Disruption of Plaque and Arterial Wall

The inflated balloon exerts pressure against the plaque and arterial wall, causing fracturing and splitting of the plaque. The concentric lesion fractures and splits at its thinnest and weakest point. Eccentric lesions split at the junction of the plaque and the arterial wall. Dissection or separation of the plaque from the medial wall releases the “splinting” effect that is caused by the lesion and results in a larger lumen. This is the major effective mechanism of balloon angioplasty.

Loss of Elastic Recoil

Balloon dilation causes stretching and thinning of the medial wall. Stretching causes the medial wall to lose its elastic properties. The degree of elastic recoil loss is affected by the balloon-to-artery size ratio. Over time (1 to 6 weeks), there may be re-narrowing of the artery as a result of elastic recoil, which is prevented by placement of a stent in the artery.

Redistribution and Compression of Plaque Components

Shear pressures cause denudation or stripping of endothelial cells and the extrusion or pushing out of plaque components. There may be some molding of the softer lipid material, but this effect accounts for a small part of the overall effect of angioplasty.

Mechanism of Stents

Stents scaffold the lumen and plaque open, holding back dissection flaps and stopping vessel recoil and re-narrowing of the lumen.

The indications, contraindications, and complications of PCI are listed in Table 10-2.

Table 10-2 Indications, Contraindications, and Complications of Percutaneous Coronary Intervention (PCI)

Restenosis is the re-narrowing of the vessel after treatment by balloon and stent leading to recurrence of anginal symptoms. Restenosis is not considered a true complication but is an adverse event requiring retreatment or CABG. Restenosis is caused mostly by intimal hyperplasia and rarely by vessel recoil after stenting. Its incidence is approximately 10% after drug eluting stents. Typically, restenosis occurs in the initial 6 months after PCI. In-stent restenosis is less than 10% with drug-eluting stents. Stent thrombosis is different than restenosis and is a potentially catastrophic event that can lead to myocardial infarction (MI) or death. It occurs in approximately 1% to 2%, especially if dual antiplatelet therapy (i.e., aspirin and Plavix) is prematurely discontinued.

Guiding Catheter

A special large-lumen catheter is used to guide the coronary balloon catheter to the vessel that has the lesion to be dilated (Fig. 10-3). Compared with diagnostic catheters, guiding catheters have thinner walls and larger lumens, which allow contrast injections to be done while the balloon catheter is in place. The guiding catheters are stiffer than diagnostic catheters to provide support for advancing the balloon-stent catheters into the coronary artery. They respond differently to manipulation than diagnostic catheters. The guiding catheter tip is not tapered, occasionally blocking the ostium and causing pressure dampening while engaging the coronary ostium. A 6 F guiding catheter is generally used. Some catheters have relatively shorter and more flexible tips than other catheters, theoretically to decrease catheter-induced trauma. Others may have side holes to help maintain blood flow during PCI. Larger guiding catheters (7 F or 8 F) may be necessary for kissing balloons/stents, rotoblator burrs larger than 2 mm, and some cutting balloons. There are many different shapes of guiding catheters for different anatomic variations.

Figure 10-3 Illustration of a guiding catheter. 1, Stiffer body; 2, variable softer primary curve; 3, wire braiding; 4, atraumatic tip; 5, large lumen (optional radiopaque marker); 6, lubricous coating

(Courtesy of Boston Scientific, Inc.)

Functions of the Guiding Catheter

There are three major functions of a guiding catheter during PCI:

Development of Coronary Angioplasty Balloon Catheters

Technologic refinements of balloon catheter equipment and increased operator experience have dramatically improved the primary success rate of PCI.

Over-the-Wire (OTW) Angioplasty Percutaneous Coronary Intervention Systems

A standard OTW PCI catheter (Fig. 10-4) has a central lumen throughout the length of the catheter for the guidewire and a separate lumen for the balloon inflation. These catheters are approximately 145 to 155 cm long and can be used with long or short guidewires, usually 0.014 inch.

Figure 10-4 Schematic design of a typical over-the-wire (OTW) angioplasty balloon catheter. The guidewire extends the entire length of the catheter.

(From Talley JD, Joseph A, Kupersmith J: Cathet Cardiovasc Diagn 20:108-113, 1990.)

The advantages and limitations of OTW angioplasty balloon catheters are listed in Table 10-3. These catheters accept multiple guidewires, which allows for the exchanging of additional devices that may require stronger, stiffer guidewires. Maintenance of distal wire position beyond the target stenosis is paramount in coronary angioplasty. For OTW balloon catheters the guidewire can be extended to help maintain distal position while the balloon catheter is withdrawn completely over the guidewire to permit another balloon catheter to be exchanged and introduced over the same guidewire for additional dilations. A 300-cm exchange wire is also commonly used.

Table 10-3 Advantages and Limitations of Angioplasty Balloon Types

OTW angioplasty balloon catheters have few limitations. A primary operator and experienced personnel are required to perform catheter exchanges. Several different types of devices can be used to fix a 155-cm guidewire in place to permit OTW catheters to be exchanged without using a 300-cm guidewire. These devices are now rarely used and have included a wire entangler, a balloon trapper, and a magnet fixation system (see later).

