Coronary Artery Surgery Study - CASS


CABG vs medical therapy in stable ischemic heart disease.


To determine whether coronary bypass surgery reduces mortality and MI rates in patients with mild angina or asymptomatic patients after MI with documented coronary artery disease.

Study Design

Study Design:

Patients Screened: 16,626
Patients Enrolled: 780
NYHA Class: Class I or II
Mean Follow Up: 10 years (initial report: mean 6 years)
Mean Patient Age: mean 51 years
Female: 10%
Mean Ejection Fraction: =50%: 73.7%, not measured: 5.8%

Patient Populations:

Patients ≤65 years of age with coronary artery stenosis ≥70%.


Prior bypass surgery, unstable angina, severe angina (Class III or IV), NYHA Class III or IV heart failure.

Primary Endpoints:

All-cause mortality

Drug/Procedures Used:

CABG surgery or medical therapy.

Principal Findings:

A trend toward lower mortality observed with CABG (1.1%/yr vs. 1.6%/yr) and was strongest in patients with ejection fraction ≤50% (p = 0.085) and three-vessel disease and ejection fraction ≤50% (p = 0.063). Among patients with three-vessel disease and ejection fraction of 35%–49%, there was a significant mortality benefit evident at subsequent follow-up [12% (CABG) vs. 35% mortality, p = 0.009; see N Engl J Med 1985;312:1665). At 10-year follow-up, 40% of medical patients had undergone CABG, and there was still no overall mortality difference (medical group 21%, surgical group 18%). Among patients with an EF <50%, CABG was associated with a mortality benefit (21% vs. 39%; p = 0.01). Among 912 patients with left main equivalent disease (e.g., severe proximal left anterior descending and left circumflex disease), long-term follow-up demonstrated that CABG prolonged life (13.1 vs. 6.2 years), but not if normal left ventricular function is present (15 year survival, 63% vs. 54%; p = NS). Follow-up of more than 16 years in CASS Registry patients with LMCD showed that CABG prolonged life in most clinical and angiographic subgroups. However, median survival was not prolonged by CABG in patients with normal LV systolic function.


Coronary bypass surgery did not improve survival compared with medical therapy in patients with mild angina or those asymptomatic after MI. However, there was a survival benefit with CABG in those with an ejection fraction <0.50.


Circulation 1983;68:939-950. N Engl J Med 1984;310:750–758. Circulation 1990;82:1629-1646. 10 year data. Circulation 1990;82:1647-1658. 10 year quality of life. 4. Circulation 1995;91:2325-34. Long-term follow-up (15 years) in left main disease.

Keywords: Coronary Artery Disease, Coronary Stenosis, Ventricular Function, Left, Coronary Artery Bypass

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