Adjunctive tools: Atherectomy devices, laser, thrombectomy

Mechanism of action

The principal mechanism for RA is differential cutting in which the diamond-tipped burr drills through rigid atherosclerotic plaque and calcium but spares the underlying elastic arterial structure. The resultant particulate matter is generally less than 10 μm in diameter, which passes through the microcirculation and is picked up by the reticuloendothelial system (without hindering the coronary microcirculation).

Indications and contraindications

Although studies have shown that routine use of RA may not render a clinical benefit, there are several scenarios in which RA improves immediate angiographic results. Most commonly it is used to prepare vessels with severe fibrocalcific disease where in balloons or stents could not be passed. Additionally, attempts to pass stents through such ridgid, calcific lesions may result in inappropriate positioning, stent dislodgement, or erosion of the polymer–drug coating and inadequate drug delivery to the vessel wall.

Another scenario involving highly calcified nonyielding lesions is the need for high-pressure balloon expansion because of increased vessel stiffness, risking balloon rupture and vessel dissection or perforation. Delivering a stent in an incompletely dilated lesion inhibits its full expansion, which is a clear risk for stent thrombosis.

RA is also used to debulk bifurcation lesions to reduce plaque shift or the “snow-plowing” effect. Nevertheless, caution is advised in these scenarios because of the increased risk of dissection or perforation. Angulation of more than 60 degrees (between the main vessel and side branch) is a relative contraindication for RA, and bends of more than 90 degrees have a strong contraindication. Other contraindications are summarized in Table 6.1 . A lesion that is more than 25 mm in length has a relative contraindication for RA. Smaller (<1.5mm) sized burrs should be used in these lesions should the operator so choose. A reduced ejection fraction (<30%) was previously a contraindication to RA, but the advent of mechanical support devices such as the Impella catheter has allowed physicians to consider RA for some of these patients (see Chapter 10 for more details).

Device

The Rotablator system (Boston Scientific, Natick, MA) consists of a nickel-coated brass burr ( Fig. 6.1A and 6.1 B ) that is coated with 2000 to 3000 microscopic diamond crystals that are 20 μm in size (with only 5 μm protruding from the nickel coating on its leading face). The burr is available in 1.25- to 2.50-mm sizes (0.25-mm increments) and is attached to a long, flexible drive shaft that is covered in a 4.3F Teflon sheath. The drive shaft can be inserted through various coronary guide catheters based on size ( Table 6.2 ) over a RotaWire, which is 0.009 inch in diameter and 330 cm in length. The drive shaft is connected to an advancing console ( Fig. 6.2 ) that houses a turbine driven by compressed nitrogen gas and that can rotate at speeds ranging from 140,000 to 220,000 rpm ( Table 6.3 ). An emulsifier solution (Rotaglide) made of egg yolk, EDTA, and olive oil is infused along with saline via a pressurized system through the driveshaft to reduce friction and improve heat dissipation. The traditional Rotablator RA system involved the use of a foot pedal, console, and advancer. This has been largely replaced by the newer RotaPro RA system, which has added a digital console, eliminated the foot pedal, added buttons to the advancer that control device activation, and added a switch to turn to Dynaglide mode for easy burr retrieval.

Technical tips

Once the decision to use RA is made based on the indications and contraindications discussed earlier, the next step is to determine the burr size. For patent but stenotic vessels, a burr-to-artery ratio of less than 0.6 is appropriate. Although a larger ratio (>0.6) can aggressively debulk the lesion, it can increase the risk of dissections and perforations. For vessels with subtotal occlusions where the arterial size is difficult to ascertain, it is prudent to start with a small burr size (1.25 or 1.5 mm) to create a pilot channel and then upsize to a ratio of less than 0.6. Additionally, a smaller burr-to-artery ratio should also be used for vessels with lesions that are longer than 25 mm or if the vessel has mild tortuosity.

