Outcomes of Orbital Atherectomy in Severely Calcified Small (2.5 mm) Coronary Artery Vessels

Abstract: Objectives. We evaluated the outcomes of plaque modification with orbital atherectomy followed by percutaneous coronary intervention (PCI) with small-diameter stents for severely calcified coronary arteries. Background. PCI of severely calcified lesions is technically complex due to difficulties in predilating the lesion, delivering the stent, and achieving optimal stent expansion. PCI of small-diameter vessels is associated with an increased risk of adverse clinical events. Methods. In our retrospective multicenter registry of 458 “all comers” with severe coronary artery calcification treated with orbital atherectomy, a total of 38 patients (8.3%) underwent stenting with a 2.5 mm diameter stent (small-vessel group) and 420 patients (91.7%) had a reference vessel diameter >2.5 mm (large-vessel group). The primary endpoint was the 30-day rate of major adverse cardiac and cerebrovascular events, which was the composite of death, myocardial infarction (MI), target-vessel revascularization (TVR), and stroke. Results. The small-vessel and large-vessel groups had similar rates of perforation (0.0% vs 0.7%; P=.80), dissection (2.6% vs 0.7%; P=.20), and no-reflow (0.0% vs 0.7%; P=.80). The primary endpoint was similar in both groups (0.0% vs 1.9%; P=.40), as were the rates of death (0.0% vs 1.4%; P=.40), MI (0.0% vs 1.2%; P=.50), TVR (0.0% vs 0.0%; P>.99), and stroke (0.0% vs 0.2%; P=.90). The small-vessel and large-vessel groups had similar rates of stent thrombosis (0.0% vs 1.0%; P=.70). Conclusions. Orbital atherectomy followed by stenting of small-diameter vessels appears to be feasible and safe. Further studies are needed to determine the ideal revascularization strategy for these patients. 

J INVASIVE CARDIOL 2018;30(8):310-314.

Key words: perforation, stent thrombosis

Coronary artery calcification is commonly observed in patients who undergo coronary angiography, as intravascular ultrasound (IVUS) detected the presence of calcification in 73%.¹ Percutaneous coronary intervention (PCI) of heavily calcified coronary arteries is technically challenging due to difficulties with adequate predilation, stent delivery, and achieving optimal stent expansion.² Furthermore, it is associated with an increased risk of ischemic complications, including death, myocardial infarction (MI), target-vessel revascularization (TVR), and stroke.³  

PCI of small-diameter coronary arteries is associated with worse clinical outcomes compared with larger-diameter coronary arteries.^4-6 Neointimal hyperplasia that develops after PCI is independent of reference vessel diameter, thereby leading to greater late lumen loss compared to larger-diameter vessels. As patients with severe coronary artery calcification have higher rates of restenosis, those with small vessels are particularly susceptible to restenosis. This highlights the importance of identifying optimal treatment strategies for this high-risk subset.

Orbital atherectomy is effective in modifying calcified plaque to facilitate stent delivery and expansion, potentially overcoming the technical barriers of treating such challenging lesions. The ORBIT II trial demonstrated the safety and efficacy of orbital atherectomy (Cardiovascular Systems, Inc. [CSI]) for the treatment of severely calcified coronary artery lesions at 30 days and 3 years.^7,8 A larger, real-world registry also demonstrated the safety and efficacy of coronary orbital atherectomy at 30 days and 1 year.^9,10 However, orbital atherectomy of small-diameter vessels may be under-utilized because of the potentially higher risk of coronary perforation and dissection. We report the feasibility and safety of coronary orbital atherectomy in patients with severely calcified small-diameter vessels. 

Methods

Study population. Our multicenter registry included 458 real-world patients with severe coronary artery calcification who underwent orbital atherectomy between October 2013 and December 2015 at three centers (UCLA Medical Center, Los Angeles, California; St. Francis Hospital, Roslyn, New York; and Northwell Health, Manhasset, New York).^9,10Severe coronary artery calcification was defined as the presence of radiopacities involving the vessel wall on fluoroscopy or ≥270° calcification present on intravascular imaging (IVUS or optical coherence tomography [OCT]). Patients were stratified by stent diameter. The small-vessel group (2.5 mm) included 38 patients, while the large-vessel group (>2.5 mm) included 420 patients. The institutional review board at the 3 sites approved the review of the data. 

