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Elective Ostial Left Main Stenting: A Tailored Approach
March 2005
Currently, percutaneous coronary intervention (PCI) worldwide is characterized by a liberal use of coronary stents. In developed countries, the average stent use is approximately 80%.1 In the early days of stenting, unacceptable high early stent thrombosis rates were observed.2 Intravascular ultrasound (IVUS) has played a key role in improving our understanding of stent thrombosis. Routine higher pressure inflation and/or dilation with a larger balloon in order to improve stent expansion were techniques employed as practical solutions.3,4 The usefulness of IVUS to reduce restenosis is still a matter of debate — certainly in the era of drug eluting stents.4–7 Left main (LM) stenting has become a popular alternative to surgical revascularization. At present, only registry data have been published with in-hospital mortality rates varying between 0% and 12%, and target vessel revascularization rates between 15% and 17.4% at one-year follow-up.8–18 Scarce data are available on the role of IVUS in defining an accurate PCI strategy and in optimizing stent deployment in LM disease. The present series reports on the usefulness of IVUS for this indication in four consecutive patients presenting with ostial LM disease.
Methods
Four consecutive patients with highly symptomatic ischemic heart disease and the presence of significant ostial LM disease are reported. Following diagnostic catheterization, informed consent was obtained to proceed with IVUS and potentially with PCI. IVUS was performed with the In Vision Gold® system and a 30 MgH solid-state ultrasound probe with an automatic pullback system (Avanar catheter and Track Back II system, Volcano Therapeutics, Rancho Cordova, California). Prior to PCI, online measurements were performed by a second operator and the interventional strategy was adopted according to the obtained results. PCI was performed according to standard practice with 6 Fr guiding catheters. Patients received a conventional antiplatelet regimen (aspirin 500 mg and clopidogrel 300 mg) prior to the procedure that was performed under appropriate anticoagulation with heparin. Once stent placement was judged optimal by angiography, IVUS was repeated followed by post-dilation if needed. The objective was to comply with the MUSIC criteria for optimal stent expansion [which is a minimal in-stent cross-sectional area (CSA) > 100% of the distal reference vessel CSA, defined as a “healthy” segment within 5 mm from the lesion within the LM].7 Patients were kept overnight in the hospital and treated with aspirin (100 mg daily, lifelong) and clopidogrel (75 mg daily for one year). Maximal stress testing and control angiography were planned at six-month follow-up.
Results
Patient 1. A 53-year-old woman, former smoker, and hypertensive, was admitted due to progressive anginal symptoms. Angina even appeared at rest just prior to hospitalization. A critical ostial left main stenosis was present on coronary angiography (Figure 1A). IVUS demonstrated negative ostial vessel remodeling with a critical fibrotic lesion (CSA 3.2 mm2; Figure 2A) and an otherwise healthy, but relatively small distal reference segment (CSA: 7.9 mm2, MLD: 3.1 mm; Figure 2B; Table 1). A 3–8 mm sirolimus-eluting stent was implanted at 14 atmospheres. IVUS indicated suboptimal stent deployment, as the minimal in-stent CSA was only 6.4 mm2 (Figure 2C; Table 1, intermediate phase). In particular, malapposition of at least one stent strut was observed. Post-dilation was therefore performed with a short, non-compliant 3.5 mm balloon. This allowed optimal stent expansion with a minimal in-stent CSA of 7.9 mm2 (Figure 2D), and a good angiographic result (Figure 1B). Six-month angiographic follow-up showed a patent stent (MLD: 2.9 mm, % stenosis: 16%; Figure 1C). The current follow-up at 19 months reveals no particular clinical problem.
Patient 2. A 54-year-old female, hypertensive and hypercholesterolemic, was hospitalized with type-IIIB Troponin-positive unstable angina. The presence of a significant ostial LM stenosis was confirmed by IVUS. IVUS dimensions were comparable to the first patient, thus a 3–8 mm sirolimus-eluting stent was implanted at 14 atmospheres. Again, as the intermediate minimal in-stent CSA was only 5.5 mm2, post-dilation with a short 3.5 mm was performed to optimize stent expansion (Table 1). Six-month angiographic follow-up was unremarkable (MLD: 3.1 mm, % stenosis: 12%), and the patient is actually clinically asymptomatic at seven-month follow-up.
Patient 3. A 43-year-old female, with a current smoking habit and hypercholesterolemia as risk factors, was admitted with type-IIIB Troponin-positive unstable angina. Angiography demonstrated a critical, isolated ostial LM stenosis. IVUS confirmed this observation and demonstrated the presence of a large and minimally diseased distal LM with a vessel reference CSA of 11.8 mm2 and a minimal luminal diameter (MLD) of 3.9 mm (Table 1). Therefore, a 4–9 mm conventional stent was implanted at 14 atmospheres. Intermediate IVUS demonstrated incomplete stent expansion (minimal in-stent CSA of 8.1 mm2), and further post-dilation at 12 atmospheres with a short 4.5 mm balloon was needed to optimize the result. Six-month angiographic follow-up showed a patent stent with no restenosis (MLD: 3.2 mm, % stenosis: 23%). Clinical follow-up to 18 months is currently unremarkable.
