Basics of Percutaneous Coronary Interventions

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1 Basics of Percutaneous Coronary Interventions

On September 16, 1977, Andreas Grüntzig performed the first human percutaneous transluminal coronary angioplasty in Zurich, Switzerland. Until then, coronary artery bypass surgery was the only alternative to medicine for the treatment of coronary artery disease. Over the past 35 years, PTCA has evolved into more sophisticated techniques involving predominantly stenting and is now called percutaneous coronary intervention (PCI). PCI is one of the most successful methods of coronary revascularization with more than 1,500,000 procedures done in the United States alone. PCI is the treatment of choice for discrete single- and double-vessel coronary lesions and plays an important role in complex revascularization in patients with multivessel coronary artery disease, including left main narrowings with and without depressed left ventricular function. Techniques and technology used in PCI extend into the treatment of peripheral arterial disease. Further evolution of PCI into the treatment of structural heart disease (valves, septal defects, etc.) is emerging as a separate discipline within interventional cardiology.

PCI encompasses various coronary techniques, such as balloons, stents, cutters, lasers, grinders, suckers, filters, and other tools. The term percutaneous transluminal coronary angioplasty (PTCA) is used when describing techniques and outcomes related to use of the original balloon inflation technique first used by Grüntzig.

This chapter is the extension of the PCI chapter from The Cardiac Catheterization Handbook, fifth edition, and presents the basic method and mechanisms of balloon angioplasty and stenting as an introduction to the practice of interventional cardiology. The various techniques of PCI can be placed into niche applications for specific devices (Table 1-1).

Table 1-1 Niche Applications of PCI Devices

Overview of the Basic PCI Method

PCI was derived from the basic procedures used for diagnostic cardiac catheterization and coronary angiography. PCI begins with vascular access by means of the same techniques for the insertion of an arterial sheath through the arm (radial artery) or leg with Seldinger’s method (needle and guidewire). In contrast to diagnostic catheters, specialized large-lumen “guiding” catheters engage the coronary artery in the same manner but are designed to provide stabilization or backup for delivery of PCI equipment.

Steps in the PCI Procedure

The steps in the PCI procedure are shown in Figure 1-1. First, a guiding catheter is seated in the coronary ostium. A thin, steerable guidewire is introduced into the guide catheter and then into the coronary artery and positioned across the stenosis into the distal aspect of the artery. A very small angioplasty balloon catheter is placed on the guidewire, inserted through the guiding catheter, and is positioned in the artery across the stenotic area by tracking it over the guidewire. Once correctly placed within the narrowed area to be treated, the balloon on the PCI catheter is inflated several times for brief periods (10–60 seconds). The inflation and deflation of the balloon expand the stenosis and restore blood flow to an area of the heart previously deprived by the stenosed artery.

Figure 1-1A,B A, How angioplasty and stenting works. 1, The artery is filled with atherosclerotic material, compromising the lumen. A cross-section of the artery is shown on the right side. 2, A guidewire is positioned past the stenosis through the lumen. 3, A balloon catheter is advanced over the guidewire. 4, The balloon is inflated. 5, The balloon is deflated and withdrawn. 6, The balloon catheter is exchanged for a stent (on a balloon). 7, The stent is expanded. 8, The expanded stent remains in place after the deflated balloon is withdrawn. B, Drawing of angioplasty balloon before (left) and during inflation (right). C, Diagrams of stent expansion. Top, Crimped stent delivered to lesion; middle, balloon-expanded stent implanted in lesion; bottom, after balloon deflation and withdrawal, stent is seen implanted in artery wall with widely patent lumen.

After the balloon expands the stenotic area, the balloon catheter is exchanged for a stent-carrying balloon catheter. The stent is a metal scaffold, mounted in a compressed form on another balloon catheter, and delivered in the same manner as the first balloon catheter was delivered. The stent is deployed by inflation of the balloon as was performed for dilating the stenosis. The stent should be carefully positioned. It is inflated with the same pressure gauge syringe (8–16 atm pressure) for 10 to 20 seconds. A full opening of the stent with complete strut apposition to the vessel wall is important for good short- and long-term results.

After the stent struts have been expanded and implanted into the artery wall, the balloon is deflated, and the delivery catheter and guidewire are removed. Intravascular ultrasound (IVUS) imaging is often used to confirm appropriate vessel-stent matching and full stent strut apposition (contact without space against the wall). After IVUS and final angiography have been performed, the guide catheter is removed. The femoral or radial arterial sheath is removed, and hemostasis is obtained in the laboratory. The patient is then transferred to a recovery area and then to the patient’s room. If no complications occur, the patient is discharged the next morning. The patient usually returns to work shortly (<2 days) thereafter. The definitions of a successful PCI procedure are summarized in Table 1-2.