Device description. The coronary orbital atherectomy device modifies severely calcified plaque to facilitate stent implantation and expansion. An eccentrically mounted 1.25 mm crown coated with 30 micron diamonds rotates on a 0.014˝ ViperWire (CSI) and orbits bidirectionally while expanding laterally with centrifugal force. The ViperSlide lubricant (CSI) is continuously infused through the drive shaft to reduce the friction during device advancement and minimize thermal injury during device activation. The other mechanism of action of orbital atherectomy is differential sanding of coronary calcification, in which the crown flexes away from soft, healthy tissue to minimize the damage to the media of the vessel wall.

Procedure and adjunctive pharmacotherapy. PCI was performed using standard techniques. After initial treatment at low speed (80,000 rpm), high-speed atherectomy (120,000 rpm) was performed at the operator’s discretion if the reference vessel diameter was ≥3 mm to maximize the orbit diameter and thus plaque modification. The crown was advanced at 1 mm/second and limited to 20 seconds per each pass. The choice of stent type, antithrombotic and antiplatelet regimen, and intravascular imaging was left to the discretion of the operator.  

Endpoints. The primary endpoint was major adverse cardiac and cerebrovascular event (MACCE), defined as the composite of death, MI, TVR, and stroke at 1 year. Myocardial infarction was defined as the recurrent ischemic symptoms with new ST-segment elevation or re-elevation of cardiac biomarkers greater than twice the upper limit of normal. Target-vessel revascularization was defined as repeat revascularization of the target vessel. Stent thrombosis was defined according to the Academic Research Consortium.¹¹ Baseline clinical, procedural, and outcomes data were obtained from medical chart review and entered into a dedicated PCI database.

Statistical analysis. Continuous variables are presented as mean ± standard deviation and were compared with the Wilcoxon rank-sum test. Categorical variables are presented as percentages and were compared using the Fisher’s exact test. Statistical analyses were performed with SAS Software System (SAS Institute, Inc). 

Results

Baseline demographic and procedural characteristics. The small-vessel and large-vessel groups were well matched with respect to age, gender, diabetes mellitus, chronic kidney disease, history of MI, previous PCI, and previous coronary artery bypass graft surgery (Table 1). The small-vessel group had a shorter total stent length (34.0 ± 18.3 mm vs 47.7 ± 23.7 mm; P=.02), lower total number of passes (2.6 ± 2.3 vs 4.3 ± 2.2; P<.01), lower total volume of contrast used (177 ± 75 mL vs 191 ± 83 mL; P=.02), and lower total fluoroscopy time (18 ± 13 minutes vs 23 ± 16 minutes; P=.01) compared with the large-vessel group (Table 2).  

Procedural results. The small-vessel and large-vessel groups had similar rates of perforation (0.0% vs 0.7%, respectively; P=.80), dissection (2.6% vs 0.7%, respectively; P=.20), no reflow (0.0% vs 0.7%, respectively; P=.08), and stent loss (0.0% vs 0.0%, respectively; P>.99) (Table 3). 

30-day clinical outcomes. The small-vessel and large-vessel groups had similar rates of the primary endpoint of MACCE (0.0% vs 1.9%, respectively; P=.20) as well as the individual endpoints of death (0.0% vs 1.4%, respectively; P=.40), MI (0.0% vs 1.2%, respectively; P=.50), TVR (0.0% vs 0.0%, respectively; P=.20), and stroke (0.0% vs 0.2%, respectively; P=.90). Stent thrombosis was similar in both groups (0.0% vs 0.2%; P=.90) (Table 4). 

Discussion

Orbital atherectomy appears to be feasible, safe, and efficacious in severely calcified small-diameter coronary arteries. Procedural complications and 30-day clinical outcomes were similar in the small-diameter coronary arteries compared with large-diameter coronary arteries.

