Final Two-Year Outcomes for the Sentry Bioconvertible Inferior Vena Cava Filter in Patients Requiring Temporary Protection from Pulmonary Embolism.

PURPOSE: To report final 2-year outcomes with the Sentry bioconvertible inferior vena cava (IVC) filter in patients requiring temporary protection against pulmonary embolism (PE). MATERIALS AND METHODS: In a prospective multicenter trial, the Sentry filter was implanted in 129 patients with documented deep vein thrombosis (DVT) and/or PE (67.5%) or who were at temporary risk of developing DVT/PE (32.6%). Patients were monitored and bioconversion status ascertained by radiography, computed tomography (CT), and CT venography through 2 years. RESULTS: The composite primary 6-month endpoint of clinical success was achieved in 97.4% (111/114) of patients. The rate of new symptomatic PE was 0% (n = 126) through 1 year and 2.4% (n = 85) through the second year of follow-up, with 2 new nonfatal cases at 581 and 624 days that were adjudicated as not related to the procedure or device. Two patients (1.6%) developed symptomatic caval thrombosis during the first month and underwent successful interventions without recurrence. No other filter-related symptomatic complications occurred through 2 years. There was no filter tilting, migration, embolization, fracture, or caval perforation and no filter-related deaths through 2 years. Filter bioconversion was successful for 95.7% (110/115) of patients at 6 months, 96.4% (106/110) of patients at 12 months, and 96.5% (82/85) of patients at 24 months. Through 24 months of follow-up, there was no evidence of late-stage IVC obstruction or thrombosis after filter bioconversion or of thrombogenicity associated with retracted filter arms. CONCLUSIONS: The Sentry IVC filter provided safe and effective protection against PE, with a high rate of intended bioconversion and a low rate of device-related complications, through 2 years of follow-up.

One-Year Analysis of the Prospective Multicenter SENTRY Clinical Trial: Safety and Effectiveness of the Novate Sentry Bioconvertible Inferior Vena Cava Filter.

PURPOSE: To prospectively assess the Sentry bioconvertible inferior vena cava (IVC) filter in patients requiring temporary protection against pulmonary embolism (PE). MATERIALS AND METHODS: At 23 sites, 129 patients with documented deep vein thrombosis (DVT) or PE, or at temporary risk of developing DVT or PE, unable to use anticoagulation were enrolled. The primary end point was clinical success, including successful filter deployment, freedom from new symptomatic PE through 60 days before filter bioconversion, and 6-month freedom from filter-related complications. Patients were monitored by means of radiography, computerized tomography (CT), and CT venography to assess filtering configuration through 60 days, filter bioconversion, and incidence of PE and filter-related complications through 12 months. RESULTS: Clinical success was achieved in 111 of 114 evaluable patients (97.4%, 95% confidence interval [CI] 92.5%-99.1%). The rate of freedom from new symptomatic PE through 60 days was 100% (n = 129, 95% CI 97.1%-100.0%), and there were no cases of PE through 12 months for either therapeutic or prophylactic indications. Two patients (1.6%) developed symptomatic caval thrombosis during the first month; neither experienced recurrence after successful interventions. There was no filter tilting, migration, embolization, fracture, or caval perforation by the filter, and no filter-related death through 12 months. Filter bioconversion was successful for 95.7% (110/115) at 6 months and for 96.4% (106/110) at 12 months. CONCLUSIONS: The Sentry IVC filter provided safe and effective protection against PE, with a high rate of intended bioconversion and a low rate of device-related complications, through 12 months of imaging-intense follow-up.

"Caval Reconstruction for Lower-Extremity Sarcoma Metastasis Trapped within Inferior Vena Cava Filter".

This report describes the management of a hematogenously spread metastasis from a lower-extremity sarcoma found trapped within an inferior vena cava (IVC) filter. Although endovascular techniques for treating thrombosed IVC filters are successful in a majority of cases, the malignant nature of this lesion required a novel approach. In this unique case, the segment of infrarenal IVC with the thrombosed filter was resected and reconstruction performed with an interposition prosthetic graft. There were no early or late complications, and the patient remains clinically free of recurrence at 24-month follow-up.

