The concept of complete revascularization in multivessel disease has generated substantial debate among surgical groups. Traditionally, “adequate” revascularization was considered as covering at least one vessel in each heart region. Consequently, surgery involved performing three or four distal anastomoses, largely dependent on the development level of diagonal and posterolateral branches towards the lateral and inferior walls. The definition of “complete” revascularization originated from the SYNTAX study, where it was defined as “therapeutic coverage (using stent or bypass) of any vessel >1.5 mm with >50% angiographic stenosis.” This concept had a limited impact on surgical practice, requiring only a slight increase in distal anastomoses to achieve the target. However, interventional cardiology soon recognized that attaining complete revascularization demanded excessive therapeutic efforts and overtreatment of lesions with stents, both in number and length, leading to known deleterious results. Thus, the solution to the SYNTAX revascularization criterion emerged with the advent of the pressure guide as a diagnostic tool, allowing assessment of the hemodynamic significance of lesions beyond the angiographic criterion. FFR, iFR, and other techniques became part of our vocabulary. With the FAME study validating the approach, showing better outcomes for intervention guided by functional studies compared to traditional angiography in treating multivessel disease. Meanwhile, other forms of functional ischemia assessment, such as MIBI scintigraphy or SPECT, focused on the benefits of revascularization in patients with ventricular dysfunction, though with limited success.
For a time, the percutaneous approach regained ground lost after the SYNTAX study, as certain “three-vessel” cases were managed as “two-vessel” cases until the recent FAME III study publication. This study made a significant challenge by comparing the optimized results of intervention, guided by functional analysis, against surgery guided by conventional angiography. The results, unexpectedly, showed the superiority of the surgical approach, supported by medium- and long-term follow-up from classic clinical trials (SYNTAXES, EXCEL, NOBLE, BEST, FREEDOM, PRECOMBAT). All of this ultimately reinforced coronary bypass as the excellent treatment option it is for multivessel disease, particularly in diabetic patients.
Nevertheless, the concept of revascularization in multivessel disease from a functional rather than anatomical perspective remains valid. After all, coronary lesions develop over time (metachronous) within the vascular tree, allowing for collateral circulation development between territories to compensate, even for occluded vessels. Consequently, vessel-to-territory correspondence becomes blurred, moving beyond strictly anatomical criteria. Moreover, if we consider that ischemic territories would be those fed by vessels with significant lesions, that angiographic assessment of intermediate stenoses (50-75%) is deficient, and that treating territories (percutaneous or surgical) without ischemia or significant lesion in their supplying vessel is harmful, then functional study-guided revascularization is justified.
Thus, if functional analysis can improve percutaneous revascularization outcomes, why wouldn’t it do so in surgical cases? In this regard, Sohn et al. designed this study to capture their center’s experience between 2006 and 2017 with 1162 patients undergoing coronary artery bypass surgery without extracorporeal circulation. In 1014 cases (87.3%), anatomical revascularization met the criteria, differing from the SYNTAX criterion, with coverage of any vessel with >70% lesion instead of >50%. In 1077 cases (92.7%), complete functional revascularization was achieved, covering all territories with ischemia demonstrated by preoperative SPECT. Following the center’s protocol, graft patency was checked on the first postoperative day using angiography to identify early graft failures. Follow-up was subsequently conducted at 5- and 10-year intervals, focusing on survival.
At early angiographic control, 98.8% of grafts remained patent, including arterial grafts from both mammary arteries, the gastroepiploic artery, and saphenous vein. The technique without extracorporeal circulation involved creating a Y-composite graft with the left internal mammary artery anastomosed to the left anterior descending artery, along with a second graft, primarily using the saphenous vein, followed by the gastroepiploic artery, and finally the right mammary artery. Coverage of the lateral and postero-inferior walls was achieved through multiple sequential anastomoses. Early mortality was seven patients. Of the remaining 1155 patients, late mortality accounted for 322 deaths, with 5- and 10-year survival rates of 84.3% and 66.7%, respectively. Univariate analysis showed that complete revascularization from a functional perspective significantly correlated with improved survival (p = 0.038), which was not observed for complete anatomical revascularization (p = 0.859). Likewise, multivariate analysis confirmed that complete revascularization from a functional perspective was an independent factor for better survival (HR = 1.54; 95% CI 1.08-2.22; p = 0.019).
The authors conclude that complete functional revascularization, assessed through ischemia analysis by SPECT rather than anatomic evaluation based on angiographic criteria, positively impacts long-term survival in patients undergoing coronary artery bypass surgery without extracorporeal circulation.
COMMENTARY
The work by Sohn et al. introduces a new approach to functional revascularization strategy, using ischemia analysis by SPECT rather than pressure-guided angiographic support. While this method is uncommon in our setting, it is a reasonable approach given the physiopathology of multivessel disease. Knowing which territories exhibit ischemia might be more critical than determining if the lesions in their supplying vessels are truly significant, as vessel-to-territory correspondence is not as precise in this disease. However, significant lesions require covering affected vessels, regardless of whether they exhibit ischemia in their territory, as a preventive measure against future coronary events or if they supply ischemic territory, which can sometimes be challenging to link, especially when a major branch is occluded. This explains why only a 5.4% difference existed in meeting one or the other revascularization criterion with the performed surgery, despite the perceived differences in functional and anatomical approaches. Had the anatomical revascularization criterion been set at >50% instead of >70%, these differences would likely have increased.
A second critique is that, if revascularization is considered from a functional standpoint, it would also be logical to verify revascularization effectiveness using a functional test, not solely an anatomical test like angiography, by repeating SPECT to demonstrate ischemia reversal after revascularization.
Other inherent aspects, such as early postoperative angiographic patency check, graft selection, and some notably low comorbidities (ventricular dysfunction with LVEF <35% in 14.5% of patients, COPD in 2.5%, and chronic renal failure with creatinine clearance <60 mL/kg/m2 in 13.9%), differentiate this population and practice from those at our centers.
Finally, the authors argue that there is insufficient evidence to support a revascularization strategy based on FFR analysis. Although there is limited research on the subject and no significant differences in survival, need for revascularization, or myocardial infarction between anatomical and functional approaches in most studies (e.g., GRAFFITI, FARGO, IMPAG), studies like Fournier et al. showed survival benefits, while Botman et al., Toth et al., and the FARGO and IMPAG studies showed better coronary graft patency with FFR-guided target selection compared to conventional angiography. Authors like Taggart and Fournier suggest that performing more grafts for intermediate lesion coverage only increases the use of venous grafts, which are more likely to fail in follow-up, increase perioperative morbidity, and promote atherosclerotic changes in the native coronary bed due to more turbulent flow hemodynamics that encourages endothelial dysfunction.
While more research in this area is needed, as mentioned previously, revascularization strategy is highly personalized. Functional data complement anatomical information and allow improved target vessel and graft selection, in type and number, adhering to each one’s properties and indications, thereby avoiding morbidity from unnecessary graft extractions or limited-use anastomoses. This way, the achieved revascularization may be termed anatomically or functionally complete, but it will almost certainly be “adequate.”
REFERENCE
Sohn SH, Kang Y, Kim JS, Paeng JC, Hwang HY. Impact of functional vs. anatomic complete revascularization in coronary artery bypass grafting. Ann Thorac Surg. 2023 Apr;115(4):905-912. doi: 10.1016/j.athoracsur.2022.10.029.
