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Angioscopy
Angioscopy T h o m a s M. Vesely, MD
Angioscopy provides a magnified, real-time, 360 ~ view of the endoluminal surface of blood vessels, yielding unique information that is often complementary to conventional angiography. This unique perspective can significantly enhance one's perception and appreciation of endovascular disease~ Although angioscopy is primarily used as a research tool, its ability to characterize accurately the morphology and color of atherosclerotic lesions may lead to improved treatment and better clinical outcomes. Copyright 9 2001 by W.B. Saunders Company
ngioscopy is unique in its ability to provide real-time, 3-di-
A mensional color visualization of the endoluminal surface of a blood vessel. Direct visualization of the vascular lumen has been shown to improye both the identification and characterization of lesions when compared with angiography or intravascular ultrasound. Interestingly, the ability to visualize the coloration of an endoluminal lesion may prove to be one of its most valuable attributes.L2 The detailed characterization of vascular lesions can also be important for selecting the most appropriate treatment method. In doing so, the use of angioscopy may ultimately improve the clinical outcome of some types of endovascular therapy. And finally, angioscopy offers a unique and interesting approach for the study of various endoluminal disease processes. Indications for Angioscopy The true value of angioseopy has yet to be fully defined. The use of angioscopy as a percutaneous imaging tool has been primarily reserved for research applications. Continued improvements in fiberoptic technology have led to the development of smaller-diameter instruments with higher resolution and superior illumination. Angioscopy has the potential to evolve from an experimental research instrument to a sophisticated imaging method for both surgical and percutaneous procedures.
angiogram or duplex ultrasound in identifying endoluminal webs, nonocclusive thrombus, and areas of previous venous thrombosis.3. 4 A second common surgical application of angioscopy is for the evaluation of arteries and grafts during thromboembolectomy procedures. 5-7Angioscopy is used to locate the thrombus, to direct the manipulation of a Fogarty catheter (Edwards Lifesciences, Irvine, CA), and to evaluate the completeness of the thrombectomy procedure. Angioscopy is particularly valuable for differentiating acute thrombus from atherosclerotic plaque during these thrombectomy procedures.
Percutaneous Indications AlthoUgh angioscopy has become an important tool in vascular surgery, there has been little clinical use of this imaging instrument by radiologists. The development of small-diameter angio_scopes has allowed easier and safer percutaneous use, but the limiting factor continues to be the difficuhy in obtaining a blood-free imaging field. Contrast angiography is safe and easy to perform and thus remains the gold standard of vascular imaging procedures. Intravascular ultrasound and magnetic resonance angiography are also excellent vascular imaging techniques. Currently, percutaneous angioscopy cannot compete with the ease of use and the amount of clinical information.provided by these more common imaging modalities. One area in which percutaneous angioscopy has been used extensively is for coronary artery applications. The ability to obtain a blood-free imaging field is easier in these small-caliber vessels. Coronary angioscopes have a balloon at the distal tip that can be inflated to briefly occlude blood flow during the imaging procedure. Coronary angioscopy has been primarily used as a research tool to study atherosclerotic plaque morphology and to differentiate thrombotic versus nonthrombotic occlusive lesions. Angioscopy has also been used to evaluate the coronary arteries both before and after endovascular interventional procedures.
Surgical Applications A well-established surgical indication for angioscopy is during the creation or repair of in situ saphenous vein bypass grafts. Angioscopy is used to assess the overall quality of the vein graft, to identify and occlude venous side branches, and to perform valvulotomy under direct visualization. Several studies have shown that angioscopy is more accurate than an intraoperative
From the Washington University School of Medicine, St. Louis, MO. Address reprint requests to Thomas M. Vesely, MD, Mallinckrodt Institute of Radiology, 510 South Kingshighway BIvd, St. Louis, MO 63110. Copyright 9 2001 by W.B. Saunders Company 1089-2516/01/0401-0008535.00/0 doi:l 0.1053/tvir.2001.22007
Limitations of Angioscopy The following list shows the 5 limitations of angioseopy: 1. The primary limiting factor of angioscopy is the inability to seethrough blood. Unlike with other intravaseular imaging techniques, all of the blood must be cleared from the endoluminal field to achieve good and consistent visualization. Even a small amount of blood mixing with the irrigation tluid substantially reduces image quality. 2. The field-of-view is small and allows visualization of only a small segment of a blood vessel. 3. The angioscope is a qualitative instrument. The interpretation of an angioscopic image is subjective, and the clinical significance of many findings is unknown.
Techniques in Vascular and Interventional Radiology, Vol 4, No 1 (March), 2001: pp 75-81
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4. The angioscopic image is always magnified. The relative magnification depends on the distance from the lens to the area of interest. The closer the angioscopic lens is to an object, the larger the image appears. Precise measurements of endoluminal dimensions, which are helpful for interventional procedures, are difficult to obtain and are often unreliable. 5. Visualization of a vascular segment distal to a stenosis may not be possible. The angioscope should not be advanced through lesions that are smaller in diameter than the angioscope.
Equipment The angioscopy system consists of 4 components: flexible fiberoptic angioscope, light source, irrigation system, and video monitor and recording systent (Fig 1). 8 An angioscope contains several thousand optical fibers, which are separated into distinct bundles and encased in a flexible outer wrapp)ng. These fiberoptic bundles are concentrically organized wi!hin the angioscope and divided into those for imaging and those for conducting light for endovascular illumination. As thediameter of the angioscope increases, the number of fiberoptic bundles increases, leading to better resolution. The use of a large number of optical fibers improves.the transmission of both the image and light source and significantly improves overall endoluminal visualization. Powerful light sources, usually quartz-halogen or xenon, are needed t o produce an intense and focused light beam. The various angioscope manufacturers have different types of light sources, and each is designed to deliver light into a specific optical coupler that connects to the angioscope. Although it is possible to interchange light sources by the use of adapters, this tends to decrease the efficiency of light transmission. Endoluminal light requirements can fluctuate rapidly as the angloscope is directed from the vascular wall to the central lumen. Some light sources have automatic gain controls and feedback control circuits to optimize endoluminal illumination. A convex lens at the tip of the angioscope captures the image and transmits it through the fiberoptic bundles. The type of lens determines the depth and size of the field-of-view. Angioscopes with a smaller diameter typically have a 55 to 60 ~ lens, whereas larger angioscopes have a 75 ~ lens. The transmitted image is
magnified by an eyepiece, where it can be viewed directly, or attached to a video camera and displayed on a monitor. The imaging system also includes a standard video monitor and videotape recorder, providing both live viewing during the procedure and an archival storage system. Flexible angioscopes are available as either reusable (after being sterilized) or single-use (disposable) instruments. After multiple procedures, a reusable angioscope can develop broken fibers, which manifest as black dots, which degrade the image quality. Angioscopes are available in a range of diameters (0.7 mm to 3.0 mm) and lengths (50 cm to 120 cm). Coronary angioscopes often have a small compliant balloon located near the distal tip. This balloon can be inflated to briefly (less than 1 minute) occlude blood flow. Most angioscopes have a channel for irrigation or passage of a guide wire. Irrigation is essential for creating a clear, bloodfree field for intravascular imaging. Two methods of irrigation have been used. A saline bag can be pressurized (by using a blood pressure cuff) and then connected to the irrigation port of the angioscope. However, as the saline bag empties, the flow rate decreases. Furthermore, there is no accurate control of the flow rate. A more controlled and consistent irrigation is achieve d by using a mechanical roller pump designed specifically.for angioscopy. These pumps typically provide an option of 2 different flow rates: a bolus rate and a low flow-ntaintenance rate. Both rates ard variable and independent of each other. The irrigation flow is controlled with the use of a foot switch. The pump setting for an infrainguinal arterial procedure is 200 to 400 mL/min. Once a column of saline has been established within a blood vessel, it can be maintained at lower flow rates and smaller volumes. Because the angioscopist's attention is often focused on the intaging procedure, an assistant should closely watch the total irrigation volume. The irrigation lluid is usually room-temperature, normal saline solution (0.9% sodium chloride) with or without heparin (1 to 2 IU/ mL). The patient's cardiovascular and respiratory status should be monitored at all times during the procedure. Alternatively, a small-caliber angioscope can be inserted into a guiding catheter or vascular sheath, and the irrigation fluid can be infused through the sheath.
