To compare the 3 - year clinical follow - up results of patients with left main bifurcation lesions treated by intravascular ultrasound(IVUS) - guided and coronary angiography(CAG) - guided percutaneous coronary intervention(PCI), and to confirm the clinical benefits of optimizing interventional therapy of left main bifurcation lesions by intravascular ultrasound(IVUS).

616 patients with primary left main coronary artery bifurcation lesions will be recruited in this study. The target lesions of patients need to be true coronary artery bifurcation lesions (Medina 1,1,1 or 0,1,1). After angiography, patients will be randomly assigned to intravascular ultrasound(IVUS) - guided and coronary angiography (CAG)- guided groups. The random number of patients will be generated by the central computer random system, and the random will be stratified according to the study sites. In coronary angiography(CAG)-guided group, two-stent technique will be used(the exact two-stent technique used was left to the operator's discretion). In intravascular ultrasound(IVUS)-guided group, minimal lumen area(MLA) in ostium of side branch will be measured by intravascular ultrasound(IVUS). If minimal lumen area(MLA)<4mm2, two-stent technique will be used(the exact two-stent technique used was left to the operator's discretion) and intravascular ultrasound(IVUS) will be repeated at the end of the procedure. If minimal lumen area(MLA) >=4mm2, one-stent technique will be used and intravascular ultrasound(IVUS) will be repeated. If minimal lumen area(MLA) in ostium of side branch is still >=4mm2, the procedure will be ended. If minimal lumen area(MLA) in ostium of side branch become <4mm2, the following interventional strategy will be left to the operator's discretion( balloon inflation, drug-eluting balloon, or switch to two-stent technique). Again, intravascular ultrasound(IVUS) will be repeated at the end of the procedure.

Inclusion Criteria:

1. Patients with stable or unstable angina pectoris, asymptomatic myocardial ischemia or attack of myocardial infarction >24 h;
2. True bifurcation lesion of left main coronary artery (Medina 1,1,1 or 0,1,1);
3. According to coronary angiography, the opening stenosis of the left anterior descending (LAD) and left circumflex (LCX) is more than 50% visually;
4. The operator judges that the lesion is suitable for drug eluting stent(DES) implantation;
5. Branch vessel diameter ≥2.5 mm by visual inspection;

Exclusion Criteria:

1. Pregnant or lactating women;
2. Combined with other diseases, life expectancy <1 year;
3. A surgery is scheduled within 6 months after the operation, and this surgery affects continuous administration of antiplatelet drugs;
4. The dual antiplatelet therapy cannot be tolerated;
5. Follow - up visits required by the protocol cannot be followed, or the investigators believe that the participation of subjects in the trial will increase the risk;
6. Unable to provide written informed consent form, or unable to follow the trial protocol;
7. Participate in another clinical trial of coronary interventional device;
8. Subjects with myocardial infarction within 24 h of onset of chest pain (including ST segment elevation or non - ST segment elevation);
9. Suffer from renal failure requiring dialysis treatment or is undergoing dialysis treatment;
10. Hemoglobin <9 g/L;
11. Uncontrolled hypertension (systolic blood pressure ≥180 mmHg or diastolic blood pressure ≥ 110 mmHg);
12. Severe cardiac insufficiency (LVEF <30%);
13. Heart failure complicated with pulmonary hypertension (mean pulmonary artery pressure(mPAP) ≥25 mmHg,pulmonary capillary wedge pressure (PCWP) >15 mmHg, and pulmonary vascular resistance (PVR)>3.0WU);
14. Complicated with hypertrophic obstructive cardiomyopathy;
15. Re-stenotic bifurcation lesion;
16. Severe calcified lesions requiring rotational atherectomy;
17. Chronic total occlusion lesion without successful recanalization;

Patients with primary left main coronary artery bifurcation lesions will be recruited in this study. The target lesions of patients need to be true coronary artery bifurcation lesions (Medina 1,1,1 or 0,1,1)

Whether to share the data will be decided by the principal investigator