The Coronary Artery Surgery Study (CASS). A critical appraisal

The applicability of the Coronary Artery Surgery Study (CASS) to clinical practice is seriously hampered by the following findings. (1) The CASS randomized study applies to only a small minority of patients with coronary artery disease. Attempts to extend the conclusions of CASS to the vast majority of patients with coronary artery disease are unjustified. (2) The high percentage of crossover of the medical group made it impossible for CASS to accomplish its primary goal of contrasting medical and surgical treatment. (3) Despite the fact that crossover of medically assigned patients created a bias against surgical treatment, the observed mortality in the surgical group was still 31% lower than that in the medical group. (4) The failure of CASS to find this difference to be statistically significant must take into account the fact that the statistical power of CASS was so low that a real difference was likely to be overlooked. (5) The conclusion that patients similar to those in the study may safely defer operation is unwarranted and violates the principles of prospective study design. In addition, CASS failed to address the possibility that deferring operation may compromise long-term survival.