Arteriovenous fistula aneurysmorrhaphy is associated with improved patency and decreased vascular access abandonment.

BACKGROUND: Upper extremity hemodialysis arteriovenous fistulas (AVFs) can become aneurysmal over time due to repeated cannulation and/or outflow steno-occlusive disease. The optimal surgical management of aneurysmal AVFs (aneurysmorrhaphy vs interposition graft) has remained unclear. METHODS: We performed a retrospective review in which current procedural terminology codes were used to screen for patients who had undergone surgical treatment of aneurysmal AVFs between 2016 and 2021 at a single hospital system. The patients were included after a review of the operative reports. The cases were divided by surgical procedure (aneurysmorrhaphy vs interposition graft placement). The patients who had undergone primary AVF ligation or other types of repair were excluded. The primary outcomes were primary assisted and secondary patency, and the secondary outcome was dialysis access abandonment. Multivariable Cox proportional hazards regression was used to test the association between the type of AVF aneurysm repair and the primary and secondary outcomes. RESULTS: From 2016 to 2021, 6951 patients had undergone 16,190 dialysis access procedures. Of these procedures, 381 (2.4%) were related to surgical treatment of an aneurysmal AVF. We excluded 58 primary AVF ligation cases and 20 cases involving other types of repair, leaving 303 cases for analysis. These were divided into two groups: aneurysmorrhaphy (n = 123; 41%) and interposition graft (n = 180; 59%). No differences were found between the groups in male gender (68% vs 63%), hypertension (98% vs 98%), or central stenosis (14% vs 22%). The patients who had undergone aneurysmorrhaphy were younger (median age, 54 years vs 59 years); had had a lower rate of diabetes (41% vs 59%), coronary artery disease (41% vs 58%), and congestive heart failure (41% vs 55%); and were less likely to have undergone upper arm access (72% vs 92%). The median follow-up was 11.1 months (interquartile range, 3.6-25.2 months). No differences were found in the incidence of 30-day wound complications (1% vs 3%) or surgical site infections (4% vs 6%). On multivariable Cox regression, interposition graft placement was associated with the loss of primary assisted patency (adjusted hazard ratio [aHR], 2.42; 95% confidence interval [CI], 1.18-4.95), loss of secondary patency (aHR, 3.10; 95% CI, 1.21-7.94), and abandonment of dialysis access (aHR, 3.07; 95% CI, 1.61-5.87; P < .05 for all) at 2 years. CONCLUSIONS: AVF aneurysmorrhaphy was associated with improved primary assisted and secondary patency and decreased abandonment of dialysis access. We suggest using aneurysmorrhaphy when AVF aneurysms are indicated for repair. However, individual factors such as patient comorbidities, AVF anatomy, remaining dialysis access options, and patient preference should be considered when planning the surgical approach.

Pre-existing Systolic Dysfunction is the Most Powerful Predictor of Failed Arteriovenous Fistula Maturation.

BACKGROUND: Patients requiring hemodialysis access creation often have significant comorbid conditions, which may impact access maturation. Underlying cardiac dysfunction likely plays an important role in the maturation of arteriovenous fistulae (AVF). The effect of specific parameters of cardiac function on successful AVF creation has not previously been explored. METHODS: A retrospective chart analysis of patients undergoing first-time AVF creation at a single center from 2011 to 2018 was performed. Patients with a transthoracic echocardiogram within the 12 months prior to surgery were included. Standard demographic and perioperative variables were collected, in addition to echocardiographic and vascular mapping data. The primary outcome was access maturation, defined as the use of the access site for hemodialysis at 3, 6, and 12 months after surgery. RESULTS: A total of 121 patients met inclusion criteria with a cumulative AVF maturation rate of 57% (69/121) in this select population. Patients with pre-existing systolic cardiac dysfunction were more than 5 times less likely to see their AVF mature by one year postsurgery (OR = 0.17, P = 0.018). Preoperative venous diameter, access site location, and the type of fistula did not differ significantly between patients with and without systolic dysfunction. Selection of the cephalic vein as the venous anastomosis and diastolic dysfunction (≥ Grade 2) were also associated with lower rates of access maturation, although these associations were less robust. CONCLUSIONS: Systolic cardiac dysfunction is the most important nonmodifiable variable associated with failed AVF maturation. Patients requiring hemodialysis with significant pre-existing cardiac dysfunction may not be appropriate for permanent access creation, and long-term catheter use should be seriously considered as an alternative.

