Continuing Education Activity

Orbital atherectomy (OA) is an adjunctive therapy used for lesion preparation of calcified plaque with percutaneous coronary intervention (PCI) and peripheral percutaneous endovascular interventions. The goal of lesion preparation with OA is to modify calcified plaque, changing lesion compliance to allow adequate balloon and stent expansion in segments with heavily calcified lesions. This activity highlights the role of the interprofessional team in evaluating and improving care for patients undergoing this procedure.

Objectives:

• Describe the pathophysiology of coronary artery calcification.
• Outline the indications for orbital atherectomy.
• Identify the common complications of orbital atherectomy
• Describe the procedural technique for performing orbital atherectomy.

Introduction

Orbital atherectomy (OA) is an adjunctive therapy used for lesion preparation of calcified plaque before percutaneous coronary intervention (PCI) and peripheral percutaneous endovascular interventions. The goal of lesion preparation with OA is to modify calcified plaque, which changes the lesion compliance and allows for the adequate balloon and stent expansion in segments with heavily calcified lesions.

Coronary artery disease (CAD) has a significant impact on overall health and continues to grow in prevalence in the United States. Data from the American Heart Association states that greater than 15.5 million people over age 20 have significant CAD.[1] The deaths due to cardiovascular disease have also steadily increased since 1990 [2], with nearly 650,000 deaths due to cardiovascular disease in 2019.[1] In patients with advanced CAD, coronary artery calcification (CAC) is associated with increased atherosclerosis and potential future cardiac events.[3] 

CAC is believed to be both gender and age-dependent. The prevalence of CAC in individuals over age 70 has been estimated to be greater than 90% in men and 67% in women.[4] CAC is better detected using intravascular ultrasound (IVUS) or optical coherence tomography (OCT) compared to coronary angiography. A previous study in patients with known CAD demonstrated that coronary angiography could detect coronary calcium in 38% of lesions versus 73% utilizing IVUS.[5] As intravascular imaging modalities are underutilized, CAC is likely underestimated in the general population.[3]

As CAD prevalence increases, the incidence of CAC follows a similar trend. Previous studies have shown that those patients with severe CAC have more complex and worse outcomes when undergoing percutaneous intervention (PCI) than patients with low CAC.[6][7] The importance of recognizing CAC is rooted in previous studies demonstrating technically more challenging cases of PCI, as well as worse outcomes. Two different meta-analyses have revealed that severe coronary calcium is associated with less complete revascularization, increased mortality, increased rate of myocardial infarction (MI), and increased rate of coronary revascularization.[8][9] The noted worse outcomes in patients with severe coronary calcium are multifactorial but are likely strongly associated with poor balloon expansion resulting in incomplete stent expansion and coronary calcium damaging stent polymer coating, decreasing efficacy.[10][11][12] 

To help decrease complication rates and improve stent deployment in patients with severe CAC, utilization of OA can be of significant benefit for vessel preparation and stent placement. In this manuscript, we provide a review of OA and the available devices, techniques, indications, complications, contraindications, and clinical trial outcomes based on the most recent data.

Anatomy and Physiology

Calcified coronary plaques pose numerous challenges to successful PCI, often prohibiting stent delivery or inhibiting complete stent expansion.[13][14] PCI of calcified lesions in which there is incomplete expansion is associated with worse long-term outcomes.[6][15][16] CAC is known to negatively affect vascular anatomy, resulting in decreased vascular compliance, decreased/atypical vasomotor responses to stimuli, and impaired oxygen delivery to the myocardium.[17] 

Vascular calcification is a complex and dynamic process for which the pathophysiology is not completely understood. Previous theories have been based on calcium/phosphate imbalance, circulating nucleation complexes, apoptotic bodies, and bone formation, while more recent studies have proposed microRNAs may play a role as regulators of vascular smooth muscle cells.[4][18] 

Though the exact pathophysiology of CAC remains unknown, certain risk factors have been associated with more severe and advanced CAC. Coronary calcification can occur in both the tunica intima and tunica media, but calcification of the media is believed to be more associated with cardiovascular events.[4][19] 

The most common risk factors for CAC include smoking/tobacco use, obesity, hypertension, diabetes mellitus, advanced age, chronic kidney disease, male gender, and Caucasian race.[1][3][18][10] These risk factors for CAC are continuing to rise in prevalence in the United States based on the Heart Disease and Stroke Statistics-2019 Update.[1]

