Elastase-induced aneurysms in rabbits: effect of postconstruction geometry on final size.

BACKGROUND AND PURPOSE: Elastase-induced aneurysms in rabbits have become an accepted model to study endovascular treatment. The size and shape of the resulting aneurysms may vary widely. Our goal was to predict the final aneurysm morphology on the basis of immediate postinduction geometry. METHODS: Thirty New Zealand white rabbits were used. Aneurysms were created at the origin of the right common carotid artery (CCA). Intraluminal incubation of elastase was applied to the origin of CCA with proximal balloon occlusion of the artery. The aneurysms were allowed to mature for 3 weeks and evaluated by digital subtraction angiography. We retrospectively measured neck diameter, dome height, and aneurysm diameter, as well as the angle between the parent artery and the main axis of the aneurysm neck. We performed correlation analysis with immediate postinduction geometry. RESULTS: The diameter of the origin of the CCA measured immediately after elastase incubation correlated positively to the mature aneurysm neck (P < .01). Moreover, the aneurysm neck both after the aneurysm creation and at 3-week follow-up had a positive correlation with the final dome height (P < .05). Finally, the dome height was related to the angle between the centerline of the innominate artery and axis of the aneurysm neck for dome diameter-to-neck ratio of <1.5 (P < .05). CONCLUSION: These results indicate that neck width immediately after creation and the curvature of the parent artery are linked to the final aneurysm dimensions, and we may be able to predict the size of aneurysm on the day of creation.

Carbon dioxide column angioscopy: a new endovascular imaging technique.

A new angioscopic technique with a CO(2) gas medium for prolonged viewing sessions in the carotid artery is described. A stationary column of CO(2) gas, angled 17-30 degrees subhorizontally and buoyed against a balloon catheter, can be safely maintained. During 10-20-min sessions in dogs, endothelia, thrombi, stent filaments, coils, and an intimal flap were visualized. This technique eliminates the need for continuous saline infusion, which has prevented the application of angioscopy in the carotid artery.

Quantitative analysis of injured, necrotic, and apoptotic cells in a new experimental model of intracerebral hemorrhage.

OBJECTIVE: To develop a new survival model of intracerebral hemorrhage (ICH) in rabbits and study the patterns of cellular injury in different regions 24 hrs after introduction of hematoma. Quantitation and characterization of injured cells in regions adjacent and distant to the hematoma have not been performed. DESIGN: Prospective case-control study. SUBJECTS: Ten New Zealand rabbits. INTERVENTION: We introduced ICH in six anesthetized New Zealand rabbits by autologous blood injection under arterial pressure in the deep white matter in the frontal lobe. MEASUREMENTS AND MAIN RESULTS: Hematoxylin and eosin staining was performed in six animals with ICH after 24 hrs to quantify intact, injured, and necrotic cells in regions proximal and distant to the hematoma, and the results were compared with four control animals. Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining was performed to quantify apoptotic cells in specified regions in five animals with ICH, and the results were compared with four control animals. All cell counts were performed by one investigator who used 100x oil emersion microscopy. The presence of localized hematoma was confirmed in all six animals with blood infusion. Compared with controls, animals with ICH had a significantly higher proportion of swollen cells in both the inner (55.9% +/- 3.0% vs. 26.8% +/- 1.7%; p < .05) and the outer (59.8% +/- 4.6% vs. 27.7% +/- 4.5%; p < .05) rim of the perihematoma region. A small proportion of shrunken dark cells were observed in both the inner (4.0% +/- 1.5%) and the outer (3.6% +/- 1.0%) rim of the perihematoma region. The remaining cells were considered morphologically intact. A large proportion of cells trapped within the matrix of the hematoma were either shrunken dark cells (48.8% +/- 16.4%) or swollen (38.8% +/- 15.1%). In the TUNEL-stained sections, a high burden of apoptotic cells was observed in the matrix of the hematoma (17.5 +/- 6.3 cells per high power field) but not in the perihematoma regions (less than two cells per high power field). CONCLUSIONS: A reproducible model of ICH in rabbits is described. At 24 hrs, the perihematoma region contains relatively large proportions of morphologically intact or reversibly injured (swollen) cells, suggesting the possibility of an extended window for therapeutic intervention.

