Endovascular Transvenous versus Open Femoropopliteal Bypass

Background and Objectives: Lower extremity arterial disease is one of the most prevalent manifestations of atherosclerosis. The results from numerous studies regarding the best revascularization method of an occluded superficial femoral artery have been conflicting. The aim of this study was to compare the patency of transvenous endovascular with open femoropopliteal bypass, both with vein and prosthetic grafts. To our knowledge, a direct patency comparison between transvenous endovascular and open femoropopliteal bypass has not been published. This could help elucidate which method is preferable and in which cases. Materials and Methods: Patients with complex TASC-C and D SFA lesions were offered endovascular transvenous or open bypass. A total of 384 consecutive patients with PAD requiring surgical treatment were evaluated for inclusion in this study. Three-year follow-up data were collected for 52 endovascular procedures, 80 prosthetic grafts, and 44 venous bypass surgeries. Bypass patency was investigated by Duplex US every 6 months. Kaplan-Meier plots were used to analyze primary, primary-assisted, and secondary patency for endovascular transvenous, autovenous, and prosthetic bypasses. Results: Primary, primary-assisted, and secondary patency in venous group at 3 years was 70.5%, 77.3%, and 77.3%, respectively. In the endovascular transvenous group, primary, primary-assisted, and secondary patency at 3 years was 46.2%, 69.2%, and 76.9%, respectively. The lowest patency rates at 3 years were noted in the prosthetic graft group with 22.5% primary, 26.6% primary-assisted, and 28.2% secondary patency. Conclusions: The saphenous vein is the best graft to perform in above-the-knee femoropopliteal bypass. Transvenous endovascular bypass is a viable option with comparable primary-assisted and secondary patency. Primary patency is substantially lower for endovascular transvenous compared to venous bypass. Patients treated with endovascular transvenous bypass will require a significant number of secondary procedures to provide optimal patency. Prosthetic grafts should only be used if no other option for bypass is available.

Diagnosis and treatment of ischemia-producing coronary stenoses improves 5-year survival of patients undergoing major vascular surgery

OBJECTIVE

Patients undergoing vascular surgery procedures have poor long-term survival due to coexisting coronary artery disease (CAD), which is often asymptomatic, undiagnosed, and undertreated. We sought to determine whether preoperative diagnosis of asymptomatic (silent) coronary ischemia using coronary computed tomography (CT)-derived fractional flow reserve (FFRCT) together with postoperative ischemia-targeted coronary revascularization can reduce adverse cardiac events and improve long-term survival following major vascular surgery METHODS: In this observational cohort study of 522 patients with no known CAD undergoing elective carotid, peripheral, or aneurysm surgery we compared two groups of patients. Group I included 288 patients enrolled in a prospective Institutional Review Board-approved study of preoperative coronary CT angiography (CTA) and FFRCT testing to detect silent coronary ischemia with selective postoperative coronary revascularization in addition to best medical therapy (BMT) (FFRCT guided), and Group II included 234 matched controls with standard preoperative cardiac evaluation and postoperative BMT alone with no elective coronary revascularization (Usual Care). In the FFRCT group, lesion-specific coronary ischemia was defined as FFRCT ≤0.80 distal to a coronary stenosis, with severe ischemia defined as FFRCT ≤0.75. Results were available for patient management decisions. Endpoints included all-cause death, cardiovascular death, myocardial infarction (MI), and major adverse cardiovascular events (MACE [death, MI, or stroke]) during 5-year follow-up.

RESULTS

The two groups were similar in age, gender, and comorbidities. In FFRCT, 65% of patients had asymptomatic lesion-specific coronary ischemia, with severe ischemia in 52%, multivessel ischemia in 36% and left main ischemia in 8%. The status of coronary ischemia was unknown in Usual Care. Vascular surgery was performed as planned in both cohorts with no difference in 30-day mortality. In FFRCT, elective ischemia-targeted coronary revascularization was performed in 103 patients 1 to 3 months following surgery. Usual Care had no elective postoperative coronary revascularizations. At 5 years, compared with Usual Care, FFRCT guided had fewer all-cause deaths (16% vs 36%; hazard ratio [HR], 0.37; 95% confidence interval [CI], 0.22-0.60; P < .001), fewer cardiovascular deaths (4% vs 21%; HR, 0.11; 95% CI, 0.04-0.33; P < .001), fewer MIs (4% vs 24%; HR, 0.13; 95% CI, 0.05-0.33; P < .001), and fewer MACE (20% vs 47%; HR, 0.36; 95% CI, 0.23-0.56; P < .001). Five-year survival was 84% in FFRCT compared with 64% in Usual Care (P < .001).