Techniques General Considerations
Fig 1. Angioscopic equipment: (A) monitor, (B) saline irrigation pump, (C) fiberoptic light source, (D) video recorder, and (E) image processing computer. 76
There is a trade-off between the size of the angioscope and the quality of the image. Angioscopes with a larger diameter provide better illumination and superior image resolution, but they require a larger vascular entry site and are limited in their ability to pass into small vessels. A common axiom is that the diameter of the angioscope should be less than two thirds of the diameter of the blood vessel to be examined. 5.9 The vascular field must be free of blood and must be replaced by a~lear column of irrigation fluid for optimal angioscopic imaging. This can be diffcuit when one uses a percutaneous approach into a peripheral artery or vein. It is often not possible to completely occlude inflowing blood. If the inflowing blood cannot be occluded, then the irrigation fluid must be infused at a high flow rate (200 to 400 mL/min) to obtain a blood-free imaging field. Even a short period of angioscopic imaging may require a significant volume (150 to 300 mL) of irrigation fluid. \Vith this in mind, the patient's medical condition becomes an THOMAS M. VESELY
important factor in determining the amount of fluid that can be safely administered during the procedure and, consequently, the duration of angioscopic imaging.
Smgical Approach The basic principle used during surgical angioscopy is to occlude all antegrade arterial blood flow, both from the main inflow artery and from any collateral channels. In the surgical setting, the surgeon can use vascular clamps to completely isolate the vascular segment to be imaged. ~~ Any remaining blood is removed with gentle irrigation. A common surgical application for angioscopy is to monitor the vessel or graft during thromboembolectomy procedures. When used in conjunction with a Fogarty thrombectomy balloon catheter, angioscopy can be used to monitor the degree of balloon inflation and thereby prevent wall damage and reduce vascular spasm caused by overinflation of the balloon. Under angioscopic guidance, endoluminal forceps can be safely used to remove residual thrombus or other intraluminal material. Angioscopic visualization of veins is more difficult because of the large number ot" venous tributaries that carry blood into the imaging field. A rapid infusion of saline can be used to clear the blood, but this fluid is quickly absorbed by the capacitanc e of the venous system. However, a bloodless field can be achieved if the venous tributaries are tied or otherwise occluded. Angioscopy h/~s been used to examine upper extremity veins during vascular access surgery. 4 A tourniquet is tied around the arm to limit back-bleeding from the central veins. The use of the tourniquet, combined with gentle irrigation, will distend the veins and allow a more thorough examination.
PercutaneousApproach The most significant obstacle for percutaneous angioscopy is the inability to obtain a bloodless field for imaging. Manual compression can be used to occlude the inflow vessel or, more commonly, an occlusion balloon is positioned within the proximal vessel and is inflated during the imaging procedure. Most investigators have used varying amounts of heparin (3,000 to 5,000 units) when using angioscopy for arterial applications. The angioscope is often used in conjunction with a long vascular sheath or a guiding catheter to provide directional control. The angioscope is advanced into the blood vessel by using fluoroscopy and direct visualization through the angloscope. Ideally, the lens of the angioscope should be positioned within the center of the vessel lumen. The best imaging is often obtained during withdrawal of the angioscope, not while advancing. The angioscope can be guided through the blood vessel by passive deflection or active steering. ~~Passive deflection occurs as the tip of the angioscope follows the natural curves of vasculature. However, it can be difficult to maintain visualization of the central lumen with this technique. A "whiteout" of the image occurs if the lens of the angioscope abuts an endoluminal wall. The use of a guiding catheter is often necessary to control and maneuver the angioscope for optimal imaging. In superficial conduits, such as hemodialysis grafts, the tip of the angioscope can be manipulated by direct compression of the overlying soft tissues. An ipsilateral antegrade approach into the common femoral artery is used for imaging the felnoropopliteal segment./2 A balloon occlusion catheter is advanced over the aortic bifurcation from a contralateral approach and is positioned in the ANGIOSCOPY
external iliac artery. The balloon is briefly inflated during the imaging procedure. Unfortunately, backflow of blood through side branches or collateral vessels can still substantially limit the field-of-view. A blood pressure cuff can be inflated around the upper thigh to reduce the amount of blood flow through these secondary vessels. A similar technique is used to image the iliac arteries. A balloon occlusion catheter is advanced over the aortic bifurcation from a contralateral approach and is positioned in the common or external iliac artery. The vascular sheath and angioscope are inserted into the ipsilateral common femoral arte D' in a retrograde direction. Inflow from the internal iliac artery often washes into the field-of-imaging, but high-flow irrigation may provide sufficient clearing of blood for a brief imaging period. Fujimoto et al reported the use of angioscopy within the inferior vena cava. 13 The common femoral vein was entered in a retrograde direction, and a guiding catheter was advanced into the vena cava. Venous blood flow was not occluded during their imaging procedures. They reported that a localized bloodfree field could be created at the tip of the angioscope by using an irrigation flow rate of 10 mL/min. They stated that their obse .ryations were made at close range, and the slow infusion ratewas sufficient to displace surrounding blood from the imaging field. Vesely et al reported the t{se ofangioscopy for the evaluation ofahrombosed hemodialysis grafts. 14 The 8F angioscope was inserted into the graft by using an apex approach to allow access to both the venous and arterial limbs. Angioscopy was performed after mechanical thrombectomy procedures. Maintenance of the arterial plug at the arterial anastomosis limited inflow into the graft. Good visualization of the graft lumen was obtained by using a saline infusion rate of 50 to 60 mL/min. Coronary angioscopy is performed by using an angioscope with a very small diameter (4F) tliat has an inflatable cuff located near the distal tip. 15 The angioseope is advanced through a long guiding catheter that is positioned within the coronary artery. For optimal imaging, the irrigation channel of the angioscope is continuously flushed (30 to 45 mL/min) with prewarmed saline while the balloon is inflated. The operator must remember that the angioscopic image is always magnified. The relative magnification depends on the distance from the angioseope lens to the area of interest. For this reason, precise measurements of endoluminal dimensions are difficult to obtain and are often unreliable. Spears et al have described the use of an intravaseular "lightwire" that can be used during angioscopy, z6 This device can provide more accurate measurement of luminal dimensions when one plans endovascular treatment procedures.
