Coronary Artery Calcium, Exercise Tests, and CHD Outcome

BACKGROUND:

Dramatic advances in medical and interventional treatment of clinically overt CHD have contributed substantially, perhaps predominately, to the decline over the past three decades in CHD mortality that has occurred despite relatively unchanged rates of myocardial infarction. By analogy, it is attractive to assume that substantial benefit could also be given to individuals with significant but asymptomatic coronary artery disease if only they could be accurately diagnosed. In this context, research to determine whether or not a non-invasive method like EBCT has sufficient independent predictive value for CHD events to play a useful role in this process has potentially considerable clinical and public health importance.

DESIGN NARRATIVE:

Follow-up of the 5,400 women and 12,600 men will be for an average of about 2.75 years with approximately 15,000 woman-years and 35,000 man-years of observations being available for analyses by June 30, 2000. An important strength of the study is the self-reported key health variables at baseline for all study participants. In addition, objective measures of blood pressure, total cholesterol, HDL- cholesterol, triglyceride, plasma glucose, resting and exercise electrocardiograms (ECG), maximal health rates, cardiorespiratory fitness, and other clinical and biochemical measurements are available for about half of the participants. CAC by EBCT has been associated with prevalent CHD and with incident CHD in recent small prospective studies. However, it is unclear whether CAC is predictive of MI or CHD deaths, because currently available studies had few individuals with evidence of hard CVD endpoints. The large cohort with CAC measurements provides the power to investigate an association between CAC and CHD morbidity, stroke, and all- cause mortality in terms of thresholds or dose-response effects. Exercise test results and measures of conventional CHD risk factors, including several health behaviors and biochemical markers, are available for about 50 percent of the participants. This will allow evaluation of the separate and independent predictive value of CAC and exercise test results and the combination of these two exposures in relation to study outcomes. Furthermore, CAC scores, exercise test results, and the presence of conventional risk factors will be used together to identify participants at the highest risk of developing CHD outcomes.