A novel intravascular drug delivery method using endothelial biotinylation and avidin-biotin binding.

In this study, a novel intravascular drug delivery system was developed in which a drug injected from a catheter was fixed to the vasculature of the targeted tissue. Cellular proteins of viable endothelial cells were first biotinylated directly by biotinylation reagents, and then bound by an avidinated drug or, using avidin as a linker, a biotinylated drug. In the initial experiments, we studied in vitro the biotinylation of cultured bovine aortic endothelial cells (BAECs) by applying biotinylation reagents (NHS-LC-biotin or sulfo-NHS-LC-biotin) onto the washed intact BAEC monolayers and showed that the amount of biotin bound to the cells depended on the concentration of the biotinylation reagents applied. The cell-bound biotin decreased with time after the biotinylation. When fluorescein-labeled avidin (FITC-avidin) was applied to the biotinylated BAEC monolayers, the FITC-avidin readily bound to the cells. An LDH-release assay showed that sulfo-NHS-LC-biotin was only slightly cytotoxic to the BAECs and a colony formation assay showed only slight adverse effects of the reagent. In vivo studies were carried out on the renal arteries of normal rabbits. A solution of NHS-LC-biotin was injected through a catheter to one kidney to biotinylate its vasculature and the vehicle to the other as control, followed by a perfusion with saline. Finally, a solution of FITC-avidin was injected to both kidneys that were then reperfused with the blood flow following the withdrawal of the catheters. In the histological sections, more than 85% of glomeruli was stained with fluorescein in the biotinylated kidney, whereas no glomeruli were stained in the control. In the kidneys harvested 2 days after the same procedure, most glomeruli were still brightly stained. In the final experiment, biotinylated kidneys were injected with a solution of avidin, followed by a solution of fluorescein-biotin. Control kidneys had no prior biotinylation but received the same injections of avidin and fluorescein-biotin as above. More than 80% of glomeruli were stained in the biotinylated kidneys but none in the controls. This indicated that biotinylated drugs can be anchored to the biotinylated vasculature through avidin without being flushed away by blood flows. No apparent adverse effect was found in the functions of biotinylated kidneys. We propose that this drug delivery system is feasible for the treatment of some pathological conditions of blood vessels such as microvascular proliferation in malignant tumors and for continuous drug delivery in certain target organs.

Angioscopy-assisted aneurysm clipping.

OBJECTIVE: To test the concept that endovascular angioscopy can assist surgical intracranial aneurysm clipping by providing an endoluminal view of the aneurysm-parent vessel complex. METHODS: A carotid bifurcation aneurysm was surgically created in a dog at the lingual artery origin. A balloon catheter was inflated proximal to the aneurysm to block proximal blood flow and allow endoluminal visualization. A flexible angioscope connected to a video monitoring system and to a high-intensity light source was then advanced within the catheter lumen and positioned immediately distal to the catheter tip. The aneurysm neck was clipped, and the clip was repositioned several times along the neck, with or without distal parent vessel compromise. Each time, the endovascular image on the monitor was interpreted by an observer blinded to the position of the clip. Clip position and image interpretation were communicated independently to a third person, who analyzed the correlation between them. RESULTS: Angioscopy allowed clear visualization of the extent of aneurysm neck occlusion (complete, incomplete, residual "dog ear") after clip application, as well as the presence or absence of distal parent vessel compromise. Aneurysm neck configuration, size, presence of thrombus, and suture line definition were depicted. Critical structures external to the aneurysm-parent vessel complex were transilluminated by the high-intensity lamp. CONCLUSION: Although acknowledged as the treatment of choice for intracranial aneurysms, surgical exclusion can be accompanied by significant morbidity related to perforator occlusion, parent artery compromise, and/or persistent residual aneurysm. The availability of a device allowing visualization of an aneurysm from an endoluminal perspective theoretically could reduce the incidence of these complications. Angioscopy has the potential to become a useful adjunct during intracranial aneurysm clipping because it provides real-time endoluminal viewing of the aneurysm-distal parent vessel complex, which is sometimes obscured to the surgeon.

Saccular aneurysm induction by elastase digestion of the arterial wall: a new animal model.

