“When you cannot cross a stenosis… bypass it.” Under this principle, coined at centers such as the Texas Heart Institute, surgical revascularization—whether myocardial or for peripheral artery disease—began its promising development. Even today, one of the main advantages of surgical revascularization over percutaneous intervention lies in its capacity to address occlusive lesions by circumventing them with conduits.

A chronic total occlusion is defined as a lesion that results in 100% interruption of the vascular lumen for a duration of at least 3 months. While such lesions share atherosclerotic pathophysiology with stenotic lesions, their approach must differ. Drawing from classic surgical teaching—“if there’s a vessel, there’s myocardium”—the management of occlusive lesions hinges on assessing the viability of the downstream myocardial territory.

In stenotic lesions, persistent luminal patency and consequent antegrade flow help maintain the distal bed. Other factors such as demand-driven ischemia or myocardial hibernation may also be relevant. In contrast, in occlusions, perfusion of the territory must rely on collateral sources—either from the same vessel (homocoronary) or from another vessel (heterocoronary)—through bridging branches or recanalization that enables retrograde filling of the microvasculature and epicardial arteries. Although distal myocardial consequences can resemble those of stenotic lesions, in occlusions, the downstream vessel typically remains patent only if it supplies viable myocardium—where active microcirculation allows retrograde filling. Nevertheless, as discussed below, an overly simplistic approach to diagnosing and managing epicardial coronary artery disease likely hinders our understanding and treatment of occlusive lesions in particular.

The study in question analyzes a subanalysis of the REGROUP trial, which included 453 patients with at least one totally occluded coronary vessel at the time of surgical revascularization. The remaining 696 patients served as controls. The groups showed preoperative and periprocedural differences, and no adjustments were made. The occlusion group had lower rates of prior PCI, higher anatomical complexity (SYNTAX score), and less frequent left main disease, among other differences. After a mean follow-up of 4.7 years, rates of major adverse cardiovascular events (MACE) did not differ significantly (23% vs 22%), nor did outcomes differ between complete and incomplete revascularization among patients with occlusive lesions (23% vs 25%). Only in right coronary dominant patients did revascularization of right coronary artery (RCA) occlusions confer a survival benefit (HR = 0.38; 95% CI = 0.17–0.843), without affecting post-revascularization angina rates.

The authors conclude that in this post hoc analysis of the REGROUP study, neither the presence of occlusive coronary lesions nor achieving complete revascularization of such lesions was associated with differences in MACE rates or symptomatic outcomes. However, revascularization of RCA occlusions in right-dominant circulation might offer a prognostic benefit.

COMMENTARY:

The rationale for myocardial revascularization stems from the fact that significant epicardial lesions (>70% stenosis, or >50% in left main) create a resistance to flow that cannot be overcome either by maximal vasodilation (abolition of arteriolar resistance) or by increasing myocardial oxygen extraction, which is nearly maximal physiologically due to myoglobin’s higher affinity for oxygen than hemoglobin. Therefore, under increased oxygen demand, the only physiological means to match supply is to augment flow—failure to do so leads to ischemia. Revascularization seeks to correct this mismatch.

This model applies well in single-vessel disease or acute lesions. Yet coronary artery disease is more complex: endothelial dysfunction, non-obstructive ischemia (MINOCA), and collateral flow between territories are frequent, especially in stable multivessel disease. Hence, the strategy of treating all angiographically significant lesions does not always translate into clinical benefit. While many patients may benefit from this approach, it is not universally applicable.

These nuances help explain discrepancies between this analysis and other studies like the SYNTAX trial or the Canadian CTO registry, where complete revascularization of CTOs was associated with better survival and symptom relief.

Several limitations affect the present analysis. It is a non-randomized subanalysis of a trial designed for another purpose—comparing endoscopic vs open vein harvesting (REGROUP). The possible influence of this variable is unclear, as is the quality of the grafts used. Notably, landmark surgical trials demonstrating CABG benefit often employed open-harvested vein grafts with one-to-one graft-vessel configurations, occasionally using in situ left internal thoracic artery (LITA), and rarely composite grafting.

It is commendable that the study mentions intraoperative assessment of graft function, especially relevant when distal beds may be compromised. Treating all affected vessels does not guarantee complete revascularization (at least anatomically). In 17.6% of cases, CTO lesions were not bypassed. Even more striking, only 68% of CTO patients and 71% of controls achieved complete revascularization—both quite low figures. It is unclear whether completeness was defined functionally or anatomically, but the average of 3.2–3.1 grafts per patient suggests a functional approach. This further raises concerns about the high rate of dysfunctional grafts. Surgical practice also reflects typical U.S. patterns: on-pump CABG, bilateral ITA use in only 9–10%, radial artery use in 1%, and multiple arterial grafting in 10–11%.

The observed survival benefit in the RCA territory versus the lack of benefit in the left territories may be due to two factors: first, more effective collateralization of left territories (via both homo- and heterocoronary supply) compared to the RCA, which depends mostly on heterocoronary collaterals; second, statistical underpowering, as left system occlusions (LAD or LCx) may have been underrepresented relative to the more frequently occluded RCA.

The lack of symptomatic improvement post-revascularization may have two explanations. First, as the authors note, patients with occlusions tend to have more scarred territories and thus less angina preoperatively. Second, the overall quality of revascularization may have been insufficient to demonstrate benefit—either due to graft failure or inability to graft some CTOs.

To conclude, consider this reflection. Structural interventions have shown us that diagnostic rigor can be enhanced to improve management—moving beyond a basic echo to detailed imaging for valvular heart disease. Similarly, the failed FAME III trial, which sought to improve PCI outcomes in multivessel disease using functional assessment, hints at a need for refined diagnostics in coronary disease. At the other extreme—CTOs—few patients are referred with proper functional studies (viability testing, ischemia induction, collateral assessment with regadenoson-induced steal, etc.). This results in unnecessary morbidity from graft harvesting, longer procedures, and complex bypasses with borderline flows and pulsatility indexes as hibernating as the myocardium they aim to salvage.

For now, we should continue to treat CTOs when distal vessels are patent and of good quality—especially in the RCA territory—to achieve the most complete revascularization possible… even if it is not the perfect solution for every case.

REFERENCE:

Gikandi A, Stock EM, Dematt E, Quin J, Hirji S, Biswas K, Zenati MA. Chronic total occlusions and coronary artery bypass grafting outcomes. J Thorac Cardiovasc Surg. 2025;170:216–227.e3. doi:10.1016/j.jtcvs.2024.08.016