The LargPAD Trial: Phase IIA evaluation of l-arginine infusion in patients with peripheral arterial disease.

OBJECTIVE: Endothelial function is improved by l-arginine (l-arg) supplementation in preclinical and clinical studies of mildly diseased vasculature; however, endothelial function and responsiveness to l-arg in severely diseased arteries is not known. Our objective was to evaluate the acute effects of catheter-directed l-arg delivery in patients with chronic lower extremity ischemia secondary to peripheral arterial disease. METHODS: The study enrolled 22 patients (45% male) with peripheral arterial disease (mean age, 62 years) requiring lower extremity angiography. Endothelium-dependent relaxation of patent but atherosclerotic superficial femoral arteries was measured using a combination of intravascular ultrasound (IVUS) imaging and a Doppler FloWire (Volcano Corporation, Rancho Cordova, Calif) during the infusion of incremental acetylcholine (10-6 to 10-4 molar concentration) doses. Patients received 50 mg (n = 3), 100 mg (n = 10), or 500 mg (n = 9) l-arg intra-arterially, followed by repeat endothelium-dependent relaxation measurement (limb volumetric flow). IVUS-derived virtual histology of the culprit vessel was also obtained. Endothelium-independent relaxation was measured using a nitroglycerin infusion. Levels of nitrogen oxides and arginine metabolites were measured by chemiluminescence and mass spectrometry, respectively. RESULTS: Patients tolerated limb l-arg infusion well. Serum arginine and ornithine levels increased by 43.6% ± 13.0% and 23.2% ± 10.3%, respectively (P < .005), and serum nitrogen oxides increased by 85% (P < .0001) after l-arg infusion. Average vessel area increased by 6.8% ± 1.3% with l-arg infusion (acetylcholine 10-4; P < .0001). Limb volumetric flow increased in all patients and was greater with l-arg supplementation by 130.9 ± 17.6, 136.9 ± 18.6, and 172.1 ± 24.8 mL/min, respectively, for each cohort. Maximal effects were seen with l-arg at 100 mg (32.8%). Arterial smooth muscle responsiveness to nitroglycerin was intact in all vessels (endothelium-independent relaxation, 137% ± 28% volume flow increase). IVUS-derived virtual histology indicated plaque volume was 14 ± 1.3 mm3/cm, and plaque stratification revealed a predominantly fibrous morphology (46.4%; necrotic core, 28.4%; calcium, 17.4%; fibrolipid, 6.6%). Plaque morphology did not correlate with l-arg responsiveness. CONCLUSIONS: Despite extensive atherosclerosis, endothelial function in diseased lower extremity human arteries can be enhanced by l-arg infusion secondary to increased nitric oxide bioactivity. Further studies of l-arg as a therapeutic modality in patients with endothelial dysfunction (ie, acute limb ischemia) are warranted.

In vivo evaluation of biomimetic fluorosurfactant polymer-coated expanded polytetrafluoroethylene vascular grafts in a porcine carotid artery bypass model.

OBJECTIVE: The objective of this study was to evaluate the potential for biomimetic self-assembling fluorosurfactant polymer (FSP) coatings incorporating heptamaltose (M7-FSP) to block nonspecific protein adsorption, the cell adhesive RGD peptide (RGD-FSP), or the endothelial cell-selective CRRETAWAC peptide (cRRE-FSP) to improve patency and endothelialization in small-diameter expanded polytetrafluoroethylene (ePTFE) vascular graft implants. METHODS: ePTFE vascular grafts (4 mm in diameter, 5 cm in length) were coated with M7-FSP, RGD-FSP, or cRRE-FSP by dissolving FSPs in distilled water and flowing solution through the graft lumen for 24 hours. Coatings were confirmed by receding water contact angle measurements on the lumen surface. RGD-FSP and cRRE-FSP grafts were presodded in vitro with porcine pulmonary artery endothelial cells (PPAECs) using a custom-designed flow system. PPAEC coverage on the lumen surface was visualized with epifluorescent microscopy and quantified. Grafts were implanted as carotid artery interposition bypass grafts in seven pigs for 33 ± 2 days (ePTFE, n = 3; M7-FSP, n = 4; RGD-FSP, n = 3; cRRE-FSP, n = 4). Patency was confirmed immediately after implantation with duplex color flow ultrasound and at explantation with contrast-enhanced angiography. Grafts were sectioned for histology and stained: Movat pentachrome stain to outline vascular layers, immunofluorescent staining to identify endothelial cells (anti-von Willebrand factor antibody), and immunohistochemical staining to identify smooth muscle cells (anti-smooth muscle α-actin antibody). Neointima to lumen area ratio was determined to evaluate neointimal hyperplasia. RESULTS: Receding water contact angle measurements on graft luminal surfaces were significantly lower (P < .05) on FSP-coated ePTFE surfaces (M7-FSP, 40 ± 16 degrees; RGD-FSP, 25 ± 10 degrees; cRRE-FSP, 33 ± 16 degrees) compared with uncoated ePTFE (126 ± 2 degrees), confirming presence of the FSP layer. In vitro sodding of PPAECs on RGD-FSP and cRRE-FSP grafts resulted in a confluent monolayer of PPAECs on the luminal surface, with a similar cell population on RGD-FSP (1200 ± 187 cells/mm(2)) and cRRE-FSP (1134 ± 153 cells/mm(2)) grafts. All grafts were patent immediately after implantation, and one of three uncoated, two of three RGD-FSP, two of four M7-FSP, and two of four cRRE-FSP grafts remained patent after 1 month. PPAEC coverage of the lumen surface was seen in all patent grafts. RGD-FSP grafts had a slightly higher neointima to lumen area ratio (0.53 ± 0.06) compared with uncoated (0.29 ± 0.15), M7-FSP (0.20 ± 0.15), or cRRE-FSP (0.17 ± 0.09) grafts. CONCLUSIONS: Biomimetic FSP-coated ePTFE grafts can be used successfully in vivo and have potential to support endothelialization. Grafts modified with the M7-FSP and cRRE-FSP showed lower intimal hyperplasia compared with RGD-FSP grafts.