Isolated blunt abdominal aortic injury without concomitant abdominal injuries treated with endovascular stent grafting.

Blunt injury of the abdominal aorta is a rare event, seen in only 0.07% to 0.17% of all blunt traumas. These injuries are frequently associated with other intra-abdominal injuries, with high rates of morbidity and mortality. We present a case of isolated blunt abdominal aortic trauma to the infrarenal aorta without concomitant abdominal or spinal injuries. The patient was treated with endovascular aortic stent grafting and is without complications 12 months after the procedure.

Papilledema due to a permanent catheter for renal dialysis and an arteriovenous fistula: a "two hit" hypothesis.

Elevated intracranial pressure in patients with chronic renal failure has several potential causes. Its rare occurrence secondary to the hemodynamic effects of hemodialysis is described and the findings support a multifactorial etiology ("two hits").

Coil embolization as a treatment alternative for dialysis-associated steal syndrome.

Steal syndrome is a rare but serious complication of arteriovenous fistulas (AVF) created as well as the angioplasty technique used for its maturation and can have severe consequences if left untreated. Standard treatment options generally lead to loss of fistula access, although newer practices such as coil embolization are being utilized to conserve the AVF. Here we illustrate a case of a 65-year-old man with end-stage renal disease on dialysis, who had a Brescia-Cimino (radiocephalic) AV fistula created and subsequently underwent balloon-assisted maturation for an underdeveloped fistula. One month later, the patient presented with a cold thumb and index finger along with parasthesias in those digits and was treated with coil embolization of the distal radial artery while leaving the AVF functional. Steal syndrome and the novel treatment option of coil embolization are reviewed here.

Expert consensus document on the treatment of descending thoracic aortic disease using endovascular stent-grafts.

Between 43,000 and 47,000 people die annually in the United States from diseases of the aorta and its branches and continues to increase. For the thoracic aorta, these diseases are increasingly treated by stent-grafting. No prospective randomized study exists comparing stent-grafting and open surgical treatment, including for disease subgroups. Currently, one stent-graft device is approved by the Food and Drug Administration for descending thoracic aortic aneurysms although two new devices are expected to obtain FDA approval in 2008. Stent-graft devices are used "off label" or under physician Investigational Device Exemption studies for other indications such as traumatic rupture of the aorta and aortic dissection. Early first-generation devices suffered from problems such as stroke with insertion, ascending aortic dissection or aortic penetration from struts, vascular injury, graft collapse, endovascular leaks, graft material failure, continued aneurysm expansion or rupture, and migration or kinking; however, the newer iterations coming to market have been considerably improved. Although the devices have been tested in pulse duplicators out to 10 years, long-term durability is not known, particularly in young patients. The long-term consequences of repeated computed tomography scans for checking device integrity and positioning on the risk of irradiation-induced cancer remains of concern in young patients. This document (1) reviews the natural history of aortic disease, indications for repair, outcomes after conventional open surgery, currently available devices, and insights from outcomes of randomized studies using stent-grafts for abdominal aortic aneurysm surgery, the latter having been treated for a longer time by stent-grafts; and (2) offers suggestions for treatment.

Mid-term outcomes of endovascular popliteal artery aneurysm repair.