CONCLUSIONS

Diagnosis of silent coronary ischemia with ischemia-targeted coronary revascularization in addition to BMT following major vascular surgery was associated with fewer adverse cardiovascular events and improved 5-year survival compared with patients treated with BMT alone as per current guidelines.

Coronary Revascularization of Patients with Silent Coronary Ischemia May Reduce the Risk of Myocardial Infarction and Cardiovascular Death Following Carotid Endarterectomy

BACKGROUND

Major adverse cardiac events (MACE) are the primary cause of death following carotid endarterectomy (CEA). We sought to determine whether selective coronary revascularization of CEA patients with asymptomatic coronary ischemia can reduce the risk of MACE, myocardial infarction (MI) and cardiac death following endarterectomy compared to CEA patients receiving standard cardiac evaluation and care.

METHODS

Two groups of patients with no cardiac history or symptoms undergoing elective CEA were compared. Group I: patients enrolled in a prospective study of non-invasive pre-operative cardiac evaluation using coronary CT-derived fractional flow reserve (FFR_CT) to detect asymptomatic (silent) coronary ischemia with selective post-operative coronary revascularization. Group II: matched Control patients with standard pre-operative cardiac evaluation and no post-operative coronary revascularization. Lesion-specific coronary ischemia in Group I was defined as FFR_CT ≤0.80 distal to coronary stenosis with severe ischemia defined as FFR_CT ≤0.75. Endpoints included MACE, cardiac death, MI, cardiovascular (CV) death, stroke and all-cause death through 3-year follow up.

RESULTS

Group I (n=100) and Group II (n=100) patients were similar in age (68 vs 67 years), gender (65% vs 62% male), co-morbidities and indications for CEA (53% vs 48% symptomatic carotid stenosis). In Group I FFR_CT analysis revealed lesion-specific coronary ischemia in 57% of patients, severe coronary ischemia in 44%, left main ischemia in 7% and multivessel ischemia in 28%. The status of coronary ischemia in Group II was unknown. CEA was performed without complications in both groups and all patients received optimal post-operative medical therapy. In Group I, elective coronary revascularization was performed in 33 patients (27 PCI; 6 CABG) 1-3 months following CEA. Group II patients had no elective coronary revascularization. During 3-year follow-up, compared to Group II, Group I patients had fewer MACE (4% vs 17%, HR 0.21 [95% CI 0.07-0.63], P=.004), fewer cardiac deaths (2% vs 9%, HR 0.20 [95% CI 0.04-0.95], P=.030), fewer MIs (3% vs 17%, HR 0.16 [95% CI 0.05-0.54], P=.001) and fewer CV deaths (2% vs 12%, HR 0.16 [95% CI 0.004-0.07], P=0.009). There were no significant differences in the rates of stroke or all-cause death.

CONCLUSIONS

Pre-operative diagnosis of silent coronary ischemia with selective coronary revascularization following CEA may reduce the risk of MACE, cardiac death, MI and CV death during 3-year follow up compared to CEA patients receiving standard cardiac evaluation and care.

Diagnosis of silent coronary ischemia with selective coronary revascularization might improve 2-year survival of patients with critical limb-threatening ischemia

BACKGROUND

Patients with critical limb-threatening ischemia (CLTI) have had poor long-term survival after lower extremity revascularization owing to coexistent coronary artery disease. A new cardiac diagnostic test, coronary computed tomography-derived fractional flow reserve (FFR_CT), can identify patients with ischemia-producing coronary stenosis who might benefit from coronary revascularization. We sought to determine whether the diagnosis of silent coronary ischemia before limb salvage surgery with selective postoperative coronary revascularization can reduce the incidence of adverse cardiac events and improve the survival of patients with CLTI compared with standard care.