Complications An gioseopy can reduce radiation exposure and the risk of contrast-related complications associated with conventional angiography. However, patients undergoing angioscopy are at risk of fluid overload from the irrigation fluid and vascular injury caused by manipulation of the angioscope, z2 As previously mentioned, the use of saline irrigation is critical for optimal angioscopic imaging. During percutaneous arterial imaging, it is often difficult to completely occlude the proximal blood flow. A high flow rate (200 to 300 mL/min) of irrigation fuid is often necessary to obtain a blood-free field-
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of-view. Under these conditions, even a short duration of angioscopic imaging requires a significant volume of intravascular fluid. Angioscopic procedures are contraindicated in patients with heart failure, puhnonary problems, or other conditions in which additional intravascular fluid may not be well tolerated.17 The tip of the angioscope is blunt, and vascular injury can easily occur if the operator is not attentive. Movements of the angioscope can also elicit vascular spasm. If necessary, this can be controlled by the direct infusion of a vasodilator drug directly through the irrigation lumen of the angioscope. The angioscope should always move freely and should never be forced against resistance. Vascular damage, including dissection and perforation, can occur if the movements of the angloscope are not carefully controlled. Intimal flaps or atherosclerotic plaques can be easily disrupted or torn off by the angioscope. If vascular injury occurs, it is often not identified during advancement of the angioscope. The damage is not apparent until the angioscope is later withdrawn across the injured site. Injuries are more common when these instruments are used in smaller arteries and at vessel bifurcations. As previously mentioned, a good rule to follow is that the diameter of the angioscope should be less than two thirds of the diameter of the blood vessel to be examined. As with any intravascular procedure, there is a risk of infection, particularly when the angioscope is used to examine pros: thetic graft material. It is very important to use sterile technique when connecting the light source and video cables to the angioscope. These cables can be inserted into a sterile plastic sleeve to prevent contamination of the operative field during the procedure (Fig 2). Single-use disposable angioscopes are now widely available and can eliminate the possibility of insufficient sterilization with reusable-type instruments.
Observations For radiologists, who are accustomed to~n angiographic image, the real-time color visualization of the inside of a blood vessel can be awe-inspiring. Lesions that would not attract a second glance on a conventional angiogram are often fascinating in their color, shape, and movement when viewed through an angioscope. This unique perspective provided by angioscopy can significantly enhance one's perception and appreciation of
endovascular disease. However, from a clinical point of view, the interpretation of angioscopic images is subjective and requires a moderate amount of experience before a level of comfort can be achieved. The recognition of normality and the appearance of different lesions associated with the progression of atherosclerotic disease are important. The endoluminal surface of a normal artery is glistening white and smooth. ~~Upon irrigation with saline, tile field should be cleared of blood. There should be no adherent fibrin or other material attached to the endoluminal surface. Early atherosclerotic lesions are identified as small patches of yellow coloration on the vascular wall. As atherosclerosis progresses, the plaques become irregular and can protrude into tile vascular lumen. A thrombus canadhere to the surface of an eroded plaque. Acute thrombus can be washed away with a saline bolus, but chronic thrombus remains adherent. Arterial dissection is often readily apparent, although angioscopy may fail to identify a dissection if the luminal flap is parallel to the vascular lumen. ~s More commonly, the intimal flap is visualized as it rapidly flutters within the lumen. This "flapping" of the dissection can be accentuated by a bolus of saline. Extensive investigational work with the use of coronary angioscopy ~ias provided valuable insight into the pathophysiology of atherosclerosis. Angioscopy has shown that intracoronat), thi'ombi in patients with unstable angina differed from those observed in patients r acute myocardial infarction. 2 Patients with unstable angina had grayish-white thrombi, whereas red thrombi predominated in patients with acute infarction. These differences in color probably reflect differences in composition of the thrombus, perhaps caused by the age of the thrombus or the presence or absence of flow in the coronary artery. Red thrombi develop under conditions of stasis, whereas white (or gray) thrombi form when blood flow is not completely interrupted. Histologic studies have confirmed this observation. White thrombi are platelet-rich, but red thrombi contain an abundance of fibrin mixed with erythrocytes and platelets. Angioscopy can also help one to distinguish important surface features of coronary atheroma. Clinical studies have shown that acute coronary syndromes are not caused by tight stenoses but are often caused by the rupture of atheromatous plaques. ~9 Stable plaques are recognized by their elevated contour, smooth configuration, and white color. The white plaques tend to rupture or crack during coronary angioplasty. 2~ The investigators speculated that white plaques are calciunt-rich, hard, and nondistensible, and they easily rupture during dilatation. In contrast, yellow plaques are less commonly observed than white plaques. Yellow plaques are thought to contain a core of lipid covered by a weak fibrous cap, which can be easily ruptured. 21 Yellow plaques were also found to have higher low-density lipoprotein cholesterol and apolipoprotein B levels. 1
Clinical Results
Fig 2. A long plastic sleeve is used to cover the light source cable and irrigation tubing to prevent contamination of the procedural field. 78
Extensive surgical experience has shown that intraoperative angioscopy can improve clinical outcomes. However, the clinical utility of percutaneous angioscopy remains unknown. There have been very few reports (and no comparative trials) regarding the use of percutaneous angioscopy for the diagnosis or treatment of peripheral vascular disease. The most extensive clinical use of percutaneous angioscopy has been for coronary artery applications. Several investigators THOMAS M. VESELY
have reported that despite the additional visual information, the clinical outcomes may not be improved by the routine use of angioscopy, zs.19 The angioscope is a qualitative instrument. The interpretation of angioscopic observations is subjective and dependent on the experience of the operator (Fig 3). Many angioscopic findings are of uncertain clinical significance. In addition, there is a tendency to overestimate the severity of the lesion because of the magnification of the angioscope. This may lead to treatment of minor defects that may not be clinically significant (Fig 4). With continued clinical experience and correlation with clinical outcomes, we should be able to further refine our interpretative skills.
Vascular Surgery The most common application for angioscopyis during in situ saphenous vein bypass surgery. Holzenbein et al reported their use of angioscopy dur!ng reoperative surgery on the failing or failed infrainguinal vein bypass graft. 22 Angioscopy was used to define the extent of thle pathology so that new sites for surgical bypass could be optimally chosen. During 79 procedures, 66 additional findings were shown by angioscopy that resulted in 61 additional interventions and surgical decisions. The amount of thrombus within the graft, as assessed by angioscopy, was thought to be a critical determinant for overall early graft pa{ tency. Angioscopy was also helpful in identifying retained competent valve leaflets and in differentiating segments of recanalized thrombus from neointimal hyperplasia. Residual intraluminal thrombus, which was not identified on angiography, was found in 47% of patients. The second most common application of angioscopy is for the evaluation of arteries or bypass grafts during surgical thromboembolectomy procedures. Angioscopy is used to assess the completeness of the thrombectomy and to clarify the nature of any retained material (ie, thrombus v atheroma). White et al reported that angioscopy identified residual throm-
Fig 4. Intraluminal image shows multiple irregular fibrous strands attached to the wall of a polytetrafluoroethylene graft. These fibrous strands were moving rapidly within the lumen of the graft,
bus in 88% of patients after completion of the surgical thrombect0my procedure. 3 Segalowitz et al reported on the use of angioscopy during thromboembolectomy procedures in 32 patients. 9 Angioscopy identified residual thrombus or other important information in all 32 patients. Their results suggest that angioscopy provides improved technical results compared with standard surgical thrombectomy. Miller et al performed a prospective trial to compare angiography with angioscopy in 250 patients undergoing infrainguinal bypass with the saphenous vein. 23 Although more interventions were performed based on angioscopic findings, the 30-day graft patency was nearly equal, with 97% in the angioscopy group and 93% in the arteriography group. Angioscopy has the ability to differentiate thrombus from atherosclerotic plaque. This type of detailed characterization of endoluminal disease has been particularly valuable for the assessment of failing saphenous vein bypass grafts. Several investigators have discussed the concept that the angioscopic appearance of the cndoluminal surface after thrombectomy may provide a clue to the health of the surface endothelium. 6,7,22 The presence of residual thrombus within a native vein bypass graft or in the run-off arteries correlates with a reduction in early patency of the graft. Native vessels or grafts that cannot be adequately cleared of adherent thrombus may contain areas of dead or dysfunctional endothelium. A healthy endoluminal surface can resist the adherence of thrombus through the actions of surface anticoagulant glycoproteins or other mediators. This suggests that the inability to remove thrombus may be related to the viability of the intima and may therefore be indicative of irreversible intimal injury.
