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Minnesota ECG Coding
For over 40 years, Minnesota ECG Coding has been a major electrocardiographic computer and visual
reading service for epidemiological studies and clinical trials nationally and internationally.
The mission of the center was to document the prognostic and diagnostic value of electrocardiography for
epidemiological studies and clinical trials. The Coding Center was at the fore front of developing and
evaluating new criteria sets for incident cardiac events including silent myocardial infarction, ischemia,
left ventricular hypertrophy, QT dispersion, and heart rate variability.
The Team
Director
Dr. Richard Crow has had 25 years of experience in designing, implementing and
executing electrocardiogram analysis in multicenter epidemiologic studies and clinincal
trials.
Dr. Crow has enlarged the Minnesota Code classsification procedures to include
standardized serial ECG comparision to document incident or recurrent (silent)
myocardial infarction, in-hospital Q wave myocardial infarction, progression or
regression of LVH (See studies MRFIT, TOMHS and ALLHAT), and ECG quality control methodology.
Director Emeritus
Dr. Ronald Prineas has served as director of the Minnesota Central ECG Laboratory and Miami ECG
Coding Center in the past.
He has 34 years of experience in the design, conduct and implementation of multicenter studies
(epidemiologic and clinical) that make use of the ECG. He is also a consultant to the World Health
Organization (WHO) on population electrocardiography.
Founding Father
Dr. Henry Blackburn is the founding father of The Minnesota Code. He developed
the original standardized criteria in the late 1950s, to meet the needs for objective
comparisions of heart disease rates amongst countries.
In 1968, Dr. Blackburn and Geoffrey Rose of London first published the Minnesota
Code with the World Health Organization in a book entitled, Cardiovascular Survey
Methods. Dr. Blackburn is also responsible for developing the idea of training
technicians to code ECG's in the laboratory setting. (See History of ECG Coding.)
About Us
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For more than 40 years, the Minnesota ECG Coding Center has been the major electrocardiographic
visual reading service center for epidemiological studies and clinical trials, both nationally and
internationally. The mission of the Center is to document the prognostic and diagnostic value of
electrocardiography for epidemiological studies and clinical trials. The Center has been at the forefront of
developing and evaluating new criteria sets for incident cardiac events, including silent or symptomatic
myocardial infarction, ischemia, left ventricular hypertrophy, QT dispersion, and heart rate variability.
The Minnesota Code is a classification system for the electrocardiogram that utilizes a defined set of
measurement rules to assign specific numerical codes according to severity of ECG findings. The
Minnesota Code, developed in the late 1950s by Dr. Henry Blackburn in response to the need for
reporting ECG findings in uniform, clearly defined, and objective terms, is the most widely used ECG
classification system in the world for clinical trials and epidemiologic studies. It incorporates ECG
classification criteria that have been validated, widely employed, and accepted by clinicians. The
Minnesota Code provides an objective ECG classification system free of impressionist physician bias, by
which different studies can have a common standard to compare or pool ECG findings. It now includes
objective procedures for defining significant pattern changes from serial ECG comparison, such as
evidence of new MI, new ischemia, progression or regression of LVH and new conduction defect.
Minnesota Code procedures have been incorporated into a computer program, the Minnesota Code
Modular ECG Analysis System (MC-MEANS). MC-MEANS also includes logic for serial ECG comparison,
developed and validated at the Center.
EpiCH faculty, along with other researchers around the world, use these facilities for service and research
activities. Active collaboration is ongoing between ECG Centers at Wake Forest University in North
Carolina and Erasmus University in Rotterdam, Netherlands.
The Center provides the following services: Visual or computer assigned standard Minnesota Codes;
amplitude, axis and duration measurements; serial ECG comparisons for documenting evolving Q-waves,
evolving ST-T waves, evolving bundle branch block and progression or regression of ECG LVH and visual
or computer determination of left ventricular mass index; prolonged heart rate corrected QT or JT
intervals; heart rate variability; QT dispersion; T-wave axis; and ECG prognostic score.
The Center currently has eight active studies that send approximately 3,500 ECGs per month for analysis.
The Minnesota ECG Coding Center also provides training and evaluation of technical staff for new studies
and refresher training for ongoing studies. Researchers wishing to use the Minnesota Code to code their
own ECGs can use the Minnesota Code interactive computer tutorial or can submit samples of their coded
ECGs for evaluation
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History of ECG Coding
In the 1950s, when most systematic population studies of heart disease
began, it became important to have standard and quantitative means to
compare disease rates. Diagnoses from death certificates or by
physicians having different training might very easily result in spurious
differences.