METHODS

Patients with CLTI and no cardiac history or symptoms who had undergone preoperative testing to detect silent coronary ischemia with selective postoperative coronary revascularization (group I) were compared with patients with standard preoperative cardiac clearance and no elective postoperative coronary revascularization (group II). Both groups received guideline-directed medical care. Lesion-specific coronary ischemia in group I was defined as FFR_CT of ≤0.80 distal to a stenosis, with severe ischemia defined as FFR_CT of ≤0.75. The endpoints included all-cause death, cardiovascular (CV) death, myocardial infarction (MI), major adverse CV events (i.MACE; CV death, MI, unplanned coronary revascularization, stroke) through 2 years of follow-up.

RESULTS

Groups I (n = 111) and II (n = 120) were similar in age (66 ± 9 vs 66 ± 7 years), gender (78% vs 83% men), comorbidities, and surgery performed. In group I, unsuspected, silent coronary ischemia was found in 71 of 103 patients (69%), with severe ischemia in 58% and left main coronary ischemia in 8%. Elective postoperative coronary revascularization was performed in 47 of 71 patients with silent ischemia (66%). In group II, the status of silent coronary ischemia was unknown. The median follow-up was >2 years for both groups. The 2-year outcomes for groups I and II were as follows: all-cause death, 8.1% and 20.0% (hazard ratio [HR], 0.38; 95% confidence interval [CI], 0.18-0.84; P = .016); CV death, 4.5% and 13.3% (HR, 0.32; 95% CI, 0.11-0.88; P = .028); MI, 6.3% and 17.5% (HR, 0.33; 95% CI, 0.14-0.79; P = .012); and major adverse CV events, 10.8% and 23.3% (HR, 0.44; 95% CI, 0.22-0.88; P = .021), respectively.

CONCLUSIONS

The preoperative evaluation of patients with CLTI and no known coronary artery disease using coronary FFR_CT revealed silent coronary ischemia in two of every three patients. Selective coronary revascularization of patients with silent coronary ischemia after recovery from limb salvage surgery resulted in fewer CV deaths and MIs and improved 2-year survival compared with patients with CLTI who had received standard cardiac evaluation and care. Prospective controlled studies are required to further define the role of FFR_CT in the evaluation and treatment of patients with CLTI.

Diagnosis and management of silent coronary ischemia in patients undergoing carotid endarterectomy

BACKGROUND

Coronary artery disease is the primary cause of death in patients with carotid artery disease and silent ischemia is a marker for adverse coronary events. A new noninvasive cardiac diagnostic test, coronary computed tomography-derived fractional flow reserve (FFR_CT) can reliably identify ischemia-producing coronary stenosis in patients with coronary artery disease and help to select patients for coronary revascularization. The purpose of this study is to determine the prevalence of silent coronary ischemia in patients undergoing carotid endarterectomy (CEA) and to evaluate the usefulness of FFR_CT in selecting patients for coronary revascularization to decrease cardiac events and improve survival.

METHODS

Patients with no cardiac history or symptoms admitted for elective CEA were enrolled in a prospective, open-label, institutional review board-approved study and underwent preoperative coronary computed tomography angiography (CTA) and FFR_CT with results available to physicians for patient management. Lesion-specific coronary ischemia was defined as FFR_CT of 0.80 or less distal to a focal coronary stenosis with an FFR_CT of 0.75 or less, indicating severe ischemia. Primary end point was incidence of major adverse cardiovascular events (MACE; defined as cardiovascular death, myocardial infarction, or stroke) at 30 days and 1 year.

RESULTS

Coronary CTA and FFR_CT was performed in 90 CEA patients (age 67 ± 8 years; male 66%). Lesion-specific coronary ischemia was found in 51 patients (57%) with a mean FFR_CT of 0.71 ± 0.14. Severe coronary ischemia was present in 39 patients (43%), 26 patients had multivessel ischemia, and 5 had left main disease. CEA was performed as scheduled in all patients with no postoperative deaths or myocardial infarctions. There were no MACE events at 30 days. After recovery from surgery, 36 patients with significant lesion-specific ischemia underwent coronary angiography with coronary revascularization (percutaneous coronary intervention or coronary artery bypass grafting) in 30 patients (33%). Survival at 1 year was 100% and freedom from MACE was 98%.

