Medical Devices

AND THE CORONARY SYSTEM 7.1. Devices and the Coronary Arteries

In recent years, several interventional medical devices have been developed to help treat coronary artery disease. These procedures involve complex medical instrumentation and delivery procedures that have evolved over time. Nevertheless, these devices have saved many lives over the years and are continually improved by scientists, engineers, and physicians.

Intricate medical devices are required for two main interventional procedures performed today on the coronary arteries. Percutaneous transluminal coronary angioplasty is a procedure during which a balloon catheter is introduced into the narrowed portion of the coronary artery lumen and inflated to reopen the artery to allow the return of a normal blood flow. During this procedure, it is common that a coronary stent is also placed such that restenosis of the artery is significantly delayed. A stent is a device made up of wire mesh that provides scaffolding to support the wall of the artery and keep its lumen open and free from the buildup of plaque. A picture of a balloon angioplasty catheter and a coronary stent are shown in Fig. 4.

Balloon angioplasty and coronary stents have prevented numerous patients from having to undergo coronary artery bypass graft surgery, which can be costly and painful. Both techniques and the devices required to make them successful have spawned a significant amount of literature defining a number of important parameters relating to the anatomy of the coro nary arteries. Such stents have been produced with a variety of drug coatings in further attempts to minimize the time for, or altogether eliminate, the possibility of restenosis. The most common drug used to coat stents is sirolimus (also known as rapamycin). Drugs like sirolimus work by stopping cell growth; they also stop scar tissue from forming within arteries that have been opened. For more details, refer to Chapter 33.

7.2. Devices and the Coronary Veins

Historically, the coronary veins have not been a focus of interventional procedure development. Recently, the coronary venous system, specifically the coronary sinus, has become a conduit for interventional devices used to treat heart failure as well as for myocardial protection during open heart surgery. These procedures involve the cannulation and catheterization of the coronary sinus, which allows access to the coronary venous network. More specifically, biventricular pacing procedures have become quite common (10-18) and have elicited greater interest in the coronary venous system.

Typically, during biventricular implant procedures, a catheter is introduced into the coronary sinus ostium with the aid of standard fluoroscopic imaging methods. Contrast dye is injected retrogradely into the coronary sinus such that the physician can understand its anatomy and that of the branches that feed it. A pacing lead is then delivered into a lateral branch of the coronary sinus, where it is positioned to pace the left ventricle. Although this procedure is relatively common, it can often be difficult and time intensive if the anatomy of the coronary system is not well understood. Figure 5 depicts such a procedure in fairly straightforward terms (see PlaceLateral.mpg on the Companion CD).

Myocardial protection is another procedure requiring device interaction with the coronary veins. During open heart surgery, the coronary sinus can be catheterized, and the coronary venous network is perfused retrograde with cardioplegia solution that helps to protect the heart from myocardial ischemia.

Both of the procedures mentioned in this section require intuition about the anatomical parameters of the coronary veins, especially the coronary sinus.

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