Prosthetic Grafts

Introduction

Arthur Voorhees and colleagues first described the use of a prosthetic graft to bridge arterial defects in 1952. Since then, numerous advances have been made in fabric technologies, and a large variety of prosthetic grafts are currently available on the market. Currently, vascular surgeons use prosthetic grafts for several different indications, including aortic aneurysm repair, arterial bypass in the upper and lower extremities, and dialysis access creation.

Prosthetic grafts can play an important role in the management of vascular disease for those patients who do not have adequate autogenous conduit. Although surgical bypass with autogenous vein has a well-established record with documented long-term patency rates, a growing proportion of patients needing bypass surgery lack suitable autogenous venous conduit. ^, Reasons for this include previous harvesting of the veins for coronary artery bypass or prior lower extremity revascularization procedures, small vein caliber, active infection at the vein harvest site, and vein varicosities or thrombosis.

The advent of endovascular technology has resulted in a corresponding reduction in the number of surgical bypasses performed in patients with arterial occlusive disease, with a concomitant increase in the complexity of patients that do require bypass such as the scenario of failed endovascular intervention. As such, lower extremity bypass with a prosthetic conduit continues to serve as a therapeutic choice in the revascularization of patients with limb ischemia.

Basic Principles

Materials

The ideal prosthetic conduit would be impermeable, compliant, biocompatible, durable, easy to sterilize, facile to implant, available in different sizes, resistant to thrombosis and infection, and cost-effective. Properties such as surface electronegativity, graft porosity, endothelial seeding, and heparin bonding have all been evaluated for their potential to improve graft function. Electronegativity on the graft surface plays a role in the inhibition of platelet aggregation with theoretic enhancement of this property by carbon coating of the luminal surface of the graft. Graft porosity has not been shown to significantly affect the rate of graft thrombosis but may be implicated in tissue ingrowth. Currently, the most commonly used prosthetic materials for revascularization surgery are Dacron and expanded polytetrafluoroethylene (ePTFE), although there are several commercially available graft materials ( Table 66.1 ).

TABLE 66.1

Selected Commercially Available Vascular Grafts in the United States

Material Type	Company	Product	Description
Standard
ePTFE	Angiotech/Edwards Life Sciences (Irvine, CA)	Lifespan	Re-enforced
	Atrium Medical Corporation (Hudson, NH)	Advanta VXT	Softwrap technology
		Advanta SST	Trilaminate, allows pulsation
		Advanta VS	60/20-μm through-pore design
		Flixene	Laminated with biomaterial film
	Bard Peripheral Vascular, Inc. (Tempe, AZ)	Impra CenterFlex	Unmodified
	Boston Scientific (Natick, MA)	Exxcel Soft Vascular Graft	Unmodified
	B. Braun (Melsungen, Germany)	VascuGraft	Unmodified
	Vascutek, Ltd. (Renfrewshire, United Kingdom)	Maxiflo Ultrathin	Thin wall, external ePTFE wrap
		Maxiflo Wrap	Regular wall, external ePTFE wrap
	W.L. Gore & Associates Inc. (Flagstaff, AZ)	Gore-Tex	Unmodified
		Gore-Tex Stretch	Stretch
		Gore Intering	Unibody, intrawall radially supported
Dacron	Braun	Protegraft	Knitted, double velour
	InterVascular, Inc. (Mahwah, NJ)	InterGard Ultrathin	Unmodified
	Vascutek, Ltd.	VP1200K	Unmodified
Sealed
ePTFE	Vascutek, Ltd.	SealPTFE Ultrathin	Gelatin sealed, thin wall
		SealPTFE Wrap	Gelatin sealed, regular wall
		Taperflo	Gelatin sealed, tapered
Dacron	Atrium Medical Corporation	Ultramax	Knitted, gelatin sealed, double velour
	Bard Peripheral Vascular, Inc.	Vasculour II	Knitted, albumin sealed
	Boston Scientific	Hemashield Gold Microvel	Knitted, collagen sealed, double velour
		Hemashield Platinum	Woven, collagen sealed
	B. Braun	UniGraft	Woven, gelatin sealed, single/double velour
	InterVascular, Inc.	InterGard Woven	Woven, collagen coated
		InterGard Knitted	Knitted, collagen coated
	Vascutek, Ltd.	Gelseal	Knitted, gelatin sealed
		Gelsoft	Knitted, gelatin sealed
		Gelsoft Plus	Köper knitted, gelatin sealed
Heparin Modified
ePTFE	W.L. Gore & Associates, Inc.	Propaten	Carmeda bioactive heparin coating
Dacron	InterVascular, Inc.	InterGard Heparin	Knitted, collagen coated
Carbon Modified
ePTFE	Bard Peripheral Vascular, Inc.	Impra Carboflo	Carbon coated
		Distaflo	Preformed cuff at distal end
		Dynaflo	Preformed cuff at distal end
Silver Modified
Dacron	B. Braun	SilverGraft	Antibacterial
	InterVascular, Inc.	InterGard Silver	Antibacterial
Others
Collagen based	Artegraft (North Brunswick, NJ)	Artegraft	Cross-linked bovine carotid artery
Polyurethane	Bard Peripheral Vascular, Inc.	Vectra	Self-bonded, trilayer Thoralon design for hemodialysis vascular access