OBJECTIVE: This study documents mid-term outcomes of a series of endovascular popliteal aneurysm repairs compared with concurrent results of open surgical repair. METHODS: A retrospective chart review was done of all popliteal artery aneurysm repairs since January 1, 2000. Patency was defined as continued presence of palpable pulses or maintenance of postoperative ankle-brachial index +/- 0.15. Statistical methods included chi(2), t test, Fisher's exact test, and Kaplan-Meier plots with log-rank comparison. RESULTS: A total of 56 popliteal artery aneurysm repairs were performed. All endovascular popliteal aneurysm repairs (EVPAR, n = 15) were performed using Viabahn endoprostheses. Patients with open repair (OR, n = 41) underwent surgical bypass and aneurysm exclusion with great saphenous vein (n = 26), short saphenous vein (n = 3), or polytetrafluoroethylene (n = 12), through either a medial (n = 28) or posterior (n = 13) approach. All urgent cases received open repair. Technical success was 100% in both groups. Mean follow-up was 16.5 +/- 3 months (range, 0.5 to 56 months). Aneurysm size, location, and outflow were similar between groups. Primary patency, secondary patency, and survival did not differ between groups. Endoleaks were observed in three (20%) of 15 endovascular cases, and type I and III endoleaks were treated with additional endografts. CONCLUSION: To our knowledge, this represents the largest United States series of EVPAR to date. Early mid-term results of elective endovascular repair of popliteal artery aneurysms are encouraging. Further studies are warranted to define optimal indications for EVPAR and to generate long-term outcomes for this technique.

Complications of carotid artery stenting are largely preventable: a retrospective error analysis.

Procedure-related complications with carotid artery stenting must be minimized for it to be a valid treatment for carotid stenosis. Failure analysis was done for 207 carotid stent procedures. All complications were reviewed and technical errors were identified. The procedure-related stroke rate was 2.9%, technical failure rate was 1.9%, and no patients died. Two strokes resulted from protocol deviations. A third stroke occurred while crossing a long, irregular lesion with a protection device instead of establishing flow reversal. Excessive instrumentation of the aortic arch resulted in 2 strokes. Distal embolization occurred after open-cell stenting a friable lesion in 1 patient. The majority of neurologic events and technical complications that occur during carotid stenting are preventable. By adhering to technical protocols, avoiding excessive instrumentation in the aortic arch, using flow reversal in selected lesions, and matching the appropriate anatomy and stent, results of carotid artery stenting can be exceptional.

Slower onset of low shear stress leads to less neointimal thickening in experimental vein grafts.

Vein grafts respond to low flow and shear stress (tau(w)) by generating thicker walls and smaller lumens through the processes of neointimal hyperplasia and remodeling. Clinically, however, vein grafts with obviously low tau(w), such as those distal to high-grade proximal obstructions, are not infrequently found to be widely patent and pliable. One possible explanation for this phenomenon may be that vein grafts remodel more favorably in response to changes in shear that occur gradually over time compared to abruptly. This hypothesis was tested in an experimental animal model in this report. Two separate models of experimental vein graft failure were created, causing either immediate exposure to ultralow tau(w) (<1 dyne/cm2) or delayed exposure to ultralow tau(w). Under general anesthesia and using a sterile technique, the right external jugular (EJ) veins of 28 New Zealand white rabbits were surgically exposed and isolated. An end-to-side distal EJ/common carotid artery anastomosis was created, resulting in a widely patent arteriovenous fistula. For the immediate exposure group (n = 5), the EJ was suture-ligated just proximal to the thoracic inlet, distal to a small 10-50 microm venous tributary. This created a reversed vein segment immediately and abruptly exposed to high wall tension (2.0 +/- 0.3 x 10(4) dyne/cm) and ultralow tau(w) (0.15 +/- 0.08 dyne/cm2). For the delayed exposure group (n = 22), the EJ was ligated over a 0.035 guidewire, leaving a small aperture to sustain some measure of blood flow and tau(w). This predictably resulted in slightly less wall tension (1.4 +/- 0.2 x 10(4) dyne/cm) and higher tau(w) (0.68 +/- 0.21 dyne/cm2) than the immediate exposure group. During the first week, the small outflow aperture in the delayed exposure grafts thrombosed, eventually exposing them to the same low level of tau(w) as the immediate exposure grafts. Thus, the only difference in the two models was that delayed exposure grafts enjoyed a slower decline in tau(w) than immediate exposure grafts. Fourteen rabbits in the delayed exposure group were harvested over the first 7 days to define the patency curve of the restricted outflow channel. As expected, the small aperture had thrombosed in all animals by 7 days. The remaining 14 grafts were harvested after 4 weeks, and 13/14 remained patent. Examination of the hemodynamic parameters at the time of death confirmed that wall tension and tau(w) had equalized (wall tension 0.9 +/- 0.1 vs. 1.1 +/- 0.1 x 10(4) dyne/cm, tau(w) 0.45 +/- 0.12 vs. 0.30 +/- 0.08 dyne/cm2). Histological examination revealed less neointimal hyperplasia in the delayed exposure group compared to the immediate exposure group (wall thickness 266 +/- 16 vs. 180 +/- 24 microm, p = 0.025) as well as a slightly greater luminal diameter (0.30 +/- 0.02 vs. 0.40 +/- 0.02 cm, p = 0.038). The results of this experiment suggest that slow exposure to reduced tau(w) results in more favorable remodeling (less thickening) than abrupt exposure. This finding may explain the occasional clinical observation of a widely patent vein graft even in the face of proximal arterial obstruction and very low flow; the change in tau(w) presumably occurred slowly mitigating the remodeling response.