Indications

For coronary arteries, orbital atherectomy (OA) is indicated to facilitate stent delivery in patients with known severely calcified coronary artery lesions who are candidates for percutaneous transluminal coronary angioplasty or stenting. The Orbital Atherectomy System has the Food and Drug Administration (FDA) approval to treat severely calcified coronary artery lesions.[3] Situations in which to consider the use or OA is dependent on the thickness and severity of calcification. Previous studies have suggested that lesions with calcium thickness < 0.24 mm are likely to fracture and can be treated with balloon angioplasty before stent placement.[20] Similarly, lesions with a calcium score of 4 or more are at increased risk of the stent under expansion.[21] In either case of increased calcium thickness or score, atherectomy before stent placement may be beneficial for successful stent placement.[22]

Though there are no further manufacturer indications, the clinical application may be extended to other situations given the crown size and the ability to adjust ablation diameter. Potential situations to utilize OA include severely calcified lesions in a patient with multi-vessel disease, lesion preparation for bioresorbable scaffold placement, unprotected left main disease, ostial lesions, and chronic total occlusions.[23] Further trials and data will be necessary to determine further clinical indications and situations for which OA will be an indicated therapy.

Contraindications

Orbital atherectomy (OA) is contraindicated in the following conditions:

1. Unable to pass the guidewire  across a lesion
2. The lesion is within a graft or stent
3. The patient is not a candidate for atherectomy, coronary angioplasty, or bypass surgery
4. The patient has evidence of thrombus on angiography
5. The patient has a multi-vessel disease with only one open coronary vessel
6. There is evidence of coronary dissection on the angiogram
7. The patient is pregnant
8. The patient is a child[3][24] 

Other warnings and precautions for consideration before utilizing OA include:

1. Very tortuous vessels which are at increased risk for vessel damage
2. Treating lesions in the right coronary or left circumflex regions as there is an increased risk for heart block and need for temporary pacing
3. On-site and available cardiothoracic surgery staff if needed
4. Patients with heart failure and reduced ejection fraction less than 25%[3]

Equipment

The orbital atherectomy system (OAS) comprises the following components:  coronary orbital atherectomy device (OAD), orbital atherectomy system pump, coronary guidewire, and lubricant. The OAD consists of a sheath-covered drive shaft, a 1.25/1.50 mm crown that slides over the VIPERWIRE coronary guidewire, a crown advancer knob, and a saline tubing connection to the OAS pump. A tableside motor handle controls crown rotation speed, guides crown advancement, and contains the guidewire brake leaver.[3]

A minimum size 6 french guide or larger is needed for the use of the OAS. The lubricant combined with saline is attached to the pump and must always be utilized during OA to help reduce the risk of thermal injury and potential heart block.[24] The saline flow rate is controlled by the pump and is approximately 18 ml/min, but can be increased throughout the procedure as needed.[3] The device setup is efficient and can be assembled in minutes by an experienced operator.[25]

Personnel

A cardiac team made up of interventional cardiologists, cath lab technicians, nurse practitioners/provider assistants, and cardiac catheterization laboratory are necessary to allow for the best possible outcomes for patients undergoing orbital atherectomy (OA). Cardiac catheterization technicians and nurses need to be available for patient check-in and laboratory testing, intra-procedure vitals monitoring, and post-procedure to evaluate the patient for any new symptoms, evidence of hemodynamic instability, or procedural complications. 

During OA, the procedure is performed by an interventional cardiologist using a single-operator technique.[25] Before using the coronary orbital atherectomy system (OAS) in the United States, the user must complete a training and certification program. Certification requirements include the completion of online training modules as well as a minimum of six proctored cases. Depending on experience, a preceptorship course may be required.[23]

Preparation

A thorough review of the patient's past medical history, surgical history, medications, and allergies is imperative to optimize outcomes. A critical review of previous cardiac imaging and tests, including electrocardiograms, echocardiograms, stress tests, and past angiograms, helps to delineate coronary anatomy in preparation for the planned intervention. Understanding any previous interventions is essential for planning before the procedure. Based on patient anatomy and the proceduralist's personal preference, an arterial access site should be chosen before starting the case. All personals who will be in contact with the patient must scrub using sterile technique. After necessary members have been donned in sterile gowns and gloves, and a time-out has been conducted, the orbital atherectomy (OA) procedure can begin.

