Worcester Heart Attack Community Surveillance Study

BACKGROUND:

Beginning in the 1920s, death rates from coronary heart disease in the United States rose in an unyielding fashion reaching epidemic proportions by the mid-1960s. Since that time, mortality attributed to coronary heart disease has leveled off and then turned markedly downwards. In the ten-year period between 1968 and 1978 there was a greater than 25 percent decline in the overall age-adjusted death rate from coronary heart disease, a phenomenon observed in both sexes, all age groups and in the three major race/ethnic groups. While this significant and encouraging decline appeared real and not due to artifactual changes in death certification practices, the causes of this decrease remain obscure and coronary heart disease continues as a major cause of death and disability in the United States. Internationally, inconsistent trends in mortality rates attributed to coronary heart disease have occurred. These rates declined from the early 1960s for Australia, Canada, France, Japan, Switzerland and Italy while mortality rates from coronary heart disease continued to increase from this period until the late 1970s for England and Wales, Ireland, Finland, Norway, New Zealand and Israel.

Despite this encouraging and enigmatic decline in mortality attributed to coronary heart disease in the United States and certain other countries, a paucity of population-based data exist to ascertain whether this temporal decline in death rates is due to changes in the incidence rates of new coronary events, changes in survival after an acute coronary episode or combinations thereof. These data are of crucial importance for formulating explanations for these declining mortality rates. A decline in the incidence rates of coronary heart disease would suggest that the mortality decline is due to measures of primary prevention and changes in the prevalence and/or levels of the major coronary risk factors such as, increased detection and control of hypertension, decreased cigarette smoking and declining serum cholesterol levels. If, however, the incidence rates of coronary heart disease are remaining steady or even increasing, a likely explanation of this downward trend in cardiovascular mortality would be that it is due to effort directed at secondary prevention including the establishment and more effective utilization of coronary care units, therapeutic interventions, and emergency medical services.

DESIGN NARRATIVE:

This longitudinal study examines recent (1997 and 1999) as compared to prior (1975, 1978, 1981, 1984, 1986, 1988, 1990, 1991, 1993, and 1995) time trends in the annual attack rates of acute myocardial infarction and out-of-hospital coronary heart disease deaths, recent (1997 and 1999) as well as prior (1975-1995) changes over time in the in-hospital and long-term survival rates of acute myocardial infarction, and the relationship of these incidence and survival patterns of acute myocardial infarction to selected demographic, clinical and medical care factors. The study also examines changes over time in the therapeutic management, diagnostic evaluation, and surgical workup of patients hospitalized with acute myocardial infarction, as well as related issues of cost.

The study was renewed in 1992 and again in 1997. The 1997 renewal study, carried out in 13 acute general hospitals in the Worcester Standard Metropolitan Statistical Area, used and extended previous approaches used in the conduct of the study. All new (incident) and recurrent episodes of definite acute myocardial infarction occurring among Worcester residents during calendar years 1997 and 1999 were identified from discharge diagnostic printouts obtained from all metropolitan Worcester hospitals. The medical records of these patients were individually reviewed for validation purposes according to pre-established diagnostic criteria for acute myocardial infarction. Abstraction of medical records of the patients satisfying the diagnostic and geographic eligibility criteria were carried out with the standardized recording of relevant data. A review of records for additional hospitalizations and a statewide and national search of death certificates were carried out to examine the long-term survival status of discharged hospital patients from each of the proposed study years as well as those identified previously (1975-1995) through the year 2000. Death certificates of Worcester SMSA residents were reviewed to identify cases of out-of-hospital deaths due to coronary heart disease occurring in 1997 and 1999 to determine temporal trends in these incidence rates.

The study was renewed in 2001 for five years to examine to examine recent (2000 and 2003) as compared to prior (1975 to 1999) trends in the annual attack and survival rates of AMI, out-of-hospital deaths attributed to CHD, and the relationship of these incidence and survival patterns of AMI to demographic, clinical, and medical care factors. An additional objective of this multi-hospital community-wide study is to examine changes over time in the use of selected therapies and coronary interventional approaches in patients hospitalized with AMI.