Approaching revascularization in a patient who previously underwent percutaneous coronary intervention (PCI) always involves a level of complexity when determining the optimal revascularization strategy. The technology for percutaneous coronary interventions has evolved significantly in recent decades, much more than surgical techniques. Although surgery has undergone refinements to improve both the safety and quality of revascularization, it is likely that many cardiac surgeons are not fully familiar with the implications of percutaneous coronary revascularization.
Briefly, once the lesion to be treated is crossed, either through simple guidewire passage or via complex procedures for highly calcified or tortuous occlusive lesions (such as subadventitial dissection or rotational atherectomy), the goal is to remodel the vascular lumen to restore patency. Balloon angioplasty was the preferred procedure for non-occlusive coronary lesions for many years. However, the advent of stents improved angiographic outcomes by reducing acute/subacute vessel occlusions and restenosis. This is because stents significantly reduce early elastic recoil and prevent dissection, thereby ensuring an excellent immediate outcome and mitigating late elastic recoil.
Any intraluminal injury results in neointimal proliferation, leading to lumen reduction. This phenomenon occurred with balloon angioplasty but is even more pronounced with the mechanical injury caused by the stent against the vessel wall, which paradoxically may counteract the effect of maintaining the coronary lumen over the long term. In this context, drug-eluting stents (DES) represented a significant advancement, as the uncoated stent mesh (bare-metal stent, BMS) is covered by a polymer that carries an antiproliferative drug, released gradually over time. These new devices reduced neointimal hyperplasia, showing significantly better angiographic and clinical outcomes compared to their predecessors.
However, the initial enthusiasm surrounding DES was somewhat dampened by findings that they did not reduce thrombosis risk. According to Moussa et al.’s 2020 study, thrombosis occurred in about 10% of cases, even with DES, especially beyond the first year after implantation. This risk was partly attributed to delayed stent endothelialization due to the antiproliferative agents. Despite being an infrequent complication, its clinical implications were substantial, as 25% of these patients experienced severe myocardial infarction. Thus, efforts shifted toward the parallel development of potent antiplatelet therapies. First, P2Y12 receptor inhibitors such as clopidogrel were introduced, followed by prasugrel and ticagrelor, and eventually, cangrelor, a parenteral agent with an ultra-short half-life, replaced IIb/IIIa glycoprotein inhibitors (abciximab, tirofiban, and eptifibatide).
Subsequent modifications to DES led to numerous clinical trials with each new product, primarily involving changes to the drug agent (from paclitaxel to sirolimus and more recently to everolimus, zotarolimus, or biolimus) and the stent mesh, with cobalt-chromium and platinum-chromium alloys providing greater radial strength and more adaptable, thinner, and flexible structures. Recently, the pursuit of a balance between intimal hyperplasia control and mechanical remodeling led to the development of bioresorbable stents and those without permanent polymers. The former use polylactic acid mesh that dissolves after two years, aiming to restore vascular function without permanent foreign materials; however, they have not met the desired clinical outcomes. Stents without permanent polymers, on the other hand, have found a more promising clinical niche and are directly applicable to surgical revascularization. Their rapid bioabsorption or absence of a permanent polymer reduces the impact on elective or deferred urgent revascularization scheduling. These stents can carry an antiproliferative drug on a short-duration biodegradable polymer, limiting the initial hyperplasia response while enabling faster endothelialization, which in turn allows for reduced intensity of antiplatelet therapy and fewer thrombotic events.
Given all these considerations, the presence of previous stents in coronary arteries should influence the surgical approach in three main aspects:
- Nature of the Stents: As previously indicated, the type of stent—either DES or BMS—has crucial implications for clinical outcomes, which will be discussed in the study analyzed below.
- Time Elapsed Since Implantation: This is particularly important concerning the minimum duration of dual antiplatelet therapy, assessing the risk-benefit balance of suspending such treatment, the need for bridging therapy with cangrelor (discontinued between 1 and 12 hours before surgery), and the continuation of therapy postoperatively. These decisions should be made jointly by cardiologists and surgeons within a Heart Team setting.