Vascular Access Surge D ,
Fig 3. Angioscopic image of a stenosis located at the venous anastomosis of a hemodialysis graft. ANGIOSCOPY
Holzenbein et al reported on their use of angioscopy during a broad range of surgical procedures related to vascular access for hemodialysis.4 Angioscopy was used to evaluate the arterial and venous anastomoses, the presence of intragraft stenoses, and
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the completeness of the surgical thrombectomy during these procedures. After surgical thrombectomy of 34 hemodialysis grafts, 52 abnormal findings were shown by angioscopy, including residual thrombus in 56% of the grafts. Although the amount of thrombus was not quantified, 21% of patients required a second procedure to remove residual thrombus. If the endoluminal pathology identified on angioscopy was corrected, the 30-day patency was 66.6%. In contrast, if no correction of the angioscopically shown pathology was performed, the 30day patency was 33.3%. These investigators reported that angioscopy had the most significant impact on surgical revisions of polytetrafluoroethylene grafts and was less helpful during the initial placement of the vascular access.
Radiology 9 Rees et al compared angioscopy with angiography in 10 patients during angioplasty of lower extremity peripheral arteries. 24 Clinically significant findings that were not seen with angiography were discovered by using angioscopy. The degree of atherosclerosis wag underestimated by angiography, and angioscopy connuonly showed more residual intraluminal thrombus than was seen by angiography. Fujimoto et al reported their experience of using angioscopy for the evaluation of intravascular neoplasms within the inferior vena cava in 10 patients. ~3 The tumor mass was success -9 fully imaged in 9 patients. These investigators concluded that angioscopy can be safely used to evaluate the extent of tumor invasion in large veins. Hill et al used angioscopy to image an aortic stent graft. 25The angioscope was inserted through a vascular sheath, which had a balloon fixed to the distal tip. The balloon displaced the surrounding blood and allowed a clear view of the endoluminal surface of the aorta and stent. Viewing of the aorta was performed through the balloon, which was filled with a 1:1 solution of contrast material and 0.9% saline.
Cardiology The introduction of small (5F), guide wire-compatible, highresolution angioscopes has led to a substantial increase in coronary angioscopy, although primarily for investigational purposes. Angioscopy has been shown to be valuable for defning the character, and possibly the composition, of lesions found within the coronary arteries. In particular, angioscopy has a high sensitivity for the identification of intracoronary thrombus. Teirstein et al compared coronary angiography with angioscopy for the detection of thrombus during interventional cardiology procednres in 75 patients. 26 Their overall thrombus detection rate with the use of angiography was 12% compared with 41% with angioscopy. White et al reported a similar observation: angiography had a sensitivity of 19% for the detection of thrombus in coronary artery bypass grafts compared with a sensitivity of 71% with angioscopy. 27 Several investigators have reported that angioscopy is superior to angiography for the characterization of coronary plaque morphology.1.2.2~ Angioscopy has been used to assess intracoronary lesions before and after endovascular interventions. 26,29,3~Angioscopy after balloon angioplasty shows that dissections and thrombus are present in almost all cases. There are often deep tears into the atherosclerotic plaque, with fronds of fibrinous or thrombotic material extending into the vessel lumen. Uchida et al has 80
shown that conventional angiography does not accurately delineate this type of complex morphology (or the true luminal dimensions) after endovascular interventions. 2~ Asakura et al made serial angioscopic observations after the insertion of intracoronary stents. 31 Their findings showed that the neointimal coverage of a stent peaked at 6 months after placement. Using angioscopy, these investigators found that the neointimal coverage over the stent became thinner and more transparent during the 3-year follow-up. Although there is continued enthusiasm regarding the usefulness of angioscopy during interventional procedures, there have been no prospective clinical trials to substantiate any improvement in clinical outcome or a reduction in complications based on angioscopic imaging.
Conclusion Angioscopy provides a magnified, real-time, 360 ~ view of the endoluminal surface of blood vessels, yielding unique information that is often complementary to conventional angiography. As the role of angioscopy continues to evolve, the ability to allow more accurate characterization of endoluminal lesions may lead'i0 improved treatment and better long-term results. Ultiniately, the ability of angioscopy to predict acute and longterm outcomes after endovascular interventions will determine the future of this imaging ~odality.
References 1. Kitamura K, Mizuno K, Miyamoto A, et al: Serum lipid profiles and the presence of yellow plaque in coronary lesions in vivo. Am J Cardiol 79:676-679, 1997 2. Mizuno K, Satomura K, Miyamoto A, et al: Angioscopic evaluation of coronary-artery thrombi in acute coronary syndromes. N Engl J Med 326:287-291, 1992 3. White GH, White RA, Kopchok GE, et al: Endoscopic intravascular surgery removes intraluminal flaps, dissections, and thrombus. J Vasc Surg 11:280-288, 1990 4. Holzenbein TJ, Miller A, Gottlieb MN, et al: The role of routine angioscopy in vascular access surgery. J Endovasc Surg 2:10-15, 1995 5. Pevec WC: Angioscopy in vascular surgery: The state of the art. Ann Vasc Surg 10:66-75, 1996 6. Miller A, Jepsen SJ, Stonebridge PA, et al: New angioscopic findings in graft failure after infrainguinal bypass. Arch Surg 125:749-755, 1990 7. White GH, White RA, Kopchok GE, et al: Angioscopic thromboembolectomy: Preliminary observations with a recent technique. J Vasc Surg 7:318-325, 1988 8. Winkelbauer FW, Lammer J: Angioscopy: I. History and technical equipment. Semin Intervent Radiol 12:28-36, 1995 9. Segalowitz J, Grundfest WS, Treiman RL, et al: Angioscopy for intraoperative management of thromboembolectomy. Arch Surg 125:1357-1362, 1990 10. White JV, Eid I: Diagnostic and interventional angioscopy. Surg Clin North Am 78:539-559, 1998 11. Miller A, Holzenbein TJ: Angioscopy in peripheral vascular surgery, in Whi~e RA, Hollier LH (eds): Vascular Surgery. Philadelphia, PA, Lippincott, 1994, pp 513-538 12. Winkelbauer FW, Lammer J: Angioscopy: II. Technique and indications of percutaneous peripheral angioscopy. Semin Intervent Radiol 12:37-46, 1995 13. Fujimoto K, Nakamura K, Takashima S, et al: Angioscopy of the inferior vena cava: Preliminary observations in cases with involvement by neoplasm. J Vasc Intervent Radiol 2:371-374, 1991 14. Vesely TM, Hovsepian DM, Darcy MD, et al: Angioscopic observations after percutaneous thrombectomy of thrombosed hemodialysis grafts. J Vasc Intervent Radiol 11:971-977, 2000 THOMAS M. VESELY
15. Annex BH: Coronary angioscopy. Clinical applications. Cardiol Clin 15:131-137, 1997 16. Spears JR, Ali M, Raza SJ, et al: Quantitative angioscopy: A novel method of measurement of luminal dimensions during angioscopy with the use of a "lightwire." Cardiovasc Intervent Radiol 17:197-203, 1994 17. Kwolek CJ, Miller A, Stonebridge, et al: Safety of saline irrigation for angioscopy: Results of a prospective randomized tdal. Ann Vasc Surg 6:62-68, 1992 18. Den Heijer P, Foley DP, Edcaned J, et al: Angioscopic versus angiographic detection of intimal dissection and intracoronary thrombus. J Am Coil Cardiol 24:649-654, 1994 19. Topoi EJ, Nissen SE: Our preoccupation with coronary luminology. The dissociation between clinical and angiographic findings in ischemic heart disease. Circulation 92:2333-2342, 1995 20. Uchida Y, Hasegawa K, Kawamura K, et al: Angioscopic observation of the coronary luminal changes induced by percutaneous transluminal coronary angioplasty. Am Heart J 117,769-776, 1989 21. Alfonso F, Fernandez-Ortiz A, Goicolea J, et al: ,~ngioscopic evaluation of angiographically complex coronary lesions. Am Heart J 134:703-711, 1997 2.2. Holzenbein TJ, Miller A, Tannenbaum GA, et al: Role of angioscopy in reoperation for the failing or failed infrainguinal vein bypass graft. Ann Vasc Surg 8:74-91, 1994 23. Miller A, Marcaccio EJ, Tannenbaum GA, et al: Comparison of angioscopy and angiography for monitoring infrainguinal bypass vein
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29. 30.