CONCLUSIONS

Patients undergoing CEA have a high prevalence of unsuspected (silent) coronary ischemia, which may place them at risk for coronary events. Preoperative diagnosis of silent ischemia using CTA and FFR_CT can identify high-risk patients and help to guide patient management. Selective postoperative coronary revascularization of patients with significant ischemia may decrease the risk of cardiac events and improve survival, but longer follow-up is needed and prospective, controlled trials are indicated.

P6172Management of silent myocardial ischemia in patients with peripheral arterial disease needing surgery

Background

Patients with peripheral arterial disease (PAD) needing surgery have increased risk for post-operative myocardial infarction (MI)/death due to coexisting coronary artery disease (CAD). Coronary CT angiography (CTA)-derived fractional flow reserve (FFRCT) can reliably identify ischemia-producing coronary stenosis in patients with suspected CAD but its value in PAD patients is unknown.

Purpose

To determine the prevalence of silent coronary ischemia in PAD patients undergoing surgery and to assess the value of FFRCT in guiding management of patients with multisite arterial ischemia.

Methods

Patients admitted for elective carotid, aortic or peripheral vascular surgery with no cardiac history or CAD symptoms were enrolled in a prospective, open-label, ethics committee-approved study and underwent pre-op CTA and FFRCT evaluation with results available to treating physicians. Ischemia-producing coronary stenosis was defined as FFRCT≤0.80 distal to stenosis in >2mm diameter vessels. Patient management was guided by a multidisciplinary team of cardiologists, cardiovascular surgeons and anaesthesiologists. Primary endpoint was major adverse cardiac events (MACE= cardiac death, MI, urgent revasc) at 30 days with follow up at 3,6,12 months.

Results

Coronary CTA and FFRCT analysis was performed in 179 consecutive patients (age 66±8 years, male 78%, hypertension 79%, diabetes 10%, dyslipidemia 31%, smoking 37%). CTA revealed extensive coronary calcification (Agatston score 995±1004, range 0–4810) and ≥50% stenosis in 64% of patients. Ischemic coronary stenosis (FFRCT≤0.80) was present in 114 patients (64%) with FFRCT ≤0.75 in 97 (54%) and multivessel ischemia in 63 (35%). Clinically indicated vascular surgery was performed as planned in 170/179 patients (95%) with cardiac anaesthesia and close monitoring and postponed in 9 patients for coronary revascularization (3) or medical/other therapy (6). There were no post-op cardiac complications. Elective coronary angiography, performed 1–3 months post surgery in 86 patients with left main, severe or multivessel ischemia, confirmed significant stenosis in each patient with revascularization in 58 patients (53 PCI and 5 CABG) including 8 for LM disease. There have been no cardiovascular deaths; 3 patients have died of lung cancer which was first discovered on CTA. One patient had peri-procedural MI at time of PCI and one had MI and urgent PCI at 6 months. MACE at 30 days=0/179, 3 months = 1/154, 6 months=2/123, 12 months=0/65.

Conclusions

Patients undergoing elective PAD surgery have a high prevalence (64%) of unsuspected ischemia-producing coronary stenosis. Pre-op diagnosis with CTA- FFRCT can help guide a multidisciplinary team approach with optimum medical management and staged peripheral and coronary revascularization. Favourable early results are promising and suggest the need for prospective controlled studies to define the role of coronary revascularization in PAD patients.

Acknowledgement/Funding

Heartflow, Inc.; Mikrotikls Ltd

Diagnostic performance of cardiac imaging methods to diagnose ischaemia-causing coronary artery disease when directly compared with fractional flow reserve as a reference standard: a meta-analysis

Aims

The aim of this study was to determine the diagnostic performance of single-photon emission computed tomography (SPECT), stress echocardiography (SE), invasive coronary angiography (ICA), coronary computed tomography angiography (CCTA), fractional flow reserve (FFR) derived from CCTA (FFRCT), and cardiac magnetic resonance (MRI) imaging when directly compared with an FFR reference standard.