- Angiographic Study: Proper identification of the distal territory supplied by the stented vessel, as well as its location, is essential. Evaluating the quality of the distal vessel for grafting is also important. Some authors have described techniques involving anastomosis by removing previously implanted stent segments. We believe this approach yields poor outcomes, and it is preferable to select territories involving native vessels, even if it means grafting more distally. Careful handling of the heart during surgery is also crucial to prevent distortion, which could result in new lesions, particularly in vessels not intended for treatment. Evaluation of in-stent restenosis (ISR) should be exhaustive, and if there is any doubt, intermediate lesions should be assessed using intravascular imaging (IVUS or OCT). Lastly, the presence of polymer within the arterial lumen could cause late endothelial toxicity, chronic inflammation, fibrin deposits, or even neoatherosclerosis, all of which could negatively impact the distal vascular bed.
The study at hand stands out for its originality as it aims to challenge a previously widely accepted paradigm. This is a comparative study with a control group, where patients undergoing surgical revascularization are evaluated regarding the grafting of previously stented vessels with nonsignificant stenosis (equal to or less than 49%). Historically, a fundamental principle of coronary artery bypass grafting (CABG) was the requirement of significant stenosis for grafts to function effectively and have adequate durability, both in the short term and during follow-up. This was due to the phenomenon of competitive flow, in which the absence of significant pressure drop across lesions without significant stenosis could result in inadequate graft flow due to a lack of a sufficient gradient between proximal and distal portions, ultimately leading to graft failure—manifesting differently depending on whether the graft was venous (thrombosis) or arterial (string sign).
The study selected 52 patients who had undergone prior percutaneous revascularization with a stent placed in the right coronary artery (RCA) or circumflex artery. Of these, 24 patients received bypass grafting to the previously stented vessels, using saphenous vein grafts, despite the vessels being patent. In the remaining 28 patients, no bypass grafting was performed distal to the stented segments. Patients with additional concomitant surgeries other than revascularization (due to potential graft distortion from greater cardiac manipulation) and those with two or more stents in different vessels were excluded. However, patients with multiple stents in the same vessel were included. Dual antiplatelet therapy was discontinued in 20 patients—16 with BMS after six weeks (implanted for recent acute coronary syndrome) and four with DES after one year of treatment. All patients received bridging with low molecular weight heparin (LMWH), and aspirin (ASA) was continued in every case. Postoperative bridging with LMWH was provided, and dual antiplatelet therapy was gradually reinitiated for at least one year.
Angiographic assessment of stent and graft patency was performed primarily through CT coronary angiography, with a median follow-up of 49 months for patients without bypass and 53.5 months for those with bypass. In 18 patients, a repeat catheterization was required due to recurrent angina or new acute coronary syndrome (ACS), and the opportunity was taken to assess the patency of both stents and bypass grafts instead of utilizing CT coronary angiography.
The study groups were comparable. No perioperative mortality occurred in either group, with a single case of late death due to a brain malignancy. In the group without bypass, 71.4% of non-grafted vessels remained patent in the native bed, whereas in the group with bypass grafting, 95.8% of the vessels remained patent distally (considering the native bed/stent and/or graft), with a statistically significant difference of p = .02. Although there was no significant mortality, morbidity was greater in the non-bypassed group, affecting 42.8% of patients compared to 25% of those who received bypass grafting. Morbidity was primarily related to the need for additional revascularization procedures.
Furthermore, differences were found in the analysis of patency between stents and bypass grafts in vessels with patent stents. For stents alone, 71.4% remained patent without grafting compared to 66.7% with bypass grafting. Occlusions primarily occurred in BMS (43.75%), which only occurred in 10% of DES. For bypass grafts, 91.6% remained patent, unaffected by the supposed phenomenon of competitive flow. The interaction between bypass grafts and stents was notable: the occlusion rate for different stent types was significantly influenced by whether they were bypassed or not—75% occlusion for non-bypassed BMS versus 30% for those bypassed; for DES, no occlusions occurred in non-bypassed stents, while 50% of the bypassed stents (2 out of 4) were occluded.
