Before the time of coronary artery stenting, probing for ways to overcome the deficiencies of percutaneous transluminal coronary angioplasty (PTCA) was solely based on small experiments, which demonstrated the healing response of the treated coronary vessels was equivalent to the degree of foisted damage. This result was found true on angiographic assessment, suggesting that the amount of late restenosis was dependent upon the diameter achieved during treatment. The long search for a mechanical approach to manipulate the atheromatous plaque surfaced from the hypothesis that clinical outcomes could improve by plaque excision and that it would lower the rate of restenosis after a percutaneous coronary intervention (PCI).
Coronary artery calcification increases the complexity of PCI, with less favorable results than in noncalcified lesions. Severely calcified coronary lesions increase the risk of dissection, inhibit stent delivery and adequate stent expansion, and are prone to stent mal-apposition. Various atherectomy techniques came into play at different times in history. Directional coronary atherectomy (DCA) was used in a randomized trial in 1987 for the first time. Excimer laser coronary angioplasty (ELCA) and percutaneous transluminal rotational atherectomy (PTRA) emerged later in 1988. Holmium laser angioplasty (HLA) was launched commercially in 1990, cutting balloon angioplasty (CBA) entered in 1991, and the latest ablative device, orbital atherectomy (OA), started in 2008.
For the past two decades, several mechanical approaches to ablate or section atheromatous plaque during PCI have undergone small mechanistic studies that reported promising findings. However, dozens of large clinical trials have failed to demonstrate that the strategy of plaque ablation can achieve better clinical outcomes than PTCA alone. Hence, randomized trials challenged the ablation hypothesis. Guidelines now specify that athero-ablative devices should not be used routinely during PCI.
Because PTRA confers an increased risk for complications, its use is in selective cases. Approximately 1% to 3% of coronary lesions that are crossable with a guidewire are not crossable with the balloon catheters or are un-dilatable with pressures even more than 20 atm. PTRA can be used successfully for such lesions, leading to improved compliance. This approach allows for a proper balloon dilatation and successful stent placement. PTRA is also indicated for small calcified lesions to alter the compliance of the vessel to allow balloon angioplasty.
Orbital atherectomy is also recommended for severely calcified coronary lesions, defined as severe calcification seen during fluoroscopy involving both sides of the arterial wall for at least 15 mm or the presence of at least a 270-degree arc of calcium detected on intravascular ultrasound (IVUS). In addition to OA, ELCA has shown improved outcomes for long, moderately calcified and ostial lesions, saphenous vein graft lesions, and total occlusions.
Bifurcating lesions are especially challenging for the conventional balloon angioplasty due to plaque shift and high rates of restenosis. CBA, when used for such interventions, confer lower rates of restenosis than PTCA (40% vs. 67%). The 2011 ACC/AHA guidelines give RA a class IIa recommendation in heavily calcified lesions, which may be difficult to cross or dilate.
In lesions with thrombus burden, atherectomy can result in distal embolization. Moreover, thrombi usually overlie unstable or ruptured plaques, which can dissect or perforate upon using these techniques. Spontaneous coronary artery dissections or those created by attempts at angioplasty can propagate further with rotational atherectomy. The presence of severe tortuosity may make it difficult to get the equipment close to the lesion, and the spinning burr may increase the chance of vessel rupture. Lack of available cardiac surgery or patient ineligibility for coronary artery bypass graft surgery are both relative contraindications.
For PTRA, the Rotablator system contains: (1) the rotablator is a pre-connected, exchangeable burr, and advancing device that houses an air turbine, driveshaft, and burr; (2) a console that regulates the air supply and monitors the rotation of the burr; and (3) a patent foot pedal to activate the device. The orbital atherectomy system is composed of a handheld device and an atherectomy controller. CBA uses the cutting balloon monorail device. It is available in over-the-wire and monorail configurations. The rotational atherectomy fluid consists of a water-based medium with a mixture of proteins and sodium.
All patients undergoing atherectomy procedures are prepared for PTCA.
For PTRA and OA, all patients receive pretreatment with aspirin. Rotary ablation is preceded by administering an anticoagulant, placing the rotation wire across the lesion, and parking the unfolded wire tip in a straight segment of the distal vessel, not in a side branch. When treating large coronary arteries, particularly the right coronary artery, many cardiologists insert a temporary prophylactic pacemaker because of the possibility of bradyarrhythmias. The burr and the drive shaft are manually advanced over the guidewire to a proximal segment of the target vessel.