Patient 4. A 53-year-old male patient was admitted because of progressive dyspnea. His past medical history revealed hypertension, type II diabetes and hypercholesterolemia. A stress test suggested myocardial ischemia, thus coronary angiography was scheduled. A striking significant ostial LM stenosis was present and IVUS was performed to prepare for a potential PCl. However, IVUS showed diffuse disease with significant plaque burden along the entire left main stem and proximal left anterior descending artery. In the absence of any suitable reference segment, PCI was abandoned and the patient was referred for surgical revascularization. Conventional bypass surgery was performed with grafting of the left mammary artery on the left anterior descending artery, and a saphenous vein graft on the circumflex branch. The patient’s clinical course was uneventful and he is presently asymptomatic at 19 months.
Discussion
PCI has become the preferred method of coronary revascularization. A growing number of patients are being treated by percutaneous means rather then by bypass surgery.19 Significant LM disease has always been considered a surgical “dogma.” Indeed, randomized trials conducted in the 1970s demonstrated the prognostic impact of surgical revascularization for this anatomical condition.20 As PCI technology developed, clinical information on percutaneous revascularization of LM disease became available. Initially, PCI was performed as a “compassionate” treatment and was reserved for poor surgical candidates. In 1989, O’Keefe et al. reported a 55% six-month mortality rate in such patients. A multi-center registry published in 1996 by Ellis and colleagues demonstrated variable outcomes depending on the baseline clinical condition.10 Good surgical candidates fared far better than poor candidates, with a one-year mortality of 16% and 70%, respectively. Interventional practice has dramatically changed since the report that indicated stent use in only 50% of patients. Several single-center and a few multi-center observations have been published in the meantime, demonstrating no in-hospital mortality following elective LM stenting in low-risk CABG patients.12–18
As elective LM stenting appears to be a safe procedure, efforts are focused on the prevention of restenosis. Drug-eluting stents have dramatically improved long-term vessel patency following PCI.21 At present, only Arampatzis and colleagues have published limited data on the efficacy of drug-eluting stents to treat LM disease. In the present paper, we strongly advocate the use of IVUS to define the PCI strategy and to guide and optimize stent placement during LM stenting — even in the era of drug-eluting stents.
First, IVUS allows precise quantification of vessel dimensions and facilitates the PCI technique. Until very recently, drug-eluting stent size was limited to 3.5 mm, and stent expansion beyond 3.7 mm was not recommend by the manufacturer. Indeed, stent oversizing could lead to strut fracture and/or inadequate drug coverage of the vessel wall. The large reference size in the second patient was incompatible with currently available drug-eluting stent sizes. Only IVUS allowed exact vessel size evaluation in this patient.
Secondly, independent of stent type, post-dilation was performed in order to optimize stent expansion. The IVUS-based minimal in-stent CSA is one of the most powerful procedural predictors of in-stent restenosis with bare metal stents.22 Again, optimal stent expansion was achieved by IVUS in the third patient. The achieved 11.6 mm2 minimal in-stent CSA predicts a restenosis rate around 4%, which compares favorably to any data on randomized drug-eluting stent trials.22 A significant increase in the minimal in-stent CSA was achieved in both patients who received a sirolimus-eluting stent. The clinical role of IVUS-based optimized drug-eluting stent expansion is currently unclear, but may prove to be important in the near future. First, a recent report by Fujii et al. showed that although related to treatment of in-stent restenosis, recurrent restenosis within sirolimus-eluting stents is mainly caused by stent underexpansion.23 In fact, even a small amount of neointimal proliferation may cause significant narrowing and lead to recurrence of symptoms. In particular, an intermediate in-stent minimal CSA of 5.5 mm2 was observed in the second patient. This seems largely insufficient and is comparable to the threshold of 5 mm2 recently suggested as the optimal value to predict target-lesion revascularization after treatment of de novo lesions with sirolimus-eluting stents at eight months follow-up.24 Another interesting observation by Lermos et al., which relates to the study population, identified ostial lesion location as an independent risk factor for restenosis following sirolimus-eluting stent placement.25 Furthermore, IVUS is the only tool to recognize any mechanical problem related to stent implantation. In the first patient, in particular, incomplete stent apposition could be identified and corrected. Finally, from a practical point of view, IVUS is the only technique that enables the operator to correctly judge stent positioning in relation to the ostium and bifurcation of the LM. This was extremely helpful in the three stented patients described in this report.
In conclusion, this clinical case series indicates that IVUS was very helpful in choosing the most appropriate interventional strategy for significant LM disease.
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