The Medicine, Angioplasty or Surgery Study - MASS


Medical therapy, CABG, or PTCA for single severe proximal LAD stenosis.


Either medical therapy, or revascularization, or balloon angioplasty is more effective in the treatment for single severe proximal stenosis of the left anterior descending coronary artery.

Study Design

Study Design:

Patients Enrolled: 67800

Patient Populations:

Stable angina and single-vessel disease with at least 80% diameter stenosis in the left anterior descending coronary artery (with normal ventricular function) before the first diagonal branch.


Total occlusion
Lesion length > 12mm
Involvement of the ostium
Heavy calcification
Severe tortuosity
Stenosis of the left main coronary artery

Primary Endpoints:

Combined incidence of cardiac death, myocardial infarction (MI) or refractory angina requiring revascularization. Surgical revascularization, but not repeat coronary angioplasty, was considered an endpoint for patients assigned to coronary angioplasty.

Secondary Endpoints:

Angina functional class at the last follow-up visit, employment status, positive exercise test results two years after enrollment, and degree of atherosclerotic involvement of the coronary arteries at the 2-year angiographic study.

Drug/Procedures Used:

Medical therapy (aspirin, nitrates, beta-blockers and calcium channel blocking agents to eliminate symptoms of angina), bypass surgery (graft using the left internal mammary artery), coronary angioplasty.

Principal Findings:

Marked suppression of angina for both revascularization strategies: 98% of bypass surgery and 82% of coronary angioplasty patients were completely asymptomatic at the last follow-up visit an average of 3 years after enrollment.
In contrast, only 32% of medical treatment patients were asymptomatic at the last follow-up visit an average of 3 years after enrollment (p <0.01 for coronary angioplasty vs. medical treatment).
No patient in any randomized group had limiting angina (functional class II or IV) at the last follow-up visit.

Treadmill test:
165 patients underwent exercise treadmill tests after 2 years of follow-up. 94% of the bypass surgery group, 79% of the coronary angioplasty group, and 34% of those assigned to the medical therapy group were ischemia free (p <0.01 for medical therapy vs. both revascularization strategies).

Employment status: no difference among the groups.


Bypass surgery for stable angina and isolated, severe proximal stenosis in the left anterior descending coronary artery (with normal ventricular function) had a higher event-free survival rate. This may have been caused by a lower reintervention rate than coronary angioplasty or medical treatment alone during an average follow-up period of 3 years.

However there was significant progression of coronary atherosclerosis in non-treated vessels in all three groups.

All three groups had a similar success rate in abolishing limiting angina and an equally low incidence of death or MI during the 3-year follow-up period.


1. J Am Coll Cardiol 1995;26:1600-5. Final results

Keywords: Coronary Artery Disease, Follow-Up Studies, Employment, Angina, Stable, Disease-Free Survival, Constriction, Pathologic, Angioplasty, Balloon, Coronary, Calcium, Nitrates, Mammary Arteries, Ventricular Function, Exercise Test

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