Noninvasive tests (as stress test, nuclear imaging, dobutamine stress echocardiography) help estimate which patients might benefit from undergoing coronary angiography. Many factors are taken into account but generally, people whose tests reviled that portions of cardiac wall receive less blood that normally should proceed with coronary angiography. There, lesions are identified and a decision is taken whether patient should undergo PCI or GABG.Generally,  CABG is preferred over PCI  when there is significant atheromatic burden on the coronaries, that is extensive and complex. According to current literature, decreased LV function, LM disease, complex triple system disease (including LAD, Cx and RCA) especially when the lesion at LAD is at its proximal part and diabetes, are  factors that point patients will benefit more from CABG rather than PCI. Acute coronary syndrome
During an acute heart event, named acute coronary syndrome, it is of vital importance to restore blood flow to the myocardium as fast as possible. Typically, patients arrive at hospital with chest pain. Initially they are treated with medical drugs, particularly the strongest drugs that prevent clots within vessels (dual antiplatelet therapy: aspirin and a P2Y12 inhibitor-like clopidogrel). Patients at risk of ongoing ischemia, undergo PCI and restore blood flow and thus oxygen delivery to the struggling myocardium. In cases where PCI failed to restore blood flow because of anatomic considerations or other technical problems, urgent CABG is indicated to save myocardium.
Significant complications of the operation include bleeding, heart problems (heart attack, arrhythmias), stroke, infections (often pneumonia) and injury to the kidneys. Uses
Coronary artery bypass surgery aims to prevent death from coronary artery disease and improve quality of life by relieving angina. Indications for surgery are based on studies examining the pros and cons of CABG in various subgroups of patients (depending on the anatomy of the lesions or how well heart is functioning) with CAD and comparing it with other therapeutic strategies, most importantly percutaneous coronary intervention (PCI). Coronary artery disease
Coronary artery disease  is caused when coronary arteries of the heart accumulate atheromatic plaques, causing stenosis in one or more arteries and place myocardium at risk of myocardial infarction. CAD can occurs in any of the major vessels of coronary circulation, which are Left Main Stem, Left Ascending Artery, Circumflex artery, and Right Coronary Artery and their branches. CAD can be asymptomatic for some time- causing no trouble, can produce chest pain when patient is exercising, or can produce angina even at rest. The former is called stable angina, while the latter unstable angina. Worse, it can manifest as a myocardial infarction, in (which the blood flow to a part of myocardium is blocked. If the blood flow is not restored within a few hours, either spontaneously or by medical intervention, the specific part of the myocardium becomes necrotic (dies) and is replaced by a scar.