Complete Revascularization in Coronary Artery Bypass Grafting: Separating the Wheat from the Chaff

Abstract

Coronary artery bypass grafting (CABG) has been established as the most effective treatment for patients with multi-vessel coronary artery disease. To maximize outcomes by restoring perfusion to the largest possible myocardial territory, complete revascularization (CR) has long been a key objective of CABG. Because the anatomic severity of coronary artery stenosis on coronary angiography has been the main criterion for selecting target vessels for several decades, the definition of CR has traditionally been based on angiographic anatomy. Numerous studies have examined the impact of anatomic CR on outcomes after CABG; however, the results remain controversial. At the same time, there has been increasing interest in ischemia-inducing coronary artery stenosis assessed by functional studies such as dobutamine-stress echocardiography, nuclear imaging tests, fractional flow reserve, and quantitative flow ratio. This has raised the importance of defining CR based on functional ischemia rather than anatomic stenosis. Nevertheless, only a few studies have reported the impact of functional CR on CABG outcomes. Therefore, this narrative review summarizes the various definitions of CR in CABG, highlights its benefits and shortcomings, and introduces the available literature evaluating the effects of anatomic and functional CR on long-term clinical outcomes.

Introduction

Coronary artery bypass grafting (CABG) has been shown to be the most effective treatment for multi-vessel coronary artery disease, with advances in surgical strategies over several decades [1-4]. Several factors contribute to the favorable long-term outcomes of CABG compared with other options such as percutaneous coronary intervention (PCI) or optimal medical therapy. These include (1) the excellent long-term patency of the left internal thoracic artery, which is usually anastomosed to the left anterior descending artery supplying a large myocardial territory, and (2) the high rate of complete revascularization (CR) [5,6]. Achieving CR has long been regarded as a fundamental goal of surgical revascularization [7,8], and this is a major reason why current guidelines recommend CABG over PCI for patients with ischemic cardiomyopathy [9]. In such patients, restoring perfusion to as much myocardium as possible may be the most critical determinant of improved myocardial function and clinical outcomes. However, previous observational studies have reported conflicting results regarding the impact of CR on CABG outcomes [10-13].

Therefore, this narrative review was conducted to summarize the definitions of CR, discuss its benefits and limitations, and present the available literature evaluating its impact on outcomes after CABG.

Definition of complete revascularization

Since the 1990s, various definitions of CR have been proposed (Table 1). Because the anatomic severity of coronary artery stenosis based on angiography has traditionally determined target vessels for myocardial revascularization [14], definitions of CR have largely relied on angiographic findings (anatomic CR). Classically, CR was defined as grafting all diseased coronary vessels, referred to as “numerical CR.” More commonly, anatomic CR has been defined as placing at least 1 bypass graft on each diseased coronary territory. In addition, studies have applied different cut-off thresholds for defining significant stenosis. Reported diameter stenosis thresholds for major coronary arteries and their branches include 50%, 70%, and 75% on visual estimation, whereas all studies consistently used 50% for left main lesions [13,15,16]. For target vessels, the usual size threshold in CABG is ≥1.5 mm in diameter, which is smaller than that for PCI, typically ranging from 2.25 to 3.0 mm [16-18].

Table 1.

Definitions of complete revascularization in coronary artery bypass grafting

Category	Modality	Definitiona)
Anatomic CR	Coronary angiography	At least 1 target vessel in each diseased territory is revascularized
	Coronary angiography	All diseased target vessels are revascularized
Functional CR	Myocardial SPECT or DSE	At least 1 or all target vessels in each ischemic myocardial territory are revascularized
	FFR or QFR	All functionally significant target vessels are revascularized

CR, complete revascularization; SPECT, single photon emission computed tomography; DSE, dobutamine stress echocardiography; FFR, fractional flow reserve; QFR, quantitative flow ratio.

^a)Target vessel is defined as diameter stenosis of ≥50%, ≥70% or ≥75% for 3 major coronary artery or their major branches, and ≥50% for the left main lesions, with a threshold of diameter of 1.5 mm.

