One of the emerging revascularization strategies for advanced coronary artery disease (CAD) is hybrid coronary revascularization (HCR), which aims to maximize some of the advantages of coronary artery bypass graft surgery (CABG) and of percutaneous coronary intervention (PCI). Hybrid coronary revascularization is a strategy that combines minimally invasive CABG to the left anterior descending artery (LAD) using the left internal thoracic artery,1 with PCI using drug-eluting stents (DES) to the other coronary distributions, as clinically necessary.
However, although the results of newer generation stents are excellent with regard to in-stent restenosis and stent thrombosis, data reveal that native CAD may be exacerbated by coronary stenting2–4 and that this phenomenon is most prevalent in patients with multivessel coronary disease.5,6 Although this native coronary disease progression (NCDP) also occurs in vessels that received saphenous vein grafts, the distal target vessel location better protects against recurrent ischemia, because the quasitotality of new lesions develops proximal to the anastomotic site.7
Native coronary disease progression is of vital importance in the symptoms of patients8–10; however, there is no literature reflecting the potential interaction between HCR and NCDP. In this review, we aim to highlight considerations around NCDP and whether it should affect the decision to perform HCR.
NATIVE CORONARY DISEASE PROGRESSION
Native coronary disease progression is the presence of a new stenosis of at least 50% or more than 20% increase in stenosis or a new occlusion.11–13 Its overall incidence varies between studies, from as much as 42% to 56% progression for 2 to 5 years11,13,14 to a slow progression of 24% to 27% for 6 to 10 years.15,16 Disease progression is not merely an angiographic concern, because it accounts for recurrent angina11 and is associated with an increased risk of myocardial infarction and death.14 Notably, the Bypass Angioplasty Revascularization Investigation showed that progression of native disease was more significant in causing angina, when compared with failed revascularization.8
Although it is difficult to predict the disease progression,9,14,17 risk factors for NCDP include male sex, left main disease, peripheral vascular disease, diabetes mellitus, hypertension, hypercholesterolemia, smoking, myocardial infarction, multivessel diffuse CAD, PCI, and competitive bypass graft flow.11,13,15,16,18,19 The left coronary system is more prone to disease progression because of higher shear stresses and contractility, as well as a more complex geometry.15,20 With respect to location within an artery, the progression of NCDP is more commonly seen in proximal segments and their bifurcations.2
Several studies have attempted to better describe the natural history of NCDP. The Medicine, Angioplasty, or Surgery Study trial showed that in patients with symptomatic multivessel CAD, surgery minimized NCDP progression when compared with PCI or medical therapy.11 Among the PCI patients in the National Heart, Lung, and Blood Institute Dynamic Registry, disease progression became evident upon follow-up of initially nonculprit, nontarget lesions. The progression developed either in a different artery or in a different segment of the same artery, and its occurrence was as high as 45% of all instrumented arteries21 and occurs in a similar rate whether a bare metal stent or DES was used.22
Among patients who have undergone CABG, Dimitrova et al18 and Alderman et al19 showed that disease progression can occur in a nonbypassed territory, in patients with or without symptoms. The Clopidogrel After Surgery for Coronary Artery Disease trial,7 the German Angioplasty Bypass Surgery Investigation trial,23 and the Veterans Administration Cooperative Study16 showed that disease progression was more commonly located proximal to the graft anastomosis. Dimitrova et al18 showed that after CABG on respective territories, disease progression rate was highest in the inferior wall and was least in the anterior wall. Notably, in the Medicine, Angioplasty, or Surgery Study trial, most of the disease progression in the PCI patients was in the anterior wall.11
The substudy by Hayward et al15 from the Radial Artery Patency and Clinical Outcomes trial, as well as the study by Dimitrova et al,18 found that a radial artery graft is protective of NCDP in all coronary territories. The mechanism of protection is hypothesized to be due to the radial artery's ability to produce vasoactive and endothelial progenitor substances.18,24
The use of a multiple arterial conduit approach to coronary bypass, particularly when both thoracic arteries are used, has been shown to improve both short- and long-term survival.25–30 In addition, because the patency of the thoracic arteries is better than that of the radial artery,24 it may be hypothesized that the protective effect to the native coronaries would even be more significant than that found in the studies of Radial Artery Patency and Clinical Outcomes and Dimitrova et al.18
We can gather from these studies that any coronary intervention elicits a potential generalized inflammation in the coronary system, such that even arteries and segments that did not have an intervention may develop NCDP. Disease progression more commonly occurs in the proximal segments, which is more risky for patients who have undergone PCI, because disease in this segment compromises the rest of the distal circulation, as reflected by the higher need for repeat revascularization in PCI patients. On the other hand, NCDP in the proximal segment is less consequential in CABG because the grafts continue to perfuse the distal system. These studies also show that arterial grafts have excellent patency rates and are protective of NCDP on all coronary territories. It is therefore apparent that in an attempt to decrease angina recurrence and potentially improve survival, the arterial conduit CABG should be encouraged.
HYBRID CORONARY REVASCULARIZATION
Hybrid coronary revascularization is an approach that aims to achieve the maximum effect of revascularization in the least invasive way possible.
The 2011 Guideline for Coronary Artery Bypass Graft Surgery by the American College of Cardiology Foundation/American Heart Association defined HCR as a planned combination of left internal thoracic artery–LAD with PCI to non-LAD coronaries. There is a class IIa recommendation in cases where there are limitations to traditional CABG (calcified aorta, poor targets), a lack of suitable conduits, or an unfavorable LAD. A class IIb recommendation was given to HCR as a possible alternative to multivessel PCI or CABG to improve the overall risk-benefit ratio.31
Studies have shown that HCR provides better short-term outcomes with decreased ventilation and intensive care unit time, reduced requirement for transfusion, and shortened hospitalization. However, there has been no strong evidence on improved mortality, and late comparative outcomes are still insufficient.32–36
The SYNTAX (Synergy Between Percutaneous Coronary Intervention with Taxus and Cardiac Surgery) trial showed that quantification of coronary disease is essential in deciding whether the optimal approach is through a PCI or a CABG. It showed that severe coronary disease, as reflected by a high score (>32), is better served with surgery.37 This concept of analyzing the coronary anatomy is crucial in determining candidacy for HCR. Because HCR employs stents for revascularization of the non-LAD targets, it should be considered only for those with a low SYNTAX score (<23); otherwise, the stent is prone to restenosis and occlusion. In addition, because the propensity for NCDP is higher in multiple and diffusely diseased vessels (i.e., high SYNTAX score), it can be hypothesized that performing the PCI arm of the HCR on these diseased vessels will accelerate disease progression and thus recurrence of angina and decreased survival.
The premise for HCR is that the patency rate of the DES is equivalent to that of vein grafts.32–36 Compared with vein grafts, however, the patency rate of arterial grafts is superior. In addition, in further comparing the effectiveness of arterial grafts versus PCI-DES, Habib et al25 and Locker et al30 showed that multiple arterial bypass grafting is superior to PCI- DES with regard to long-term survival and intervention-free survival, up to at least 8 to 9 years of follow-up.
Although most of the studies available for us at present are of an observational nature, we need to take the best of it and apply it to clinical practice. With current data on the superiority of multiarterial grafting on all territories and outcomes,15,18,24–30,38–40 we recommend this approach for low- to medium-risk patients and that HCR be reserved for the high-risk patients with relatively poor long-term prognosis.
We then summarize that for high-risk patients with a low syntax score, HCR may be considered. However, for low-to medium-risk patients, with high syntax scores, and a consequent high propensity for NCDP, CABG with the use of arterial grafts may remain the most efficacious approach.
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