Modulation of vascular remodeling induced by a brief intraluminal exposure to the recombinant R7020 strain of Herpes simplex-1.

OBJECTIVE: Vascular remodeling in response to injury or low shear stress (or both) is characterized by neointimal hyperplasia and luminal contraction. When profound, the response leads to restenosis after percutaneous endovascular intervention as well as to de novo stenosis in vein grafts. It has recently been reported that exposure of vein patches to neurovirulence-attenuated Herpes simplex virus-1 (HSV-1) decreases neointimal hyperplasia and increases luminal area. This experiment tested the hypothesis that R7020, a more highly attenuated mutant of HSV-1, would modulate the vascular remodeling response of experimental vein grafts chronically exposed to low shear stress. METHODS: The external jugular veins of 31 New Zealand white rabbits were clamped and intraluminally exposed to vehicle (phospate-buffered saline solution, n = 11), R7020 2.5 x 10(8) plaque forming units [PFU]/mL (n = 8), or R7020 2.5 x 10(9) PFU/mL (n = 12) for 10 or 30 minutes at an average pressure of 80 mm Hg. After exposure, an end-to-side distal external jugular-to-common carotid artery anastomosis was created, resulting in a widely patent arteriovenous fistula. The external jugular was suture-ligated just proximal to the thoracic inlet, distal to a small 10- to 50-microm venous tributary, creating a reversed vein "graft" segment immediately and abruptly exposed to arterial pressure (48 +/- 3 mm Hg) and low shear stress (0.12 +/- .02 dyne/cm(2)). In the 29 animals (N = 31) that survived to harvest, 26 grafts were found to be patent and were analyzed further. Nine grafts were harvested within the first week after operation, snap frozen in liquid nitrogen, and assayed for the presence of the Herpes viral immediate-response protein ICP0 by Western blot analysis. The 17 remaining grafts were perfusion-fixed, excised, stained, and analyzed morphometrically by digital planimetry. RESULTS: In patent grafts, the hemodynamic environment of low shear stress was maintained (shear stress at harvest, 0.26 +/- .06 dyne/cm(2)). Western blot analysis revealed the presence of ICP0 in R7020-exposed vein grafts after 2, 3, 7, and 14 days; ICP0 was not detected in unexposed vein grafts or adjacent carotid arteries. After 4 weeks, vein grafts exposed to R7020 exhibited a statistically significantly increased ratio of luminal radius to wall thickness, indicating altered remodeling (vehicle, 6.7 +/- 1.3; R7020 2.5 x 10(8), 9.1 +/- 1.3; R7020 2.5 x 10(9) ratio, 11.3 +/- 1.4; P < .05 for high dose compared with vehicle). CONCLUSION: A brief exposure of the neurovirulence-attenuated HSV-1 strain R7020 results in an increased ratio of luminal radius to wall thickness in experimental vein grafts chronically exposed to low shear stress.