Although most studies have used anatomic definitions to analyze the impact of CR on CABG outcomes, discrepancies between the anatomic severity of stenosis and the presence of functional ischemia in the corresponding myocardium have been observed [14,19]. Consequently, the importance of CR guided by functional ischemia rather than by anatomic stenosis has been increasingly emphasized [20,21]. Conventional diagnostic methods for myocardial ischemia include treadmill testing, dobutamine stress echocardiography, and nuclear imaging studies such as myocardial single-photon emission computed tomography (SPECT) and positron emission tomography. A limitation of these modalities is their ability to assess ischemia only at the level of myocardial segments or major coronary territories, rather than at the level of each major vessel or branch. With the advent of tools to directly measure the functional significance of individual target vessels, such as fractional flow reserve (FFR) and quantitative flow ratio (QFR), these have been widely adopted in clinical decision-making, particularly in PCI [9,22]. However, studies applying these tools to define functional CR in CABG remain limited, and the evidence regarding the comparative impact of functional ischemia-guided versus angiography-guided CABG on clinical and angiographic outcomes is not yet conclusive [23,24].

Benefits and shortcomings of complete revascularization

Theoretical benefits of anatomic CR include (1) improved clinical outcomes by reducing or eliminating myocardial ischemia, (2) enhanced exercise capacity, (3) a reduced risk of arrhythmic events, and (4) greater tolerance to future acute coronary ischemic events [6]. These advantages, however, come at the cost of longer operative times, the need for additional conduits, and higher early postoperative risks [25].

In contrast, functional CR allows surgeons to defer stenotic lesions that do not cause functional ischemia in the corresponding myocardium. The theoretical advantages of functional CR are: (1) fewer distal anastomoses required, (2) simplified grafting strategy with more efficient use of conduits, (3) a higher likelihood of achieving off-pump CABG by avoiding technically challenging but functionally insignificant moderate lesions, and (4) prevention of future adverse events associated with flow competition and low wall shear stress, which can accelerate atherosclerotic plaque formation [26,27]. Critics argue, however, that deferring lesions based on functional assessment may allow disease progression during follow-up, potentially leading to adverse events, whereas graft occlusion rarely causes significant clinical consequences [23,28]. This traditional surgical belief requires further validation, as a recent meta-analysis suggested that bypass grafts to functionally insignificant vessels are more prone to flow competition, resulting in low wall shear stress. Such hemodynamic changes may accelerate atherosclerotic plaque progression in both the grafted vessel and the corresponding native coronary artery [27,29].

Impact of anatomic complete revascularization on outcomes after coronary artery bypass grafting

A seminal study from the Coronary Artery Surgery Study (CASS) registry first emphasized the importance of anatomic CR in patients with multi-vessel disease undergoing CABG [30]. This study included 3,372 patients with 3-vessel disease and demonstrated that patients with severe angina derived survival and event-free survival benefits from CR during 6 years of follow-up. Among patients who achieved CR, outcomes did not differ between those who received 3 grafts and those who received more than 3. Conversely, among patients with incomplete revascularization (ICR), those with only 1 graft had lower survival and event-free survival rates compared with those receiving 2 grafts. Subsequent studies confirmed the clinical importance of anatomic CR in CABG [10,11]. However, other reports presented contradictory findings [12,13]. For example, 1 retrospective analysis of 1,914 patients with multi- vessel disease included 514 who underwent CABG [13]. In this study, anatomic CR—defined as revascularization of all diseased vessels ≥1.5 mm in diameter—was achieved in 344 patients (67%). At 5 years, all-cause mortality was higher in patients with CR (13.2%) than in those with ICR (9.6%), although the difference was not statistically significant (p= 0.260).