Arteriovenous grafts have higher secondary patency in the short term compared with autologous fistulae.

BACKGROUND: To estimate patency of arteriovenous fistulas (AVFs) and grafts (AVGs) for dialysis access. METHODS: Records of all adult patients who had a dialysis access placed from January 2008 to June 2011 were retrospectively reviewed. RESULTS: A total of 494 patients with 655 accesses (390 AVFs, 265 AVGs) were examined. We found that AVG fared worse in assisted primary patency. But AVG had superior secondary patency up to 1.2 years (hazard ratio [HR] .6, confidence interval [CI]: [.4 to .8]) and was no different than AVF after 1.2 years. (HR 1.6, CI: [.9 to 3.1]). On univariate analysis, dialysis catheters negatively impacted assisted primary patency (HR 1.4, CI: [1.09 to 1.77]). CONCLUSIONS: AVG can be maintained with higher rates of secondary patency in the short term and are no different in the long term. This result suggests that in patients with limited life expectancy an AVG may be an effective alternative to an AVF to reduce both catheter time and associated complications.

The use of dextran and carbon dioxide for optical coherence tomography in the superficial femoral artery.

The following case report describes using carbon dioxide (CO2) as contrast media for intravascular optical coherence tomography (OCT) imaging in the superficial femoral artery. For initial OCT imaging, 20 mL of iodinated contrast was used during automated pullback. This was followed by 20 mL of hand-injected dextran 40 in normal saline, and finally hand-injected 50 mL of CO2. CO2 gave comparable erythrocyte clearance and imaging quality compared with dextran and iodinated contrast. To our knowledge, this is the first reported case using both dextran and CO2 with OCT imaging of the superficial femoral artery. Using CO2 is a viable option in patients with contraindications to contrast or dextran use.

Heparin bonding does not improve patency of polytetrafluoroethylene arteriovenous grafts.

BACKGROUND: Heparin-bonded polytetrafluoroethylene (PTFE) grafts (hepPTFE) were developed to decrease rates of graft thrombosis. Our objective was to compare the patency of arteriovenous grafts (AVGs) for dialysis access with and without heparin bonding in a tertiary care setting. METHODS: Records of patients who had an AVG placed between January 2008 and June 2011 were retrospectively reviewed. Outcome measures were primary, assisted primary, and secondary patency. Marginal survival models (to account for correlation of accesses within subjects) using Cox proportional hazard regression were used for statistical comparisons. RESULTS: A total of 223 patients had 265 grafts placed. Of these, 62 (23%) were hepPTFE grafts. The average age was 66 ± 15 years in the hepPTFE group and 59 ± 17 years in the non-heparin-bonded control group (PTFE; P < 0.01). Of the hepPTFE group, 39% were men, 81% were African American, 63% were diabetic, and 81% had a tunneled catheter at the time of access placement. Of the PTFE group, 35% were men, 85% were African American, 56% were diabetic, and 83% had a tunneled catheter. HepPTFE grafts failed to improve rates of primary, assisted primary, or secondary patency based on univariate analysis (hazard ratio [HR]: 1.37 [95% confidence interval {CI}: 0.99-1.88]; HR: 1.39 [95% CI: 0.98-1.96]; and HR: 1.20 [95% CI: 0.73-1.96], respectively). The number of secondary interventions was similar in the 2 groups (1.1 interventions per person-year of follow-up PTFE versus 1.4 hepPTFE; P = 0.13). A multivariable model including age, diabetes, peripheral artery disease, tobacco use, previous access placement, and tunneled catheter found that the HR for hepPTFE was not significantly different than PTFE in primary, assisted primary, or secondary patency (HR: 1.32 [95% CI: 0.91-1.90]; HR: 1.35 [95% CI: 0.91-1.99]; and HR: 1.15 [95% CI: 0.62-2.16], respectively). CONCLUSIONS: hepPTFE AVGs failed to improve patency or decrease secondary interventions compared to standard PTFE grafts. Prospective studies are needed to confirm these results.

