Coronary Artery Surgery Study (CASS)

BACKGROUND:

Although it was generally agreed that many patients with severe angina pectoris improved symptomatically after coronary artery surgery, there was less consensus concerning, for example, other effects of the procedure, such as its long-term benefit and the criteria for patient selection. In addition, there were fewer data and less agreement on the effects and proper role of this procedure in other clinical circumstances. Both the surgical procedure and the prior diagnostic procedures represented substantial costs in both monetary and manpower terms; moreover, they entailed morbidity and mortality risks.

There existed an urgent need for reliable and quantitative information regarding the effects of coronary artery surgery in patients with ischemic heart disease. To be meaningful, these data had to be set into the perspective of the clinical course of such patients under medical treatment.

This assessment presupposed a meaningful classification of these patients and of the therapeutic interventions as well as evaluations of the effects of surgical and medical regimens in terms of mortality, the quality of life, and objective hemodynamic and other physiological measurements. Only such information could provide sufficient background for determining the suitability of coronary artery surgery for a particular patient.

In 1972, the National Heart and Lung Advisory Council identified these questions as topics of high priority, and the National Heart and Lung Institute established an Ad Hoc Policy Advisory Board on Coronary Artery Surgery to assist it in developing a program of research activities. In its report, the Board noted a 'critical need for objective data on the long- and short-term effects of coronary artery surgery.' Requests for proposals were issued to carry out the recommendations of the Board.

Planning of the trial was conducted between June 1973 and April 1975 and included protocol design, the development of a manual of operations, and a pilot study of the registry. In August 1975, registry patients' entry and randomization began at the 11 clinical centers and coordinating center. Initial projections of patient population numbers were underestimated; therefore, five clinical centers were added to the trial in 1976.

The five clinical subgroups of patients in the randomized studies included: stable angina with normal resting left ventricular function; stable angina with impaired left ventricular function; post-myocardial infarction without angina; congestive heart failure due primarily to ischemic heart disease; and patients previously asymptomatic who were discovered to have serious coronary artery disease. All of the above subgroups must have met specifically outlined clinical and angiographic criteria to be placed in the randomized subset. The other two subsets (as distinguished from subgroups) of the study included those patients who were unsuitable for randomization because surgery was the treatment of choice in the judgment of many physicians and those patients for whom medical management was the treatment of choice. The patients enrolled in both the registry and randomized trial were followed for a 10-year period. This allowed evaluation of the primary endpoints, death and myocardial infarction, and the secondary endpoints, angina, status, and quality of life.

A total of 24,959 patients were entered into the registry; 780 patients were entered into the trial. Recruitment ended in 1979. Intervention ended in June 1983. Follow-up was extended for an additional five years to June 1989. Data analysis continued through May 1995 with grant support.

DESIGN NARRATIVE:

Randomized, non-blind, sequential. Some 780 patients meeting the criteria of specific subsets based on history, physical exam, laboratory tests, catheterization, and angiography were randomized to either surgical or medical therapy. Primary endpoints included death and myocardial infarction.