Limb salvage after infrainguinal bypass graft failure.

OBJECTIVE: The purpose of this study was to examine the outcome of patients in whom an infrainguinal bypass graft failed. METHODS: This was a retrospective analysis of consecutive patients undergoing infrainguinal bypass grafting in a single institution over 8 years. RESULTS: Six hundred thirty-one infrainguinal bypass grafts were placed in 578 limbs in 503 patients during the study period. The indication for surgery was limb-threatening ischemia in 533 patients (85%); nonautologous conduits were used in 259 patients (41%), and 144 (23%) were repeat operations. After a mean follow-up of 28 +/- 1 months (median, 23 months; range, 0-99 months), 167 grafts (26%) had failed secondarily. The rate of limb salvage in patients with graft failure was poor, only 50% +/- 5% at 2 years after failure. The 2-year limb salvage rate depended on the initial indication for bypass grafting: 100% in patients with claudication (n = 16), 55% +/- 8% in patients with rest pain (n = 49), and 34% +/- 6% in patients with tissue loss (n = 73; P <.001). The prospect for limb salvage also depended on the duration that the graft remained patent. Early graft failure (<30 days; n = 25) carried a poor prognosis, with 2-year limb salvage of only 25% +/- 10%; limb salvage was 53% +/- 5% after intermediate graft failure (<2 years, n = 110) and 79% +/- 10% after late failure (>2 years, n = 15; P =.04). Multivariate analysis revealed shorter patency interval before failure (P =.006), use of warfarin sodium (Coumadin) postoperatively (P =.006), and infrapopliteal distal anastomosis (P =.01) as significant predictors for ultimate limb loss. CONCLUSION: The overall prognosis for limb salvage in patients with failed infrainguinal bypass grafts is poor, particularly in patients with grafts placed because of tissue loss and those with early graft failure.

Theoretical hydraulic consequences of vein graft taper.

OBJECTIVE: Internal diameter is a strong predictor of patency of infrainguinal vein grafts. However, most vein grafts are tapered, with variable diameter along their length. It is unknown which diameter is most important in determining graft resistive properties, that is, its mean diameter, minimum diameter, or some geometric combination thereof. The purpose of this analysis was to examine the hydraulic consequences of vein graft tapering, with longitudinal impedance (Z(L)), a conduit-specific measure of pulsatile resistance along straight rigid tubes. METHODS: Proximal and distal graft pressure, pressure gradient (DeltaP), and blood flow (Q) were measured intraoperatively in a 100 cm bypass graft and digitally recorded for 10 seconds at 200 Hz. With the Womersley solution for fully developed fluid flow in a rigid tube, a series of DeltaP waveforms were generated for graft diameters ranging from 1.2 to 8.2 mm. With an axisymmetric form of the Navier-Stokes equations, a second series of DeltaP waveforms were computed for grafts with long smooth symmetric tapers ranging from 0% to 90%, with geometric mean diameter of 3.2, 4.2, and 5.2 mm (%Taper = 100 x [proximal diameter - distal diameter]/proximal diameter). For each set of DeltaP and Q, Z(L) was calculated as DeltaP/Q, plotted over a range of 8 Hz, and integrated over 4 Hz to yield integral Z(L). RESULTS: The architecture of the calculated DeltaP and Z(L) waveforms closely approximated their measured counterparts, validating the method. As expected, Z(L) was highly diameter-dependent in a nonlinear fashion. With a clinically relevant boundary of less than 50 x 10(3) dyne/cm(5) as "acceptable," the minimum acceptable diameter of nontapered 100 cm bypass conduits was 4.3 mm. Analysis of graft taper revealed that small amounts of taper in large conduits were well-tolerated. For example, introduction of 32% taper in a 5.2 mm graft (6.2 mm --> 4.2 mm) caused only an 8% increase in integral Z(L) (from 32 to 35 x 10(3) dyne/cm(5)). More pronounced taper in smaller conduits rendered them unacceptable. For example, 53% taper of a 4.2 mm graft (5.7 mm --> 2.7 mm) created a conduit with integral Z(L) of 70 x 10(3) dyne/cm(5), well above the acceptable limit. The relationship between Z(L) and percent taper was nonlinear and strongly dependent on mean diameter. CONCLUSIONS: The relationship between Z(L) and diameter in vein grafts is nonlinear; thus Z(L) increases rapidly in conduits smaller than 4 mm. Tapered vein grafts behave hydraulically like nontapered grafts, provided their geometric mean is greater than 4 mm and their degree of taper is less than 40%. Tapered veins are satisfactory conduits for long-segment bypass grafts, provided their mean diameter is acceptable.

