Experimental and clinical applications of angioscopic guidance for laser angioplasty.

The role of angioscopic monitoring and aiming for control of laser intervention in the vascular system was initially investigated in 48 vessels in 33 dogs, and the techniques were then applied to 30 patients undergoing intraoperative or percutaneous laser-probe angioplasty treatment for long atherosclerotic occlusions of the femoral and popliteal arteries or well-localized lesions of the superficial femoral artery. Experimental bare argon fiber laser application in 20 normal canine arteries in vivo demonstrated that small-diameter laser fibers could be accurately aimed by manipulations of the scope. However, advancement of the fiber resulted universally in perforation, with extravasation and thermal damage of surrounding tissues after 2 seconds of argon laser energy at low power. In 28 canine and 2 human veins, angioscopically guided metallic-tipped laserprobes were used to divide 82 valve cusps in preparation for in-situ bypass, with satisfactory aiming and monitoring achieved expeditiously by manipulations of the angioscope. We conclude that angioscopic aiming of lasers is feasible in normal vessels or localized lesions. In contrast, angioscopy has a restricted role for guidance of laser angioplasty in atherosclerotic, occluded arteries, and does not prevent perforation. Postprocedural inspection allows immediate detection of complications and may avert or predict poor outcome.

Intravascular ultrasonography.

Intravascular ultrasonography is developing rapidly as a method for defining the transmural anatomy of vascular structures, with diagnostic and therapeutic applications. The ultrasound technology not only has unique diagnostic capabilities by defining the distribution and character of lesions, but also provides accurate control information regarding efficacy of angioplasty methods. An exciting recent development is the three-dimensional reconstruction of two-dimensional images which permits global examination of luminal and transmural vessel morphology. This technology may enable improved guidance of intraluminal devices to enhance lesion removal without damaging adjacent normal wall structure and appropriate device selection by differentiating specific plaque characteristics.

The impact of intravascular ultrasound (IVUS) on endovascular interventions.

Intravascular ultrasound (IVUS) has undergone rapid evolution with the recent expansion of endovascular techniques and devices. This device can aid the surgeon, cardiologist, and interventional radiologist by increasing the accuracy of imaging and by adding important information to peripheral vascular and coronary interventions. Modern intravascular ultrasound provides a detailed view of the lumen, wall, and surrounding structures of blood vessels. Compared with other modalities, the diagnostic advantages of IVUS for examining arterial wall architecture and lesion morphology are evident. IVUS can determine lesion shape, length, and configuration, as well as identifying and examining the origins of branches and tributaries. Using this information, IVUS can guide the choice of appropriate angioplasty techniques, aid in the placement of endovascular devices, and assess and follow the efficacy of such interventions. IVUS helps reduce the use of radiation and contrast agents. Even though intravascular ultrasound requires additional equipment, personnel, and interpretative skills, it can be invaluable as a sensitive real-time imaging tool for complex endovascular interventions, therapeutic challenges, and diagnostic dilemmas.

Three dimensional vascular ultrasound imaging.

Intravascular ultrasound (IVUS) is a new catheter-based system that produces two-dimensional (2D) images of vascular structures. Existing systems produce real-time, cross-sectional "slices" of vessels using 5.0 French (Fr) (30 MHz) and 8.0 Fr (20 MHz) IVUS catheters containing ultrasound transducers at the tip. Computerized, three-dimensional (3D) reconstruction of these 2D images using a personal computer- (PC) based image analysis system is described. A set (n = 90) of longitudinally aligned, consecutive images is sampled from a 5.0 cm vessel segment, and computerized processing creates rendered 3D images. By adjusting image density threshold and viewing angle, the morphology, location, and spatial distribution of arterial pathology can be seen. Refinements in computer hardware and software have reduced processing time and improved image resolution to the point where 3D IVUS imaging is a clinically applicable tool. Possible applications include diagnosis of complex arterial pathology, guidance of intraluminal instruments, and assessment of the effects of endovascular interventions.

Forward-looking intravascular ultrasonography: in vitro imaging of normal and atherosclerotic human arteries.