Even independent diagnoses by specially trained physicians may be
highly variable. This problem of comparability in clinical assessment led
to consideration of the electrocardiogram (ECG) as an objective measure
for assessing heart disease. Why? Because its findings are strongly
related to heart disease manifestations of greatest interest, that is, death
of heart muscle (infarction), increased heart size (hypertrophy), and disturbances of rhythm or
conduction.
The ECG seemed particularly promising because it is a graphic record, amenable to standard procedures
of collection, measurement, and classification. It also seemed ideal because it is so acceptable, painless,
simple, and inexpensive to record.
This was all very well until several facts quickly emerged. Differences between physicians’
“impressionistic” reading of ECGs were large; sizable differences were found by the same cardiographer at
different times, and no objective criteria existed for abnormality or for specific cardiac findings, only a
pattern recognition. Clearly, the challenge of standard criteria measurement had first to be met before
endpoint cardiac “events” and population rates could be reliably assessed and compared.
My first approach was to compile all existing ECG criteria and attempt to sort them into quantitative
classes. Where this was not possible, “reasonable” criteria were devised and empirically tested for
sensitivity and specificity in well-defined populations containing different proportions of normals versus
patients having specific abnormalities, from both living and autopsy series.
Finally, all these ECG criteria were assembled, unambiguously described, rank ordered by magnitude and
amplitude according to a clinical impression of their importance and assigned code numbers. The
resulting classes were quantitative, mutually exclusive, and generally relevant to important disease states.
However, they were objectively described as Q-QS waves, negative T-waves, etc., rather than given
clinically diagnostic labels. Finally, records from many different living populations were classified and
evaluated for “reasonableness” of the population distributions obtained. Test-retest reliability improved
among the collaborating physicians closely involved in development of the code: Pentti Rautaharju, Sven
Punsar, Gunnar Blomqvist, and me.
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Early on, between 1958-59, other investigators in cardiovascular disease population studies received a
version of the criteria and code.
Someone, possibly Frederick Epstein at the University of Michigan or Geoffrey Rose in London, termed it
“Minnesota Code.” They began to use the criteria and provide suggestions for minor revisions, and were
enthusiastic about an increasing ability to classify prevalence and incidence data quantitatively.
About this time we also shared records to assess variation between us in coding. We were a little surprised
to find out how sizable was the coding variation, despite the unambiguous and quantitative criteria and
awareness of standard laboratory procedures.
The extent of observer variability, of course, should not have surprised us at all but should have been
anticipated. Clear definitions and objective criteria do not guarantee, in themselves, their similar
application by different observers. In consequence, more attention was given to the conditions of
recording and measurement and to coding procedures and rules. Measuring devices were developed,
particularly for assessing Q wave duration, to improve classifications at the borderlines between criteria.
Rules were devised to account for pattern variation between beats. The system was generally shored up by
quality control procedures for individual code and standardization by a system of duplicate independent
readings and adjudication.
By the early 1960s the burden of coding still lay mainly on me and a few visiting physicians in this
laboratory, while the volume of ECGs increased from population studies. High interest in the
developmental phases of Minnesota coding was replaced by a tedious chore. At about the same time,
independently, Geoffrey Rose in London and I in Minnesota hit upon an idea to make coding by
technicians practical.
My resolution of the issue grew out of a special experience of ECG coding.
In the summer of 1962 I was solicited by the National Health Examination Survey of the National Center
for Health Statistics to classify electrocardiograms on 6000 individuals, a true sample of the United States
population. Standard coding was designed in the only existing objective classification system. I agreed to
do this as a summer undertaking. It offered only the princely reward of twenty-five cents a record, but
seemed a worthwhile undertaking, that is, until I received the shipment of actual ECGs.
They were unmounted strips stowed in tiny cardboard cubicles as tightly wrapped cylinders some 6 to 9
feet long. They required to be removed from the case, unrolled, held flat, read, measured, codified,
tabulated, rerolled, and reinserted in the packing. The reading, classification, and tabulation involved
approximately one-fifth of the total time required for handling. At the inducement of one cent per record
per person, I was able to enlist the enthusiastic aid of two alert, though very young, non-technical persons
who happened to be close at hand that summer. While one, aged 8, would extract and unroll the record,
the other, aged 9, would hold it down while I coded and then rolled and refilec it. Their summer wage was
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thus 6000¢ each, and mine, 6000 x 23¢. However, their work reduced mine substantially and allowed an
increasingly pleasant relationship among these very close relatives.