^{Table 1-2} Definitions of PCI Success

Percutaneous coronary intervention (PCI) success may be defined by angiographic, procedural, and clinical criteria.

Angiographic Success

• Angiographic success in a stented artery is a minimum stenosis diameter reduction to <20%.

Procedural Success

• A successful PCI should achieve angiographic success without in-hospital major clinical complications (e.g., death, myocardial infarction [MI], emergency coronary artery bypass surgery) during hospitalization. MI is often defined as the development of Q waves in addition to elevation of troponins three times the upper limit of the laboratory’s normal value. Cardiac troponin T and I as measurements of myocardial necrosis are more sensitive and specific than CK-MB. Enzyme elevation in the absence of new Q waves is counted as MI, peri-procedural. There is no consensus on what level of troponin alone is clinically important enough to change major management following the interventional procedure.

Clinical Success

• A clinically successful PCI is an anatomical and procedural success with relief of signs and/or symptoms of myocardial ischemia after recovery from the procedure. The long-term clinical success requires that the patient have persistent relief of signs and symptoms of myocardial ischemia for more than 6 months. Restenosis is the principal cause of lack of long-term clinical success when short-term clinical success has been achieved.

Mechanisms of Angioplasty and Stenting

1. Disruption of plaque and the arterial wall

The inflated balloon exerts pressure against the plaque and the arterial wall, causing fracturing and splitting. Concentric (round or circumferential) lesions fracture and split at the thinnest and weakest points. Eccentric lesions split at the junction of the plaque and the normal arterial wall. Dissection or separation of the plaque from the vessel wall releases the restraining effect caused by the lesion and results in a larger lumen. This is the major mechanism of balloon angioplasty.

2. Loss of elastic recoil

Balloon dilatation causes stretching and thinning of the medial wall. Stretching causes the vessel wall to temporarily lose its elastic (recoil) properties. The degree of elastic recoil is affected by the balloon/artery size ratio. Almost all vessels have some elastic recoil. The major initial benefit of stenting is the elimination of elastic recoil, maintaining a large lumen over time.

3. Redistribution and compression of plaque components

During angioplasty, balloon pressure causes denudation of the vessel wall lining (endothelial) cells and the extrusion or pushing out of plaque components. There may be some molding and extrusion longitudinally of the softer lipid material, but this effect accounts for a very small part of the overall effect.

Indications for PCI

Guidelines and recommendations for the performance of PCI are provided in extensive detail in the updated (2009) PCI guidelines written by the American Heart Association (AHA), the American College of Cardiology (ACC), and the Society for Cardiovascular Angiography and Interventions (SCAI). Specific anatomical and clinical features for each patient should be considered for the likelihood of success, failure, and risk of complications with vessel closure, morbidity, mortality, and restenosis. Restenosis and incomplete revascularization must also be weighed against the outcome anticipated for coronary artery bypass graft (CABG) surgery.

In general, PCI is indicted for patients with the following:

• Stable angina pectoris unrelieved by optimal medical therapy with objective evidence of ischemia (abnormal stress test or abnormal stress thallium) and a coronary lesion in a vessel supplying a large area of myocardium

• Unstable angina

• Acute myocardial infarction

• Angina pectoris after CABG surgery

• Symptomatic restenosis after previous PCI

• Relative contraindications to PCI

• Unsuitable coronary anatomy (e.g., multiple severe complex lesions or diffuse distal disease)

• High-risk coronary anatomy in which closure of vessel would result in death

Contraindications to PCI

• Bleeding diathesis (low platelet count, peptic ulcer disease, coagulopathy, etc.)

• Patient noncompliance with procedure and post-PCI instructions and inability to take dual antiplatelet therapy (acetylsalicylic acid [ASA], Plavix, etc.)

• Multiple PCI restenoses

Note: Some patients with contraindications may have PCI as their only alternative to revascularization.

Complications of PCI (see also Chapter 4)

For most elective procedures:

1. Death (0.1%)

2. Myocardial infarction (1%–3%)

3. Emergency CABG surgery (0.5%–2%)

All complications that can occur during diagnostic cardiac catheterizations can also occur during PCI: access-site bleeding, especially with larger sheaths and prolonged anticoagulation (1:250 patients); contrast-medium reactions; cerebrovascular accident; myocardial infarction; and vascular injury (e.g., pseudoaneurysm of femoral artery)

• Restenosis (see Chapter 7).