Inadequate guidance of angioplasty devices limits the endoluminal treatment of high grade atherosclerotic stenoses and total occlusions. Conventional intraluminal ultrasound systems (IVUS) enable lateral cross-sectional imaging of tomographic sections of the vessel wall, but do not offer imaging in front of the catheter. This study describes our initial experience with a forward-looking intravascular ultrasound (FL-IVUS) system (Echoeye, EchoCath, Inc., Princeton, NJ). The acoustic beam from a 25.5 MHz piezoelectric transducer on a 7.5 Fr catheter is mechanically rotated in a forward-looking spiral fashion at 300 cycles/second. Sixty-four axially aligned, cross-sectional, real time images are obtained from a truncated, 60 degree conical volume located 5 to 10 mm from the catheter tip. Luminal dimensions (n = 51) of human cadaveric femoral arteries (cast in agar and submerged in saline) measured by the FL-IVUS were compared to histologic cross-sections of the vessel with a correlation of r = 0.92. FL-IVUS accurately imaged the narrowing lumen in front of total occlusions and the geometry at vessel branches, and identified the location of lesions and the shape and morphology of vessel wall thickness. The 7.5 Fr FL-IVUS over-estimated luminal dimensions in vessels larger than 5 mm. We conclude that FL-IVUS imaging shows promise as a new, accurate method for identifying and characterizing high grade atherosclerotic stenoses and total occlusions, and expands the current capabilities of conventional IVUS systems.

Computerized surgical databases: introduction to design and function.

There has been an enormous increase in the variety and volume of information encountered in surgical practice, either as measurable clinical variables or laboratory research data over the last three decades. Despite its form and origin, this information remains the basis of both daily clinical decision making and analytical research. Inferences drawn from past experience will modify an individual's approach to disease and treatment. However, when the demands of information processing cannot be met, mischief begins and quality of care declines. Modern computers offer an extraordinarily powerful method of processing the large volumes of medical data that are acquired, and provide techniques for analysis that would have been impossible, and often inconceivable, without computers. The applications of computer technology to surgical data management range from such simple and repetitive tasks as practice administration and accounting to elegant statistical and image analysis. This paper outlines the utility of computerized data management in clinical surgery and surgical research, and describes techniques for designing and implementing a customized surgical database system.

Biochemical mechanisms of laser vascular tissue fusion.

This study examines the biochemical changes that occur in argon laser-fused canine veins compared with control segments of vein. Laser fusions were formed using 0.5 W argon laser energy (1100-1500 J/cm2). Immediately following tissue fusion, blood flow was reestablished to test the integrity of the welds. 1-mm3 sections of the anastomoses and control sections were minced and protein extraction was performed by solubilizing the tissue in hot SDS Laemmli gel sample buffer. The proteins were separated electrophoretically on 5 and 10% polyacylamide SDS gels and silver stained. The analysis demonstrated significant biochemical differences between control and lased veins. We noted increases in several proteins after laser welding: the putative beta chain of type V collagen (5/5 gels), the putative gamma chain of type I collagen (4/5 gels), a 156-kDa protein (based on collagen molecular weight standards) 7/7 gels), an 82-kDa protein (8/9 gels), and several proteins of lower molecular weight (3/8 gels). The increases may be due to crosslinking of lower molecular weight proteins, degradation of higher molecular weight proteins, or increased solubility of certain proteins. These findings suggest that laser welding may occur by formation of crosslinks or by denaturation and reannealment of structural proteins.

The role of internal elastic laminae damage in the development of canine arteriosclerosis.

This study was designed to test the hypothesis that the extent of damage to the internal elastic lamina (IEL) may be a factor in determining the development of atheromatous lesions (lesion area). A bilateral iliac artery arteriosclerotic (AS) model in seven dogs prepared by intimal denudation and fracture of the IEL plus 5% cholesterol diet was investigated. The animals were sacrificed at 10-52 weeks (10, n = 1; 16, n = 3; 20, n = 1; 32, n = 1; 52, n = 1). Histologic analysis of sections (n = 42) of 14 canine iliac AS arteries harvested bilaterally from identical locations along the vessels (2, 7, and 12 cm from the aortic bifurcation) were compared with control segments of caudal and femoral arteries (n = 12) that had intact lamina and no luminal trauma. AS segments at all sites along the length of the traumatized iliac vessels demonstrated significant lesions, while control vessels had no arteriosclerotic changes. AS lesion area was calculated using ocular micrometry and a multiple regression model to test the predictability of the lesion area from the following independent variables: (1) proportion of intact IEL to total IEL (IEL/IELt), (2) sacrifice intervalens (3) frequency of disruptions to the IEL, (4) side and level of the arterial lesion, and (5) respective animals. This analysis revealed that none of the coefficients for the independent variables used in the multiple regression model was significant, suggesting that the extent of AS lesions is not related to the size, frequency, or location of breaks in the IEL, although a break in IEL is required to initiate the lesions. This observation suggests that the migration of cells from the arterial media through the broken laminae or the release of medial biochemical mediators which are normally contained by the elastic lamina is required to develop the AS lesions in this canine model, and that any size break in the lamina initiates the process.

