In cases of multivessel disease, particularly with coronary occlusions, blood flow paths deviate from typical topographic routes, becoming collateral. These collateral vessels provide supplementary blood flow to regions initially served by other branches. Moreover, they sustain the epicardial vessels by retrograde filling from capillary networks, which discharge into both the venous area and the previously closed epicardial vessel due to a loss of coronary autoregulation, where the pre-capillary sphincters of the occluded vessel remain permanently open.
This collateral flow, whether homocoronary or heterocoronary, may stay compensated (chronic coronary syndrome or stable angina) or decompensate, leading to the clinical spectrum of ischemic heart disease. In compensated situations, conservative management strategies may be considered, especially in light of the ISCHEMIA study findings. Except in cases such as single-vessel patency, left main coronary artery disease, or ventricular dysfunction where revascularization provides a prognostic advantage. However, misinterpretations of this study have influenced the surgical revascularization indications in American guidelines, as previously discussed in prior blog entries.
In exacerbated disease (unstable angina and acute coronary syndrome), revascularization becomes essential when the balance between perfusion and myocardial demand is insufficient for one or more ventricular segments. Identifying the culprit vessel, assessing whether the occluded vessel contributes to the acute ischemic scenario, and selecting the optimal revascularization strategy based on coronary anatomy, technical options, clinical presentation, and surgical risk are vital.
For treating occlusive coronary lesions in multivessel disease, a debate exists: does revascularization of the remaining coronary tree sufficiently resolve ischemia by covering other regions and leveraging collateral circulation for the occluded vessel’s territory? This study examines this issue specifically for the right coronary artery territory. The controversy arises between two opposing arguments:
- Against: Coronary grafts with native flow competition, as seen with collateral supply, may impair graft patency. Additionally, it adds morbidity due to graft harvesting and may accelerate atherosclerosis in the native bed. Often, these beds are hard to evaluate as epicardial vessels appear hypoperfused or belong to regions with transmural infarcts. Thus, without viability studies, bypass may be deemed a futile effort.
- In Favor: If a preserved epicardial vessel exists, bypass grafting could logically support the myocardial territory, as achieving a nearly anatomical complete revascularization is among the best predictors of improved survival and favorable outcomes in multivessel disease revascularization.
To address this question, the outcomes of 200 patients treated from 2015 to 2022 with multivessel disease were retrospectively analyzed, including 76 with occluded right coronary arteries and 124 with significant but non-occlusive lesions. Cases involving reoperations, sequential anastomoses between the circumflex and right coronary artery, and grafts using the gastroepiploic artery were excluded to ensure series homogeneity. In most cases, independent grafts were used, primarily saphenous vein grafts for the right coronary artery, and intraoperative flow verification and postoperative dual antiplatelet therapy were administered.
No major differences were found between the groups. Patients with occluded right coronary arteries had a higher incidence of prior myocardial infarction (p = 0.015) and fewer distal anastomoses (4.0 ±0.8 vs. 4.3 ± 0.9; p = 0.036). Intraoperative flow measurements showed no significant differences (30 cc/min vs. 25 cc/min; p = 0.114), nor did pulsatility (2.1 vs. 2.4; p = 0.079) or diastolic filling indices (65% vs. 64%; p = 0.844) between the groups. Patency checks a week post-surgery revealed no significant differences between grafts in occluded and non-occluded right coronary arteries (94.7% vs. 96%; p = 0.733). When grading occlusion severity according to Rentrop classification (grade 0-1: low collateral, 32 patients; grade 2: moderate collateral, 26 patients; grade 3: high collateral, 18 patients), saphenous graft patency worsened with increased competitive flow: 96.9%, 96.2%, and 88.9% for grades 0-1, 2, and 3, respectively, though differences were not statistically significant.
The authors conclude that right coronary artery occlusions do not compromise coronary graft patency in multivessel revascularization.
COMMENTARY
This Japanese study, despite its limitations as a single-center, non-randomized, statistically limited study, seems adequate to address the previously discussed controversy: effective revascularization of multivessel disease requires anatomical completeness, including territories supplied by vessels with significant lesions, such as right coronary artery occlusions.
Therefore, the strategies commonly used in off-pump revascularization surgery, where the length of the mammary artery grafts may be insufficient to cover both lateral-posterior and inferior territories, may not be entirely appropriate. When a preserved epicardial coronary vessel is present, whether the posterior descending, posterolateral trunks, or the right coronary artery itself, bypass yields similar outcomes to vessels with non-occlusive significant lesions. Additional grafts, usually saphenous vein grafts, may be required; however, with a favorable distal bed, a radial artery may be considered for lesions >90% in the right territory. This approach may challenge the “no-touch aorta” strategy in off-pump surgery, as proximal anastomoses on the aorta may be needed. However, the authors report no stroke penalty (<2%) by following a “touch the aorta well” strategy using epiaortic ultrasonography, thus preserving revascularization outcomes.
A notable outcome is the 12% graft occlusion rate in cases with substantial collateral supply. Although speculative, based on personal experience, leaving right coronary artery occlusions untreated may be suitable in limited graft availability and preserved ventricular function cases with Rentrop 3 collateral supply and epicardial vessel diameter below 1.5 mm, formally meeting the SYNTAX criterion.
In summary, this study reinforces that, except in rare cases, “doing less is indeed the enemy of good.” Achieving perfect revascularization across all territories is key to successful multivessel disease revascularization, regardless of occlusive lesion collateral supply or myocardial viability study findings.
REFERENCE
Nishigawa K, Horibe T, Hidaka H, Numaguchi R, Takaki J, Yoshinaga T, et al. Do chronic total occlusive lesions affect patency of coronary bypass grafts to the right coronary artery? Asian Cardiovasc Thorac Ann. 2023 Nov;31(9):768-774. doi: 10.1177/02184923231205967.