Rapid-Exchange (Monorail) Percutaneous Coronary Intervention Catheters

Rapid-exchange balloon catheters are the most popular catheters used today and were developed to allow a single operator to exchange the PCI catheters unassisted. This rapid exchange catheter differs from over the wire PCI catheters in that only a variable length of the shaft has two lumens (Fig. 10-5, A). One lumen is for balloon inflation and the other, which extends through only a portion of the catheter shaft, houses the guidewire. Because only a limited portion of the balloon requires dual lumens, the catheter shafts can be made smaller than over the wire systems.

Figure 10-5 A, Schematic design of a typical rapid-exchange angioplasty balloon catheter. The guidewire extends on “through” the distal part of the catheter allowing for single-operator use. B, Schematic design of a standard fixed-wire angioplasty balloon catheter. This design has only one “through” lumen for balloon inflation, and the device itself serves as a “steerable guidewire.”

(A Courtesy SciMed Life Systems, Maple Grove, MN. B from Talley JD, Joseph A, Killeavy ES, et al: Cathet Cardiovasc Diagn 22:310-316, 1991.)

Rapid-exchange balloon catheters address certain inherent limitations of OTW systems. First, OTW balloon exchanges requiring extension of the distal wire or a long wire are unnecessary because the rapid-exchange portion of the catheter is short. Second, a single operator can use rapid-exchange balloon catheters without the aid of other assistants to maintain distal guidewire position or facilitate balloon navigation.

Monorail catheters also have limitations, including the need for excellent guiding catheter support and more operator skill for the complexity in manipulation of the guidewire, balloon catheter, and guiding catheter. Blood loss during removal of the monorail balloon catheter at the rotating hemostatic valve can be a problem but can also be reduced with better technique and valved connectors.

Fixed-Wire Angioplasty Balloon Catheters

The fixed-wire catheter is rarely used today and has the balloon mounted on the wire with a distal flexible steering tip (Fig. 10-5, B). The proximal end of the catheter consists of a single, nonremovable port connected to a hollow metal tube (hypotube). A core wire extends from the hypotube to the end of the distal steerable tip. This assembly is coated with a thin plastic shaft that enhances flexibility. Fixed-wire balloons have only one enclosed lumen for balloon inflation.

The advantages and limitations of fixed-wire angioplasty balloon catheters are listed in Table 10-2. The small shaft size of the single-lumen design provides excellent coronary visualization. Because the balloon is mounted on the distal guidewire, the device can easily be used by a single operator. Fixed-wire balloon catheters are particularly useful for distal lesions, subtotal stenoses, and lesions located in tortuous small vasculature.

Fixed-wire catheters have significant limitations. These catheters lack the inherent safety advantage of OTW and rapid-exchange systems because the balloon is mounted on a guidewire. To exchange this catheter for a different balloon size, the catheter is removed completely, and the lesion recrossed with a different size catheter. Alternately, the catheter remains across the lesion, and a second guidewire is advanced to secure access to the lesions. The fixed-wire balloon can be withdrawn and the procedure completed with standard techniques. A narrowed or dissected lesion may not permit balloon advancement or even may close the vessel. The lack of a distal lumen prevents measurement of distal pressure or injection of contrast media to evaluate distal vessel runoff. This catheter is not commonly used in clinical practice.

Procedure Notes for Percutaneous Coronary Intervention

The balloon is inflated and deflated using a hand-held syringe device with a pressure gauge. Balloon catheters come in different sizes (ranging from 1.5 to 5 mm for coronary arteries), which refer to the inflated diameter of the balloon. The balloon diameter is selected according to the angiographic size of the vessel to be dilated. Coronary balloon catheters are made of plastic materials that determine the flexibility of the catheter shaft and the balloon characteristics (e.g., burst pressure and actual diameter under different pressure levels). There are special-purpose coronary balloon catheters (e.g., noncompliant high-pressure balloons, extra long, or equipped with microblades). Cutting balloons are special balloons with three to four atherotomes or blades that run longitudinally on the balloon to score the lesion in a more controlled fashion.

Angioplasty Guidewires

Coronary angioplasty guidewires are small-caliber (0.0104- to 0.018-inch) steerable wires. They are advanced into the coronary artery or branches beyond the lesion that is to be dilated. A J tip of varying degree may be shaped by the operator to negotiate side branches and tortuous artery curves. The balloon-stent catheter is advanced over the wire and, after artery dilation, removed from the artery with the wire remaining in place beyond the dilated lesion. Extra-long guidewires (300 cm) are used to exchange OTW balloon catheters. The tip flexibility and torque control characteristics of these coronary guidewires vary. Generally the softer wires are safer and easier to advance into tortuous branches, whereas the stiffer wires give better torque control and may be useful for crossing difficult or total occlusions. Some guidewires have special coatings to cross subtotally or totally occluded stenoses better. These hydrophilic wires generally carry a small risk of perforation if the tip position is not kept in the major vessel lumen and dissection if the guidewire is advanced under an intimal flap.

Exchange and Extension Guidewires and Wire Fixation Devices

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