Although the study has several limitations that will be addressed later, the authors conclude that in patients with patent stents undergoing surgical revascularization, the strategy of leaving stented vessels ungrafted appears acceptable for DES but may not be safe for BMS.
COMMENTARY:
The analyzed study likely raises more questions than it answers, representing one of those original works that inspire not only further research in the field but also a reflection that might explain its findings. The results obtained seem to contradict the principles of surgical revascularization. However, they may be influenced by different factors that could even be considered biases within the study design.
Aside from the fact that the study uses a small sample size with limited statistical power, the first point that stands out is the low volume of DES implanted—accounting for less than half of all implanted stents—despite the study covering the period between 2015 and 2020. Secondly, there was also an imbalance in the distribution of BMS and DES between the two groups: only 4 out of 20 DES were bypassed compared to 20 out of 32 BMS. The study was non-randomized, and patients for whom bypassing patent stents was selected were mostly those with BMS. It is well-known that BMS outcomes are significantly inferior to those of DES, which could explain the favorable patency results for the distal vessel and lower rates of repeat revascularization when stents were covered by grafts.
Thirdly, a bias could have been introduced in assessing preoperative stenosis severity, as only simple angiography was used. Given the number of BMS, the extent of ISR might have been underestimated, particularly since ISR is more common in BMS than in DES. Thus, patients selected for bypass may have had significant ISR, while others were left uncovered and likely contributed to the postoperative coronary events. Indeed, in terms of patency, DES outcomes were noteworthy, with the majority remaining patent without bypass grafting. Hence, more than expanding the grafting of BMS, the takeaway is the need for a diagnostic study that leaves no room for doubt, using IVUS or OCT for any ISR of uncertain significance. This measure would effectively reduce future morbidity and mortality associated with new ACS.
Regardless, the surgical revascularization of patients who previously underwent percutaneous coronary interventions remains a therapeutic challenge, with ongoing uncertainty about the best management strategy. The outcomes for these patients are notably poorer compared to those without prior stent implantation. This is because, even considering that revascularization decisions may have been made outside current guidelines, these patients typically have more complex coronary artery disease, a longer disease progression, and likely have already experienced an acute coronary syndrome (ACS) that led to the percutaneous revascularization. In terms of surgical revascularization, factors such as the loss of proximal vascular territory or the distal bed disease resulting from drug release from the permanent polymer of DES may be major obstacles to successful surgical intervention. In this respect, stents without permanent polymers fit perfectly into a context of sequential revascularization following ACS.
Once again, studies like this remind us that the treatment we offer our patients is the product of a collaborative effort between cardiologists and surgeons, utilizing two therapeutic options that each have their indication and timing within the natural history of coronary heart disease—in this case, ischemic heart disease. Interference is inevitable, but above all, an adequate study and discussion of the best therapeutic management typically leads to the best outcomes. To that end, joint assessment of angiographic findings, completion of the study with functional or intravascular diagnostics in case of doubt, and optimal antiplatelet therapy strategies are all critical aspects. Thus, the simplistic message that might be drawn from this study—grafting all previous BMS regardless of their patency—could be seen as negligent and unacceptable within modern, responsible clinical practice.
In this way, this study, while providing evidence that grafting patent stented vessels (especially BMS) might be beneficial, also highlights the nuanced decision-making required in each case. Particularly, it emphasizes the importance of individualized patient care based on thorough assessment, advanced diagnostic tools, and, whenever possible, the collaborative decision-making process of a Heart Team to tailor the strategy to each patient’s unique condition.
REFERENCE:
Basgöze S, Sen O, Güner Y, Zihni Duman M, Karacalilar M, Demirel A, et al. The fate of patent stents in patients undergoing coronary artery bypass grafting. EJCM. 2023;11(22):60-69. Doi: 10.32596/ejcm.galenos.2023.2023-01-03