Sustained inhibition of experimental neointimal hyperplasia with a genetically modified herpes simplex virus.

OBJECTIVE: Reported herein is a potential strategy for sustained smooth muscle cell (SMC) inhibition with a virulence-attenuated herpes simplex virus (HSV). Experiments were conducted in vitro to demonstrate selective SMC cytotoxicity and in vivo to demonstrate reduced neointimal hyperplasia (NIH) in a clinically relevant animal model. METHODS: In vitro: Cultured human umbilical artery smooth muscle cells (UASMC) and venous endothelial cells (HUVEC) were exposed to varying multiplicities of infection (MOI) of a gamma(1)34.5-deleted HSV-1 virus (R849). Cell survival was assessed at 48 and 72 hours with a colorimetric MTT viability assay. In vivo: New Zealand White rabbit external jugular veins (n = 21) were exposed to R849 (2.5 x 10(6) pfu/mL) or culture medium at 110 to 120 mm Hg for 10 minutes, then fashioned as vein patches on carotid arteries. Carotid arteries were ligated distally to decrease blood flow and stimulate a hyperplastic response (ultra-low shear stress model). After 2, 4, 12, and 24 weeks, patched segments were perfusion-fixed with glutaraldehyde and morphometrically examined for NIH formation. RESULTS: In vitro: At 48 hours, R849 exhibited preferential cytotoxicity to UASMC compared with HUVEC, with 11% +/- 10% of UASMCs and 49% +/- 8% of HUVECs surviving after infection with MOI = 25 (P <.05). Higher MOI resulted in poor survival of both cell lines. In vivo: Blood flow was similarly reduced in all animals both at surgery (0.9 +/- 0.1 mL/min vs 1.6 +/- 0.3 mL/min) and at harvest (2.7 +/- 0.4 mL/min vs 2.5 +/- 0.5 mL/min). R849-infected patches exhibited markedly less NIH than control patches did at 2 weeks (162 +/- 14 microm vs 49 +/- 6 microm; P <.05), 4 weeks (190 +/- 27 microm vs 67 +/- 8 microm; P <.05), and 12 weeks (233 +/- 18 microm vs 113 +/- 2 microm; P <.05). CONCLUSION: The virulence-attenuated HSV strain R849 demonstrates selective cytotoxicity for SMC and is capable of sustained inhibition of NIH in an experimental model of vein graft failure.

Long-term outcome of infrainguinal bypass grafting in patients with serologically proven hypercoagulability.