ePTFE , expanded polytetrafluoroethylene.

Dacron

British chemists Whinfield and Dickinson developed the polyester fabric Dacron in 1941, and it is one of the oldest continuously used fabrics on the market. ^, Dacron grafts can be knitted or woven and can also be reinforced by external rings for support ( Fig. 66.1 ). Knitted grafts have the advantage of better compliance but have larger pores that tend to leak and require pre-clotting. As such, modern versions of knitted Dacron grafts are coated with albumin to prevent leakage from such pores. Dacron is a highly resilient fabric that is estimated to last over 30 years, but these grafts are at a higher risk of dilation compared with other graft materials. It is currently used primarily as a large-diameter graft in aortic and lower-extremity bypass surgery.

Expanded Polytetrafluoroethylene

ePTFE was described by Matsumoto and colleagues from Japan in 1973. It is configured on a mandrel process with a nodal–fibril porous configuration with carefully constructed inter-nodal distances to optimize function and healing properties. ePTFE grafts are available in several configurations: thin walled, ringed, and pre-cuffed ( Fig. 66.2 ). The pre-cuffed configuration was an attempt to optimize graft hemodynamics, but this has been difficult to confirm. The graft is produced by extruding a low porosity tube producing a graft that is compliant, easy to suture, and does not need to be pre-clotted, in contrast to knitted Dacron grafts.

Polypropylene and polyurethane

Developed in the early 1990s, the early experience with the use of this hydrocarbon material was promising. Polypropylene’s high tensile strength and relative inertness gave it an advantage over other prosthetic materials. It also had a long history of successful use in suture and hernia mesh. Polyurethane grafts are produced by the reaction of isocyanates with an alcohol group. The main advantage of polyurethane is high elasticity, but this material demonstrates poor biostability and loss of compliance after implantation limiting widespread clinical use.

Composite Grafts and Allografts

The successful implementation of prosthetic grafts has triggered the development of novel materials such as composite grafts including biologic materials using human umbilical vein, or bovine collagen. While this type of material has yet to be used for lower extremity bypass, the conduit has been used in a hemodialysis access. ^,

Cryopreserved Vein and Human Umbilical Vein Grafts

Cryopreserved vein and human umbilical veins are alternative conduits that were first utilized in the 1960s. Cryopreserved grafts are relatively expensive compared with other prosthetic conduits and have a greater incidence of aneurysmal degeneration and thrombosis from late rejection. The current data from multiple centers reported a 30%–58% patency rate at 1 year using cryopreserved veins for infrapopliteal bypass, which is inferior to autologous conduits and heparin bonded ePTFE grafts. However, given the biologic nature of the material, this graft may have value in bypasses that traverse infected fields in the absence of any autogenous conduit options, particularly as a temporizing procedure.

Clinical Applications