31.
grafts: Results of a prospective randomized trial. J Vasc Surg 17: 382-398, 1993 Rees MR, Gehani AA, Ashley S, et al: Percutaneous video angioscopy in peripheral vascular disease. Clin Radiol 40:347-351, 1989 Hill BB, Neville R, Hyde GL, et al: Angioscopic evaluation of an endoluminal aortic graft: The first clinical experience. J Endovasc Surg 2:248-254, 1995 Teirstein PS, Schatz RA, DeNardo SJ, et al: Angioscopic versus angiographic detection of thrombus during coronary interventional procedures. Am J Cardiol 75:1083-1087, 1995 White CJ, Ramee SR, Collins T J, et al: Percutaneous angioscopy of saphenous vein coronary bypass grafts. J Am Coil Cardiol 21:11811185, 1993 Waxman S, Zarich SW, Mittleman MA, et al: Predictive value of angiography to assess plaque morphology: In vivo comparison with angioscopy. Circulation 94:1-438, 1996 (suppl I) Teirstein PS, Schatz RA, Wong SC, et al: Coronary stenting with angioscopic guidance. Am J Cardiol 75:344-347, 1995 Rodes J, Bilodeau L, Bonan R, et al: Angioscopic evaluation of thrombus removal by the Possis AngloJet thrombectomy catheter. Cathet Cardiovasc Diagn 43:338-343, 1998 Asakura M, Ueda Y, Hirayama A, et al: Neointima covering stent became thinner and transparent at 3 years follow-up: Serial angioscopic and angiographic observations. Circulation 94:1-454, 1996 (suppl I)
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Angioscopy provides a magnified, real-time, 360 ~ view of the endoluminal surface of blood vessels, yielding unique information that is often complementary to conventional angiography. This unique perspective can significantly enhance one's perception and appreciation of endovascular disease~ Although angioscopy is primarily used as a research tool, its ability to characterize accurately the morphology and color of atherosclerotic lesions may lead to improved treatment and better clinical outcomes. Copyright 9 2001 by W.B. Saunders Company
ngioscopy is unique in its ability to provide real-time, 3-di-
A mensional color visualization of the endoluminal surface of a blood vessel. Direct visualization of the vascular lumen has been shown to improye both the identification and characterization of lesions when compared with angiography or intravascular ultrasound. Interestingly, the ability to visualize the coloration of an endoluminal lesion may prove to be one of its most valuable attributes.L2 The detailed characterization of vascular lesions can also be important for selecting the most appropriate treatment method. In doing so, the use of angioscopy may ultimately improve the clinical outcome of some types of endovascular therapy. And finally, angioscopy offers a unique and interesting approach for the study of various endoluminal disease processes. Indications for Angioscopy The true value of angioseopy has yet to be fully defined. The use of angioscopy as a percutaneous imaging tool has been primarily reserved for research applications. Continued improvements in fiberoptic technology have led to the development of smaller-diameter instruments with higher resolution and superior illumination. Angioscopy has the potential to evolve from an experimental research instrument to a sophisticated imaging method for both surgical and percutaneous procedures.
angiogram or duplex ultrasound in identifying endoluminal webs, nonocclusive thrombus, and areas of previous venous thrombosis.3. 4 A second common surgical application of angioscopy is for the evaluation of arteries and grafts during thromboembolectomy procedures. 5-7Angioscopy is used to locate the thrombus, to direct the manipulation of a Fogarty catheter (Edwards Lifesciences, Irvine, CA), and to evaluate the completeness of the thrombectomy procedure. Angioscopy is particularly valuable for differentiating acute thrombus from atherosclerotic plaque during these thrombectomy procedures.
Percutaneous Indications AlthoUgh angioscopy has become an important tool in vascular surgery, there has been little clinical use of this imaging instrument by radiologists. The development of small-diameter angio_scopes has allowed easier and safer percutaneous use, but the limiting factor continues to be the difficuhy in obtaining a blood-free imaging field. Contrast angiography is safe and easy to perform and thus remains the gold standard of vascular imaging procedures. Intravascular ultrasound and magnetic resonance angiography are also excellent vascular imaging techniques. Currently, percutaneous angioscopy cannot compete with the ease of use and the amount of clinical information.provided by these more common imaging modalities. One area in which percutaneous angioscopy has been used extensively is for coronary artery applications. The ability to obtain a blood-free imaging field is easier in these small-caliber vessels. Coronary angioscopes have a balloon at the distal tip that can be inflated to briefly occlude blood flow during the imaging procedure. Coronary angioscopy has been primarily used as a research tool to study atherosclerotic plaque morphology and to differentiate thrombotic versus nonthrombotic occlusive lesions. Angioscopy has also been used to evaluate the coronary arteries both before and after endovascular interventional procedures.
Surgical Applications A well-established surgical indication for angioscopy is during the creation or repair of in situ saphenous vein bypass grafts. Angioscopy is used to assess the overall quality of the vein graft, to identify and occlude venous side branches, and to perform valvulotomy under direct visualization. Several studies have shown that angioscopy is more accurate than an intraoperative
From the Washington University School of Medicine, St. Louis, MO. Address reprint requests to Thomas M. Vesely, MD, Mallinckrodt Institute of Radiology, 510 South Kingshighway BIvd, St. Louis, MO 63110. Copyright 9 2001 by W.B. Saunders Company 1089-2516/01/0401-0008535.00/0 doi:l 0.1053/tvir.2001.22007
Limitations of Angioscopy The following list shows the 5 limitations of angioseopy: 1. The primary limiting factor of angioscopy is the inability to seethrough blood. Unlike with other intravaseular imaging techniques, all of the blood must be cleared from the endoluminal field to achieve good and consistent visualization. Even a small amount of blood mixing with the irrigation tluid substantially reduces image quality. 2. The field-of-view is small and allows visualization of only a small segment of a blood vessel. 3. The angioscope is a qualitative instrument. The interpretation of an angioscopic image is subjective, and the clinical significance of many findings is unknown.