Note: Restenosis at the site of PCI occurs in approximately 10% of patients and may lead to recurrence of anginal symptoms. Typically, restenosis occurs most frequently within the initial 12 months after PCI. This biologic effect is not considered a complication but rather a clinical part of angioplasty.

PCI Equipment

The most commonly used PCI equipment consists of four basic elements: a guiding catheter, a balloon catheter, a coronary guidewire, and a stent (Fig. 1-2 and Table 1-3 list approximate costs of such equipment).

Figure 1-2 Diagram of components of percutaneous coronary intervention equipment.

(Adapted from Safian RD, Freed MS, eds. The manual of interventional cardiology, 3rd ed. Birmingham, MI: Physicians’ Press, 2001.)

^{Table 1-3} Approximate Costs of Coronary Angioplasty Equipment

Equipment	Cost ($US)
Balloon dilatation catheter	300 OTW/250 Rx
Guiding catheter	65
Guidewire	80
Exchange guidewire (300 cm)	120
Indeflator	55
Y connector	31
Sheath introducer	8
Torque tool	18
Nonballoon devices
Stent (noncoated)	1300
Stent (drug-eluting)	2300
Rotablator	1330
IABP	840

IABP, intra-aortic balloon pump; OTW, over-the-wire; Rx, rapid exchange.

There are three major operational challenges with PCI: (1) placing the guide catheter in a stable position, (2) negotiating tortuous vessel segments with the guidewire, and (3) delivering the stent through tortuous segments. To complete the PCI, the operator must control the three principal movable components (guide catheter, balloon catheter, and guidewire) simultaneously.

Guiding Catheter

A special large-lumen catheter is used to deliver the coronary balloon catheter and other interventional devices to the vessel that contains the lesion to be dilated. The features of the guide catheter noted in Figure 1-3 differentiate it from diagnostic catheters.

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

(Courtesy Boston Scientific, Inc.)

The improved quality and size of currently used stents have reduced the need for robust backup support in most situations. For more complex and technically difficult lesions, the choice of an appropriate guiding catheter for extra support and lesion visualization remains essential (see Chapter 3). When there is insufficient backup in crossing a very tight stenosis, the guiding catheter will disengage from the coronary ostium and back out into the aortic root. When pressure is applied to the stent catheter during attempts to cross the lesion, repositioning the guide catheter in a stepwise fashion while the stent is advanced may overcome this loss of support. However, aggressive intubation of the coronary ostium may damage the vessel, stopping the procedure prematurely, or may require additional stenting for an ostial dissection.

Deep seating of the guide catheter is achieved by manipulating the guide catheter over the balloon catheter shaft, past the aortocoronary ostium, and farther into the vessel. This maneuver is used to obtain increased backup support for crossing difficult lesions and is typically a last resort maneuver because of the increased chance of guide catheter–induced dissection of the left main or proximal vessel.

Pressure Monitoring

The guiding catheter measures aortic pressure during the case. Pressure wave damping may occur during coronary artery engagement if there is plaque in the coronary ostium. In addition, pressure measured through the guide catheter proximal to the stenotic area can be compared with distal transstenotic pressure measured with a pressure sensor guidewire for assessment of hemodynamic lesion significance before and after PCI. Some catheters have side holes near the tip to permit perfusion into the artery when the catheter is deeply seated and obstructing flow.

Characteristics

Compared with the diagnostic catheters, the guiding catheters have thinner walls, larger lumens, and stiffer shafts (Fig. 1-3). A large catheter lumen is achieved at the expense of catheter wall thickness and thus may result in decreased catheter wall strength, less torque control, or catheter kinking. The guiding catheters are generally stiffer to provide backup support during the PCI catheter advancement into the coronary artery and, therefore, respond differently to manipulation than diagnostic catheters. The guiding catheter tip is not tapered. Pressure-wave damping upon engaging the coronary ostium is seen more often than with similar-sized diagnostic angiographic catheters. Some guide catheters have relatively shorter and more flexible tips to decrease catheter-induced trauma.

Guiding catheters with small side holes near the tip permit blood to enter the coronary artery when the ostium is blocked by the guide catheter. Side holes are used when the guide catheter either partially or totally occludes blood flow into the coronary artery. The guide catheter coronary occlusion is noted by the change in the arterial pressure waveform to one of “damping.” Catheter side holes reduce ischemia when the guiding catheter is seated in a small artery. However, side holes may lead to inadequate artery visualization from loss of contrast media exiting the catheter before entering the artery. Although side holes may provide reliable aortic pressure, coronary flow can still be compromised during the angioplasty procedure. The guide catheter and side holes act as a “second stenosis” at the coronary ostium.