Technique or Treatment

Before starting, the procedural team should gather all necessary equipment (coronary orbital atherectomy system, guide catheter, IV pole, normal saline, and fluoroscopy imaging equipment), set up the OAS pump to an IV pole with the saline level sensor connected, and a stiff coronary guidewire prepped for insertion.

With all equipment assembled and personal in place, the atherectomy procedure can be initiated. Start with obtaining arterial vascular access using a 6 Fr sheath or larger using the provider's preferred approach. Access the lesion with a guide catheter, and use angiography, IVUS, or OCT to localize and evaluate the target lesion. Once located, cross the lesion with the coronary guidewire. Prepare the lubricant, connect the OAD to the OAS, and prime the pump. Before inserting the OAD into the vessel, perform testing to ensure appropriate crown advancement via advancer knob and crown rotation using the on/off button. Verify the flow of saline with crown rotation. Ensure the brake lever is open, and advance the OAD drive shaft over the guidewire. Using fluoroscopy, advance the crown to approximately 10 mm proximal to the target lesion. Verify the OAD distal tip is beyond the lesion. Press down on the brake lever to engage the brake and press the on/off button to activate crown rotation at low speed (80,000 rpm), which can be verified via the LED light on the OAD.

Advance the crown to begin atherectomy via the advancer knob no faster than 1 mm per second. Once the crown is orbiting, maintaining continuous movement is important as remaining in one location can cause damage to the coronary vessel. Under fluoroscopy, ensure the crown and crown advancer knob move in a 1 to 1 fashion. Perform a series of intermittent treatment intervals back and forth across the lesion, followed subsequently by a rest period with the crown on the proximal side of the lesion.

Each rest period should be of equal length or greater than the treatment time. A maximum recommended treatment interval is 30 seconds (the OAS pump will emit a beep after 25 seconds of treatment time). If the desired result is not observed at low speed, consider high speed (120,000 rpm) if no tortuosity is identified and vessel size is adequate.[3][22][23]

Due to wear that can result in the equipment, the maximum treatment time per OAD is 5 minutes. The OAD does not keep track of treatment time; thus, this should be timed by a team member during each procedure. Lastly, a replacement bag of saline and lubricant should be readily available if needed during complex procedures. Following the completion of OA to the target lesion, lock the control, and then the OAD can be safely removed from the vessel. Evaluate the lesion with a balloon for complete expansion. If balloon under-expansion is noted, further runs of OA may be needed for particular lesion segments. Alternatively, intravascular imaging can be used to assess the treatment of the target lesion before stent placement.[22]

Complications

Orbital atherectomy (OA) has been demonstrated to be a safe and effective device in both clinical studies and all-comer real-world registries.[26][27][28][29] Complications have been reported to be low in high-risk patient cohorts and lesion sub-types including females, diabetics, elderly, and patients with chronic kidney disease, low ejection fraction, previous coronary artery bypass grafts, subtotal occlusions, left main coronary artery lesions, aorto-ostial lesions, bifurcations, and small coronary vessels.[30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]

The most commonly reported complications associated with orbital atherectomy include dissections, slow or no-reflow, and perforations. In the ORBIT I trial involving 50 patients, there were six coronary dissections without clinical sequelae and only one perforation. There was no noted incidence of slow flow or distal emboli.[48] Similar results were noted in the much larger ORBIT II with 443 patients enrolled, with rates of dissection, perforation, and no flow being 3.4%, 1.8%, and 0%, respectively.[49] 

A transient heart block is uncommon with orbital atherectomy, but bradycardia has been observed. In a 2017 study by Lee et al. involving 50 patients, 4% experienced bradycardia, none of which required pacemaker implantation.[50][51] 

Rare complications have been reported and include pseudoaneurysm and dislodged microtip.[52][53][54][55] A more recent review using the MAUDE database revealed 317 submitted cases in which there was device failure. The most common device malfunctions included detachment/separation of pieces and device structural damage. Structural damage was reported involving the following components: crown, body, and tip of guidewire tip, driveshaft tip, and driveshaft body.[56]