Techniques in Vascular and Interventional Radiology, Vol 4, No 1 (March), 2001: pp 75-81
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4. The angioscopic image is always magnified. The relative magnification depends on the distance from the lens to the area of interest. The closer the angioscopic lens is to an object, the larger the image appears. Precise measurements of endoluminal dimensions, which are helpful for interventional procedures, are difficult to obtain and are often unreliable. 5. Visualization of a vascular segment distal to a stenosis may not be possible. The angioscope should not be advanced through lesions that are smaller in diameter than the angioscope.
Equipment The angioscopy system consists of 4 components: flexible fiberoptic angioscope, light source, irrigation system, and video monitor and recording systent (Fig 1). 8 An angioscope contains several thousand optical fibers, which are separated into distinct bundles and encased in a flexible outer wrapp)ng. These fiberoptic bundles are concentrically organized wi!hin the angioscope and divided into those for imaging and those for conducting light for endovascular illumination. As thediameter of the angioscope increases, the number of fiberoptic bundles increases, leading to better resolution. The use of a large number of optical fibers improves.the transmission of both the image and light source and significantly improves overall endoluminal visualization. Powerful light sources, usually quartz-halogen or xenon, are needed t o produce an intense and focused light beam. The various angioscope manufacturers have different types of light sources, and each is designed to deliver light into a specific optical coupler that connects to the angioscope. Although it is possible to interchange light sources by the use of adapters, this tends to decrease the efficiency of light transmission. Endoluminal light requirements can fluctuate rapidly as the angloscope is directed from the vascular wall to the central lumen. Some light sources have automatic gain controls and feedback control circuits to optimize endoluminal illumination. A convex lens at the tip of the angioscope captures the image and transmits it through the fiberoptic bundles. The type of lens determines the depth and size of the field-of-view. Angioscopes with a smaller diameter typically have a 55 to 60 ~ lens, whereas larger angioscopes have a 75 ~ lens. The transmitted image is
magnified by an eyepiece, where it can be viewed directly, or attached to a video camera and displayed on a monitor. The imaging system also includes a standard video monitor and videotape recorder, providing both live viewing during the procedure and an archival storage system. Flexible angioscopes are available as either reusable (after being sterilized) or single-use (disposable) instruments. After multiple procedures, a reusable angioscope can develop broken fibers, which manifest as black dots, which degrade the image quality. Angioscopes are available in a range of diameters (0.7 mm to 3.0 mm) and lengths (50 cm to 120 cm). Coronary angioscopes often have a small compliant balloon located near the distal tip. This balloon can be inflated to briefly (less than 1 minute) occlude blood flow. Most angioscopes have a channel for irrigation or passage of a guide wire. Irrigation is essential for creating a clear, bloodfree field for intravascular imaging. Two methods of irrigation have been used. A saline bag can be pressurized (by using a blood pressure cuff) and then connected to the irrigation port of the angioscope. However, as the saline bag empties, the flow rate decreases. Furthermore, there is no accurate control of the flow rate. A more controlled and consistent irrigation is achieve d by using a mechanical roller pump designed specifically.for angioscopy. These pumps typically provide an option of 2 different flow rates: a bolus rate and a low flow-ntaintenance rate. Both rates ard variable and independent of each other. The irrigation flow is controlled with the use of a foot switch. The pump setting for an infrainguinal arterial procedure is 200 to 400 mL/min. Once a column of saline has been established within a blood vessel, it can be maintained at lower flow rates and smaller volumes. Because the angioscopist's attention is often focused on the intaging procedure, an assistant should closely watch the total irrigation volume. The irrigation lluid is usually room-temperature, normal saline solution (0.9% sodium chloride) with or without heparin (1 to 2 IU/ mL). The patient's cardiovascular and respiratory status should be monitored at all times during the procedure. Alternatively, a small-caliber angioscope can be inserted into a guiding catheter or vascular sheath, and the irrigation fluid can be infused through the sheath.
Techniques General Considerations
Fig 1. Angioscopic equipment: (A) monitor, (B) saline irrigation pump, (C) fiberoptic light source, (D) video recorder, and (E) image processing computer. 76
There is a trade-off between the size of the angioscope and the quality of the image. Angioscopes with a larger diameter provide better illumination and superior image resolution, but they require a larger vascular entry site and are limited in their ability to pass into small vessels. A common axiom is that the diameter of the angioscope should be less than two thirds of the diameter of the blood vessel to be examined. 5.9 The vascular field must be free of blood and must be replaced by a~lear column of irrigation fluid for optimal angioscopic imaging. This can be diffcuit when one uses a percutaneous approach into a peripheral artery or vein. It is often not possible to completely occlude inflowing blood. If the inflowing blood cannot be occluded, then the irrigation fluid must be infused at a high flow rate (200 to 400 mL/min) to obtain a blood-free imaging field. Even a short period of angioscopic imaging may require a significant volume (150 to 300 mL) of irrigation fluid. \Vith this in mind, the patient's medical condition becomes an THOMAS M. VESELY
important factor in determining the amount of fluid that can be safely administered during the procedure and, consequently, the duration of angioscopic imaging.
Smgical Approach The basic principle used during surgical angioscopy is to occlude all antegrade arterial blood flow, both from the main inflow artery and from any collateral channels. In the surgical setting, the surgeon can use vascular clamps to completely isolate the vascular segment to be imaged. ~~ Any remaining blood is removed with gentle irrigation. A common surgical application for angioscopy is to monitor the vessel or graft during thromboembolectomy procedures. When used in conjunction with a Fogarty thrombectomy balloon catheter, angioscopy can be used to monitor the degree of balloon inflation and thereby prevent wall damage and reduce vascular spasm caused by overinflation of the balloon. Under angioscopic guidance, endoluminal forceps can be safely used to remove residual thrombus or other intraluminal material. Angioscopic visualization of veins is more difficult because of the large number ot" venous tributaries that carry blood into the imaging field. A rapid infusion of saline can be used to clear the blood, but this fluid is quickly absorbed by the capacitanc e of the venous system. However, a bloodless field can be achieved if the venous tributaries are tied or otherwise occluded. Angioscopy h/~s been used to examine upper extremity veins during vascular access surgery. 4 A tourniquet is tied around the arm to limit back-bleeding from the central veins. The use of the tourniquet, combined with gentle irrigation, will distend the veins and allow a more thorough examination.
