Regression of coronary disease after bypass surgery: Urban myth or common finding?

How to deal with nonsevere stenoses in coronary artery bypass grafting - a critical perspective on competitive flow and surgical precision

PURPOSE OF REVIEW

For invasive treatment of coronary artery disease (CAD), we assess anatomical complexity, analyse surgical risk and make heart-team decisions for percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG). With PCI, treating flow-relevant lesions is recommended, and reintervention easily treats disease progression. For CABG, some stenoses may only be borderline or nonsevere despite a clear surgical indication. As reoperations are not easy, the question on how to address these lesions has been around from the start, but has never satisfactorily been answered.

RECENT FINDINGS

With a new mechanistic perspective, we had suggested that infarct-prevention by surgical collateralization is the main prognostic mechanism of CABG in chronic coronary syndrome. Importantly, the majority of infarctions arise from nonsevere coronary lesions. Thus, surgical collateralization may be a valid treatment option for nonsevere lesions, but graft patency moves more into focus here, because graft patency directly correlates with the severity of coronary stenoses. In addition, CABG may even accelerate native disease progression.

SUMMARY

We here review the evidence for and against grafting nonsevere CAD lesions, suggesting that patency of grafts (to moderate lesions) may be improved by increasing surgical precision. In addition, we must improve our ability to predict future myocardial infarctions.

Resilience of the Internal Mammary Artery to Atherogenesis: Shifting From Risk to Resistance to Address Unmet Needs

Fueled by the global surge in aging, atherosclerotic cardiovascular disease reached pandemic dimensions putting affected individuals at enhanced risk of myocardial infarction, stroke, and premature death. Atherosclerosis is a systemic disease driven by a wide spectrum of factors, including cholesterol, pressure, and disturbed flow. Although all arterial beds encounter a similar atherogenic milieu, the development of atheromatous lesions occurs discontinuously across the vascular system. Indeed, the internal mammary artery possesses unique biological properties that confer protection to intimal growth and atherosclerotic plaque formation, thus making it a conduit of choice for coronary artery bypass grafting. Its endothelium abundantly expresses nitric oxide synthase and shows accentuated nitric oxide release, while its vascular smooth muscle cells exhibit reduced tissue factor expression, high tPA (tissue-type plasminogen activator) production and blunted migration and proliferation, which may collectively mitigate intimal thickening and ultimately the evolution of atheromatous plaques. We aim here to provide insights into the anatomy, physiology, cellular, and molecular aspects of the internal mammary artery thereby elucidating its remarkable resistance to atherogenesis. We propose a change in perspective from risk to resilience to decipher mechanisms of atheroresistance and eventually identification of novel therapeutic targets presently not addressed by currently available remedies.

Arterial Grafts for Coronary Bypass

Observational and randomized evidence shows that arterial grafts have better patency rates than saphenous vein grafts (SVGs) in coronary artery bypass grafting. Observational studies suggest that the use of multiple arterial grafts is associated with longer postoperative survival, but this must be interpreted in the context of treatment allocation bias and hidden confounders intrinsic to the study designs. Recently, a pooled analysis of 6 randomized trials comparing the radial artery with the SVG as the second conduit and the largest randomized trial comparing the use of single and bilateral internal thoracic arteries have provided apparently divergent results about a clinical benefit with the use of >1 arterial conduit. However, both analyses have methodological limitations that may have influenced their results. At present, it is unclear whether the well-documented increased patency rate of arterial grafts translates into clinical benefits in the majority of patients undergoing coronary artery bypass grafting. A large randomized trial testing the arterial grafts hypothesis (ROMA [Randomized Comparison of the Clinical Outcome of Single Versus Multiple Arterial Grafts]) is underway and will report the results in a few years.

Atherosclerotic Plaque Regression: Cause of Bypass Graft Oclussion

We present a case of a patient who had coronary artery bypass grafting during surgery for severe aortic stenosis. Seven months after surgery the arterial graft was occluded following native coronary artery disease regression. The heart team must consider this possibility when assessing the requirement for bypass grafts in a borderline lesion.

Progression from stenosis to occlusion in the proximal native coronary artery after coronary artery bypass grafting

Coronary artery bypass grafting (CABG) is an established treatment for multivessel coronary artery disease. However, problematic situations are occasionally encountered after CABG, such as disease progression in the native coronary artery with graft occlusion, which causes difficulty in revascularization. The purpose of this study was to evaluate changes in the native coronary artery after CABG. Between 2009 and 2012 in our institution, 351 patients underwent CABG, and 768 bypass grafts were anastomosed to non-occluded coronary arteries. Of these, 489 bypass grafts had available early postoperative angiographic results (≤6 months) suitable for assessment in this study. We defined malignant graft failure after CABG to be bypass graft occlusion and de novo complete occlusion of the target native coronary artery proximal to the graft anastomosis site. In the early angiographic results, 17 grafts were occluded (17/489; 3.5 %). Two of the grafts displayed malignant graft failure (a saphenous vein graft to the right coronary artery and a saphenous vein graft to the diagonal branch) (2 of 17 occluded grafts, and 2 of 489 studied grafts). Of the patent bypass grafts, 24 involved progression to occlusion in the proximal native coronary artery (19 saphenous vein grafts, 4 left internal thoracic artery grafts, and 1 right internal thoracic artery graft). Malignant graft failure was uncommon during short-term follow-up after CABG. At the same time, disease progression in the proximal native coronary artery from stenosis to occlusion following patent bypass grafting was relatively common, especially for vein grafts.

Mid-term results of the Radial Artery Patency and Clinical Outcomes randomized trial

BACKGROUND

The radial artery (RA), as an alternative to the saphenous vein or the right internal thoracic artery (RITA) for coronary artery bypass grafting, has gained considerable interest over the years. A randomized controlled trial was undertaken to assess the suitability of the radial artery as a conduit.

METHOD

The Radial Artery Patency and Clinical Outcomes (RAPCO) trial is a double-armed randomized controlled trial comparing the RA with the free RITA in a younger cohort of patients undergoing elective coronary bypass surgery, and the RA with the saphenous vein in an older group. The trial conduit was grafted to the most important coronary target after the left anterior descending artery, which received the gold standard left internal thoracic artery. Clinical outcomes and angiographic patency up to 10 years was recorded during careful follow up, with annual clinical review and a program of randomly assigned, staggered angiography. The final trial results will be available in 2014.

RESULTS

Mid-trial results have shown equivalent survival and event-free survival and graft patency in both arms at median follow up of approximately 6 years. The demographic and clinical data, pre- and postoperative angiographic findings of the trial database have led to a number of substudies focusing on the role of lipid exposure in patency and disease progression, the fate of moderate lesions when grafted or left alone, patterns of disease regression, and patient satisfaction with graft harvest sites.

CONCLUSIONS

While the final analysis of the primary trial end points is eagerly awaited, the additional insight into the natural history of grafted coronary artery disease with modern secondary prevention will be of considerable interest.