Vascular Surgeons Carry an Increasing Responsibility in the Management of Lower Extremity Vascular Trauma.

BACKGROUND: There is preliminary evidence that vascular surgeons are increasingly relied on nationally to assist with the management of lower extremity vascular trauma. Current trauma center verification, however, does not require any level of vascular surgery coverage. We sought to assess practice patterns regarding vascular surgery consultation and temporal trends in the surgical management of these patients. METHODS: A retrospective analysis was performed on all patients who underwent surgical repair for vascular trauma of the lower extremity at a single, academic, public hospital from 2011 to 2018. Demographic data and procedural data were collected. Patients were assigned to a vascular surgery (VS) or nonvascular surgery (NV) group. The primary outcome measure was the rate of VS consultation. Secondary outcome measures included 30-day mortality, length-of-stay, and limb salvage. RESULTS: One hundred eighty patients were identified (77 VS group, 103 NV group). There was an increase in the proportion of repairs done by VS from 2011 to 2018 (P < 0.05). There were significant management differences between the 2 groups, with vascular surgeons more likely to perform primary end-to-end anastomosis for both arterial (21.33% vs. 6.90%) and venous (19.15% vs. 5.26%) injuries (both P < 0.05). Patients in the VS group were less likely to have balloon embolectomy, fasciotomy, or intravascular shunting than the NV group (all P < 0.05). There were no significant differences in mortality (5.35% vs. 4.85%), length-of-stay (15.05 vs. 18.38 days), or limb salvage (94.81% vs. 95.15%). CONCLUSIONS: Lower extremity vascular trauma is increasingly managed by vascular surgeons. Furthermore, vascular surgeons are more selective in the use of potentially unnecessary adjunctive maneuvers. Current accreditation guidelines should be revisited to mandate vascular surgery coverage in trauma centers that frequently treat this patient population.

The Nephrologist as an Ultrasonographer.

Ultrasonography is increasingly being used in the practice of nephrology, whether it is for diagnosis or management of acute or chronic kidney dysfunction, until progression to end-stage kidney disease, including preoperative assessment, access placement, and diagnosis and management of dysfunctional hemodialysis access. Point-of-care ultrasounds are also being used by nephrologists to help manage volume status, especially in patients admitted to the intensive care units, and more recently, for guiding fluid removal in the outpatient dialysis units. Fundamental knowledge of sonography has become invaluable to the nephrologist, and performance and interpretation of ultrasound has now become an essential tool for practicing nephrologists to provide patient-centered care, maximize efficiency, and minimize fragmentation of care. This review will address the growing role of ultrasonography in the management of a patient with CKD from the point of initial contact with the nephrologist throughout the spectrum of kidney disease and its consequences.

Rationale and design of a smartphone-enabled, home-based exercise program in patients with symptomatic peripheral arterial disease: The smart step randomized trial.

BACKGROUND: Supervised exercise therapy (SET) is recommended in patients with symptomatic peripheral arterial disease (PAD) as first-line therapy, although patient adoption remains low. Home-based exercise therapy (HBET) delivered through smartphones may expand access. The feasibility of such programs, especially in low-resource settings, remains unknown. METHODS: Smart Step is a pilot randomized trial of smartphone-enabled HBET vs walking advice in patients with symptomatic PAD in an inner-city hospital. Participants receive a smartphone app with daily exercise reminders and educational content. A trained coach performs weekly phone-based coaching sessions. All participants receive a Fitbit Charge HR 2 to measure physical activity. The primary outcome changes in 6-minute walking test (6MWT) distance at 12 weeks over baseline. Secondary outcomes are the degree of engagement with the smartphone app and changes in health behaviors and quality of life scores after 12 weeks and 1 year. RESULTS: A total of 15 patients are randomized as of December 15, 2019 with a mean (SD) age of 66.1 (5.8) years. The majority are female (60%) and black (87%). At baseline, the mean (SD) ABI and 6MWT were 0.86 (0.29) and 363.5 m, respectively. Enrollment is expected to continue until December 2020 to achieve a target size of 50 participants. CONCLUSIONS: The potential significance of this trial will be to provide preliminary evidence of a home-based, "mobile-first" approach for delivering a structured exercise rehabilitation program. Smartphone-enabled HBET can be potentially more accessible than center-based programs, and if proven effective, may have a potential widespread public health benefit.

