; revised manuscript received August 8,
1996, accepted September 9, 1996.
Address for correspondence: Dr. Joseph P. Ornato, Department of Internal
Medicine (Cardiology), Medical College of Virginia, Box 980525, Richmond,
JACC Vol. 28, No. 7
?1996 by the American College of Cardiology
Published by Elsevier Science Inc.
Individual institutions participating in NRMI-1 designated
a physician investigator to oversee the entire hospital project
and an NRMI-1 coordinator who was a physician, nurse,
pharmacist, resident or quality assurance representative. The
NRMI-1 coordinator conducted periodic retrospective chart
reviews of all patients with confirmed AMI, and completed a
case report form for each patient. This form contained perti-
nent data about each patient with AMI, such as time from
symptom onset, demographic data and interhospital transfer,
infarct location, method of diagnosing AMI, pharmacotherapy,
ancillary procedures performed, patient outcome and clinical
complications. Completed case report forms were then sent to
an independent data coordinating center (ClinTrials Research,
Inc.) that compiled the data and generated the reports.
The NRMI-1 coordinator was instructed as to the impor-
tance and benefit of correctly completing the case report
forms. NRMI-1 coordinators and physician investigators re-
ceived detailed training manuals to increase their knowledge of
how to collect data in a uniform, accurate manner. The data
coordinating center generated quarterly reports including ta-
bles and charts of aggregate data from the completed case
report forms. Each hospital received its own data and the
national aggregate data for comparison. Biannual trend re-
ports that compared these data sets in 6-month intervals were
also distributed. Patient confidentiality was preserved assidu-
For purposes of this analysis, we defined the northern
hemisphere climatic seasons based on the official “calendar”
definitions: winter (December 21 to March 19 [89 days]);
spring (March 20 to June 20 [93 days]); summer (June 21 to
September 22 [94 days]); fall (September 23 to December 20
[89 days]). We adjusted the length of each season to 91 days to
take into account the difference in the length of each season.
A core group of 138 high volume hospitals that participated
in NRMI-1 during the entire study period from July 1, 1990 to
June 30, 1994 and consistently treated at least six patients for
1 month with AMI were chosen from the 1,073 participating
NRMI-1 hospitals. These characteristics were not present in
the remaining, excluded non-core hospitals. Non-core hospi-
tals were enrolled continuously and were being added to the
study at varying times during the 3-year data collection period.
Submission of AMI data from sites other than the core
hospitals was highly sporadic, resulting in the capture of only
occasional AMI cases rather than a continuous series.
Only cases of AMI from high volume core hospitals were
included in the analysis to increase the likelihood that the
sample represented sites that were fully engaged in completing
case reports on the majority of admitted patients with AMI.
The date of AMI symptom onset was the variable analyzed in
this study, not the date that the case report form was submitted
to the Data Coordinating Center. The adjusted seasonal mean
number of AMI cases was chosen as the outcome variable.
Study exclusion characteristics. We excluded from analy-
sis all data collected during the 1st year of the study because
hospitals were coming “on line” in the study and a steady state
number of participating centers had not yet been reached. We
excluded the last 6 months of data collection to avoid including
only1⁄2 year of data. Thus, the study period consisted of 3 full
years, beginning December 21, 1990 and ending December 20,
1993. Geographic subgroup analysis was also performed to
compare the primary outcome variable in northern (Maine,
New Hampshire, Vermont, New York, Ohio, Michigan, Wis-
consin, Minnesota, North Dakota, Montana, Washington) and
southern (Florida, Georgia, Alabama, Mississippi, Louisiana,
Texas, New Mexico, Arizona, California) states.
All data in this study were collected using the NRMI-1 data
collection form. In the fall of 1994, a new data collection form
was implemented and all subsequent cases are being entered
into a new data base entitled NRMI-2.
Statistical analysis. Statistical analysis was conducted us-
ing general linear modeling and analysis of variance (ANOVA)
to analyze the mean of the adjusted number of AMI cases. The
factors in the model included season (treatment) effect (winter,
spring, summer, fall) and year effect (1991, 1992, 1993). The F
test from ANOVA (type III) determined the overall main
effect of season. If it was significant (i.e., p ? 0.05), then the
least significant difference test was used for post-hoc compar-
ison of multiple means to determine which seasons were
High volume core hospitals reported 83,541 cases of AMI
to NRMI-1 during the study period. The number of cases
reported was significantly higher in winter or spring than in
summer in the model analysis (Fig. 1). The seasonal variation
was of substantial magnitude. Approximately 10% more pa-
tients with AMI were entered into NRMI-1 by the core
hospitals in winter or spring than in summer (Table 1). There
was no significant difference between the number of AMI cases
in fall and that in any other season in the model analysis.