PercutaneousApproach The most significant obstacle for percutaneous angioscopy is the inability to obtain a bloodless field for imaging. Manual compression can be used to occlude the inflow vessel or, more commonly, an occlusion balloon is positioned within the proximal vessel and is inflated during the imaging procedure. Most investigators have used varying amounts of heparin (3,000 to 5,000 units) when using angioscopy for arterial applications. The angioscope is often used in conjunction with a long vascular sheath or a guiding catheter to provide directional control. The angioscope is advanced into the blood vessel by using fluoroscopy and direct visualization through the angloscope. Ideally, the lens of the angioscope should be positioned within the center of the vessel lumen. The best imaging is often obtained during withdrawal of the angioscope, not while advancing. The angioscope can be guided through the blood vessel by passive deflection or active steering. ~~Passive deflection occurs as the tip of the angioscope follows the natural curves of vasculature. However, it can be difficult to maintain visualization of the central lumen with this technique. A "whiteout" of the image occurs if the lens of the angioscope abuts an endoluminal wall. The use of a guiding catheter is often necessary to control and maneuver the angioscope for optimal imaging. In superficial conduits, such as hemodialysis grafts, the tip of the angioscope can be manipulated by direct compression of the overlying soft tissues. An ipsilateral antegrade approach into the common femoral artery is used for imaging the felnoropopliteal segment./2 A balloon occlusion catheter is advanced over the aortic bifurcation from a contralateral approach and is positioned in the ANGIOSCOPY
external iliac artery. The balloon is briefly inflated during the imaging procedure. Unfortunately, backflow of blood through side branches or collateral vessels can still substantially limit the field-of-view. A blood pressure cuff can be inflated around the upper thigh to reduce the amount of blood flow through these secondary vessels. A similar technique is used to image the iliac arteries. A balloon occlusion catheter is advanced over the aortic bifurcation from a contralateral approach and is positioned in the common or external iliac artery. The vascular sheath and angioscope are inserted into the ipsilateral common femoral arte D' in a retrograde direction. Inflow from the internal iliac artery often washes into the field-of-imaging, but high-flow irrigation may provide sufficient clearing of blood for a brief imaging period. Fujimoto et al reported the use of angioscopy within the inferior vena cava. 13 The common femoral vein was entered in a retrograde direction, and a guiding catheter was advanced into the vena cava. Venous blood flow was not occluded during their imaging procedures. They reported that a localized bloodfree field could be created at the tip of the angioscope by using an irrigation flow rate of 10 mL/min. They stated that their obse .ryations were made at close range, and the slow infusion ratewas sufficient to displace surrounding blood from the imaging field. Vesely et al reported the t{se ofangioscopy for the evaluation ofahrombosed hemodialysis grafts. 14 The 8F angioscope was inserted into the graft by using an apex approach to allow access to both the venous and arterial limbs. Angioscopy was performed after mechanical thrombectomy procedures. Maintenance of the arterial plug at the arterial anastomosis limited inflow into the graft. Good visualization of the graft lumen was obtained by using a saline infusion rate of 50 to 60 mL/min. Coronary angioscopy is performed by using an angioscope with a very small diameter (4F) tliat has an inflatable cuff located near the distal tip. 15 The angioseope is advanced through a long guiding catheter that is positioned within the coronary artery. For optimal imaging, the irrigation channel of the angioscope is continuously flushed (30 to 45 mL/min) with prewarmed saline while the balloon is inflated. The operator must remember that the angioscopic image is always magnified. The relative magnification depends on the distance from the angioseope lens to the area of interest. For this reason, precise measurements of endoluminal dimensions are difficult to obtain and are often unreliable. Spears et al have described the use of an intravaseular "lightwire" that can be used during angioscopy, z6 This device can provide more accurate measurement of luminal dimensions when one plans endovascular treatment procedures.
Complications An gioseopy can reduce radiation exposure and the risk of contrast-related complications associated with conventional angiography. However, patients undergoing angioscopy are at risk of fluid overload from the irrigation fluid and vascular injury caused by manipulation of the angioscope, z2 As previously mentioned, the use of saline irrigation is critical for optimal angioscopic imaging. During percutaneous arterial imaging, it is often difficult to completely occlude the proximal blood flow. A high flow rate (200 to 300 mL/min) of irrigation fuid is often necessary to obtain a blood-free field-
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of-view. Under these conditions, even a short duration of angioscopic imaging requires a significant volume of intravascular fluid. Angioscopic procedures are contraindicated in patients with heart failure, puhnonary problems, or other conditions in which additional intravascular fluid may not be well tolerated.17 The tip of the angioscope is blunt, and vascular injury can easily occur if the operator is not attentive. Movements of the angioscope can also elicit vascular spasm. If necessary, this can be controlled by the direct infusion of a vasodilator drug directly through the irrigation lumen of the angioscope. The angioscope should always move freely and should never be forced against resistance. Vascular damage, including dissection and perforation, can occur if the movements of the angloscope are not carefully controlled. Intimal flaps or atherosclerotic plaques can be easily disrupted or torn off by the angioscope. If vascular injury occurs, it is often not identified during advancement of the angioscope. The damage is not apparent until the angioscope is later withdrawn across the injured site. Injuries are more common when these instruments are used in smaller arteries and at vessel bifurcations. As previously mentioned, a good rule to follow is that the diameter of the angioscope should be less than two thirds of the diameter of the blood vessel to be examined. As with any intravascular procedure, there is a risk of infection, particularly when the angioscope is used to examine pros: thetic graft material. It is very important to use sterile technique when connecting the light source and video cables to the angioscope. These cables can be inserted into a sterile plastic sleeve to prevent contamination of the operative field during the procedure (Fig 2). Single-use disposable angioscopes are now widely available and can eliminate the possibility of insufficient sterilization with reusable-type instruments.
Observations For radiologists, who are accustomed to~n angiographic image, the real-time color visualization of the inside of a blood vessel can be awe-inspiring. Lesions that would not attract a second glance on a conventional angiogram are often fascinating in their color, shape, and movement when viewed through an angioscope. This unique perspective provided by angioscopy can significantly enhance one's perception and appreciation of
endovascular disease. However, from a clinical point of view, the interpretation of angioscopic images is subjective and requires a moderate amount of experience before a level of comfort can be achieved. The recognition of normality and the appearance of different lesions associated with the progression of atherosclerotic disease are important. The endoluminal surface of a normal artery is glistening white and smooth. ~~Upon irrigation with saline, tile field should be cleared of blood. There should be no adherent fibrin or other material attached to the endoluminal surface. Early atherosclerotic lesions are identified as small patches of yellow coloration on the vascular wall. As atherosclerosis progresses, the plaques become irregular and can protrude into tile vascular lumen. A thrombus canadhere to the surface of an eroded plaque. Acute thrombus can be washed away with a saline bolus, but chronic thrombus remains adherent. Arterial dissection is often readily apparent, although angioscopy may fail to identify a dissection if the luminal flap is parallel to the vascular lumen. ~s More commonly, the intimal flap is visualized as it rapidly flutters within the lumen. This "flapping" of the dissection can be accentuated by a bolus of saline. Extensive investigational work with the use of coronary angioscopy ~ias provided valuable insight into the pathophysiology of atherosclerosis. Angioscopy has shown that intracoronat), thi'ombi in patients with unstable angina differed from those observed in patients r acute myocardial infarction. 2 Patients with unstable angina had grayish-white thrombi, whereas red thrombi predominated in patients with acute infarction. These differences in color probably reflect differences in composition of the thrombus, perhaps caused by the age of the thrombus or the presence or absence of flow in the coronary artery. Red thrombi develop under conditions of stasis, whereas white (or gray) thrombi form when blood flow is not completely interrupted. Histologic studies have confirmed this observation. White thrombi are platelet-rich, but red thrombi contain an abundance of fibrin mixed with erythrocytes and platelets. Angioscopy can also help one to distinguish important surface features of coronary atheroma. Clinical studies have shown that acute coronary syndromes are not caused by tight stenoses but are often caused by the rupture of atheromatous plaques. ~9 Stable plaques are recognized by their elevated contour, smooth configuration, and white color. The white plaques tend to rupture or crack during coronary angioplasty. 2~ The investigators speculated that white plaques are calciunt-rich, hard, and nondistensible, and they easily rupture during dilatation. In contrast, yellow plaques are less commonly observed than white plaques. Yellow plaques are thought to contain a core of lipid covered by a weak fibrous cap, which can be easily ruptured. 21 Yellow plaques were also found to have higher low-density lipoprotein cholesterol and apolipoprotein B levels. 1
Clinical Results
Fig 2. A long plastic sleeve is used to cover the light source cable and irrigation tubing to prevent contamination of the procedural field. 78
Extensive surgical experience has shown that intraoperative angioscopy can improve clinical outcomes. However, the clinical utility of percutaneous angioscopy remains unknown. There have been very few reports (and no comparative trials) regarding the use of percutaneous angioscopy for the diagnosis or treatment of peripheral vascular disease. The most extensive clinical use of percutaneous angioscopy has been for coronary artery applications. Several investigators THOMAS M. VESELY
have reported that despite the additional visual information, the clinical outcomes may not be improved by the routine use of angioscopy, zs.19 The angioscope is a qualitative instrument. The interpretation of angioscopic observations is subjective and dependent on the experience of the operator (Fig 3). Many angioscopic findings are of uncertain clinical significance. In addition, there is a tendency to overestimate the severity of the lesion because of the magnification of the angioscope. This may lead to treatment of minor defects that may not be clinically significant (Fig 4). With continued clinical experience and correlation with clinical outcomes, we should be able to further refine our interpretative skills.