Lower Socioeconomic Status Is Associated with Groin Wound Complications after Revascularization for Peripheral Artery Disease.

BACKGROUND: Surgical site infections (SSIs) after lower extremity revascularization are a common cause of increased morbidity in patients with peripheral artery disease (PAD). Understanding the multifaceted risk factors for SSIs may suggest closer monitoring for certain patients. The objective of this study is to evaluate the risk factors associated with incidence of SSIs, including patient demographics, operative factors, and socioeconomic status. METHODS: A retrospective review of a prospectively maintained database was queried for all patients who underwent any femoral exposure for the purposes of treating PAD from 2014 to 2017 at a single, academic, public hospital. Patient demographics, procedural data, and a variety of socioeconomic parameters were collected from chart review. Zip code geocoding was also used to obtain surrogates for local socioeconomic factors. The primary outcome measure was SSI within 90 days of operation. RESULTS: A total of 136 patients were identified, of which 19 (14%) developed an SSI. The only demographic variable associated with an increased risk of infection was body mass index (24.8 vs 30.1, P < 0.05). Major preoperative comorbid conditions, smoking status, and insurance status were not associated with an increased risk of complications. In addition, the type of procedure performed [infrainguinal bypass (n = 68), femoral endarterectomy (n = 36), aortofemoral bypass (n = 17), femoral-femoral bypass (n = 8), axillofemoral bypass (n = 7)] was not associated with any trend toward SSI. Estimated blood loss (292 vs 463 mL, P < 0.05), postoperative glucose (169 vs 212, P < 0.05), and postoperative white blood cell count (13.6 vs 18.3, P < 0.05) were the only periprocedural variables associated with SSIs. Lower mean household income, mean family income, and per capita income were all associated with an increased risk of postoperative infection (all P < 0.05). CONCLUSIONS: Socioeconomic factors, including poorer household income, are strongly associated with an increased risk of postoperative SSIs after lower extremity revascularization. Modifiable variables, such as preoperative optimization and procedural conduct, also display an effect on the development of an SSI. As a result, health care providers should maintain a high index of suspicion for the development of SSI in patients with lower socioeconomic status.

Surgical Intervention for Peripheral Artery Disease Does Not Improve Patient Compliance with Recommended Medical Therapy.

BACKGROUND: Nonadherence to smoking abstinence, antiplatelet therapy, and statin therapy in patients with peripheral artery disease (PAD) is associated with worse long-term outcomes. We hypothesized that patients who underwent invasive revascularization procedures would be more likely to adhere to these therapies than patients who were managed medically. METHODS: Prospective survey-based interviews pertaining to medication and behavioral compliance of patients with symptomatic PAD were performed. Specifically, adherence to smoking cessation, antiplatelet therapy, and antilipid therapy was evaluated. A retrospective review of the electronic medical record was then performed to obtain procedural data and divide patients into medically managed or surgically managed (open revascularization, percutaneous revascularization, amputation) cohorts. RESULTS: One hundred patients met criteria for inclusion and took part in the study. Overall, 62% were nonsmokers, and 59.1% of those with a history of smoking had quit; 66.7% were adherent to statin therapy; and 72.7% were adherent to antiplatelet therapy. Among patients treated with or without surgery, respectively, there was no difference in regards to rates of smoking abstinence (64.8% vs. 55.2%, P = 0.37), successful smoking cessation (61.5% vs. 53.6%, P = 0.51), antiplatelet adherence (73.9% vs. 74.1%, P = 0.99), or statin adherence (65.2% vs. 70.4%, P = 0.24). Major amputation was also not associated with adherence to these therapies. CONCLUSIONS: Surgical revascularization does not influence the likelihood of adherence to smoking abstinence, smoking cessation, antiplatelet therapy, or statin therapy in patients with symptomatic PAD. Patients should be counseled regarding revascularization options with the understanding that their likelihood of medical treatment compliance will be unaffected by any proposed intervention.

Hemodialysis Vascular Access: Rising Costs as a Surrogate Marker for Patency and Function of Arteriovenous Fistulas.

