Completeness of Revascularization
A fundamental surgical tenet has been anatomic complete revascularization, namely, graft all TVECAs large enough to bypass, usually >1.5–1.75 mm in diameter, with either a >50 or >70% proximal stenosis. Failure to graft a TVECA with these criteria has been defined as incomplete revascularization, and incomplete anatomic revascularization was associated with adverse outcomes in an era where patients had much less extensive disease than currently. From a physiological perspective, leaving a major TVECA ungrafted would be expected to have an adverse outcome, as it usually meant a large area of the myocardium was left in jeopardy (Box 1).
In contrast to this initial investigation, a number of other studies failed to demonstrate a difference in mortality based on anatomic versus incomplete surgical revascularization, including the CASS registry of three-vessel disease patients, the BARI trial and the ARTS trial CABG subset.[54,55] In explaining these findings, the importance of left internal mammary artery grafting to the LAD has been implicated in a number of studies. Other factors beyond graft patency and progression of native coronary disease likely relate to the underlying status of the myocardium and the extent of SIHD, including the presence of collateral flow from prior myocardial injury. By contrast, incomplete angiographic revascularization in PCI is stongly associated with 1-year MI, ischemia-driven unplanned revascularization and major adverse cardiac events.[55,56]
This physiologic evolution in the DEFER and FAME studies have forced a functional reconsideration of the completeness of revascularization in SIHD, by differentiating the nature of TVECA stenoses into anatomic and functional categories. This differentiation makes ischemia-guided revascularization possible, but conflicts with the traditional definition of complete revascularization.
Kim et al., in an analysis of the Asan Medical Center Multivessel Registry, analyzed the impact of angiographic complete revascularization in PCI and CABG patients. Unlike many PCI analyses, they found no impact of incomplete PCI revascularization on mortality at 5 years; the outcome in CABG patients was not different between groups, but only 4.7% of three-vessel disease patients received incomplete revascularization. Since angiographic completeness did not improve long-term clinical outcomes, they interpreted these findings as supporting ischemia-guided revascularization.
Dauerman adapted the term 'reasonable incomplete revascularization' from Rastan et al., and comments that function (areas of nonviability and areas of minimal [<5%] ischemia) and physiologic FFR (>0.80) can be reasonably left unrevascularized in pursuing a general strategy of reasonable incomplete revascularization.
As mentioned, Head et al. found incomplete revascularization in 36.8% of CABG patients in SYNTAX. This surgical incomplete revascularization rate was higher than anticipated, in part because completeness of revascularization was prespecified prior to surgery. Technical and other issues discovered at the time of surgery likely led to the lower revascularization rates. Despite this, incomplete revascularization by anatomic criteria in the CABG group did not affect outcomes.
In commenting on these findings from SYNTAX, Taggart postulated that the most likely reason for incomplete revascularization during CABG is an operative finding of a small or diffusely diseased vessel that may not subtend a particularly large area of myocardium. An alternative interpretation of these SYNTAX data could be that these patients received adequate revascularization of functional stenoses, and that nonrevascularization of nonfunctional stenoses was very well tolerated physiologically in these patients. This could be because the area was not ischemic in the first place, or because through myocardial integrity components (collaterals or viability), the nongrafted area was adequately perfused. In addition, the functional revascularization completeness must have contributed to the long-term survival and freedom from MI benefit seen in SYNTAX and FREEDOM CABG patients.
Future Cardiol. 2014;10(1):63-79. © 2014 Future Medicine Ltd.