Endoscopic surgery training: application of an in vitro trainer and in vivo swine model.

The development of endoscopic surgical procedures is changing general surgery, with many operations such as cholecystectomy, appendectomy, and hernia repair being performed using laparoscopic surgical techniques. Training and credentialing of surgeons are key issues for the safe and ethical introduction of these new procedures. This article reviews techniques employed at our institution for laparoscopic surgical training and certification including didactic instruction, an in-vitro model for learning instrumentation and hand-eye coordination, and in-vivo training using the porcine animal model.

Canine peripheral vascular arteriosclerosis following myointimal fragmentation and atherogenic diet.

The development of arteriosclerotic peripheral vascular lesions following balloon catheter and mechanical fragmentation of the arterial myointima combined with an atherogenic diet was studied in a canine model. The ileofemoral arteries of five mongrel dogs (mean wt 22 +/- 2 kg) were selectively cannulated and subjected to balloon catheter and mechanical myointimal injury by repeated longitudinal and transverse shearing forces. Twenty grams of hydrogenated coconut oil and a 5.0% cholesterol diet were fed to the animals daily during the study period. Followup angiographic studies obtained at 4 weeks (n = 2), 10 weeks (n = 3), 16 weeks (n = 3), and 24 weeks (n = 2) demonstrated changes of progressive peripheral vascular occlusion. Concurrent duplex Doppler studies correlated well with the angiographic results. At 10 (n = 1), 18 (n = 2), and 24 (n = 2) weeks, the animals were sacrificed and the vessels were perfusion-fixed in situ with 2% glutaraldehyde or formaldehyde solutions and excised. Histological examination demonstrated extensive arteriosclerotic changes including (i) fragmentation and reduplication of the internal elastic membrane, (ii) myointimal hyperplasia with fibroblastic proliferation including the development of fibrous intimal plaques, and (iii) transmigration and proliferation of smooth muscle cells with scattered monohistiocytes. The specimens showed a range of stenotic changes from 25% to total occlusion of the vascular lumen. These preliminary data demonstrate the feasibility of providing intense arteriosclerotic myointimal histologic changes in the canine peripheral vasculature within a 24-week period. Further refinement of this methodology may provide a practical model for studies of localized peripheral vascular occlusive disease.

The ideal guidance imaging system for endovascular interventions.

Endovascular interventions enable a minimally invasive approach to a variety of cardiovascular lesions. Small catheter-based delivery systems have rapidly evolved, diversifying endovascular therapeutic options. Coronary and peripheral vascular occlusive lesions may be amenable to angioplasty dilatation, intravascular stenting and ablation with mechanical atherectomy devices or lasers. New experimental transluminally placed endovascular stented grafts (TPEGs) have demonstrated feasibility for treating aneurysmal arteries, arteriovenous fistulas, and atherosclerotic occlusions. Improvements in imaging systems have provided better resolution of lesions, have improved patient selection and interventional strategy, and are invaluable for precise performance of procedures. The ideal guidance system should provide realtime imaging by a combination of complimentary modalities. These include cinefluoroscopy and contrast angiography, catheter-based intravascular ultrasound and angioscopy.

Intravascular ultrasound imaging: an essential component of angioplasty assessment and vascular stent deployment.

Potential early complications of balloon angioplasty include occlusion due to vessel wall recoil, medial dissection, creation of intimal flaps, spasm and luminal thrombosis. These features have also been implicated in the development of restenosis and late occlusion. As a possible solution to these problems, an endovascular scaffold (stent) was proposed by Dotter in the 1960s, and initial studies suggested that use of such a device in specific circumstances may reduce complications related to major dissection, vessel recoil and spams. This paper reports the utility of two- and three-dimensional intravascular ultrasound (IVUS) imaging in assessing arterial morphology following balloon angioplasty, and guiding the need for, and adequacy of deployment of intravascular stents. IVUS imaging provides a technique to accurately assess the immediate results of angioplasty and examine both the luminal size and contour following intervention. Accurate imaging such as this is essential for the successful use of balloon expandable stents, by ensuring correct initial positioning and complete deployment at the time of balloon expansion. Two cases are reported which highlight the important issues which are critical to the ongoing development of endovascular therapies: (i) accurate assessment of the angioplasty results, and (ii) selection and confirmation of stent deployment. We conclude that IVUS imaging may provide a new standard for the assessment of angioplasty procedures and will play a pivotal role in identifying failure mechanisms of endovascular interventions.