BACKGROUND: Establishment and maintenance of vascular access for hemodialysis is life-sustaining for patients needing renal-replacement therapy. Arteriovenous fistulas (AVFs) are the preferred type of access, but the costs associated with creation and maintenance are poorly characterized, especially with respect to patient characteristics. METHODS: A prospectively maintained registry has been established at The Mount Sinai Hospital for patients undergoing access procedures since 2007. We studied 163 patients undergoing successfully placed and cannulated AVFs as their first permanent ipsilateral access and for whom 3-year follow-up was available, including 18 patients with failed contralateral AVFs. Records were analyzed for institutional inpatient and outpatient procedures related to access maturation, imaging, catheter-related procedures, and revisions. We determined hospital costs for 3 AVF locations, assessing the contribution of various factors to variation in costs and patency. RESULTS: The median first-year cost of patent AVFs was $8,662, with $4,754 attributable to initial creation. For fistulas remaining patent for at least 3 years, median cumulative 36-month costs were $11,639, with $1,343 attributable to imaging and $10,478 to creation and interventions. Fistulas with patent lifetimes of 19-30 months (3.7%) had median cumulative costs of $26,035. Those with patent lifetimes of 6 months or shorter (6.7%) had median cumulative costs of $17,526. Right-sided fistulas were associated with 41% higher 1-year costs and 38% higher 3-year costs when compared with left-sided fistulas. Human Immunodeficiency Virus (HIV) status and prior history of complex contralateral access were also associated with higher 1-year and 3-year costs. CONCLUSIONS: Hemodialysis access maintenance contributes significantly to the healthcare burden of renal disease. Our data suggest that particular patient characteristics factor into patency and costs. Short-term mounting costs associated with AVF maintenance may portend poor long-term patency. Rising healthcare costs cannot be easily controlled without understanding the clinical factors driving them.

Inflow stenosis as a contributing factor in the etiology of AV access-induced ischemic steal.

OBJECTIVE: To determine how frequent inflow stenosis is a contributing factor in the etiology of arteriovenous access-induced steal (AVAIS). METHODS: A retrospective review of hemodialysis patients who underwent interventions from October 1998 to December 2011 for AVAIS was conducted at Mount Sinai Hospital. Patients with grade 3 AVAIS and complete arch and upper extremity vascular imaging were included. Demographics, access history, time to AVAIS, preoperative angiographic imaging and interventions performed were analyzed. RESULTS: A total of 52 patients were diagnosed with grade 3 (severe) AVAIS requiring intervention over the study period. Forty-seven percent of the patients were male, average age was 62 years, 47% were of African American race and 88% were diabetic. Seventeen consecutive patients, with imaging, were included in this study. The average time to presentation of steal symptoms was 147±228 days. All of the accesses were proximal, and 65.7% were autogenous. Imaging studies consisted of angiography (14) and computed tomography angiography (3). Five patients had imaging evidence of >50% luminal inflow stenosis (29.4%). The location of stenosis was the subclavian (3 cases) and brachial (2 cases) arteries. Patients underwent distal revascularization and interval ligation (3), ligation (1) and angioplasty/stenting (1). CONCLUSION: In our population, nearly one-third of the patients with severe AVAIS had a significant subclavian or brachial artery stenosis. The implications of this finding suggest the importance of complete preoperative imaging. The treatment of the inflow stenosis by itself may not be curative, but the correction may serve as an adjunct and contribute to the success of other therapeutic procedures.

Dual-isotope SPECT/CT impact on hospitalized patients with suspected diabetic foot infection: saving limbs, lives, and resources.

BACKGROUND: Foot ulcer with suspected infection is one of the most common reasons for hospitalization and a major factor contributing to morbidity and high healthcare-related expenses among diabetic patients. Many patients will require amputation; however, major amputation is associated with an alarmingly high 5-year mortality rate. In this study, we assess the diagnosis and management of suspected foot infection in diabetic patients using dual-isotope (DI) single-photon emission computed tomography/computed tomography (SPECT/CT) compared with conventional imaging. METHODS: The diagnostic accuracy in and management of 227 patients who had undergone DI SPECT/CT was compared with that of 232 similar patients who had undergone conventional imaging including plain radiography, CT, planar bone scanning, planar indium-111 white blood cell scanning, and MRI. The duration of hospitalization was additionally compared between these two groups of patients after excluding patients with other active comorbidities. RESULTS: Soft-tissue infection, osteomyelitis with or without soft-tissue infection, and other bony pathologies were more accurately and confidently identified with DI SPECT/CT than with conventional imaging. DI SPECT/CT use was associated with significantly fewer major amputations and more selective bony resection as well as with shorter duration of hospitalization when compared with conventional imaging. CONCLUSION: In this large population of diabetic patients with suspected foot infection DI SPECT/CT was more accurate in diagnosing and localizing infection compared with conventional imaging. In addition, DI SPECT/CT provided clear guidance and promoted many limb salvage procedures. Of equal importance to health economics, DI SPECT/CT use was associated with considerably reduced length of hospitalization compared with conventional imaging.

