Cardiac Interventions

CHAPTER OBJECTIVES

After completing this chapter, the reader will be able to perform the following:

List the percutaneous coronary interventional techniques

List and describe the various cardiac intervention procedures that can be performed

Identify the indications and contraindications for the various procedures

Identify the complications associated with each procedure

Describe balloon angioplasty

Describe stent placement in the coronary vasculature

Define the debulking techniques

Explain the methods used for cardioversion

The conventional diagnostic angiographic techniques used to demonstrate the anatomy of the heart have already been discussed in Chapter 12. In this chapter we will discuss some of the interventional techniques that are in use today. Interventional cardiology primarily focuses on several major areas: hemodynamic studies, techniques to improve the flow of blood to the myocardium, techniques to improve valve performance, extraction techniques (biopsies, foreign body removal), and electrophysiologic procedures. The techniques for transseptal left-sided heart catheterization as well as hemodynamic measurements have also been discussed in Chapter 12. These techniques can be considered as diagnostic rather than therapeutic (interventional).

Cardiac catheterization is a specialty area that is used for the diagnosis, assessment, and treatment of abnormalities of the heart and great vessels. The procedures are accomplished with standard angiographic catheterization techniques. They are relatively safe and, as we have already seen, may be used as diagnostic studies to determine the nature of the anatomy and any pathology and in conjunction with interventional procedures to effect a nonsurgical treatment.

PERCUTANEOUS CORONARY INTERVENTIONS

Coronary artery disease results from a buildup of plaque in the vessels supplying the heart muscle with blood. This is referred to as the stenosis or narrowing of the vessel lumen. Coronary bypass surgery is the invasive method for treatment of this disease. The process of plaque buildup is no different in the heart than it is in any of the vessels that we have already discussed in previous chapters. The development of percutaneous interventional techniques and selective and subselective catheterization equipment has made percutaneous coronary interventional cardiology possible.

Percutaneous Transluminal Angioplasty

Percutaneous transluminal angioplasty is the interventional technique of enlarging the lumen of a stenosed vessel. Three methods are used to recanalize the vessel: balloon angioplasty, balloon angioplasty with stent placement, and transluminal atherectomy. The procedural technique for the three methods is similar. The thoracic aorta is catheterized using the transfemoral approach and an arterial sheath catheter. The guiding sheath is placed in the orifice of the intended coronary artery, and a guide wire is introduced through it into the coronary artery. The guide wire is passed through the area of stenosis, and the angioplasty catheter is placed across the stenotic area. The method may vary slightly depending upon the type of catheter system that is used.

The angioplasty catheter can be a simple balloon catheter arrangement or a balloon-stent catheter system. The delivery system for the angioplasty catheter will be either over the guide wire or fixed guide wire system. Once the balloon is determined to be in the correct position, it is inflated a number of times. The inflation can last from several seconds to minutes. This action has the result of compressing the plaque against the lumen wall, restoring the flow of blood through the vessel. The expansion of the balloon has the effect of stretching and weakening the vessel wall. Some of the elasticity of the vessel is lost; however, after a period of time the diameter of the vessel lumen can shrink, causing restenosis. This is referred to as “recoil.” The restenosis caused by this phenomenon can be reduced by the use of the balloon-stent system because the stent provides additional support for the arterial wall.

The balloon-stent, as its name implies, has the balloon encased in a metallic stent. The process is slightly different from the balloon catheter alone. The initial expansion of the plaque is usually accomplished by means of a separate balloon catheter, which is subsequently removed once the amount of compression has been achieved and replaced by a “stent over balloon” catheter. When this catheter is placed in the expanded lumen and the balloon is inflated, the stent is compressed into the plaque, providing a firmer support for the compressed plaque. The stent remains in place and the deflated balloon catheter can be removed, leaving a patent vessel (Fig. 18-1). Another type of stent is the self-expanding stent. This type of stent is mounted over the catheter and held in a compressed state by a sheath or membrane. When placed in the area of stenosis the covering sheath or membrane can be removed, allowing the stent to expand to its full diameter. This type of stent is held in place by means of its own expansion force against the vessel wall. Figure 18-2 illustrates the placement of a typical self-expanding stent.

FIGURE 18-1 Schematic illustration of the procedure used to restore patency to a stenosed vessel using both the balloon catheter and the balloon/stent catheter combination. A, Guide wire passed through area of stenosed vessel. B, Balloon catheter passed through the stenosed area over the guide wire and expanded to allow the balloon/stent sheath to pass through the area. C, Balloon/stent sheath passed through stenosed area. D, Balloon/stent positioned across the stenosis within the sheath. E, The sheath is withdrawn and the balloon/stent is inflated, further expanding the vessel’s lumen. F, The sheath and balloon catheter are withdrawn, leaving the stent in place, and finally the guide wire is removed.

Restenosis of the vessel is possible with either system; however, stents have the added advantage of supporting the vessel wall in cases in which the expanding balloon may have caused it to be weakened. The newer “drug eluting” stent systems show promise in reducing the incidence of restenosis of the vessel. As discussed in Chapter 17, these stents are coated with certain drugs that reduce the incidence of restenosis.

Transluminal atherectomy has already been discussed in Chapter 17. Atherectomy, also referred to as “debulking,” has the advantage over simple transluminal angioplasty of accomplishing the physical removal of the plaque from the artery. This would decrease the probability of rapid restenosis of the vessel. The procedure has some drawbacks. Among these is the relative size of the catheter system compared to angioplasty. Atherectomy systems are much larger and therefore require a larger access sheath. This fact can increase the potential for severe complications in certain at risk patients. This procedure is best utilized in cases in which the vessel lumen is larger or the stenosis is confined to the vessel orifice. Atherectomy is generally not the method of choice and is rarely applied today in the recanalization of stenotic vessels.