After only a few experiences, from normal curiosity, my assistants could soon identify P-, QRS-, and Twaves. After a little time, they were careful to point out to me when a P-wave or a T-wave was “upside
down” or when a Q-wave was “big and fat” or an R-wave particularly tall, and so on. After a few more
days, by which time they spontaneously associated the code numbers I was writing down with tall or flat
or inverted or prolonged waves, it was clear that they were embryonic Minnesota Coders.
With a little more incentive and a little more time and instruction they could become excellent ECG
coders, even at ages 8 and 9. I resolved soon thereafter never to read numbers of ECGs from population
studies, having read some 20,000 to 30,000 records a year for several years. I therefore proceeded in the
fall of 1962 to recruit University students and instruct them in the Minnesota Coding procedures. This has
been going on ever since, and several hundreds of student coder alumni have, over the decades, helped in
this service to national and international studies, while helping themselves through the University with
part-time employment.
It had not been my intention to develop a coding system for export. It was my intention only to develop
sound methodological procedures for assigning objective “events” related to cardiac disease for our
extensive laboratory studies. However, the Minnesota Code became widely used because it met a need in
the burgeoning new field of cardiovascular epidemiology. It became used internationally when it was
included in the World Health Organization monograph series as Cardiovascular Survey Methods,
published in 1968.
Since, the code has been expanded and updated to classify endpoints of clinical trials and to better
characterize arrhythmias and conduction defects.
This manual provides standard procedure for its application. In a blinded, centrally standardized
approach to the ascertainment of disease endpoints in clinical trials it complements clinical data from
physicians who may inadvertently be biased by knowledge of the drugs being administered, or otherwise.
The ECG has a different set of “errors” from clinical assessments, and thus is independent of them.
Finally, it came to be used, and a new set of criteria were developed to estimate significant serial change in
the ECG over time. Interestingly, the original 1960 publication in Circulation was recently cited by the
Cumulative Index Medicus as one of the most extensively referenced articles in the scientific literature.
This, then, is the story of the Minnesota Code up to the presentation of this new manual of procedure for
training and testing. It has long been the intention that these observations, measurements, and
classifications be made by machine rather than by humans.
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Drs. Prineas and Crow have collaborated with numerous computer centers to develop Minnesota Code
logic and programs, most of which have succeeded more or less. But the differing natures of man and
machine leave a problem in that the computer’s determination of wave onset and offset, and of baselines,
though much more repeatable, are often systematically different from human-visual interpretation.
The present strategy of the Minnesota group is to use the computerized Minnesota Code for things the
computer does best, i.e., measurement repeatability, and to complement its classification by things that
the human does best, judging baselines and resolving borderline situations. The group has demonstrated
that combined human / machine adjudication obtains the more reliable and valid electrocardiographic
classification.
I have only a few words more about visual coding of ECGs by student technicians. First, there is no
absolute “right or wrong” in classification. The job is to get as close to the truth and as repeatably as
possible by the means taught in this manual. After an instruction period, learning occurs best by reading
ECGs entirely independently and as rapidly as possible, by making a firm commitment to a code and then
comparing that decision to a standard.
As one becomes a more confident and productive senior coder, the most important thing to remember is
to remain scrupulously honest, and to read sets of cardiograms independently of all others’ readings.
Then, afterwards, it is important to be curious to compare your independently coded findings with the
others. Independent coding helps us learn causes for differences, and as always, “two heads are better
than one” in detecting codable findings in the first place.
Few student coders at Minnesota go on to medical or health-related careers. However, this coding course
allows one to become highly competent in a discipline which to this day remains a “medical mystique”
(while it provides good fees to cardiological specialists to interpret electrocardiograms in the hospital
setting). In a few months of on-the job training, student technicians often become superior to most
interns or even medical residents in their ability to detect, differentiate, and classify repeatedly most ECG
abnormalities. Keep in mind that this technical function you are learning should give no basis for the
interpretation of those findings or the diagnosis of heart disease.
Thus, we talk very little about the significance of these findings to the individuals learning them. Rather,
we want you to take pride in your accomplishment and in the excellent research function you provide to
the scientific community.
Coders must never let themselves be put in the position to misuse their ECG reading skills outside the
laboratory. Once we had a student who tried to “sell” her skills to record rooms in local hospitals as an
“electrocardiographic coder.” They, of course, did not know what she was talking about and called us for
fear she was mentally “unbalanced.”
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The Minnesota Code is not standard in any hospital practice. Rather, it is a system designed for rigorous
population researches and clinical trials. Then, we had another student who once read her grandmother’s
electrocardiogram saying, “Oh, what a nice big 7-1. You have a complete left bundle branch block,
Grandma!” It took some hours of medical persuasion and sedation to calm the old lady down - she
thought she’d had a heart attack!
