Ann Thorac Surg 1997;63:37-40
© 1997 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Effects of Surgical Manipulation on Coronary Stents: Should Surgical Strategy Be Altered?
Eduard A. Tovar, MD,
Alan Borsari, MD
Departments of Cardiothoracic Surgery and Cardiology, St. Jude Medical Center, Fullerton, and the University of California, Irvine Medical Center, Orange, California
Accepted for publication June 11, 1996.
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Abstract
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Background. Coronary artery bypass grafting is usually indicated for those patients who undergo open heart surgical procedures who have previously undergone percutaneous transluminal coronary angioplasty regardless of the absence of stenosis. Occasionally, however, if the treated artery has remained patent for many years and there is a shortage of conduit material or the patient is undergoing a complex operation, the branch is left ungrafted. With the gaining popularity of coronary stent placement, patients with these devices are undergoing open heart operations with increasing frequency.
Methods. To determine whether normal surgical manipulation during open heart surgical procedures results in obliteration of the Palmaz-Schatz stents previously deployed in the epicardial arteries, we developed an experimental model using ten isolated adult pig hearts. This allowed us to perform stent deployment and surgical manipulation and to apply direct pressure on the stented areas, with each heart evaluated by angioscopy and angiography and, finally, stent explantation.
Results. Retraction of the heart resulted in severe deformity of all left anterior descending artery stents, mild deformity of those in the circumflex artery, and mild or no deformity of those in the right coronary artery. However, direct pressure over the stented epicardial arteries (enough to retract the heart) resulted in complete obliteration of every intracoronary stent.
Conclusions. The findings from this study indicate that once the need for surgical revascularization arises, a previously stented coronary artery should be bypassed even if the angiographic findings are normal, because of the likelihood that manipulation during an open heart operation will result in significant deformity or obliteration of the stent.
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Introduction
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See also page 220.
Despite intense research in the past decade, restenosis and acute vessel closure continue to be the main limitations of percutaneous transluminal coronary angioplasty. Their incidence remains 30% to 40% and 5%, respectively [1–3]. Intracoronary stents were developed to overcome these complications, and were introduced in 1986 [4]. Coronary stenting is now replacing percutaneous transluminal coronary angioplasty as the interventional procedure of choice in some centers. The restenosis rate after Palmaz-Schatz coronary stenting at 4 to 6 months reported for different series ranges between 13% and 36% [5–7].
See also page 220.
Occasionally during an open heart operation, a coronary artery previously treated by percutaneous transluminal coronary angioplasty that has remained patent for several years is left ungrafted. To establish whether the same is possible for stented arteries, we developed a model that permitted us to evaluate the effects of surgical manipulation on intracoronary stents.
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Material and Methods
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Angiography was performed in ten isolated adult pig hearts, followed by the deployment of Palmaz-Schatz stents (Johnson & Johnson Interventional Systems, Warren, NJ), one in each heart. Of the ten stents, four were placed in the left anterior descending distribution, three in the circumflex artery, and three in the right coronary artery. Stent implantation was accomplished using a previously described technique [8, 9]. Angiography and angioscopy (1.5-mm Angioscope; Applied Medical Resources Corp, Laguna Hills, CA) corroborated the adequacy of the deployments. Normal surgical retraction and manipulation of the heart, such as that routinely done during exposure of epicardial coronary arteries, were performed, followed by angioscopic evaluation. Direct pressure was then applied, followed by radiologic examination of the stent, repeat coronary angiography and angioscopy, and finally, stent explantation.
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Results
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All ten stents were adequately deployed, as shown by angiography (Fig 1
) and angioscopy (Fig 2). Retraction of the heart, such as that normally done to expose the right coronary artery or circumflex artery systems, resulted in severe deformity of all left anterior descending artery stents, mild deformity of those in the circumflex artery, and mild or no deformity of those in the right coronary artery as assessed by angioscopy (Fig 3). However, direct pressure over the stented epicardial arteries (enough to retract the heart) resulted in complete obliteration of every intracoronary stent, as demonstrated by angioscopy (Fig 4). Radiologic (Fig 5) and angiographic (Fig 6) evaluations failed to clearly reveal the deformity observed on direct examination (Fig 7). In comparing the accuracy of the radiologic, angiographic, and angioscopic findings with the findings noted on direct examination of the explanted stents, the angioscopic findings were the only ones found to be uniformly consistent with those observed on direct examination.
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Fig 1. . Stent (arrow) deployed in the mid-left anterior descending coronary artery, as shown by angiography.
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Fig 2. . Angioscopic view of same stent as that shown in Figure 1 . Notice adequate stent-to-vessel apposition.
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Fig 3. . Angioscopic image of the same intracoronary stent as that shown in Figure 1 after surgical manipulation. Notice the deformity of the stent and lack of stent-to-vessel apposition.
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Fig 4. . Angioscopic image of the same intracoronary stent as that shown in Figure 1 after direct pressure. Notice complete obliteration of the stent, which has become an intraluminal artifact.
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Fig 5. . Two radiologic images of the same intracoronary stent as that shown in Figure 1, after surgical manipulation and direct pressure. These studies fail to reveal the existing significant deformity.
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Fig 6. . Angiographic image of the same intracoronary stent (arrow) as that shown in Figure 1, after surgical manipulation and direct pressure. This study fails to reveal the existing significant deformity.
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Fig 7. . The explanted stent (the same as that shown in Figure 1) in the lateral (A) and anteroposterior (B) views, showing complete obliteration after surgical manipulation and direct pressure.
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Comment
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The Palmaz-Schatz stent is composed of two 7-mm-long, slotted, stainless steel tubes connected by a 1-mm bridging strut to allow for longitudinal flexibility [3]. When the balloon is expanded, the stent slots take on a diamond configuration that resists compression and lacks elastic recoil [3, 10]. The stent strut is 0.07 mm thick [11]. When expanded to 4 mm, the radial compressive force of a Palmaz-Schatz stent is 6.6 psi (Johnson & Johnson Interventional Systems; data on file). The surface area of the index finger applied to the site of a 4-mm diameter tube is approximately 0.038 square inches. Therefore, 6.6 psi equals 4 oz/0.038 square inch. In other words, a force of 4 oz is all that is needed to crush a 4-mm stent with the tip of the finger. The average normal human heart weighs approximately 11 oz. When lifting the empty heart with one finger, one applies more than twice the force needed to obliterate a Palmaz-Schatz stent.
The status of stent-to-vessel apposition and the presence or absence of thrombus or dissection have conventionally been determined on the basis of angiographic findings [12, 13]. Unfortunately, angiographic images capture only luminal features. As such, they are insufficient to accurately assess most endovascular therapies [12, 14, 15]. This is clearly shown by our experience, in which lack of stent-to-vessel apposition could not be demonstrated angiographically despite complete obliteration of the stent.
In conclusion, standard manipulation of the heart during open heart surgical procedures will likely result in geometric changes in the Palmaz-Schatz stents. Because angioscopy is not a practical way to evaluate them in the operating room, revascularization of all stented vessels should be performed. By the same token, multiple overlapping stents may become intraluminal artifacts in a large portion of the target artery, decreasing the effectiveness of surgical revascularization should the patient require this procedure.
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Acknowledgments
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We gratefully acknowledge Jean L. Burnette for her assistance in the preparation of the manuscript, and Carol Bondurant, St. Jude Medical Center Library, for the compilation of material.
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Footnotes
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Address reprint requests to Dr Tovar, 100 E Valencia Mesa Dr, Suite 301, Fullerton, CA 92835.
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References
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Abstract
Introduction