Severe coronary artery disease involving small-diameter vessels is commonly observed on coronary angiography. Approximately one-third to over one-half of PCIs involve smaller coronary arteries with reference vessel diameters ranging from 2.5-3 mm.^12-16 The risk of angiographic complications including perforation and dissection is theoretically higher with severely calcified small-diameter vessels with coronary atherectomy. A rotational atherectomy burr-to-artery ratio of 1:2 is generally considered to be safe. Therefore, the smallest rotational atherectomy burr of 1.25 mm represents an acceptable treatment option for severely calcified arteries. The orbital atherectomy crown of 1.25 mm at low speed creates a larger diameter due to the elliptical orbit of the device. Orbital atherectomy advanced at 1 mm/second at low speed after 2 passes provides a maximum lumen diameter of 1.80 mm.¹⁷ One patient (2.6%) had coronary dissection in the small-vessel cohort. However, no patients with small vessels had perforation, no-reflow, or stent loss. Furthermore, no patient had an adverse clinical event. 

One potential benefit of orbital atherectomy over rotational atherectomy is that the risk of crown entrapment has not been observed with orbital atherectomy.^18-20 In severely calcified small-diameter vessels, a 1.25 mm rotational atherectomy burr is typically used. The 1.25 mm burr only ablates during forward advancement as the diamond chips are only at the distal half of the burr. If the calcified plaque is inadequately ablated during forward advancement, the burr can be entrapped in the calcified lesion during retrograde advancement of the burr due to the lack of diamond chips in the proximal half of the burr. This renders it unable to ablate during retrograde movement. Orbital atherectomy by contrast, can ablate bidirectionally, potentially reducing the likelihood of entrapment. 

There are limited data on outcomes with coronary atherectomy of smaller-diameter vessels. In the only other report of orbital atherectomy of small-vessel coronary disease, a total of 55 out of 443 patients in the ORBIT II trial had reference vessel diameters of 2.5 mm.²¹ The rates of severe angiographic complications and the primary endpoint of the composite of cardiac death, MI, and TVR at 3 years were similar in the patients with reference vessel diameters of 2.5 mm and >2.5 mm. In coronary arteries not treated with atherectomy, in-stent restenosis was higher in smaller-diameter vessels.²² Rates of in-stent restenosis were particularly high in patients with concomitant risk factors including complex lesions and diabetes mellitus. PCI with drug-eluting stents of small-diameter vessels is associated with higher rates of stent thrombosis compared to non-small vessel disease (1.3% vs 0.7%, respectively; P<.001), predominantly driven by early events.²³ Saucedo et al reported that the <2.75 mm vessel group had an increased incidence of death at 1 year (P<.01), with multivariate analysis demonstrating a stepwise increase in the risk of target-lesion revascularization (P<.001).²⁴ 

Study limitations. This was a retrospective study with a small number of patients. The limited duration of follow-up precludes adequate assessment of patency rates. No comparison with rotational atherectomy was conducted. Quantitative coronary angiography was not performed by an angiographic core laboratory. Angiographic and clinical endpoints were not adjudicated by a clinical events committee. The MI rates were likely under-estimated because periprocedural cardiac biomarkers were not obtained in all patients.  

Conclusion 

The treatment of severely calcified small coronary arteries appears to be feasible and safe. Meticulous technique is required to minimize the risk of complications due to the small diameter of the vessel. A randomized trial is needed to identify the ideal revascularization strategy for severely calcified small coronary arteries. 

References 

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From the ¹Divsion of Interventional Cardiology, UCLA Medical Center, Los Angeles, California; ²Division of Interventional Cardiology, Columbia University Medical Center, New York, New York; and ³Division of Cardiology, St. Francis Hospital, Roslyn, New York. 

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Drs Lee, E. Shlofmitz, and R. Shlofmitz report honoraria from Cardiovascular Systems, Inc.

Manuscript submitted March 19, 2018, provisional acceptance given March 26, 2018, final version accepted April 5, 2018.

Address for correspondence: Dr Michael S. Lee, UCLA Medical Center, 100 Medical Plaza, Suite 630, Los Angeles, CA 90095. Email: mslee@mednet.ucla.edu