Peripheral arterial disease in women.

Peripheral arterial disease (PAD) affects a significant portion of the United States population, and much research has been conducted on identifying populations at risk for PAD, evaluating appropriate diagnostic modalities for PAD, studying the effect of risk factor reduction on PAD progression, and determining the best method of treatment for symptomatic PAD. However, most PAD research and clinical trials have focused on whole populations, or populations consisting mostly of men. Little data exist with respect to PAD in women. The goal of this review is to highlight what is known about gender-related differences for PAD.

Chronic kidney disease and dialysis access in women.

Chronic kidney disease currently affects one in nine Americans and over 500,000 have progressed to failure requiring kidney replacement therapy, with nearly 45% being women. Clinical Practice Guidelines have been developed in an effort to synthesize the latest literature, particularly randomized controlled trials, to assist clinical decision making. Women have different levels of kidney function than men at the same level of serum creatinine and may also lose kidney function over time more slowly than men. Although the arteriovenous fistulae have long been recognized as the preferred access for hemodialysis, women are less likely to initiate dialysis with an arteriovenous fistula in place. In addition, the female sex is regarded as a risk factor for access failure as well for complications such as steal. This article reviews treatment of women with chronic kidney disease, focusing on the difficulties they are perceived to have with dialysis access.

Experience of HeRO dialysis graft placement in a challenging population.

OBJECTIVE: To assess the outcomes of the hemodialysis reliable outflow (HeRO) device in a subset of hemodialysis access-challenged patients with central venous obstruction. METHODS: Retrospective analysis of a series of patients in 2 centers who underwent placement of the HeRO device between September 2009 and November 2010. Patients' demographics, access history, HeRO patency, and number of reinterventions were analyzed. RESULTS: Eleven patients underwent 12 HeRO implantations. The average duration of dialysis prior to HeRO placement was 5.55 ± 3.64 years. Primary and secondary patencies at 6 months and 1 year were 36.4% and 54.5% and 9.1% and 45.5%, respectively. CONCLUSIONS: In the end-stage renal disease population with central venous occlusive disease, the HeRO device offers the best long-term dialysis option when an arteriovenous fistula or graft is not possible. Close follow-up and subsequent aggressive interventions can prolong the use of the HeRO and avoid the last resort of dialysis catheters.

Percutaneous intervention for infrageniculate arterial disease in women may be associated with better outcomes when compared to men.