The same seasonal trends were seen in all subgroups
studied (northern and southern states, men and women,
patients ?70 vs. ?70 years of age and those with Q wave vs.
non-Q wave AMI) (Table 1). In the model analysis, the results
achieved statistical significance only for southern states,
women and patients ?70 years of age. We could not test for
the effect of other potentially interesting variables such as
aspirin or beta-blocker usage because such information was
not captured in the NRMI-1 data base.
Abbreviations and Acronyms
? acute myocardial infarction
? analysis of variance
MONICA ? Monitoring Trends and Determinants in
? National Registry of Myocardial Infarction
? National Registry of Myocardial Infarction Phase 1
? World Health Organization
JACC Vol. 28, No. 7
OMATO ET AL.
SEASONAL PATTERN OF AMI IN NRMI-1
Identification of specific patterns in the timing of the onset
of AMI is of scientific importance because such patterns imply
that there are triggers external to the atherosclerotic plaque.
Using death certificate data, a large number of studies have
confirmed that there is a seasonal pattern to deaths from AMI
in the United States as a whole (23), Australia (23), New
England (7), Philadelphia (8), Pittsburgh (9), New York (10),
Boston (11), Cincinnati (12), Minneapolis-St. Paul (13), the
Smolyan District of Bulgaria (16), London (14,17), England
and Wales (18) and Romania (15). Only a handful of small,
inadequately powered investigations (25–28) have not detected
the seasonal pattern.
Muller et al. (6) recently discussed the appropriateness and
limitations of using death certificate data to analyze the pattern
of death from acute cardiovascular events such as AMI.
Although death certificate diagnoses of specific causes of death
are often inaccurate, general categories, such as death from
ischemic heart disease, have been found to be reliable (6,29).
The primary purpose of the previously cited studies was not to
define the prevalence of death due to AMI but rather to
determine whether there is a seasonal pattern to deaths
attributed to AMI by the physician who signed the death
certificate. Such studies cannot answer the most important
question, which is whether there is a seasonal pattern to the
actual prevalence of AMI.
The only way to definitively answer this question would be
to look for a seasonal pattern in the prevalence of AMI in a
large registry containing all cases of AMI in a geographic area
(or in a representative sample of that area). All cases of AMI,
including those presenting as sudden death or with atypical or
no symptoms (i.e., “silent” infarction), would theoretically
need to be confirmed in some way and counted. Unfortunately,
there is no all inclusive, nationwide registry of cases of AMI in
the United States and there is no practical way to detect and
confirm the correct diagnosis in all AMI cases (e.g., “silent”
The World Health Organization (WHO) MONICA (Mon-
itoring Trends and Determinants in Cardiovascular Disease)
Project uses a registry to track cardiovascular event and case
fatality rates (30,31). Some sites, such as Augsberg, have
captured virtually all hospitalized patients with AMI within a
confined geographic area (32). Although most published re-
ports from the MONICA Project have not reported looking for
a seasonal patterns, a seasonal effect has been described in an
Australian MONICA Project population (33). Coronary
events, both fatal and nonfatal, were 20% to 40% more likely
to occur in winter and spring than at other times of the year. It
would be interesting to see whether such a trend exists in data
from other MONICA Project centers and, if so, whether
factors such as geographic latitude influence the pattern.
Limitations of the present study. The present study was
undertaken to look for additional data that might support or
refute the hypothesis that the onset of AMI has a seasonal
prevalence. The NRMI-1 data base contains information on
354,435 patients with AMI and has been shown to be of great
value in detecting trends in the treatment of AMI over time
(24). However, it has certain limitations. NRMI-1 is not a
random sample of all U.S. hospitals, but it does contain data
from ?15% of all U.S. general medical/surgical hospitals.