Beyond anatomic complete revascularization

Although many studies have defined CR as the placement of at least 1 bypass graft in every diseased major coronary artery system, a recent study argued that this definition may be insufficient to achieve optimal outcomes after CABG [31]. The authors screened 1,070 patients who underwent off-pump CABG for 3-vessel disease and in whom the conventional definition of anatomic CR was met. After excluding 67 patients with only 3 target vessels, 1,008 patients were enrolled and categorized into 2 groups: the MD group (829 patients with more than 3 distal anastomoses) and the 3D group (179 patients with only 3 distal anastomoses). Inverse probability treatment weighting-adjusted multivariate analysis demonstrated a significant difference in long-term survival, with 10-year all-cause mortality rates of 34.9% in the MD group and 41.9% in the 3D group (p= 0.047) (Fig. 1). This finding highlights the importance of placing as many grafts as possible, even beyond the traditional definition of anatomic CR. These results appear to contradict the earlier CASS registry findings [30], which reported no outcome differences between patients with 3 versus more than 3 grafts. However, the CASS study lacked detailed data on whether additional potential target vessels were left untreated in patients who received only 3 grafts, limiting direct comparison.

Fig. 1.

Significant difference in the cumulative incidence of all-cause mortality (A) and cardiac death (B) between 829 patients who underwent coronary artery bypass grafting with more than 3 distal anastomoses (the MD group) and 179 patients who had 1 distal anastomosis in each coronary territory (the 3D group). The inverse probability of treatment weighting-adjusted multivariate analyses showed significant differences in these incidences between the 2 groups. Reprinted from Cho H, et al. Ann Thorac Surg 2025;119:546-54 [31], with permission from Elsevier.

Functional complete revascularization matters

Previous studies have demonstrated discrepancies between the functional significance of coronary artery stenosis and its anatomic severity. Since earlier studies showed better outcomes with functional ischemia-based PCI compared with angiography-guided PCI, the importance of functional assessment of coronary stenosis has been emphasized in the PCI field. The concept of functional CR in CABG has also been derived from this principle. However, only a few studies have evaluated the impact of functional CR on outcomes after CABG [20,21]. One retrospective study used myocardial SPECT data to identify ischemic major coronary artery territories [20]. In this study, functional CR was defined as at least 1 graft to each ischemic coronary artery territory, based on the most common definition of CR. Among 1,162 patients, functional CR was achieved in 1,077 (92.7%). The authors reported that functional completeness of revascularization (hazard ratio, 1.54; 95% confidence interval, 1.08–2.22; p=0.019), as well as established baseline factors including age, underweight status, diabetes mellitus, chronic kidney disease, chronic obstructive pulmonary disease, and left ventricular dysfunction, were significantly associated with long-term survival (Fig. 2). Another study employed QFR to identify ischemia-inducing target vessels [21]. Among 2,655 patients enrolled in a randomized controlled trial [32], QFR values were available in 2,024 patients. Target vessels were defined as those with ≥50% diameter stenosis, a reference vessel diameter of ≥1.5 mm by visual assessment, and a QFR ≤0.8. Functional CR was achieved in 1,846 patients (91.2%), while 178 patients had ICR. The results showed that functional ICR significantly increased the risk of 12-month major adverse cardiac or cerebrovascular events (hazard ratio, 2.91; 95% confidence interval, 1.56–5.43; p=0.001).

Fig. 2.

Risk factor-adjusted curve from a Cox proportional hazards model showing overall survival between 85 patients in the functional incomplete revascularization (FI) group and 1,077 patients in the functional complete (FC) revascularization group. Reprinted from Sohn SH, et al. Ann Thorac Surg 2023;115:905-12 [20], with permission from Elsevier.

Conclusion

CR has long been a central goal of CABG and represents 1 of the most important theoretical advantages of CABG compared with PCI or medical therapy. Although controversies remain regarding the definition of CR and its precise impact on CABG outcomes, current evidence suggests that achieving CR may improve long-term clinical results after CABG. Future studies should aim to identify the optimal definition of CR that maximizes clinical benefit for patients with ischemic heart disease while avoiding unnecessary increases in surgical risk.