If the procedure is unsuccessful because the lesion cannot be crossed, the downsizing of the burr may be required. After successful crossing, a polishing run completes lesion preparation for definitive treatment, most commonly using a stent. Both DCA and OA require specialized device-specific wires. These serve to wire the calcified lesion via microcatheters or over-the-wire (OTW) balloons. With both devices, shorter runs with a slower passage of the atherectomy device result in less microthrombi and no-reflow. Following atherectomy, the safe approach for device removal is the meticulous withdrawal of the device over the wire while taking extreme care not to pull the wire. Alternatively, parallel wiring or working over the OA wire is an option.
The guidewires, catheters, and techniques used for CBA are similar to those used for conventional PTCA. However, the cutting balloons are less compliant and may not track as well as conventional PTCA catheter equipment.
Intravenous heparin boluses are administered to keep the activated clotting time of more than 300 seconds. This anticoagulation is vital to avoid the slow-flow/no-reflow phenomenon during the procedure. Slow-flow or no-reflow usually occurs as a result of the distal embolization of microparticles or clots. It is treatable by intra-coronary administration of verapamil, nitroprusside, nicorandil, adenosine, and nitroglycerine.
There are several adverse events which can take place in the setting of atherectomy. If the devices are used in selected patients after careful planning, the complication rate is low. However, based on multi-center registries, numerous complications may arise.
These complications include myocardial infarction in 1.3%, emergency coronary artery bypass (CABG) in 2.5%, and death in 1% of the cases. Apart from clinical complications, angiographic complications include dissection (10%), perforations (1.5%), slow-flow (1.2%), and abrupt vessel closure (1%). Coronary dissection following atherectomy occurred with a frequency of 3.3 % in clinical trials, respectively, while perforation occurred in 1.7 %. Slow or no reflow is another potential complication (≤1%). Burr trapping can occur.
Several trials have defined the optimal use of PTRA. The Study to Determine Rotablator and Transluminal Angioplasty Strategy (STRATAS) trial compared an aggressive debulking strategy (burr/artery ratio of 0.7 to 0.9 followed by balloon inflation of less than 1 atm or no inflation) with a moderate debulking strategy (burr/artery ratio of less than 0.7 followed by conventional balloon angioplasty). The clinical success was similar, but the aggressive strategy caused more myocardial infarctions (11% vs. 7%) and a higher rate of restenosis (58% vs. 52%).
In the Pivotal Trial to Evaluate the Safety and Efficacy of the Orbital Atherectomy System in Treating De Novo, Severely Calcified Coronary Lesions (ORBIT II), a registry of 443 patients with severely calcified coronary lesions treated at 49 U.S. sites, the primary safety endpoint of freedom from 30-day MACE was achieved in 89.6% of patients. Stent delivery was successful in 97.7% of cases with less than 50% diameter stenosis (DS) achieved in 98.6% of subjects. Low rates of in-hospital Q-wave myocardial infarction (0.7%), cardiac death (0.2%), and TVR (0.7%) were reported. Angiographic complications included severe dissections in 15 patients (3.4%) and perforations in 8 patients (1.8%).
Several small trials, all enrolling fewer than 200 patients, compared CBA with PTCA and reported that CBA reduced restenosis by 41% to 69%. However, other small studies that compared CBA with PTRA or balloon PTCA as a pretreatment before brachytherapy for ISR found no difference in restenosis, and several large trials that compared CBA with PTCA generally found no difference in restenosis.
Several randomized studies have compared pulsed-wave lasers with other treatment modalities, but none have shown a benefit over conventional PTCA. A recent large scale trial ROTAXUS randomized 240 patients with moderate to severe calcification to PCI with or without DCA. Although there was a higher procedural success with the assigned treatment (92.5% vs. 83.3%; p=0.03), the late lumen loss at nine months was higher in the DCA arm. A large-scale randomized trial comparing all the devices is unlikely to occur, and due to the paucity of literature, a direct comparison of outcomes is not possible. RA, however, has a long record and data in terms of outcomes. Presently, device choice is dependant on the discretion of the operator.
Improved outcomes after atherectomy are dependent on the skills and knowledge of the operator and the teamwork and preparedness of cardiac catheterization laboratory staff. Important healthcare team consideration include: a) equipment-specific training and certification for nurses, technologists, and midlevel practitioners focused on knowledge of equipment, standardization of protocols, and preparation for emergencies; b) minimum volume of PTCA at the medical center to establish competency; c) cardiac surgery available on-site or immediately available via interhospital transfer. Available data suggest that centers with higher atherectomy volumes have a lower risk of major adverse events. Post-procedure rehabilitation is essential to improve functional quality.
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