The COMPASS study was designed to assess the benefits of antithrombotic therapy in the postoperative period of coronary surgery patients. It included 27,395 patients from 83 centers across 22 countries. Three groups were compared: aspirin (ASA) + rivaroxaban, ASA + placebo, and placebo + rivaroxaban. The study was terminated early after a 23-month follow-up due to demonstrated benefit of dual therapy in reducing primary endpoint events: a composite of all-cause mortality + new stroke + new myocardial infarction (HR = 0.76; p < 0.01). However, these results have had limited impact on clinical practice.

The proposed sub-analysis aimed to utilize the study protocol with patients randomized between weeks 4 and 14 to assess one-year graft patency via CT angiography. Thus, 1,142 patients and 3,480 individual grafts were analyzed (with a 20% follow-up loss). Angiographic graft failure was defined as stenosis >75%, string sign, and/or occlusion. With this, an ambitious set of answers was pursued to guide optimal revascularization strategies for multivessel disease, within the range of technical possibilities available. Findings for each graft type were analyzed:

• Left Internal Mammary Artery (LIMA): Results for non-anterior territories or alternative configurations were limited, as 98% were anastomosed to the left anterior descending artery (LAD) and 91% were used in situ. The failure rate was the lowest among all grafts (6.4%), doubling when LAD proximal stenosis was <90% (4.7% vs. 8.2%).
• Radial Artery (RA): The failure rate was the second lowest at 9.9%. The primary limitation was competitive flow, with better patency when anastomosed to territories with >90% lesions (6.8% vs. 13.3%). Outcomes were better in the circumflex artery (Cx) territory compared to the right coronary artery (RCA) territory (6.8% vs. 21.7%), aligning with current revascularization guidelines.
• Saphenous Vein (SV): This was a surprising outcome, consistent with findings from previous studies. The failure rate was 10.4% at one year, independent of the treated vessel’s stenosis severity (> or <90%) (10% vs. 11.1%). Although the quality of venous grafts varies among patients, they were unaffected by these results at one year, though marginally influenced by the quality of the target bed (good 10% vs. acceptable-poor 13.1%) and different bypass configurations, i.e., sequential or composite grafts (9.4% vs. 14.8%).
• Right Internal Mammary Artery (RIMA): This graft showed the worst outcomes, with a 26.8% failure rate at one year. As an arterial graft, it was again affected by target vessel stenosis <90% (33% vs. 17%). While adverse outcomes were associated with its use for lateral territories, versus anterior or RCA territories (42% vs. 19% vs. 11.8%, respectively), results were conditional on use. In situ configuration (via transverse sinus) showed worse outcomes than composite configurations to another arterial graft (T or Y from LIMA or RA) or as a free graft from the aorta, which showed the best results (34.1% vs. 22.2% vs. 15.4%).

The authors concluded that results for LIMA and RA were as expected, while SV results exceeded expectations (likely due to one-year follow-up duration), at the expense of RIMA outcomes. Until further analysis identifies the factors impacting RIMA outcomes, findings should guide the use of multiple arterial grafts in multivessel disease.

COMMENTARY:

The COMPASS sub-analysis is an ambitious project, with conclusions that are thought-provoking. It has even inspired a commentary by Taggart and a rebuttal from the authors on whether the study. In reference to the name of the study, it serves as a compass for guidance, leading astray surgeons regarding graft selection.

Beyond methodological issues that may influence these results, several valuable lessons can be drawn. First, arterial grafts are sensitive to lesions <90% in any territory. This had been assumed only for RA, permitting greater flexibility with LIMA grafts. However, findings indicate that the biology of arterial grafts is similar despite differing properties. Possibly, SV is the preferred graft for intermediate lesions. Second, RIMA as an in situ graft, though attractive for proximal-mid RCA territory and exotic for the left side, is detrimental, and use as a free graft is preferable. Third, sequential versus direct grafting is detrimental for SV grafts, though insufficient data were available for arterial grafts. Despite theoretical hemodynamics (parallel resistances), poor geometry/configuration may underlie these results. However, Y or T composite configurations offer a good alternative for graft length optimization, particularly when LIMA does not reach the proximal ascending aorta. Fourth, the quality of the distal vessel affects SV and RA outcomes, while mammary arteries better tolerate poor run-off.

The study addresses various methodological comments explaining the findings. First, it is a sub-analysis of a study not designed for this purpose. The selected sample potentially could introduce biases not accounted for, such as patients’ varying antithrombotic regimens and significant follow-up losses. Second, as highlighted by Taggart: despite the multicenter approach, surgeon experience with multiple arterial grafts was limited (8%). Third, although the primary aim was to analyze one-year patency segmented by various factors, these factors interrelate, impacting other results, as seen with in situ RIMA. Fourth, statistical significance may be compromised in small subsamples due to variable atomization.

Nonetheless, this work provides valuable insights into graft configuration in multivessel disease revascularization with multiple arterial grafts. Given the multiple technical variations available for complete coronary artery revascularization using multiple arterial grafts, not all configurations can be equivalent. Findings likely depend on timing and group expertise. In each place and at each time, only by applying learned principles, common sense, and case-by-case individualization can the best revascularization strategy be offered for each patient. Radically changing techniques, especially if outcomes are within standards, would lead to unnecessary disorientation.

REFERENCE:

Alboom M, Browne A, Sheth T, Zheng Z, Dagenais F, Noiseux N, et al. Conduit selection and early graft failure in coronary artery bypass surgery: A post hoc analysis of the Cardiovascular Outcomes for People Using Anticoagulation Strategies (COMPASS) coronary artery bypass grafting study. J Thorac Cardiovasc Surg. 2022 Jun 2(22)00629-8. doi: 10.1016/j.jtcvs.2022.05.028.