Method and results

PubMed and Web of Knowledge were searched for investigations published between 1 January 2002 and 28 February 2015. Studies performing FFR in at least 75% of coronary vessels for the diagnosis of ischaemic coronary artery disease (CAD) were included. Twenty-three articles reporting on 3788 patients and 5323 vessels were identified. Meta-analysis was performed for pooled sensitivity, specificity, likelihood ratios (LR), diagnostic odds ratio, and summary receiver operating characteristic curves. In contrast to ICA, CCTA, and FFRCT reports, studies evaluating SPECT, SE, and MRI were largely retrospective, single-centre and with generally smaller study samples. On a per-patient basis, the sensitivity of CCTA (90%, 95% CI: 86-93), FFRCT (90%, 95% CI: 85-93), and MRI (90%, 95% CI: 75-97) were higher than for SPECT (70%, 95% CI: 59-80), SE (77%, 95% CI: 61-88), and ICA (69%, 95% CI: 65-75). The highest and lowest per-patient specificity was observed for MRI (94%, 95% CI: 79-99) and for CCTA (39%, 95% CI: 34-44), respectively. Similar specificities were noted for SPECT (78%, 95% CI: 68-87), SE (75%, 95% CI: 63-85), FFRCT (71%, 95% CI: 65-75%), and ICA (67%, 95% CI: 63-71). On a per-vessel basis, the highest sensitivity was for CCTA (pooled sensitivity, 91%: 88-93), MRI (91%: 84-95), and FFRCT (83%, 78-87), with lower sensitivities for ICA (71%, 69-74), and SPECT (57%: 49-64). Per-vessel specificity was highest for MRI (85%, 79-89), FFRCT (78%: 78-81), and SPECT (75%: 69-80), whereas ICA (66%: 64-68) and CCTA (58%: 55-61) yielded a lower specificity.

Conclusions

In this meta-analysis comparing cardiac imaging methods directly to FFR, MRI had the highest performance for diagnosis of ischaemia-causing CAD, with lower performance for SPECT and SE. Anatomic methods of CCTA and ICA yielded lower specificity, with functional assessment of coronary atherosclerosis by SE, SPECT, and FFRCT improving accuracy.

Effect of the ratio of coronary arterial lumen volume to left ventricle myocardial mass derived from coronary CT angiography on fractional flow reserve

BACKGROUND

We hypothesize that in patients with suspected coronary artery disease (CAD), lower values of the ratio of total epicardial coronary arterial lumen volume to left ventricular myocardial mass (V/M) result in lower fractional flow reserve (FFR).

METHODS

V/M was computed in 238 patients from the NXT trial who underwent coronary computed tomography angiography (CTA), quantitative coronary angiography (QCA) and FFR measurement in 438 vessels. Nitroglycerin was administered prior to CT, QCA and FFR acquisition. The V/M ratio was quantified on a patient-level from CT image data by segmenting the epicardial coronary arterial lumen volume (V) and the left ventricular myocardial mass (M). Calcified and noncalcified plaque volumes were quantified using semi-automated software.

RESULTS

The median value of V/M (18.57 mm³/g) was used to define equal groups of low and high V/M patients. Patients with low V/M had greater diameter stenosis by QCA, more plaque and lower FFR (0.80 ± 0.12 vs. 0.87 ± 0.08; P < 0.0001) than those with high V/M. A total of 365 vessels in 202 patients had QCA stenosis ≤50% and measured FFR. In these patients, those with low V/M had higher percent diameter stenosis by QCA, greater total plaque volume and lower FFR (0.81 ± 0.12 vs. 0.88 ± 0.07; P < 0.0001) than those with high V/M. In multivariate logistic regression analysis, V/M was an independent predictor of FFR ≤0.80 (all p-values < 0.001).

CONCLUSIONS

Patients with a low V/M ratio have lower FFR overall and in non-obstructive CAD, independent of plaque measures.

How Many Patients with Infrarenal Aneurysms are Candidates for Endovascular Repair? The Northern California Experience

Purpose:

To determine how many patients with abdominal aortic aneurysms (AAA) meet the anatomical selection criteria for AneuRx stent-graft repair in community hospitals of Northern California.

