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Joo et al. Vessel Plus 2018;2:2 I http://dx.doi.org/10.20517/2574-1209.2017.36 Page 3 of 8

[39]
populations . Furthermore, OPCABG is associated with improved resource utilization and increased cost-
effectiveness [36,40] .

However, the relative merits of OPCABG and on-pump CABG remain debatable and there has been
[41]
national decline in the utilization of OPCABG . Randomized trials have demonstrated that short-term
death or complications within a month of surgery occurred at similar frequency, but long-term mortality
and complications occurred similarly if not at higher rates in patients undergoing OPCABG [42,43] . Meta-
analyses have also failed to demonstrate any significant benefit of OPCABG in mortality rates and showed
comparable organ protection to conventional methods [44,45] .

Another aspect of understanding the comparative advantages of OPCABG [46,47] is that patients who require
intraoperative conversion from off-pump to on-pump surgery or abortion of the OPCABG procedure
have poorer outcomes compared to patients undergoing successful OPCABG or on-pump operations [48-51] .
Additionally, patients who underwent OPCABG generally had fewer anastomoses than their on-pump
counterparts, limiting the conclusions that can be drawn about OPCABG in patients with multiple targets
and raising concerns about the completeness and effectiveness of revascularization in OPCABG [39,52] .

There are limited data regarding primary OPCABG for the treatment of ACS. In two studies, mortality was
lower in off-pump vs. on-pump procedures (5% vs. 24%, P = 0.015 and 3.5% vs. 5.4%, P = 0.690) [53,54] . Additionally,
a European study with a cohort of 624 patients demonstrated that stratification and preselection of patients, as
well as the timing of the intervention, are crucial considerations for ensuring that only appropriate candidates
undergo and derive benefits from the procedure . An updated algorithm to stratify patients and better address
[55]
the issue of conversion from off- to on-pump CABG has been put forth, which may help to reduce the frequency
of off-pump to on-pump conversion in ACS patients [54,56] .

OTHER POTENTIAL SURGICAL INTERVENTIONS
It has been approximately two decades since several groups first described endoscopic techniques for
less invasive, closed-chest totally endoscopic coronary artery bypass (TECAB) with the da Vinci robotic
system [57,58] . After a multicenter trial showed promising results, the US Food and Drug Administration
approved robotically-assisted TECAB for non-emergent left internal mammary artery to LAD myocardial
[59]
revascularization . Subsequently, there has been interest both in traditional arrested-heart TECAB with
cardiopulmonary bypass and in beating-heart, off-pump TECAB with the use of endoscopic stabilizers.
Although issues have been raised regarding technical challenges and conversion rates [60-62] , there are also
data that suggest that with appropriate techniques and experience, excellent graft patency rates can be
[63]
achieved .
More recent advancement in this field is hybrid coronary revascularization (HCR), a procedure that combines
PCI with OPCABG via minimally invasive entry through an anterolateral thoracotomy . In patients with
[64]
multivessel and left main disease, HCR has been shown to be comparable to OPCABG performed via
midline sternotomy with respect to short- and mid-term outcomes, without significant differences in repeat
revascularization rates [64,65] .

Although no study has specifically examined the use of TECAB or HCR in the treatment of ACS, they
may be alternative techniques to consider as the technology continues to advance and additional data are
gathered regarding their outcomes and safety. Currently, only a few medical centers worldwide perform
robotic TECAB due to the high complexity of operations, corresponding long learning curves and lack of an
endoscopic surgical tradition . Therefore, more evidence is needed to quantify the benefits of HCR as an
[66]
emerging procedure for ACS.