I am sure you won’t take your work (or skills) home with you!
Coding Services
The Minnesota Code was created in response to the need for reporting ECG findings in uniform, clearly
defined, and objective terms with the least risk of confusion regarding interpretation. As such, it provides
an objective description of bio-electrical phenomena. It incorporates ECG criteria for classification which
have been validated, widely employed and accepted by clinicians.
The Minnesota Code provides an objective ECG classification system free of impresssionist physician bias,
by which different studies throughout the world can have a common standard to compare or pool ECG
findings. It includes objective procedures for defining significant pattern changes from serial ECG
comparison. The Minnesota Code is the most widely used ECG classification system in the world for
clinical trials and epidemiologic studies.
Minnesota Code procedures have been incorporated into a computer program, the Minnesota Code
Modular ECG Analysis System (MC-MEANS) which has been extensively validated. MC-MEANS also
includes logic for serial ECG comparison which was developed and validated at the Minnesota Coding
Laboratory.
MN Central ECG Laboratory (CEL)
The Minnesota Central ECG Laboratory offered:
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Visual or computer assigned standard Minnesota Codes.
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Visual or computer determined amplitude, axis and duration measurements.
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Visual or computer serial ECG comparsions for documenting evolving Q-waves, evolving ST-T
waves, evolving bundle branch block and progression or regression of ECG-LVH.
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Visual or computer determination or prolonged heart rate corrected QT or JT intervals.
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Visual or computer determination of:
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- Left ventricular mass index.
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- Heart rate variability.
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- QT dispersion
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- T-wave axis
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- ECG prognostic score.
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Automatic logging, tracking and inventory of received ECGs
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Computerized billing based on the number of ECGs completed
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Standardized quality control procedures and transfer of data in computer compatible form
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Central training of ECG technicians, certification and quality assurance monitoring of technical
staff.
Frequently Asked Questions
The Minnesota Central ECG is dedicated to informing medical specialists and average persons alike. The
following list of questions represents a sampling from both populations.
Q: What is an ECG?
A: An ECG, or electrocardiogram, is a graphic display of the time-varying voltage of the electrical activity
occurring in the muscle of the heart.
Q: Can hardcopy paper records of ECG's be coded by computer?
A: Yes, but only for specially designed and limited measurement programs, not the Minnesota Code or
diagnostic codings.
Q: Can ECG hardcopy records already recorded, but lacking a study protocol, be coded by
the Minnesota ECG Coding Center?
A: Yes, all paper records can be coded with standard measurement codes, despite varying or absent
aquisition protocols.
Q: Do extant ECG recordings need to be mounted in a particular manner before
submission to the Service Center?
A: Yes or No, the mounting can be done by either the client or the Service Center.
Return to MN ECG Coding Home
MN ECG Coding Manual
Contents
Download the Minnesota Code Classification
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What is the Electrocardiogram or
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ECG?
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ECG Leads
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Measuring Devices
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Q-QS Waves (1-Codes)
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Frontal Plane QRS Axis (2-Codes)
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High R Waves (3-Codes)
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ST Segment Depression (4-Codes)
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and Negative T-Waves (5-Codes)
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Atrioventricular (A-V) Conduction Defects (6-Codes)
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Intraventricular Conduction Defects (7-Codes)
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Arrhythmias (8-Codes)
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Miscellaneous Codes (9-Codes)
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Exact Measurements
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Coding the Whole ECG
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ECG Data Acquisition Procedures
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Criteria for Significant ECG Pattern Change
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Quality Control
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Appendix- Minnesota Code 1982
The Minnesota Code Manual presents a systematic, objective measuring system for electrocardiographic
findings in clinincal trials and population studies of cardiovascular disease. The current edition published
in 1982 classifies endpoints of clinical trials and characterizes arrhythmias and conduction defects. This
edition also provides standard procedure for the codes application by trained medical or technical
personnel. In addition, it is used by experienced investigators to teach measurement and coding of the
ECG in the Core ECG Lab.
The Minnesota Code Manual of Electrocardiographic Findings constitutes an essential source of reference
for clinincal trials and population-based cardiovascular studies.
New Edition
In the late 1990s work began on revision of the current Manual of Electrocardiographic Findings. The
Second Edition will be updated and expanded to include Serial Change criterion, the use of Computer
Analysis and a Tutorial Edition. The format media is also under review and expected to include hardcover
as well as CD ROM.
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Download the Minnesota Code Classification
Studies Using the MN ECG
The Minnesota Central ECG Laboratory was the core ECG center of numerous clinical trials and
epidemiologic studies.
These trials and studies ranged from international multicenter complex efforts (40,000 plus participants)
to simple local trials.
