J. Richard Spears

Coronary angioscopy during cardiac catheterization

Coronary angioscopy should permit direct inspection of the luminal cross section and identification of disease. The feasibility of introducing a 5F Olympus Ultrathin fiberscope into the obstructed right coronary artery in five patients after routine cardiac catheterization by the brachial approach was therefore tested. An 8.3F USCI woven Dacron angioplasty guiding catheter was modified to enlarge its lumen. After engaging the right coronary ostium with the catheter, an attempt was made to pass the angioscope coaxially to the tip of the catheter. Visualization of the coronary lumen was then achieved in three patients by manually injecting 5 to 10 cc of normal saline solution through the guiding catheter at 2 to 3 cc/s. White atheromatous plaque could be seen near the site of obstruction in each case. In two patients, a lack of sufficient flexibility in the distal 2 cm of the angioscope prevented passage to the catheter tip. Preliminary experience with a videoendoscopic system suggests that this monitoring technique is essential for the adequate performance of angioscopy and for recording dynamic changes during blood displacement. Geometric distortion of the image and nonlinearities in magnification and light reflex with a decreasing lens to object distance make quantitative evaluation of the lumen difficult. Lack of an angulation system further contributes to this problem and, more importantly, restricts passage of the angioscope to the proximal 1 to 2 cm segments of coronary arteries. Although coronary angioscopy may have research and clinical applications in the future, these technical problems should first be addressed.

In vivo coronary angioscopy.

The feasibility of in vivo coronary angioscopy was tested utilizing a 1.8 mm angioscope in vessels where blood had been replaced by optically clear liquids, including a new perfluorocarbon emulsion. After trials in postmortem canine and human coronary arteries, in vivo intraluminal visualization was accomplished in the dog with a catheterization technique and in patients during open heart surgery. The results demonstrate the feasibility and potential clinical usefulness of direct visualization of intravascular anatomy and disease, analogous to endoscopy of other organ systems.

Percutaneous transluminal coronary angioplasty restenosis: Potential prevention with laser balloon angioplasty

Restenosis after percutaneous transluminal coronary angioplasty may result primarily from the combination of a thrombogenic surface and local flow separation produced by disruption of the arterial wall and lumen. Elastic recoil and, perhaps, cellular proliferation further contribute to luminal compromise after percutaneous transluminal coronary angioplasty. Laser balloon angioplasty, performed during the final inflation of an otherwise conventional balloon angioplasty procedure, uses the coagulative properties of Nd:YAG laser radiation to weld together disrupted tissue elements thermally, to reduce elastic recoil and to destroy viable arterial tissue. Studies in human postmortem atheromatous arteries and in animal models in vivo indicate that laser balloon angioplasty, by creating a lumen that approximates the size and smooth cylindrical shape of the balloon, should be effective in the treatment of important causes of restenosis.

Uptake of hematoporphyrin derivative by atheromatous plaques: Studies in human in vitro and rabbit in vivo

Hematoporphyrin derivative, a photosensitive material used to identify and treat neoplastic tissue in humans, has been found to localize in atheromatous plaques in animals and has recently been found in postmortem human atherosclerotic plaques. It is not known whether human plaques take up hematoporphyrin derivative in vivo. In five patients undergoing surgical vascular procedures, specimens containing atheromatous plaques were removed and immediately incubated in autologous oxygenated blood at 37 degrees C with hematoporphyrin derivative at a clinically relevant concentration for 2 hours. On exposure to ultraviolet light, porphyrin fluorescence was noted throughout each plaque, whereas adjacent plaque-free tissue showed no fluorescence. To compare in vitro with in vivo hematoporphyrin derivative uptake by plaques, the fluorescence of three types of arterial lesions (induced by a high cholesterol diet, catheters or balloon injury) was studied in 16 New Zealand White rabbits. Each lesion fluoresced selectively with the same intensity whether hematoporphyrin derivative exposure was performed in vitro or in vivo. Fluorescence microscopy did not show a difference in the pattern of hematoporphyrin derivative fluorescence between in vitro and in vivo specimens. The results suggest that human atheromatous plaques should take up hematoporphyrin derivative in vivo and are, therefore, potentially suitable for photochemical treatment as a new therapeutic approach to atherosclerosis.

Percutaneous laser treatment of atherosclerosis: An overview of emerging techniques

In recent years, rapid progress in the application of lasers to the percutaneous treatment of atherosclerosis has been made. An overview of this progress is provided herein in terms of a description of promising laser approaches and problems to be solved. Direct vaporization of obstructing atheroma with fiberoptic delivery of laser energy has been associated with a high incidence of mural perforation, but each of a variety of techniques, including those for improved energy delivery, plaque recognition, alignment of the fiberoptic, and, perhaps, reduction of unnecessary thermal injury, has shown promise for reducing this complication. Nonablation applications of laser energy may also have a role in the treatment of atherosclerosis. During laser balloon angioplasty, the tissue coagulation effects of laser-thermal energy may be used during balloon inflation to eliminate arterial dissections and to reduce elastic recoil, thereby potentially eliminating abrupt reclosure and, perhaps, reducing the incidence of restenosis associated with conventional balloon angioplasty. Photochemical destruction of viable plaque tissue and vasa vasorum with porphyrins and intraarterial light represents a nonthermal, laser-based approach that could have a prophylactic role in slowing progression of diffuse atherosclerotic disease. The remarkable versatility of lasers is responsible for the multiplicity of approaches being investigated and for the current optimism that lasers will eventually play an important role in the percutaneous treatment of atherosclerosis.

