Coronary artery bypass graft surgery improved survival in asymptomatic and mildly symptomatic patients with extensive coronary artery disease and LV dysfunction, but conferred no prognostic benefit in patients with preserved left ventricular function - 10 year follow-up of the Coronary Artery Surgery Study (CASS)
ACP J Club. 1991 Mar-Apr;114:37. doi:10.7326/ACPJC-1991-114-2-037
Alderman EL, Bourassa MG, Cohen LS, et al. Ten-year follow-up of survival and myocardial infarction in the randomized Coronary Artery Surgery Study. Circulation. 1990; 82:1629-46.
To assess the effectiveness of coronary artery bypass surgery combined with continued medical therapy in improving long-term (10 years) survival in patients with coronary artery disease when compared with medical therapy alone.
Randomized controlled trial of 10 years' duration.
11 clinical sites in North America.
Patients were included if they had operable coronary vessels containing at least 1 lesion of ≥ 70% luminal diameter narrowing for any vessel segment. Patients were excluded if they had previous coronary bypass graft surgery; an ejection fraction < 0.35; overt heart failure or shock as the main symptom of myocardial ischemia; left main coronary artery lesions ≥ 70%; angina severity of Canadian Cardiovascular Society class 3 or 4; or were older than 65 years of age. Of 2099 eligible patients, 780 (37%) were randomized. 2 patients were lost to follow-up.
Assignment to coronary bypass graft surgery combined with medical therapy (n = 390) or medical therapy alone (n = 390). Medical therapy comprised risk factor modification and use of anti-anginal agents as required.
Main outcome measures
Long-term survival and subsequent myocardial infarction.
6% of medically randomized patients had surgery within 6 months and an additional 34% had surgery over the next 9.5 years. No differences existed in medical compared with surgical 10-year survival (79% vs 82% P = 0.25) or percentage of patients free from death and nonfatal myocardial infarction (69% vs 66%, P = 0.41). Patients who had a normal ejection fraction and mild stable angina had longer event-free survival with medical therapy when compared with surgery (76% vs 66% P = 0.03). Conversely, patients who had an ejection fraction between 0.35 and 0.50 with stable mild angina had higher 10-year survival rates with initial surgery when compared with medical therapy (80% vs 59% P = 0.01).
No significant differences in survival and freedom from death or nonfatal myocardial infarction existed in the entire group of randomized patients when initial coronary bypass graft surgery was compared with medical therapy. Patients with normal ejection fraction and mild stable angina benefited from initial medical therapy, whereas patients with an ejection fraction between 0.35 and 0.50 with stable mild angina benefited from initial surgery.
Source of funding: The National Heart, Lung, and Blood Institute.
Address for article reprint: Dr. K.B. Davis, CASS Coordinating Center, University of Washington, 1107 NE 45th Street, Room 530, Seattle, WA 98015, USA.
Although controversy continues concerning the efficacy of coronary artery bypass surgery in prolonging the survival of patients with coronary heart disease, a number of studies have indicated that surgical intervention prolongs life in patients with left main coronary artery disease and in those with extensive multivessel disease and left ventricular dysfunction. On the other hand, use of coronary artery bypass surgery does not appear to extend survival in patients with lesser degrees of coronary vessel involvement. Aggressive mechanical interventions, including coronary angioplasty and coronary artery bypass surgery, are also being increasingly used in the management of patients hospitalized with acute myocardial infarction as a means of revascularizing the acutely ischemic myocardium; the role and proper timing of these therapeutic approaches, however, remain unclear.
The results of the well-done Coronary Artery Surgery Study (CASS) are impressive and extend our current knowledge of the risks and benefits of bypass surgery. The results show a low operative mortality, a beneficial effect on survival of coronary bypass surgery in patients with left ventricular dysfunction, (defined as ejection fraction < 50%) and comparable survival benefits from a conservative approach of medical therapy and risk factor reduction among patients with mild clinical presentations of coronary artery disease and preserved left ventricular function. However, the exclusion criteria used for trial entry (severely symptomatic coronary disease, ejection fraction < 35%, and age > 65 years) restrict extrapolation to the broader universe of patients having coronary bypass surgery. Further, the narrow focus of this report on survival should be considered in the context of relief from angina pectoris and other aspects of functional status. It should be recognized that both surgical and medical treatments have improved since the time that the CASS trial was done in the late 1970's. Widespread use of internal mammary grafts, improvements in medical therapy (both in patients with and without previous CABG) - in particular, the more extensive use of lipid-lowering interventions, and antiplatelet agents and β-blockers - as well as improved management of acute coronary syndromes (affecting overall survival) and the emergency of angioplasty as a viable revascularization option have greatly changed the overall management of patients with coronary artery disease. The 780 patients in the CASS were included in a larger meta-analysis (1) of 1324 patients enrolled in 7 similar studies. This larger meta-analysis confirms the general trend in the CASS that patients at highest risk for cardiovascular events benefit the most from bypass surgery.
Robert J. Goldberg, PhD
University of Massachusetts Medical SchoolWorcester, Massachusetts, USA