Catheterdelivered Devices

The delivery of specialized devices that can be introduced intravascularly or intracardially has been on the rise. Such devices include stents, septal occluder devices, leads, and ablation tools (see also Chapters 6, 22, 23, and 29).

4.1. Stents

An intraluminal coronary artery stent is a small, self-expanding, wire mesh tube that is placed within a coronary artery to keep the vessel patent (open). Stents are commonly deployed: (1) during coronary artery bypass graft surgery to keep the grafted vessel open; (2) after balloon angioplasty to prevent reclosure of the blood vessel; or (3) during other heart surgeries. For delivery, a stent is collapsed to quite a small diameter and inserted over a balloon catheter. Typically with the guidance of fluoroscopy, the catheter and stent are moved into the area of the blockage. When the balloon on the delivery catheter is inflated, the stent expands, locking it in place within the vessel, thus forming a scaffold that holds the artery open.

Stents are intended to stay in the vessel permanently, keeping it open to improve blood flow to the myocardium, thereby relieving symptoms (usually angina). Note that a stent may be used instead of angioplasty. The type of stent to be deployed depends on certain features of the artery blockage (i.e., size of the artery and where the blockage is specifically located).

Stents are now considered to reduce the incidence of restenosis, which generally occurs within 4-6 months following an angioplasty procedure. Before stents, the incidence of restenosis was about 35-45%. Restenosis is a renarrowing of the treated coronary artery, which is largely related to the development of neointimal hyperplasia (that which occurs within an artery after it has been treated with a balloon or atherectomy device). In general, restenosis can be considered as scar tissue that forms in response to a previous mechanical insult. Hence, restenosis is somewhat different from atherosclerosis, which is related to calcium, fat, or cholesterol plaque buildup. Some individuals are considered genetically predisposed to develop restenosis.

To date, stents are the only widely employed devices that have been proven to reduce the incidence of restenosis (reduction by approximately one-third). Stents alone are not considered as "cures" for coronary artery disease, but their use will

Atherectomy Devices Design

Fig. 5. The CorCap™ Cardiac Support Device (Acorn Cardiovascular Inc.™, St. Paul, MN) is a fabric mesh multifilament implant that is surgically positioned around the ventricles of the heart. Acorn developed a new fabric made from implant-grade polyethylene terepthalate (PET polyester) fabricated into a proprietary mesh design. The CorCap™ Cardiac Support Device fabric is composed of many interlinked filaments, each one-fifth the size of a human hair. The multifilament knit construction provides optimal support with conformability that evenly distributes support over the heart's surface. The proprietary processing of the device produces a highly biocompatible and durable material designed and tested for permanent implantation without adverse effects.

Fig. 5. The CorCap™ Cardiac Support Device (Acorn Cardiovascular Inc.™, St. Paul, MN) is a fabric mesh multifilament implant that is surgically positioned around the ventricles of the heart. Acorn developed a new fabric made from implant-grade polyethylene terepthalate (PET polyester) fabricated into a proprietary mesh design. The CorCap™ Cardiac Support Device fabric is composed of many interlinked filaments, each one-fifth the size of a human hair. The multifilament knit construction provides optimal support with conformability that evenly distributes support over the heart's surface. The proprietary processing of the device produces a highly biocompatible and durable material designed and tested for permanent implantation without adverse effects.

continue to have a major impact on decreasing the need for repeat procedures.

Nevertheless, one of the major goals for improving the outcome of stenting procedures is to minimize further the potential for vessel restenosis. To accomplish this, several new types of stents, called drug-eluting stents, have been employed (Table 1). Such stents are coated with agents that are slowly released, further promoting the vessel from renarrowing and closing.

Yet, it should also be noted that, typically, patients who have had a stent procedure must take one or more blood-thinning agents such as aspirin, ticlopidine, or clopidogrel. Aspirin is typically used indefinitely, and one of the other two drugs is generally prescribed for 2 to 4 weeks. Therefore, goals for future stent technologies will continue to include the development of coatings that will minimize restenosis or the use of anticoagulation therapy (Table 1).

Table 1

Currently Leading Stent Companies

Table 1

Currently Leading Stent Companies

Company

Stent

Stent coatings

Cook Cardiology

Gianturco-Roubin stents

Pacltaxel (Taxol)

Guidant/ACS

Multilink/Duet/Tetra/Penta Stents

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