Vascular Surgery The most common application for angioscopyis during in situ saphenous vein bypass surgery. Holzenbein et al reported their use of angioscopy dur!ng reoperative surgery on the failing or failed infrainguinal vein bypass graft. 22 Angioscopy was used to define the extent of thle pathology so that new sites for surgical bypass could be optimally chosen. During 79 procedures, 66 additional findings were shown by angioscopy that resulted in 61 additional interventions and surgical decisions. The amount of thrombus within the graft, as assessed by angioscopy, was thought to be a critical determinant for overall early graft pa{ tency. Angioscopy was also helpful in identifying retained competent valve leaflets and in differentiating segments of recanalized thrombus from neointimal hyperplasia. Residual intraluminal thrombus, which was not identified on angiography, was found in 47% of patients. The second most common application of angioscopy is for the evaluation of arteries or bypass grafts during surgical thromboembolectomy procedures. Angioscopy is used to assess the completeness of the thrombectomy and to clarify the nature of any retained material (ie, thrombus v atheroma). White et al reported that angioscopy identified residual throm-
Fig 4. Intraluminal image shows multiple irregular fibrous strands attached to the wall of a polytetrafluoroethylene graft. These fibrous strands were moving rapidly within the lumen of the graft,
bus in 88% of patients after completion of the surgical thrombect0my procedure. 3 Segalowitz et al reported on the use of angioscopy during thromboembolectomy procedures in 32 patients. 9 Angioscopy identified residual thrombus or other important information in all 32 patients. Their results suggest that angioscopy provides improved technical results compared with standard surgical thrombectomy. Miller et al performed a prospective trial to compare angiography with angioscopy in 250 patients undergoing infrainguinal bypass with the saphenous vein. 23 Although more interventions were performed based on angioscopic findings, the 30-day graft patency was nearly equal, with 97% in the angioscopy group and 93% in the arteriography group. Angioscopy has the ability to differentiate thrombus from atherosclerotic plaque. This type of detailed characterization of endoluminal disease has been particularly valuable for the assessment of failing saphenous vein bypass grafts. Several investigators have discussed the concept that the angioscopic appearance of the cndoluminal surface after thrombectomy may provide a clue to the health of the surface endothelium. 6,7,22 The presence of residual thrombus within a native vein bypass graft or in the run-off arteries correlates with a reduction in early patency of the graft. Native vessels or grafts that cannot be adequately cleared of adherent thrombus may contain areas of dead or dysfunctional endothelium. A healthy endoluminal surface can resist the adherence of thrombus through the actions of surface anticoagulant glycoproteins or other mediators. This suggests that the inability to remove thrombus may be related to the viability of the intima and may therefore be indicative of irreversible intimal injury.
Vascular Access Surge D ,
Fig 3. Angioscopic image of a stenosis located at the venous anastomosis of a hemodialysis graft. ANGIOSCOPY
Holzenbein et al reported on their use of angioscopy during a broad range of surgical procedures related to vascular access for hemodialysis.4 Angioscopy was used to evaluate the arterial and venous anastomoses, the presence of intragraft stenoses, and
79
the completeness of the surgical thrombectomy during these procedures. After surgical thrombectomy of 34 hemodialysis grafts, 52 abnormal findings were shown by angioscopy, including residual thrombus in 56% of the grafts. Although the amount of thrombus was not quantified, 21% of patients required a second procedure to remove residual thrombus. If the endoluminal pathology identified on angioscopy was corrected, the 30-day patency was 66.6%. In contrast, if no correction of the angioscopically shown pathology was performed, the 30day patency was 33.3%. These investigators reported that angioscopy had the most significant impact on surgical revisions of polytetrafluoroethylene grafts and was less helpful during the initial placement of the vascular access.
Radiology 9 Rees et al compared angioscopy with angiography in 10 patients during angioplasty of lower extremity peripheral arteries. 24 Clinically significant findings that were not seen with angiography were discovered by using angioscopy. The degree of atherosclerosis wag underestimated by angiography, and angioscopy connuonly showed more residual intraluminal thrombus than was seen by angiography. Fujimoto et al reported their experience of using angioscopy for the evaluation of intravascular neoplasms within the inferior vena cava in 10 patients. ~3 The tumor mass was success -9 fully imaged in 9 patients. These investigators concluded that angioscopy can be safely used to evaluate the extent of tumor invasion in large veins. Hill et al used angioscopy to image an aortic stent graft. 25The angioscope was inserted through a vascular sheath, which had a balloon fixed to the distal tip. The balloon displaced the surrounding blood and allowed a clear view of the endoluminal surface of the aorta and stent. Viewing of the aorta was performed through the balloon, which was filled with a 1:1 solution of contrast material and 0.9% saline.
Cardiology The introduction of small (5F), guide wire-compatible, highresolution angioscopes has led to a substantial increase in coronary angioscopy, although primarily for investigational purposes. Angioscopy has been shown to be valuable for defning the character, and possibly the composition, of lesions found within the coronary arteries. In particular, angioscopy has a high sensitivity for the identification of intracoronary thrombus. Teirstein et al compared coronary angiography with angioscopy for the detection of thrombus during interventional cardiology procednres in 75 patients. 26 Their overall thrombus detection rate with the use of angiography was 12% compared with 41% with angioscopy. White et al reported a similar observation: angiography had a sensitivity of 19% for the detection of thrombus in coronary artery bypass grafts compared with a sensitivity of 71% with angioscopy. 27 Several investigators have reported that angioscopy is superior to angiography for the characterization of coronary plaque morphology.1.2.2~ Angioscopy has been used to assess intracoronary lesions before and after endovascular interventions. 26,29,3~Angioscopy after balloon angioplasty shows that dissections and thrombus are present in almost all cases. There are often deep tears into the atherosclerotic plaque, with fronds of fibrinous or thrombotic material extending into the vessel lumen. Uchida et al has 80
shown that conventional angiography does not accurately delineate this type of complex morphology (or the true luminal dimensions) after endovascular interventions. 2~ Asakura et al made serial angioscopic observations after the insertion of intracoronary stents. 31 Their findings showed that the neointimal coverage of a stent peaked at 6 months after placement. Using angioscopy, these investigators found that the neointimal coverage over the stent became thinner and more transparent during the 3-year follow-up. Although there is continued enthusiasm regarding the usefulness of angioscopy during interventional procedures, there have been no prospective clinical trials to substantiate any improvement in clinical outcome or a reduction in complications based on angioscopic imaging.
Conclusion Angioscopy provides a magnified, real-time, 360 ~ view of the endoluminal surface of blood vessels, yielding unique information that is often complementary to conventional angiography. As the role of angioscopy continues to evolve, the ability to allow more accurate characterization of endoluminal lesions may lead'i0 improved treatment and better long-term results. Ultiniately, the ability of angioscopy to predict acute and longterm outcomes after endovascular interventions will determine the future of this imaging ~odality.
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