Intraoperative coronary angioscopy: development of practical techniques.

Techniques and equipment for intraoperative coronary angioscopy were studied in the coronary arteries and cardiac veins of excised and in vivo animal hearts. These studies then allowed development of safe, practical techniques for human clinical use. In coronary artery bypass operations, multichannel angioscopes of 2.3 to 2.8 mm diameter gave the best results for examinations of the bypass vein and anastomosis, whereas smaller optical fibers of 1 mm diameter were required for inspection of the native coronary artery. Abnormalities were detected in 11 of 48 (23%) coronary bypass anastomoses, and significant discrepancy in the degree of coronary artery stenosis as compared with the preoperative angiogram was revealed in 2 patients. The authors concluded that a new design of ultrafine, multichannel angioscope would be more suitable to the different requirements for inspection of both the anastomosis and the recipient artery.

Intravascular ultrasound: a new potential modality for angioplasty guidance.

Current angioplasty devices are limited by significant rates of arterial perforation and dissection, due to inadequate techniques of guidance, and by restenosis, which may be partly attributed to inadequate debulking of lesions. This paper describes the authors' initial experience in-vitro and in-vivo with intravascular ultrasound as a possible method of enhancing the three-dimensional guidance of devices through atherosclerotic obstructions. Using an in-vitro model they correlated the dimensions and histologic morphology of animal and human arteries with ultrasound images of the specimens. Additional in-vivo evaluations of this technology in canine arteriosclerotic and human atherosclerotic arteries preliminarily support the hypothesis that intravascular ultrasound defines the transmural arterial morphology and may enhance the accuracy of angioplasty procedures. Simultaneous imaging with angioscopy and intravascular ultrasound is demonstrated as a potential method of accurately defining both intraluminal and transmural arterial wall characteristics.

Aortic aneurysm morphology for planning endovascular procedures.

Endovascular prosthesis repair of abdominal aortic aneurysms is based upon the development of low-profile devices that can be expediently deployed within the aneurysm, excluding it from intraluminal pressure. Many factors affect the treatment of patients in this manner, including the morphology of the proximal and distal fixation sites, the diameter and disease state of the access vessels, and the ability of the device to conform to the many anatomic variations of aneurysms. In addition, preliminary data suggest there is progressive shrinkage and morphologic change in the configuration of an aneurysm following exclusion, which not only affects the alignment of the device but may also influence its healing and stability. This paper reviews the morphologic parameters of aneurysms relevant to endovascular repair and describes the imaging technologies used to assess these parameters before, during, and after intervention.

Utility of intravascular ultrasound in peripheral interventions.

Endovascular imaging techniques encompass a variety of methods, including angiography, computed tomography, magnetic resonance imaging, angioscopy, and intravascular ultrasound. Each method provides unique information regarding the continuity of vascular structures and the morphology and distribution of lesions. Although arteriography has been the "gold standard" for imaging arterial anatomy, recent data have confirmed that even sophisticated arteriographic imaging substantially underestimates the degree of residual lesions, and that future observations and end-points for treatment will most likely be determined by data accumulated by computed tomography, magnetic resonance imaging, angioscopy, and intravascular ultrasound. Successful therapeutic applications of endovascular devices have developed because of improved patient selection using computed tomography, spiral computed tomography, magnetic resonance imaging, and computerized high-resolution angiography. Procedural success has been enhanced by improved mobile cinefluoroscopy, angioscopy, intraluminal ultrasound monitoring of angioplasty procedures, and the use of intravascular ultrasound for stent and stent-graft sizing and deployment. Newly developed methods and low-profile delivery systems enabling deployment and fixation of vascular prostheses by an endoluminal approach have heightened the interest of many interventionalists, particularly surgeons, in the use of endovascular surgical techniques. The evolution of this method promises to add a new dimension to the treatment of vascular lesions and relies heavily on the incorporation of miniaturized imaging systems, such as intravascular ultrasound, as a means to provide precise placement of devices.

Optimal imaging for endovascular procedures: redefining the gold standard.

Minimally invasive techniques have been gaining popularity in all fields of surgery. Their application to vascular surgery has spawned advances in endovascular treatment of aneurysmal and atherosclerotic arterial disease. These procedures are dependent on various imaging modalities, including angiogra- phy, intravascular ultrasound, and computerized tomography scanning to choose appropriate candidates and devices, and to assure precise en doluminal treatment. No single imaging method is adequate for all aspects of endovascular surgery; however, an algorithmic approach may judiciously reduce the inherent inaccuracy and morbidity associated with current methods.