OBJECTIVE: To develop a rabbit aneurysm model that is more realistic in gross appearance and histological features than previous models and to enable the development of a larger animal model. METHODS: Ten rabbits received porcine pancreatic elastase, five at the right common carotid artery bifurcation and five others at the right superior thyroid artery origin. One control animal received collagenase and another received papaverine, each at the right superior thyroid artery origin. The agents were topically delivered to the arterial adventitia with a microsyringe after surgical exposure of the targeted arteries. The arteries were monitored for aneurysm growth with a video camera for up to 3 hours and were then removed and processed for histology. RESULTS: Saccular aneurysms developed in one of five animals after elastase application at the carotid bifurcation and in all five animals receiving elastase at the superior thyroid artery origin. Among the six aneurysms, recurrent minor hemorrhages occurred in four, thrombosis of the aneurysm sac in three, and rupture causing severe bleeding in one. Histological sections revealed thin-walled aneurysms composed only of collagen fibers and some cellular elements. No saccular dilation resulted from papaverine application. Collagenase application resulted in a hemorrhagic-thrombotic lesion in the arterial wall but no aneurysm formation. CONCLUSION: Arterial saccular aneurysms were induced in rabbits by topical application of elastase with an easy and efficient method. These aneurysms are histologically similar to natural aneurysms, and their arterial nature renders them more authentic than those of surgical models. This aneurysm model may serve as a foundation for further aneurysm research.

Rapid saccular aneurysm induction by elastase application in vitro.

OBJECTIVE: To develop a new saccular aneurysm model in vitro using elastase to study aneurysm initiation, growth, and rupture and to create a new in vivo aneurysm model to test endovascular therapies. METHODS: Seventeen common carotid arteries excised from freshly killed pigs and sheep were treated with seven different methods of elastase delivery. The arteries were mounted in a saline-filled flow chamber. They received pulsatile flow for 48 hours, or until the resulting aneurysms ruptured. Changes were continuously monitored with video camera recordings and validated with histological sections. RESULTS: All eight arteries treated topically, either on the intimal or on the adventitial surface, with elastase concentrations greater than 1 U/mm2, developed saccular aneurysms; five of them ruptured within 48 hours. All four arteries treated with surface concentrations of 0.1 U/mm2 via microcatheter infusion into the lumen developed fusiform aneurysms. None of the arteries that received surface concentrations less than 0.1 U/mm2 developed aneurysms. Histological sections revealed a reduced number of cellular element in a stretched collagen matrix at the dome of the saccular aneurysms. CONCLUSION: After empirically testing several methods of elastase delivery, we were able to induce saccular, bifurcation-type aneurysms in animal arterial specimens. These aneurysms are histologically similar and more authentic than surgical models. The procedure is easy and reproducible. Our results suggest a possible enzymatic role in aneurysm formation and highlight the dramatic effects of selective arterial elastic damage. Also, the rapid growth of our experimental aneurysms may reflect the speed of the natural process.

Depiction of carotid plaque ulceration and other plaque-related disorders by intravascular sonography: a flow chamber study.

PURPOSE: To evaluate the ability of intravascular sonography to depict plaque ulceration and to identify the limitations of and the artifacts associated with this technique. METHODS: Twenty-eight human carotid arteries were mounted in a pulsatile flow chamber and examined with intravascular sonography. We compared 140 intravascular sonograms with gross pathologic and histologic sections. Ulcerations with a diameter or depth of at least 0.5 mm were sought. RESULTS: All eight arteries with ulcerated plaques and nine of 10 individual ulcerations were depicted by intravascular sonography. One artery (one of 140 arterial cross sections) with a small mural thrombus was misinterpreted as ulcerated. Our intravascular sonographic measurements underestimated the gross ulceration dimensions by 22% (depth) and 17% (orifice diameter). CONCLUSIONS: Intravascular sonography is highly accurate for the diagnosis of plaque ulceration. The central position of the high-frequency transducer within the target vessel facilitates high resolution of the arterial lumen-wall border, permitting more powerful definition of small ulcerations than available by other diagnostic methods. However, the utility of invasive intravascular sonography for detecting carotid ulcerations cannot be determined until the pathologic significance of plaque ulceration is clearly defined.