National/ International
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ALLHAT Atrial Fibrillation Study
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the Anemia Study
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Anti-Lipid Lowering Heart Attack Trial (ALLHAT)
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Australian National Blood Pressure Study (ANBPS)
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Atheroclerosis Risk in Communities Study (ARIC)
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Beta Blocker Heart Attack Trial (BHAT)
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Boston Health Care Project (BHC)
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Budapest WHO Test ECG Coding
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Cardiovascular Disease among Seattles Japanese (NDP)
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Center for Disease Translation Study (CDT)
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the China 1990 Study
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Community Diabetes Project (RTI)
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Comparison of ECG Algoritms for Ischemic Endpoints Study
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Coronary Artery Risk Development in Young Adults (CARDIA)
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Coronary Drug Project (CDP)
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Coronary Risk in Seniors Program (CRISP)
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Chicago Western Electric (CHE)
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CVD Risk Factors and Brain Morphology in NHLBI Twins (TWINS)
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Diabetes Control and Complications Trial (DCCT)
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Diabetes Prevention in Yupik Eskimos (ESKIMO)
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Early Treatment of Diabetic Retinopathy Study (ETDRS)
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Enhancing Recovery in Coronary Heart Disease (ENRICH)
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Epidemiology of Diabetes Intervention and Complications (EDIC)
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Evans County and Charleston Heart Studies
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Gaurdian ECG Minnesota Code Analysis (GAURDIAN)
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HDL Intervention Trial (HIT)
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Healthy Heart Study (HHS)
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Heart Rate Variability and Survival after MI Study
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Hip Fracture Study (HIP)
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Hypertension Control Program (HCP)
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Hypertension Detection and Follow-up Program (HDFP)
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Indian Heart Study
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Inter-Tribal Heart Project (ITHP)
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the Kronhort Study
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Lipid Researech Centers Study (LIPID)
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Lorsartan Intervention for Endpoint Reduction in Hypertension Project (LIFE)
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Lorsartan NIDDM Endpoint Study
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Lorsartan Post MI Study
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Meharry Cohort Study (MCS)
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Mexico City Diabetes Study
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Miami Senior Health Trial (MSHT)
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Multiple Risk Factor Intervention Trial (MRFIT)
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Munich Transit Worker Cardiovascular Risk Factor Intervention Study (GERMANY)
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National Health and Nutrition Examination Study (NHANES)
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National Hypertension Study (NHP)
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Nicotine Patch Study (NPS)
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Normative Aging Study (NRM)
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New York Bridge and Tunnel Workers Study (BNT)
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New York State MI Validation Study
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NIDDM Primary Prevention Trial
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Occupational Exposure Study
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Otsego-Schoharie Healthy Heart Program (OSH)
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Pawtucket Heart Health Program
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Pfizer/Parke-Davis TNT Program (GDXI)
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Poland Study- Warsaw and Cracow
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the Precursors Study
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Prevention of High Blood Pressure in Children Study (PHBPC)
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the Reaven Study
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Renal and Cardiovascular Disease in Navajo Indians with Type II Diabetes (NAVAJO)
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Renal Protective Effects of Lorsartan Study
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San Antonio Heart Study
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San Luis Valley Diabetes Study (SLV)
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Scandinavian Simvastatin Survival Study (4S)
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Seven Countries Study, 9 Hypertension Control Program (HCP)
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the SHEPII Study
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Should We Emergently Revascularize Occluded Coronaries for Cardiogenic Shock (SHOCK)
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Sodium-Potassium Study in Children (NAKS)
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Solomon Island ECG Study
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the Southeastern Kidney Council Study
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Spinal Cord Injury and Carsiovascular Disease Study
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Stanford Heart Disease Prevention Program (STANFORD)
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Strong Heart Study (SHS)
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Systolic Hypertension in Elderly Program (SHEP)
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Tamoxifen and Risk of Subsequent Thrombembolic Disease (TKP)
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Tiawan- case control study of myocardial ischemia and injury (TIAWAN)
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Treatment of Mild Hypertension Study (TOMHS)
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the Trichlorotrifluorethane Study
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VA Collaborative Study on Insulin Dependent Diabetes
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VA Cooperative 344 Study
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Vascular Disease in Women Study
Local/ Regional
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Mayo Clinic Study (MAYO)
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Minnesota Heart Health Program (MHHP)
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Minnesota Heart Survey (MHS)
https://docs.google.com/document/d/1iNzZ0S0GaI5X7LjHSPYdyKrEzSir45R15r7lACxZkqQ/edit
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Stratis Health Acute MI Validation (STRATIS)