Pulse volume recording does not enhance segmental pressure readings for peripheral arterial disease stratification.

BACKGROUND: Noninvasive vascular laboratory determinations for peripheral arterial disease (PAD) often combine pulse volume recordings (PVRs), segmental pressure readings (SPs), and Doppler waveform traces (DWs) into a single diagnostic report. Our objective was to assess the corresponding diagnostic values for each test when subjected to interpretation by 4 vascular specialists. METHODS: A total of 2226 non-invasive diagnostic reports were reviewed through our institutional database between January 2009 and December 2011. Data from noninvasive records with corresponding angiograms performed within 3 months led to a cohort of 76 patients (89 limbs) for analysis. Four vascular specialists, blinded to the angiographic results, stratified the noninvasive studies as representative of normal, <50% "subcritical," or ≥50% "critical" stenosis at the upper thigh, lower thigh, popliteal, and calf segments using 4 randomized noninvasive modalities: (1) PVR alone; (2) SP alone; (3) SP+DW; and (4) SP+DW+PVR. The angiographic records were independently graded by another 3 evaluators and used as a standard to determine the noninvasive diagnostic values and interobserver agreements for each modality. Statistical tests used include the Fleiss-modified kappa analysis, Kruskal-Wallis analysis of variance with Dunn's multiple comparison test, the Kolmogorov-Smirnov test, and the unpaired t-test with Welch's correction. RESULTS: Interobserver variance for all modalities was high, except for SP. When surveying for any stenosis (<50% and ≥50%), sensitivity (range 25-75%) was lower than specificity (range 50-84%) for all modalities. When surveying for critical stenosis only (≥50%), sensitivity (range 27-54%) was also lower than specificity (range 68-92%). Accuracy for detecting any stenosis with SP+DW was significantly higher than with PVR alone (66 ± 7% vs. 56 ± 12%, P = 0.017). There was a significant reduction in accuracy when including incompressible readings within the SP-only analysis compared with exclusion of incompressible vessels (P = 0.0006). However, the effect of vessel incompressibility on accuracy was removed with the addition of DW (P = 0.17) to the protocol. CONCLUSIONS: SP has the greatest interobserver agreement in evaluation of PAD and can be used preferentially for PAD stratification. Given the lower accuracy of PVR for detecting either subcritical or critical disease, PVR tests can be omitted from the noninvasive vascular examination without a significant reduction in overall diagnostic value and can be reserved for patients with incompressible vessels.

In vivo assessment of endothelial function in human lower extremity arteries.

OBJECTIVE: Endothelial function has been measured in preclinical studies in human brachial and coronary arteries but not in lower extremity arteries affected by atherosclerosis. We describe a novel, first-in-man evaluation of endothelial function of the superficial femoral arteries (SFAs) in patients with peripheral arterial disease (PAD). METHODS: Enrolled were 25 patients with PAD requiring lower extremity angiography. Endothelial-dependent relaxation was measured using intravascular ultrasound (IVUS) imaging and a Doppler flow wire after the infusion of acetylcholine (Ach). IVUS-derived virtual histology of the same vessel was calculated. Endothelial-independent relaxation was measured with an infusion of nitroglycerin (200 µg). Levels of nitric oxide and serum nitric oxide metabolites were determined by laboratory analysis. RESULTS: Patients (48% male; mean age, 62 years) had a history of hypertension (80%), coronary disease (36%), and diabetes (40%). The mean SFA diameter was 5.2 ± 1 mm (range, 3.2-6.9 mm). Patients tolerated Ach infusion with no adverse events. Endothelial-dependent relaxation increased over baseline for all patients with Ach infusion of 10(-6) to 10(-4). At Ach 10(-4), diameter (0.5%) and area (1.8%) changes in the diseased SFAs were modest and insignificant; however, average peak velocity of blood flow significantly increased 26%, 46%, and 63% with an Ach 10(-6) to 10(-4) infusion. Calculations of limb volumetric flow (68% at Ach 10(-4)) were significantly increased after Ach infusion. Lower extremity nitric oxide levels were slightly lower than systemic venous levels (P = .04). Nitroglycerin infusion indicated normal smooth muscle responsiveness (3% diameter, 9% area, and 116% velocity change over baseline). IVUS-virtual histology plaque stratification indicated predominantly fibrous morphology (46%; necrotic core, 29%; calcium, 18%). Atheroma burden was 14.9 ± 5.5 mm(3)/cm and did not correlate with endothelial responsiveness. CONCLUSIONS: Endothelial function can be measured directly in human lower extremity arteries at the sites of vascular disease. Despite extensive atherosclerosis, endothelial function is still intact. These data support the application of regional endothelial-specific biologic therapies in patients with PAD.

