Strong Heart Study
Condition: Cardiovascular Diseases; Heart Diseases; Atherosclerosis; Asthma; Carotid Artery Diseases; Coronary Disease; Hypercholesterolemia; Hypertension; Diabetes Mellitus; Obesity
MeSH terms: Carotid Artery Diseases; Cardiovascular Diseases; Heart Diseases; Atherosclerosis; Coronary Disease; Hypercholesterolemia
Study type: Observational

Summary: 
      To determine morbidity and mortality from cardiovascular disease among American Indians and
      to compare cardiovascular disease risk factor levels among Indian groups living in different
      geographic areas.
    

Detailed description: 
      BACKGROUND:

      Available data indicate that cardiovascular disease has become the leading cause of death in
      American Indians. Some Indian groups appear to be participating in the decline in
      cardiovascular disease rates occurring within the overall United States population, but,
      among other Indians, rates appear to be increasing. In addition, there appears to be
      excessive mortality attributed to cardiovascular disease in younger Indians.

      Several problems have made it difficult to obtain adequate data on the prevalence and
      severity of cardiovascular disease as a health problem among American Indians. The small
      size, relatively young age, cultural and anthropological diversity and the geographic
      dispersion of the American Indian population have made it impractical to examine large
      numbers of subjects for research and vital statistics surveys. Excess mortality among younger
      Indians from noncardiovascular causes may have obscured the true risk of cardiovascular
      disease in this population. Definitions of the term 'Indian' are variable in published
      reports. The denominators from which disease rates were calculated often were based on
      uncertain estimates of the population at risk. Definitions of disease and methods of its
      ascertainment have varied in different studies. In addition, health care services available
      to Indians vary considerably in different geographic areas, and possibly contribute to
      differences in reported morbidity and mortality.

      States with the largest Indian populations are Arizona, Oklahoma, California, New Mexico and
      North Carolina. Because the major concentrations of Indian tribal groups in the United States
      are located in the Southwest, more than half of the reported studies of cardiovascular
      disease and cardiovascular disease risk factors have been conducted in these groups. Studies
      have been reported in the Pima, Papago, Navajo, Apache, Hopi and other tribes in the Arizona
      and New Mexico region. In general, these studies have concluded that cardiovascular disease
      rates are lower in these Indian groups than in the United States population.

      The etiology, manifestations and natural history of cardiovascular disease among Indians are
      not well known. Current information indicates 43 percent of heart disease deaths among Native
      Americans are secondary to myocardial infarction and 32 percent are due to chronic ischemic
      heart disease. Below the age of 35 years, the heart disease death rate in Native Americans
      exceeded reported United States rates. A significant portion of this excess may be due to
      congenital heart disease.

      Limited data are available on current levels and time related changes in risk factors for
      ischemic cardiovascular disease among American Indians. Because of the absence of systematic
      surveys of defined populations and the lack of standardization of methodology employed in
      studies of different groups, it is difficult to interpret apparent increases in risk factors
      over time or to explain apparent differences in cardiovascular disease rates by differences
      in risk factor distributions. Studies of current risk factor levels and distributions are of
      great importance, however, since they may provide the best estimates of the future relative
      risk of cardiovascular disease within the Indian population.

      Multiple factors may contribute to current risk factor levels in American Indians. Variations
      may exist among tribal groups, secondary to genetic admixture and to both the degree and
      duration of acculturation and in relation to attained socioeconomic status. It is important
      to recognize that generalizations about risk factors for cardiovascular disease in American
      Indians are inappropriate and that available data only apply to groups with similar origins
      and history.

      The study was recommended by the Subcommittee on Cardiovascular and Cerebrovascular Disease
      of the Secretary of Health and Human Services Task force on Black and Minority Health in 1986
      and was approved by the National Heart, Lung, and Blood Advisory Council in May 1987. The
      Request for Applications was released in October 1987 with awards made in September 1988. The
      study was renewed and expanded twice.

      DESIGN NARRATIVE:

      The study is conducted on defined populations of Indians living on reservations and involves
      two components: a review of death certificates and health care records: and a population
      survey of the prevalence of and risk factors for cardiovascular disease. The population
      survey phase consists of three examinations for cardiovascular disease risk factors, clinical
      cardiac disease, and the use of medical services for cardiovascular disease care. Elisa Lee
      of the University of Oklahoma is studying members of the seven tribes of Oklahoma. Thomas
      Welty at the Aberdeen Area Indian Health Service follows three Northern Sioux tribes. Barbara
      Howard of Medlantic studies Pima Indians from the Gila River and Salt River Indian
      communities.

      After the initial three years the Strong Heart Study was renewed to: extend surveillance of
      the community for mortality; and to reexamine the cohort after an approximate four year
      interval to assess the development of cardiovascular disease and change in CVD risk factors.
      Echocardiography and pulmonary function testing were added to the examination protocol for
      the second examination. In 1996 the study was funded to continue the follow-up for morbidity
      and mortality and to complete a third examination of the study cohort. New measures added to
      the third exam included measures of carotid atherosclerosis, arterial stiffness, a substudy
      of asthma, and a family study pilot. The third examination of the cohort was completed in
      August, 1999 with 3,200 members reexamined. In addition, more than 560 participants were
      included in the substudy of asthma. There have been approximately 1,000 deaths among cohort
      members in the 12 years since the initial examination.

      Phase IV of the study began in FY 2000 for a five-year extension to expand the family study
      and to continue morbidity and mortality surveillance of the original cohort. Each of the
      three field centers will recruit an additional 900 participants who are members of families
      containing at least two SHS cohort members. Furthermore, the pilot study family members will
      be invited to a follow-up exam after the 900 members are enrolled at each center. The Phase
      IV family study exams will include cardiac and carotid ultrasound exams, blood pressures,
      noninvasive measurements of arterial stiffness (tonometry), ECGs, anthropometry, medical
      history, behavioral assessments (socio-economic status, diet, smoking, alcohol, and physical
      activity), blood chemistries, lipids, and DNA. The specific aims of the Phase IV study are to
      expand the family study to increase the power for genetic analyses, to continue surveillance
      of the original cohort to ascertain more CVD cases, to investigate the association of some
      pertinent biomarkers and cardiac functions with the development of CVD, and to initiate
      mortality surveillance in the family members.

      The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) provided funding
      for a gallstone component.