**2. Hybrid coronary revascularization (HCR)**

#### **2.1. Rationale of HCR**

Despite the increasing use of percutaneous coronary intervention (PCI) for coronary artery disease during the past decade [5], coronary artery bypass grafting (CABG) remains the gold standard for multivessel coronary artery disease or left main disease [6]. A number of major trials such as SYNTAX [7], ASCERT [8], and FREEDOM [9] reported superior long-term survival rates of CABG compared with PCI.

The main factor of the superiority of CABG over PCI is the use of left internal mammary artery (LIMA) to left anterior descending (LAD) artery [10, 11]. The excellent long-term patency of LIMA to LAD graft has been established [12–14], whereas the long-term outcomes of other conduits such as saphenous vein graft and radial artery have been reported to be poorer than those of LIMA. The patency rates of saphenous vein grafts were 71–87% at 1-year after surgery in previous studies [15–17], and up to 50% at 10-years [15–19].

On the other hand, newer generation of drug-eluted stents are associated with fewer restenosis and repeat revascularization compared to conventional bare metal stents [20], and are associated with similar or even better long-term patency rates than saphenous vein grafts [11, 17, 21–23]. Thus, the combination of LIMA-LAD bypass and PCI using new generation of drug-eluting stents to non-LAD lesions takes the advantage of both procedures. The rationale of HCR is to combine the survival benefit and high patency rates of LIMA graft with the lower restenosis rates of new generation drug-eluting stents for non-LAD lesions [11, 24, 25].

#### **2.2. Indications of HCR**

HCR is applicable in patients having multivessel coronary artery disease with CABG-suitable LAD disease and PCI-suitable non-LAD disease [1, 11, 26–28]. HCR takes the most advantage in patients with comorbidities such as diabetes mellitus, obesity, chronic kidney disease, chronic occlusive pulmonary disease, and advanced age [11, 28], because these comorbidities are known to increase the risk of conventional CABG.

On the other hand, there is a couple of situations where HCR is not suitable, such as left subclavian artery stenosis, nonusable LIMA graft due to prior radiation to the left chest, intramyocardial LAD, previous stent to the target lesions, and extensive calcification on LAD [27, 29].

American guidelines for HCR demonstrate that HCR is reasonable in patients with one or more of the following: limitations to traditional CABG, such as heavily calcified proximal aorta or poor target vessels for CABG but amenable to PCI; lack of suitable graft conduits; unfavorable LAD for PCI such as excessive vessel tortuosity or chronic total occlusion with Class IIa recommendation with level of evidence of B. Also, HCR may be reasonable as an alternative to multivessel PCI or CABG in an attempt to improve the overall risk-benefit ratio of the procedures with Class IIb recommendation with level of evidence of C [3].