Statistical considerations on the precision of assessing blood vessel diameter in cine coronary angiography

Problems related to the precision of computerized measurement and analysis of blood vessel diameter from digitized cineangiographic vessel images are described, and shortcomings of the conventional definition of percent stenosis are discussed. Formulae for the precision of percent stenosis, for the minimum significant measurable changes in blood vessel diameter, for the necessary scanning resolution, and for absolute vessel diameter measurement are provided. A Monte Carlo procedure-based technique for assessing the effect of radiographic noise on the location of vessel boundaries within the transverse densitometric image profile is presented and applied to contrast-filled cylindrical phantoms. The results demonstrate the feasibility for achieving subpixel resolution in computerized detection of vessel edges and diameter measurement.

Densitometric Determination Of Changes In The Dimensions Of Coronary Arteries

A computer-aided operator-interactive method has been developed to measure changes in the diameter of the coronary arteries as a result of the contractile motion of the heart and of vasodilators and constrictors. The method has been tested in animal models: mongrel dogs of 15-20 kg weight were subjected to cinefluorograohic procedures taken at a rate of 30 frames/sec. The selected width of segments of coronary arteries were measured with an EyeCom image analyzer interfaced to a VAX 11/780 comnuter at a resolution of -20 microns on 100 frames per injection. Ten scan lines were averaged for each segment: furthermore, in order to reduce scanning noise, each scan line was taken four times and averaged. The blood vessel diameter was determined as the horizontal distance of the base points in the blood vessel image profile. Autocorrelograms, power spectra and an ad-hoc method termed F-technique were used to analyze periodicities in the data. It was found that the amplitudes of periodic oscillations in the blood vessel diameters may be almost as large as the changes caused by some vasodilators and constrictors.

Computer Reconstruction of Luminal Cross-Sectional Shape from Multiple Cineangiographic Views

Knowledge of coronary luminal shape, in addition to diameter information as routinely obtained from a cineangiogram, may be useful in assessing lesions which deviate from circular symmetry. We have developed an image analysis system for automated tracking of luminal edges and measurement of diameter form cine frames digitized by a video camera/digitizer interfaced to a Vax 11/780 computer. Between vessel edges, cinedensitometric profiles across the vessel long axis are used to provide a rotationally invariant measure of relative luminal cross-sectional area. A maximum entropy iterative algorithm is used to reconstruct the lumen cross section from a set of projection data consisting of the cinedensitometric profiles from multiple radiographic views. Nonaxisymmetric model coronary lumena, such as a crescent shape and a double lumen simulating a coronary artery dissection, were filmed under cineradiographic conditions similar to clinical exposures. Radiographic views at 10° increments about the model lumen long axis over 360° were available for analysis. Graphic display of reconstructed model lumena indicate that as few as three to five radiographic views may be useful in reconstructing coronary luminal shape.

Laser Balloon Angioplasty: Experimental In-Vivo and In-Vitro Studies

Important causes of suboptimal angiographic results following percutaneous transluminal coronary angioplasty (PTCA) include elastic recoil, arterial dissection, and the presence of thrombus. Although increased vasomotor tone may contribute to a reduction of luminal diameter improvement, passive recoil probably accounts for most of the latter. Typically, in most clinical series [1–4] a mean residual diameter of acute stenosis of approximately 30%, which roughly corresponds to a 50% luminal cross-sectional area stenosis, is found after successful PTCA, presumably as a result of such recoil. Intimal tears may further compromise an apparently successful PTCA procedure, even without propagation of a dissection, by local disruption of laminar flow patterns. When thrombus is associated with a lesion treated with PTCA, a poor result is frequently encountered, perhaps as a result of the difficulty in attempting to remodel this tissue with pressure and the possibility that spreading the thrombus along the luminal surface may increase the number of sites of potential propagation of the thrombus.

Laser balloon angioplasty: potential for reduction of the thrombogenicity of the injured arterial wall and for local application of bioprotective materials.

Mitigation of adverse biologic reactivity after balloon angioplasty is necessary before the incidence of restenosis can be appreciably reduced. A brief review of experimental evidence supports the hypothesis that the thrombogenicity of the injured arterial wall can be reduced by a suitable level of thermal denaturation or cross-linking of thrombogenic proteins. In addition, the concept of local pharmacologic therapy, which can be provided with laser balloon angioplasty at the site of arterial injury, is introduced. Preliminary in vitro and in vivo data suggest that guide catheter-injected albumin-heparin conjugates fabricated as water-insoluble microspheres remain adherent to the injured luminal surface and deeper arterial layers after physical trapping by the inflated balloon and subsequent laser/thermal exposure. The combination of initially adequate luminal morphology, reduction of the thrombogenicity of the injured arterial wall and application of local pharmacologic therapy with laser balloon angioplasty may eventually prove helpful in reducing the incidence of restenosis.