Small shaft diameter guide catheters (e.g., 6F) are the most frequently used size of guiding catheter. The use of small-diameter guide catheters results in fewer femoral vascular complications and allows earlier ambulation of patients. Small-size (<5F) guide catheters do not allow for the use of some stents. Guide catheters sized 7F or 8F are used for complex procedures involving larger PCI devices or two stents for treatment of bifurcation lesions. Use of 6 F (or, in some patients, 7F) guide catheters from the radial artery approach may become the favored access because of the markedly reduced vascular complications associated with radial PCI procedures.

Balloon Dilatation Catheter Systems

Types

There are three types of PCI balloon catheters (Fig. 1-4):

1. Over-the-wire (OTW)

2. Monorail

3. Fixed-wire

Figure 1-4 Three common types of coronary balloon angioplasty catheter design.

(Adapted from Freed MS, Grines C, eds. New manual of interventional cardiology. Birmingham, MI: Physicians’ Press, 1992: 29.)

The OTW and monorail balloons, but not fixed-wire balloons, are also used to deliver stents that are mounted by the manufacturer on a specific balloon. The advantages and limitations are summarized in Table 1-4.

^{Table 1-4} Advantages and Limitations of Angioplasty Balloon Types

Advantages	Limitations
Over the wire
Distal wire position	Two experienced personnel required
Distal port available for pressure measurement or contrast media injection	Larger profile
Accepts multiple guidewires
Rapid exchange
Distal wire position Enhanced visualization Low-profile balloons Single-operator system	Exchanging balloons at hemostatic valve may be technically demanding
Fixed wire
Enhanced visualization	Lack of through lumen
Single-operator system	Inability to recross lesion without removing
Use with small guiding catheters system
Low-profile balloons

Modified from Kern MJ, ed. The cardiac catheterization handbook, 2nd ed. St Louis, MO: Mosby, 1995.

OTW Angioplasty Balloon Catheters

Historically, the OTW balloon was the first introduced and has remained popular in a few centers. A standard OTW angioplasty balloon catheter has a central lumen throughout the length of the catheter for the guidewire and another, separate lumen for balloon inflation (Fig. 1-5). These balloons are approximately 145 to 155 cm long and are designed to be used with guidewires of various dimensions (0.010–0.014 inches). The major OTW advantage is the ability to maintain distal artery access with the balloon beyond the lesion while one guidewire is exchanged for another. The OTW system tracks very well because the whole balloon length has a wire lumen. It permits long guidewire exchanges, and because of the through lumen, it allows for delivery contrast and drugs distally in an artery. To exchange PCI catheters, the balloon is advanced over the wire to a distal position. The standard short (145-cm) wire is then removed from the balloon. A longer guidewire (300 cm) is then inserted to maintain distal wire position while the balloon catheter is completely withdrawn over the guidewire and another balloon catheter is introduced over the same long guidewire for additional dilatations. OTW catheters can accept multiple guidewires, which allows for exchanging additional devices that may require stronger, stiffer, or specialized guidewires.

Figure 1-5 Typical over-the-wire balloon (OTW) catheter. Quantum Maverick OTW. OTW “Quantum” Maverick Balloon.

(Courtesy SciMed-Boston Scientific, Boston, MA.)

Limitations of OTW balloon catheters include a slightly larger diameter than the rapid-exchange (monorail) and fixed-wire catheters and the need for additional personnel to help with long guidewire catheter exchanges.

Rapid-Exchange (Monorail) Balloon Catheters

“Rapid-exchange” or monorail catheters were developed to permit the exchange of angioplasty balloon catheters by a single operator. Rapid-exchange catheters have only a short (30–40 cm) length of the catheter shaft containing two lumens (Fig. 1-6). One lumen, in the distal 30-cm portion of the catheter shaft, houses the guidewire. The remaining lumen runs the entire length of the catheter and is used for balloon inflation. Because only a limited portion of the balloon requires dual lumens, rapid-exchange catheters are smaller in diameter than are OTW balloon catheters.

Figure 1-6 Typical rapid-exchange or monorail balloon catheter. Maverick 2 Monorail. Monorail balloon catheter.

(Courtesy SciMed-Boston Scientific, Boston, MA.)

Rapid-exchange balloon catheters address certain inherent limitations of OTW catheters. First, OTW balloon exchanges require a long (or extension) guidewire, which is unnecessary for the rapid-exchange balloon. Second, a single operator can use rapid-exchange balloon catheters without the aid of other assistants to maintain distal guidewire position.

