Stents Covered by Autologous Venous Grafts: Feasibility and Immediate and Long-Term Results

Christodoulos Stefanadis, MD, FACC, FESC, Konstantinos Toutouzas, MD, Eleftherios Tsiamis, MD, Charalambos Vlachopoulos, MD, Ioannis Kallikazaros, MD, Costas Stratos, MD, Manolis Vavuranakis, MD, FACC, Pavlos Toutouzas, MD, FACC, FESC, Department of Cardiology, Hippokration Hospital, University of Athens, Athens, Greece.

Am Heart J. 2000;139(3) 

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The results of this study imply that covered stents by autologous venous grafts may be safely applied in human coronary vessels. This is the first report of the long-term follow-up results after AVGCS implantation. The thickness of the venous graft is an important factor for the long-term outcome. In patients with ACS, a larger MLD was achieved and a trend toward a better clinical outcome after covered stent implantation was observed.

Randomized trials demonstrated that stenting compares favorably with balloon angioplasty in selected patients.[1,2] However, the TVR rate is increased in patients with thrombus-containing lesions and ostial and diffuse diseased vessels.[3,4,5] Moreover, the efficacy of stents and other techniques[12] in the treatment of coronary dissections, aneurysms, and perforations is not well defined.

Coating or covering of stents by several materials has been proposed as an appealing approach to these problems.[13,14,15,16] A new type of covered stent, consisting of a conventional stent covered by an autologous venous graft, was developed to address current problems of stenting.[6] The current study reports the results after the implantation of AVGCS in human coronary vessels, which to our knowledge is the largest series.

During the procedure of harvesting the vein, caution should be taken to maintain the intact endothelial layer. Accordingly, all the required manipulations during the removal of boundary tissues should not be harmful to the venous graft. Moreover, previous studies with the AVGCS have shown that the selection of the appropriate vein, in terms of diameter of the vein and thickness of the venous wall, is significant for successful deployment.[6,7] The veins of the upper limbs have the appropriate diameter with respect to the diameter of coronary arteries. The thickness of the venous wall, however, varies among the veins of the upper limbs. In this study, stents covered by venous grafts with greater thickness had superior results. Other investigators have successfully used the saphenous vein as a covering material.[17] These results are in accordance with the favorable outcome of patients, in which arterial graft was used as coverage of the stents.[11]

To cover the entire surface of the stent, a segment without side branches was selected. However, complete coverage of the stent was accomplished in every stent despite its length. This issue is important in covering coronary aneurysms, pseudoaneurysms, perforations, or extended dissections of the arterial wall.

In addition, the venous graft should not be overstretched over the external surface of the stent because the venous graft may be ruptured during the delivery over tortuous coronary segments. Therefore the venous graft was sutured in a slightly loose mode on the stent. In our experimental and clinical experience with type B AVGCS, the venous graft was trimmed to approximately 1 mm shorter than the length of the stent without observing complications during stent deployment.

The delivery of the AVGCS to the culprit lesion was performed without complications. The type A AVGCS was delivered through a 10F guiding catheter and was implanted only in vessels with diameter >3 mm. This limitation is resolved by type B AVGCS preparation. Additionally, the delivery of an AVGCS to the target lesion may be more easily facilitated, possibly by eliminating the occasional contact between the metal and the atherosclerotic plaques that may impede the delivery of the device. The expansion of the AVGCS was successful in all cases.

In this study, the AVGCS was prepared as 2 types. The experimental data with type A AVGCS, in which the stent is completely wrapped by the venous graft, showed thromboresistance of the endoprosthesis accompanied by minimal intimal hyperplasia.[6] However, the clinical application of this type is restricted because of the increased profile of the endoprosthesis. The type B AVGCS also sequestrates the atherosclerotic plaque and provides biocompatibility. Moreover, a statistically significant difference was not detected in the angiographic and clinical outcome of patients receiving either type A or type B AVGCS.

An important observation of this study was the steep learning curve of the technique. Although the majority of the investigators did not have experimental experience with the preparation of covered stents, the learning process was fast. Thus the procedure of stent coverage may be performed by any interventional cardiologist because special skills are not needed.

Although the rate of stent thrombosis is reduced by new developments, delayed endothelialization and protrusion of the atheromatic plaque remain significant thrombogenic factors.[18,19,20,21] Experimental data with covered stents suggest that the endothelialization procedure is accelerated[7,8] and that the accumulation of thrombotic factors may be prevented. Thus the impact of covered stents in the treatment of ACS may be significant. The underlying stenotic lesion is associated with plaque fissure, resulting in perturbation of the coronary blood flow. Accordingly, the continuous contact of the bloodstream with the ruptured atheromatic plaque may intensify thrombosis. The implantation of an AVGCS may sequestrate the culprit lesion. In addition, the dissection of the vessel wall, which usually exists in ACS, may be treated successfully by the placement of covered stents.

Stents reduce the restenosis rate in comparison with standard balloon angioplasty.[1,2,22,23,24] Conventional stents are resistant to arterial remodeling and are associated with minimal chronic recoil.[25,26,27] However, the injury of the arterial wall is the major factor for the development of intimal hyperplasia.[25,26,27] Covered stents reduce the injury of the arterial wall by avoiding the contact between the metal and the atheromatic plaque.[7] Another antirestenotic mechanism may be the atrophy across the arterial media circumference that was observed in the experimental studies of covered stents.[6,7]

The results of the current study are preliminary and depict our early experience with AVGCS because the numbers of patients in both groups are small. However, the study was not performed in highly selected patients but in patients of everyday clinical practice. Although repeat angiography was not performed in all patients because of refusal by either the patient or the referring physician and concomitant medical problems, the percentage of patients with angiographic follow-up was representative for the study group, including all patients with clinical restenosis. Also, the results of this study are constrained from 1 center, although to the best of our knowledge this is the largest experience.

The learning curve of this technique was steep, and the entire procedure was performed successfully by interventional cardiologists. The procedure of AVGCS preparation is not prolonged, which is important in emergency cases. However, in extremely urgent cases, the AVGCS may not be the treatment of choice. Furthermore, a minimal surgical procedure is required for harvesting the venous graft and thus the technique may not be performed in patients who received thrombolysis. In such patients, another limitation is the use of larger guiding catheters for the delivery of covered stents to the culprit lesion, which increases the risk for access site complications. Moreover, several case reports have shown the successful use of venous-covered stents for other indications besides coronary artery disease, such as coronary or peripheral aneurysms and pseudoaneurysms, rupture of coronary vessels, and closure of arteriovenous fistulas.[28,29,30]

The results of this study suggest that autologous venous graft-covered stents may be safely implanted in human coronary arteries without complications. Stents covered by thick venous grafts were associated with improved clinical outcome. This type of covered stent has encouraging long-term results and a trend to improve the event-free survival rate in patients with ACS. Accordingly, these angiographic and clinical benefits have plausible mechanistic explanations, and evaluation in trials is indicated. Moreover, the long-term outcome indicates that this technique may be safely applied for the treatment of disruptions of the integrity of vessel wall.