OBJECTIVE: The purpose of this study was to identify any gender-associated differences in the percutaneous treatment of infrageniculate lesions in individuals with chronic critical limb ischemia. METHODS: A retrospective chart review was performed on 112 index tibial lesions in 81 consecutive patients operated on from January 2005 to February 2011. All patients were treated for critical limb ischemia-defined as rest pain or tissue loss. Patient demographics, comorbidities, clinical presentation, vascular studies, lesion characteristics, procedures, and postoperative complications were entered into a database for review. Patients were evaluated for primary patency, secondary patency, limb salvage, and mortality rates. RESULTS: Sixty-three index tibial lesions were treated percutaneously in 43 women, compared to 49 lesions in 38 men. There was a trend toward increased cardiac disease (65.8% men vs 44.2% women; P = .052) and smoking (52.6% men vs 32.6% women; P = .070) in men. Men were more likely than women to have TransAtlantic Inter-Society Consensus (TASC) C and D lesions (83.7% vs 65.1%; P = .023) and to be treated for total occlusion (44.9% vs 25.4%; P = .031). There were no significant gender-related differences in length of stay or postoperative complications. Women had statistically better primary patency rates than men at 12 and 24 months (77.5% ± 6.9% and 72.9% ± 7.8% in women vs 58.7% ± 9.3% and 45.2% ± 9.9% in men; P = .032). Women also had statistically better secondary patency rates than men at 12 and 24 months (90.4% ± 4.8% and 85.1% ± 6.8% in women vs 76.0% ± 8.1% and 58.5% ± 10.8% in men; P = .028). Female gender remained an independent predictor of superior patency even after controlling for gender-related differences in TASC grade. There were no significant differences in limb salvage rates at 12 and 24 months (92.1% ± 4.4% and 85.0% ± 7.9% in women vs 88.3% ± 6.4% and 83.4% ± 7.7% in men; P = .985). Overall survival rates were similar (59.8% ± 7.6% for women and 68.0% ± 8.1% for men at 24 months; P = .351). CONCLUSIONS: Percutaneous intervention may be an equally effective or better treatment option for women with chronic limb ischemia and tibial disease when compared to men. In this study, male gender was an independent predictor of poorer primary and secondary patency rates after infrageniculate intervention. There were no differences in postoperative wound complications between genders. Endovascular procedures may lessen the gap in gender-related treatment outcomes and postoperative complications seen after open arterial reconstructions.

A randomized, controlled pilot study of autologous CD34+ cell therapy for critical limb ischemia.

BACKGROUND: Critical limb ischemia portends a risk of major amputation of 25% to 35% within 1 year of diagnosis. Preclinical studies provide evidence that intramuscular injection of autologous CD34+ cells improves limb perfusion and reduces amputation risk. In this randomized, double-blind, placebo-controlled pilot study, we evaluated the safety and efficacy of intramuscular injections of autologous CD34+ cells in subjects with moderate or high-risk critical limb ischemia, who were poor or noncandidates for surgical or percutaneous revascularization (ACT34-CLI). METHODS AND RESULTS: Twenty-eight critical limb ischemia subjects were randomized and treated: 7 to 1 × 10(5) (low-dose) and 9 to 1 × 10(6) (high-dose) autologous CD34+ cells/kg; and 12 to placebo (control). Intramuscular injections were distributed into 8 sites within the ischemic lower extremity. At 6 months postinjection, 67% of control subjects experienced a major or minor amputation versus 43% of low-dose and 22% of high-dose cell-treated subjects (P=0.137). This trend continued at 12 months, with 75% of control subjects experiencing any amputation versus 43% of low-dose and 22% of high-dose cell-treated subjects (P=0.058). Amputation incidence was lower in the combined cell-treated groups compared with control group (6 months: P=0.125; 12 months: P=0.054), with the low-dose and high-dose groups individually showing trends toward improved amputation-free survival at 6 months and 12 months. No adverse safety signal was associated with cell administration. CONCLUSIONS: This study provides evidence that intramuscular administration of autologous CD34+ cells was safe in this patient population. Favorable trends toward reduced amputation rates in cell-treated versus control subjects were observed. These findings warrant further exploration in later-phase clinical trials. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00616980.

Duplex ultrasound evaluation of hemodialysis access: a detailed protocol.

A detailed protocol for the performance and interpretation of duplex ultrasound evaluation of hemodialysis access is described.

The role of anatomic factors in predicting success of endovascular repair of thoracic aortic aneurysms.

OBJECTIVE: We evaluated the results of thoracic endovascular aneurysm repair (TEVAR) to determine what anatomic factors influenced the clinical outcomes. METHODS: Preoperative computed tomography (CT) angiograms of 65 patients who underwent TEVAR were analyzed using 3-dimensional imaging. The proximal and distal neck, thoracic aneurysm, and iliac arteries were measured for angulation, diameter, length, calcification, and tortuosity. Immediate technical success and clinical success were measured. RESULTS: Immediate technical success was achieved in 91% (59 of 65) of the patients analyzed. One patient died in the operating room during treatment of rupture. Clinical success was achieved in 83% (54 of 65) of patients at follow-up. Four patients had small endoleaks with no sac enlargement at follow-up. One patient was converted to open repair. Severe iliac calcification was found to be significant for deployment failure. The mean follow-up is 8 months (1-36 months). CONCLUSION: Increased iliac calcification and increased iliac tortuosity correlate with an inability to successfully deploy the device.