Limitations of monorail catheters include the need for more care in manipulation of the guidewire, balloon catheter, and guiding catheter. Excessive blood loss at the rotating hemostatic valve during removal of the balloon catheter (back-out) maneuver may occur, but valved Y connectors have reduced this problem. More caution when moving the balloon is needed. If the monorail balloon is advanced beyond the distal end of the guidewire, the wire may come out of its short lumen, necessitating catheter withdrawal and reassembly of the balloon and guidewire. This is especially true when catheters with relatively short “rail” segments are used. If the balloon catheter requires force to advance beyond a lesion, a loop of guidewire may sometimes form outside the guide catheter in the aorta. This loop is nearly invisible but should be considered if the operator advances the catheter without seeing motion at the balloon tip.

Fixed-Wire Angioplasty Balloon Catheters

The fixed-wire catheter was the first catheter designed by Grüntzig. It has the balloon mounted on a central hollow wire with a distal flexible steering tip. The proximal end of the catheter consists of a single port connected to a thin metal tube (hypotube) used to inflate the balloon. 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.

In the balloon on-the-wire catheter system, the guidewire cannot be advanced independently of the balloon and the balloon cannot be exchanged without removing the entire system. Because the wire is attached to the distal end of the balloon, there is no central balloon lumen, resulting in a lower total profile than an OTW or monorail system. Its principal advantages relate to its low profile, enabling passage through very tight stenoses, and good contrast visualization of the lesion being dilated around the balloon catheter.

The small shaft size provides excellent coronary visualization. Because the balloon is mounted on the distal guidewire, the device was designed to be used by a single operator. Fixed-wire balloon catheters are particularly useful for distal lesions, subtotal stenoses, and lesions located in tortuous vasculature.

The limitations of fixed-wire catheters include lack of stent capability and the loss of the inherent safety advantage of OTW and rapid-exchange systems because there is no movable wire available to exchange for a stent if a dissection occurs. To exchange this catheter for another, the operator either must remove the entire system and recross the stenosis or dissection anew or, while leaving the fixed-wire balloon in place, advance another guidewire next to it to secure distal position and proceed with stenting in the usual fashion. A dissected lesion may not permit recrossing with a guidewire or advancing another balloon catheter.

Characteristics

The plastic material of the balloon determines its compliance (defined as the amount of expansion or diameter size for given amount of pressure) and strength. Compliance is the main differentiating feature among balloon catheters. Inflation of a compliant balloon above factory-determined average mean pressure (also called nominal or a set pressure for a known balloon size) will lead to further expansion of the balloon size approximately 10% to 20% over the predicted diameter. Noncompliant balloons, on the other hand, remain very close to their rated diameter even when inflated several atmospheres above nominal pressure. The advantages and disadvantages of balloon materials remain controversial. A compliant balloon may produce oversizing, particularly on second and third high-pressure inflations, resulting in dissections. After most stents are deployed, post-deployment high-pressure inflations are performed with low-compliance or noncompliant balloons to implant the stent struts into the vessel wall. Most balloons are also coated with low-friction surface polymers to facilitate lesion crossing.

The mechanical aspects of balloon inflations apply the following fundamental principles:

• Overinflation at balloon ends. According to Laplace’s law, wall stress increases with radius. At a given pressure, a larger balloon undergoes more wall stress than a smaller balloon, promoting balloon rupture. The arterial segment next to the lesion has a larger luminal radius than the lesion. Thus artery sites adjacent to the lesion may be traumatized. At high pressures, balloons weaken over time. The balloon burst pressure may be decreased during subsequent inflations of the same balloon. When inflating a balloon above the rated burst pressure, operators should consider limiting the number and duration of inflations.

• Balloon diameters always increase with increasing pressure. Even noncompliant balloons will grow in diameter (usually by <10% over nominal) with high pressure. Compliant balloons may increase by more than 20%. The balloon diameter–pressure relation is usually linear, reflecting the compliance characteristics. Figure 1-7 shows the balloon during inflation and a graph for pressure versus diameter.

• Balloons do not return to their original dimensions after deflation. At any given pressure, the balloon diameter during a subsequent inflation will be larger than during the first inflation. When dilating two lesions with a compliant balloon, cardiologists should consider approaching the narrower lesion first.

Figure 1-7 A, Balloon size changes proposed to occur during increasing inflation pressure when compliant balloon material is used.

(From Clinical issues in angioplasty balloon material: a review of the literature regarding polyethylene terephthalate (PET), USCI Division of C.R. Bard, Inc.) B, Diameter–pressure relationships of three balloon materials. All three balloons have a nominal size of 3.0 mm at 6 atm. (From Raymenants E, Bhandari S, Desmet W, et al. The impact of balloon material and lesion characteristics on the incidence of angiographic and clinical complications of coronary angioplasty. Cathet Cardiovasc Diagn 1994;32:303–309.)