OBJECTIVE: The purpose of this study was to test the hypothesis that the long-term outcome of infrainguinal bypass grafting in patients with congenital or acquired hypercoagulability is inferior to the results in patients without documented clotting disorders. METHODS: The study was a retrospective analysis of consecutive patients from January 1994 to January 2001. RESULTS: Five hundred eighty-two infrainguinal bypass grafts were created in 456 patients. Indication for surgery was limb-threatening ischemia in 84%; prosthetic conduits were implanted in 38%. Seventy-four grafts were created in 57 patients with one or more serologically proven hypercoagulable states, including heparin-induced platelet aggregation (n = 37), anticardiolipin antibodies (n = 11), lupus anticoagulant (n = 8), protein C or S deficiency (n = 7), antithrombin III deficiency (n = 3), and factor V Leiden mutation (n = 1). Patients with hypercoagulability were younger (63 +/- 2 years versus 69 +/- 1 years; P =.007), more likely to have undergone prior revascularization attempts (38% versus 21%; P =.003), and more likely to have chronic anticoagulation therapy after surgery (46% versus 25%; P =.001). After 5 years (median follow-up, 19 months), patients with hypercoagulability had poorer primary patency (28% +/- 7% versus 35% +/- 5%; P =.004), primary assisted patency (37% +/- 7% versus 45% +/- 6%; P =.0001), secondary patency (41% +/- 7% versus 53% +/- 6%; P =.0001), limb salvage (55% +/- 8% versus 67% +/- 6%; P =.009), and survival (61% +/- 8% versus 74% +/- 4%; P =.02) rates. Multivariate analysis identified only prosthetic conduit choice (P =.0001), hypercoagulability (P =.0003), and limb salvage indication (P =.01) as independent predictors of graft failure. CONCLUSION: Patients with serologically proven hypercoagulability have inferior long-term patency, limb salvage, and survival rates after infrainguinal bypass. The high prevalence rate (13%) of diverse hypercoagulable states in this patient population supports serologic screening, especially in referral practices.

The changing face of abdominal aortic aneurysm management.

In summary, endovascular therapy represents a new and exiting paradigm in the treatment of abdominal aortic aneurysms. Its detractors have now largely been silenced, and a working knowledge of the devices and techniques is essential for all surgeons who care for patients with aneurysms. The first 25,000 stent-graft procedures have been attended by significant risks of implantation and endoleak, but the patients' acceptance of the technique has been heard loud and clear. The surgeon's task is not to convince the patient to undergo a more painful and invasive open procedure, but to advance the understanding, design, and implementation of this new technique such that its long-term results will someday rival those of the time-tested traditional operation.

Longitudinal impedance is independent of outflow resistance.

BACKGROUND: Many investigators have measured outflow resistance (R) following peripheral bypass procedures, but correlations with graft patency have been weak. This is because the primary determinants of graft patency are the size and quality of the conduit, not its outflow bed. Efforts at separating conduit resistance from outflow resistance have been unsuccessful. Recently, the concept of longitudinal impedance ( integral Z(L)) has been suggested as a measure of conduit resistance independent of outflow resistance. The purpose of this in vitro experiment was to test the hypothesis that integral Z(L) is independent of R within physiologically relevant ranges. METHODS: Rigid polyethylene tubing of known internal diameter and length (4.3 mm, 375 cm) was perfused with a glycerin/saline mixture mimicking the viscosity of blood (4.1 cp), utilizing a variable pulsatile pump and Windkessel, with outflow into multiply branched tubes of decreasing diameter simulating the hemodynamic conditions of arterial bypass. Flow and pressure were measured using ultrasonic transit time and catheter transduction, respectively, and waveforms digitized at 200 Hz. Flow was varied while maintaining "systemic" pressure and resistance. After Fourier transformation, integral Z(L) was calculated as deltaP/Q at each harmonic and integrated over 4 Hz. RESULTS: integral Z(L) calculations were remarkably reproducible within the same day with a coefficient of variation (CV) = 4.0% (at 100 dyne. s/cm(5); n = 4) or over 4 successive days (CV = 4.3%). Furthermore, integral Z(L) was largely independent of R over the physiologic range tested, with integral Z(L) remaining relatively constant as R was increased sixfold. CONCLUSION: integral Z(L) is a consistent and reproducible measure of conduit resistance independent of R over a wide physiologic range. It may be useful for measuring the adequacy of bypass graft conduits.

Differential mechanical activation of mitogen-activated protein kinases in intact human blood vessels.