The next step is preparing the patient for RA. The patients usually already have aspirin on board; some operators use verapamil preemptively to prevent spasm. Heparin or bivalirudin can be given next to fully anticoagulate the patients. Traditionally, operators have chosen heparin because of its reversibility in case of vessel perforation, but studies have shown safety with bivalirudin as well. RA is associated with rotational speed-dependent platelet activation, and glycoprotein (GP) IIb/IIIA receptor antagonists can be used to counteract this effect. Standard use of temporary pacemakers before intervening on calcified lesions in the RCA left main is no longer needed. Smaller burrs at lower speeds have led to lower incidence of transient heart block. Many operators opt to use atropine, aminophylline, or vagolytic maneuvers as part of initial management of bradyarrhythmias, avoiding any complications of temporary pacemaker placement on a routine basis. Alternatively, a test run can be performed before RA of the RCA or dominant left circumflex to make sure bradycardia is not being induced.

A guide catheter with a gentle curve should be sized depending on the burr size (see Table 6.2 ). It is important to make sure that the guide catheter is coaxial to the vessel to prevent dissection of the vessel or retraction of the wire during RA. The RotaFloppy wire should be used for lesions that are more proximal and easily crossable to prevent guidewire bias in which a burr would differentially debride more on the lesser curvature of the vessel, which is straightened by a stiffer wire. The extrasupport RotaWire can be used for difficult-to-cross, heavily calcified or distal lesions. If a lesion cannot be crossed by the RotaWire, a 0.014-inch guidewire can be used to cross the lesion and then be exchanged for the RotaWire using a low-profile over-the-wire balloon or microcatheter.

Once the RA manifold is assembled, the burr speed is tested outside the body (140,000–160,000 rpm). Either saline or the Rotaflush solution (mix 4 mg of nitroglycerin and 5 mg of verapamil in 500 mL of saline to decrease spasm) is used to flush and lubricate the system. The Rotaglide solution is added to reduce friction. Before inserting the burr into the Y-adapter, one must also check for free movement of the burr with the advancer and test that the braking system holds the wire in place during rotation. The advance knob should be locked 2 cm from the distal end of its slidder slot.

After this, the burr is inserted via a Y-adapter and advanced over the wire through the guide catheter into the vessel to about 1 to 2 cm proximal to the lesion. The operator should hold the back end of the wire and apply gentle traction on the guidewire and catheter to limit acquired tension and thereby prevent the burr from leaping forward during the initial pass. This acquired tension is alleviated further by transiently activating the system proximal to the lesion. The system is then activated and the burr is brought into contact with the lesion in a “pecking” fashion in which 1 to 3 seconds of contact with the plaque is followed by pulling back the burr from the plaque surface for 3 to 5 seconds. This decreases the risk of sudden deceleration of the burr and allows the debris to clear from the distal circulation. It is important to prevent deceleration over 5000 rpm because such decelerations can lead to plaque heating, torsional dissection of the vessel, and formation of larger particles, which can lead to slow reflow or no reflow. Another important consideration during RA is that the operator should hold gentle forward pressure on the guide catheter and the wire to maintain wire position in the distal vessel. The total time taken for each pass should not exceed 30 seconds. There should be a 30- to 60-second interval wait between each atherectomy run to avoid no reflow phenomenon. Fig. 6.3 and Videos 6.1A – G demonstrate the use of RA in a severe left main stenosis. The slow pecking technique is important to prevent device entrapment beyond the target lesion, which is a rare but serious complication requiring expertise to extract the device or emergent surgery if other measures fail.

The most important factor in successfully using RA is to avoid complications such as dissection, perforation, and preventing no reflow or slow reflow (reduction in blood flow by 1 thrombolysis in myocardial infarction [TIMI] grade). Technical tips to prevent these adverse effects are listed in Box 6.1 . When performed by an experienced operator with the appropriate precaution, RA proves to be an excellent method to debulk and modify plaque in preparation for stenting – with recent data suggesting that operator experience (i.e., number of cases performed every year) significantly reduces the occurrence of complications.