Techniques to harvest diseased human peripheral arteries and measure endothelial function in an ex vivo model.

OBJECTIVE: Endothelial dysfunction has been studied in animal models. However, direct evidence of endothelial function from human vessels is limited. Our objectives were to optimize methods in harvesting human arteries from amputation specimens, determine endothelial function, and measure responsiveness to l-arginine, a nitric oxide precursor. METHODS: Fresh amputation specimens were transferred expeditiously from the operating room to the bench laboratory for dissection and arterial harvest in an Investigational Review Board-approved protocol. Popliteal and tibial vessels were examined in pilot experiments leading to the use of the anterior tibial artery in consecutive experiments. Human lower extremity anterior tibial artery segments were harvested from 14 amputation specimens. Specimens were rapidly collected and divided for endothelial-dependent relaxation (EDR) studies in a tissue bath apparatus, immunohistochemistry, and intravascular ultrasound-derived virtual histology. A total of 47 ring segments were studied. The data were compared with two-way analysis of variance. RESULTS: Human lower extremity arteries exhibited low responsiveness to acetylcholine (EDR, 24.9%; acetylcholine, 10(-4)). L-arginine supplementation enhanced EDR by 38.5% (P < .0001). N-nitro-L-arginine methyl ester abrogated EDR (P < .0001) in vessels exposed to L-arginine. Arterial responsiveness was intact in all vessels (endothelial independent relaxation to sodium nitroprusside, 113.2% ± 28.1%). Histology and immunohistochemistry confirmed intact endothelium by morphometric analysis, cluster of differentiation 31, endothelial nitric oxide synthase, and arginase II staining. Intravascular ultrasound-derived virtual histology indicated atheroma burden was 11.9 ± 4.7 mm(3)/cm, and plaque stratification indicated fibrous morphology was predominant (59.9%; necrotic core, 16.9%; calcium, 11.2%). Variations in plaque morphology did not correlate with endothelial function or responsiveness to L-arginine. CONCLUSIONS: Human lower extremity arteries demonstrate low baseline endothelial function in patients requiring amputation. Endothelial dysfunction is improved by L-arginine supplementation in an ex vivo model. These results support strategies to increase local levels of nitric oxide in human vessels.

The contemporary management of splenic artery aneurysms.

OBJECTIVES: The management of patients with splenic artery aneurysms (SAAs) is variable since the natural history of these aneurysms is poorly delineated. The objective of this study was to review our experience with open repair, endovascular therapy, and observation of SAAs over a 14-year interval. METHODS: Between January 1, 1996 and December 31, 2009, 128 patients with SAAs were evaluated. Sixty-two patients underwent surgical repair (n = 13) or endovascular coil/glue ablation (n = 49), while 66 patients underwent serial observation. The original medical records and computed tomography (CT) imaging were reviewed. Statistical analyses were performed using χ(2) or Fisher's exact test for categorical patient characteristics and t-test for continuous variables. Kaplan-Meier estimates for survival were calculated. Mortality was verified via the Social Security Death Index. RESULTS: Patients (61 ± 11 years, 69% female) were investigated for abdominal symptoms (49%) or had the incidental finding of SAA (mean size, 2.4 ± 1.4 cm). Seven patients (5.5%) presented with rupture and were treated emergently with two perioperative mortalities (29%). Patients requiring surgical or endovascular treatment were more likely male (40% vs 21%, P = .031), younger (58 vs 64 years; P = .004), and current smokers (18% vs 5%; P = .035). Increased aneurysm calcification was associated with decreased SAA size (P = .013). The mean aneurysm size at initial diagnosis was 1.67 cm for patients undergoing observation and 3.13 cm for the treated group (P < .001). Endovascular repair was safe and durable with a mean 1.5-mm regression in SAA size over 2 years. The mean rate of growth for observed SAA was 0.2 mm/y. Ten-year survival was 89.4% (95% confidence interval: 82.0, 97.4) for all patients (observed group, 94.9%; treated group, 85.1%; P = .18). No late aneurysm-related mortality was identified. CONCLUSIONS: Ruptured SAAs are lethal. Large SAAs can undergo endovascular ablation safely with durable SAA regression. Smaller SAAs (<2 cm) grow slowly and carry a negligible rupture risk.