BACKGROUND: Vascular tissue remodels in response to a variety of hemodynamic factors, often transduced through activation of mitogen-activated protein kinases such as extracellular signal-related kinase (ERK1/2) and c-jun N-terminal kinase (JNK). This study tests the hypothesis that these kinases are involved in mechanical signal transduction in intact human arteries and veins. METHODS: Unused portions of human saphenous vein and radial artery were obtained fresh at the time of peripheral or coronary bypass. A sample of the vessel was immediately snap frozen (control(0)) and the remainder separated into three segments. One segment was placed in sterile medium and left undisturbed for 2 h (control(2)), one was perfused with sterile medium for 2 h at a steady rate of 150 ml/min, yielding shear stress values of 8-20 dyne/cm(2) (flow), and one was statically pressurized without flow at 110 mm Hg for 2 h (pressure). After treatment, samples were tested for phosphorylated ERK1/2 and JNK using Western blot. RESULTS: Two hours of culture produced mild increases in ERK1/2 activity in both vessel types. Stimulation with continuous rapid flow produced significantly increased ERK1 activity and a nearly 100% increase in ERK2 in veins. Static pressurization also stimulated ERK1/2, although slightly less than continuous flow. ERK1/2 phosphorylation was only mildly increased in flow-stimulated radial arteries, and exposure to normal systemic pressure showed no appreciable effect. Significant phosphorylation of JNK was not observed in either vessel. CONCLUSION: ERK1/2 phosphorylation is increased in human saphenous veins and radial arteries exposed to the hemodynamic conditions of arterial grafting. This pathway may be involved in the transduction of external stimuli leading to remodeling.

Aortic reconstruction in patients with functioning renal allografts.

Patients with functioning renal allografts requiring aortic reconstruction pose a considerable challenge to the vascular surgeon. A variety of strategies for renal allograft preservation during intervention have been described including hypothermia, indwelling shunts, cold renal perfusion, axillofemoral bypass, and endovascular stent-grafting. Reported here are two cases of successful aortic reconstruction utilizing standard open surgical techniques designed simply to minimize warm renal ischemia. The first case was that of a 55 year-old patient with a functional renal allograft originating from the right external iliac artery, who presented acutely with large symptomatic aortic and bilateral iliac artery aneurysms. He was treated with aorto-right femoral/left iliac bypass grafting. The right femoral anastomosis was performed first so that warm renal ischemia was limited to the 34 min required to perform the proximal end-to-end aortic anastomosis. The second case was that of a 44-year-old patient also with a transplanted kidney originating from the right external iliac artery. He presented with worsening hypertension, decreasing renal function, claudication, and severe aortoiliac occlusive disease. He was treated with aorto-left femoral bypass grafting via a retroperitoneal approach, followed by femorofemoral crossover bypass for retrograde perfusion of the kidney (total warm ischemia time 20 min). Both patients recovered uneventfully without a decrement in renal function and remain well on follow-up. It is concluded that standard open surgery without adjunctive shunts or bypasses remains a viable treatment option for these patients, provided warm renal ischemia can be minimized.

Paravisceral aortic thrombus as a source of peripheral embolization--report of three cases and review of the literature.

Spontaneous embolization resulting in peripheral arterial occlusion remains a significant cause of morbidity and limb loss. Accurate localization and correction of the embolic source is paramount for the prevention of further episodes and for the preservation of long-term patency and limb salvage. Common well-recognized embolic sources include intracardiac thrombus or myxoma, and thrombus within arterial aneurysms or complex atherosclerotic plaques. Less common is thrombus arising de novo in an otherwise normal aorta, possibly as a result of prior trauma, occult arteriopathy, and/or hypercoagulability. Reported herein are three cases of peripheral or mesenteric embolization arising from large thrombi within the visceral aortic segment, with minimal evidence for atherosclerosis or other aortic pathology. Each patient was treated with visceral aortic thrombectomy using a direct surgical approach.