Participating hospitals tend to be larger and are more likely to
have a coronary care unit, a cardiac catheterization laboratory
or a cardiovascular surgery program than is the nationwide
average hospital. None of these characteristics would be
Table 1. Cases of Acute Myocardial Infarction (AMI) Reported Each Season to the National Registry of Myocardial Infarction by All Core
Hospitals During the Study
Winter SpringSummer Fall
All cases 7,218 (6,869–7,567) 7,222 (6,873–7,571)6,574 (6,225–6,922)6,765 (6,417–7,114)
Age ?70 years
Age ?70 years
Q wave AMI
Non-Q wave AMI
Data are presented as the mean (95% confidence interval) for all cases. Seasonal counts were adjusted on the basis of the number of days in each season.
Figure 1. Number (N) of cases of acute myocardial infarction reported
to the National Registry of Myocardial Infarction by all core hospitals
per month. Monthly counts were adjusted on the basis of number of
days in each month.
OMATO ET AL.
SEASONAL PATTERN OF AMI IN NRMI-1
JACC Vol. 28, No. 7
expected to influence the seasonal pattern of AMI cases
reported to NRMI-1.
Unlike other studies that have shown a higher prevalence of
deaths attributed to AMI in the winter than in the summer, this
investigation found more cases of AMI in both winter and
spring than in summer (7–18,23). It is possible that the
differences may be due to the fact that other studies have
defined the seasons as arbitrary blocks of 3 months rather than
by the official calendar definition.
Possible causes of the seasonal pattern. The cause of the
seasonal pattern of AMI cases in NRMI-1 is unclear. Case
report forms are sent into the data coordinating center from
participating hospitals on a continuous basis. There are no
administrative procedures (e.g., submission of reporting forms
to meet a specific deadline at certain times of the year) that
would generate an artificial, apparently seasonal pattern of
cases. We do not believe it likely that an artifact, such as
NRMI-1 coordinator summer vacations, had anything to do
with the seasonal pattern because the analysis was based on the
date of AMI onset rather than on the dates that the case report
forms were submitted to NRMI-1. We believe that the most
logical explanation is that the seasonal pattern of AMI
NRMI-1 cases may, in fact, reflect an increased prevalence of
AMI onset at certain times of the year.
Several theories have been proposed to explain an in-
creased prevalence of AMI or its complications in winter
(13,14,18,19,21,25,27,28) Cold weather or a sudden change in
the climate can increase arterial blood pressure (22,34–39),
arterial spasm (34–37,40), platelet and red blood cell counts
(40), blood viscosity (40), plasma fibrinogen (41,42) and factor
VII (42) and serum cholesterol levels (by ?2% to 3%) (43,44).
Exposure to the cold also has important hemodynamic effects,
including an increase in systemic vascular resistance, myocar-
dial oxygen consumption and body metabolism. (34–37,40) It
is unlikely that migration of persons from northern to southern
states can explain the seasonal variation because similar trends
were noted in both locations. Concurrent infections during the
winter months, particularly those involving the respiratory
tract, have also been postulated as a trigger for acute cardio-
vascular morbid events. Other mechanisms that have been
proposed to explain the rise in cardiovascular events during
cold weather include seasonal change in physical activity, diet,
weight, stress during the holiday season and seasonal modula-
tion in the secretion of physiologically active substances anal-
ogous to those that trigger seasonal depression (13,14,18,
19,21–23,25,27,28). The other possibility is that the seasonal
pattern observed in this and other studies could be due to a
summer decrease in events relative to other times of the year.
Magnitude of the seasonal variation. In the present study,
the magnitude of the seasonal variation was relatively modest
(?10%) compared to the 20% to 30% variation reported in
the number of cardiovascular events in an Australian
MONICA Project population (33). It was also less than the
20% to 38% seasonal variation reported in the incidence of
cardiac death attributed to AMI based on death certificate
data in the United States and Australia as a whole (23). The
reason for these differences among studies is unclear.
Conclusions. We conclude that there is a winter and spring
increase or summer decrease in the number of cases of AMI
reported to a large, prospective United States registry of AMI
cases. These observations, together with data indicating that
there is a circadian pattern to the onset of AMI and a seasonal
distribution of deaths reported to be due to AMI, further support
the hypothesis that acute cardiovascular events may be triggered
by events that are external to the atherosclerotic plaque.
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JACC Vol. 28, No. 7