Clinical Significance

The utilization of atherectomy has been increasing but remains low compared with the prevalence of heavily calcified lesions.[57] The first study in humans was ORBIT I, a nonrandomized study with 50 patients that evaluated the safety and feasibility of orbital atherectomy (OA) to treat de novo heavily calcified lesions.[48] In this study, procedural success was 94%.[22] This was followed by the ORBIT II trial, a multicenter, prospective, open-label trial with 443 patients. The study lacked a control arm as no other device had FDA approval for lesion preparation for comparison. ORBIT II's primary endpoint was measured as a 30-day major adverse cardiovascular event (MACE). Following OA, 89.6% had freedom from 30-day MACE (95% CI 86.7%-92.55%). The in-hospital MACE, 1-year MACE, and 3-year MACE were 9.8%, 16.4%, and 23.5%, respectively.[48][58][26] The MACE results in ORBIT II were lower at three years compared to two years in the ROTATAXUS study, in which patients underwent rotational atherectomy (RA).[26][59] Given the results of ORBIT II, OA gained FDA approval in 2013.

Despite the success seen in the ORBIT II trial, multiple high-risk groups were not included: patients with unprotected left main disease and those with ejection fraction < 25%. These high-risk individuals were included in a 2018 study, including all patients undergoing OA at three separate institutions. One year following OA, 87.3% had not experienced a MACE or cerebrovascular event, demonstrating that OA is an option for treatment in patients with severely calcified and complex coronary anatomy.[28]

Since the advent of OA, there have been questions on the economic value of atherectomy and preparation of calcified lesions before PCI. This was addressed by performing a cost savings analysis using the ORBIT II data and comparing it with medicare provider analysis and review (MedPar) data. In the study, the first significant finding was the decrease in the index procedure cost of $3590 per patient. This was considered to be due to decreased average length of stay for patients in ORBIT II (1.8 days vs. 4.24 days). The second major finding was a decreased procedure-related readmission rate for coronary artery bypass surgery at one month in ORBIT II compared with MedPar data, resulting in a decreased cost of $704. In total, the combined savings per patient was $4294 in patients undergoing OA.[60][61][24]

Given the outcomes of the ORBIT II and real word multicenter trials, larger trials are needed to evaluate the utility of OA in patients with severe coronary calcification. This is being addressed in the ongoing evaluation of treatment strategies for severe calcific coronary arteries: orbital atherectomy vs. conventional angioplasty technique, before implantation of drug-eluting stents: ECLIPSE trial. This is a multicenter, randomized control since 2017, with an estimated end date in February 2022. Primary endpoints include the final minimum stent area after the procedure via OCT and target vessel failure.

Enhancing Healthcare Team Outcomes

Undergoing cardiac catheterization is a common yet complicated procedure in which complications can be life-threatening. As orbital atherectomy (OA) is still a relatively new procedure, no guidelines are written that incorporate its use by the major governing bodies in cardiology. To help optimize outcomes, especially when implementing a new procedure, utilizing an interprofessional healthcare team is paramount. While the interventional cardiologist is significantly involved when the patient is in the catheterization laboratory, an entire team is necessary from beginning to end to help minimize poor outcomes.

Based on the 2016 SCAI expert consensus statement for best practices in the cardiac catheterization laboratory (CCL), a multidisciplinary team made up a cardiologist, cardiac trainees, cardiothoracic surgeons, an anesthesia provider for cases involving more than moderate sedation, provider assistants/nurse practitioners, registered nurses, and catheterization laboratory technicians are required to help ensure the success of any procedure.[62] It is recommended that 1 or 2 CCL staff are always present at tableside, with at least two additional CCL staff available for monitoring, recording, providing moderate sedation, and circulating.[Level 5]

With further complexities in patient care, incorporating medical teams from multiple disciplines will be essential to ensure the best care possible and improve outcomes for patients. The Heart Team has well exemplified this, first described by Holmes et al., and has now been included in the European Society of Cardiology and American College of Cardiology/American Heart Association guidelines.[63][64] [Level 5] With this multidisciplinary approach being a class I indication, it has been proven safe and efficacious when initiated at various institutions.[65][66] [Level 1]

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Disclosure: Justin Shipman declares no relevant financial relationships with ineligible companies.

Disclosure: Pradyumna Agasthi declares no relevant financial relationships with ineligible companies.