Methods:

The records were reviewed of 220 AAA patients (171 men, 49 women) who were considered for endovascular repair by the treating vascular surgeon at 28 community hospitals in Northern California between January and October 2001. Contrast computed tomographic angiography (CTA) and selective arteriography were performed at each institution and reviewed by a centralized, independent image-reading center. Selection criteria determined by the manufacturer and published in the indications for use were applied to each set of imaging studies. The number of patients who met inclusion criteria were recorded, as were the anatomical characteristics of each aneurysm.

Results:

The mean aneurysm size in the 220 patients was 55.3±0.7 mm. Among these patients, 122 (55%) were judged to be candidates for endovascular repair and 98 (45%) were considered ineligible. The primary anatomical reason for ineligibility was a short infrarenal neck in 43 (44%) patients, followed by a large proximal neck diameter (25, 25%), iliac aneurysms (10, 10%), extremely tortuous or calcified neck (7, 7%), iliac occlusion (6, 6%), and small distal aortic bifurcation and accessory renal arteries (5, 5%). Four (4%) patients were classified as non-candidates due to poor quality imaging. There was no difference in aneurysm diameter (54.0±0.8 versus 57.1±1.2 mm, p=NS) or age (72.2±1.2 versus 74.6±2.2 years, p=NS) between candidates and non-candidates. However, proportionally more men (60%) than women (39%) were eligible for endovascular repair with the AneuRx stent-graft (p<0.05). All 122 patients who were considered candidates for endovascular repair were treated, with successful stent-graft placement achieved in 121 (99%).

Conclusions:

Fifty-five percent of patients considered for endovascular AAA repair in community hospitals in Northern California met the anatomical selection criteria for the AneuRx stent-graft. Men appeared to be twice as likely to meet the eligibility requirements as women. Unfavorable infrarenal neck anatomy was the primary exclusion criterion for endovascular repair in this community setting.

Ten Years of Advancements in Interventional Cardiology

The past decade has seen the evolution of an exciting technology that has changed forever the treatment of aortic aneurysmal disease. From rather crude homemade stent-grafts constructed in the surgical suite to elegant commercially manufactured devices in a variety of configurations and sizes, the aortic endograft has experienced a meteoric rise in popularity to become a beneficial, minimally invasive therapy that can obviate the risk of rupture and death. There are now 3 approved endovascular devices on the market for infrarenal abdominal aortic aneurysm repair, and it is likely that additional and improved devices will become available in the future. This review revisits the developmental history of the aortic endograft, noting the ongoing refinements that have arisen from our experiences with the growing population of stent-graft patients. Although research continues to search for solutions to the problems of endoleak and migration, long-term results even with the earlier second and third-generation devices are better than has been achieved with open surgical repair.

Preservation of hypogastric flow and control of iliac aneurysm size in the treatment of aortoiliac aneurysms using the Nellix EndoVascular Aneurysm Sealing endograft

OBJECTIVE

The purpose of this study was to determine the long-term effectiveness of endovascular aneurysm sealing (EVAS) in the treatment of complex aortoiliac aneurysms with preservation of hypogastric artery flow.

METHODS

We reviewed all patients with abdominal aortic aneurysms (AAAs) and common iliac aneurysms (CIAs) enrolled and treated in prospective studies of EVAS using the Nellix endograft (Endologix, Irvine, Calif) at two centers from 2008 to 2014. Patients with 1 year or more of computed tomography follow-up underwent quantitative morphometric assessment by two independent vascular radiologists blinded to clinical outcome results. Hypogastric patency and CIA diameter changes over time were assessed and compared in three treatment groups: totally excluded CIA, partially excluded CIA, and untreated CIA.

RESULTS

Among 125 patients with EVAS, 68 patients (mean age, 75 ± 8 years; 79% men) had both AAA (mean diameter, 55.8 ± 2.0 mm) and CIA (median diameter, 23.4; interquartile range, 21.3-27.0 mm), with bilateral CIAs in 33 patients. Treatment of 101 CIAs included complete CIA exclusion in 40 (39.6%), partial CIA exclusion in 33 (32.7%), and no CIA treatment in 28 (27.7%), with successful AAA exclusion in all patients. Internal iliac flow was preserved in all 122 hypogastric arteries that were patent before treatment (14 hypogastric arteries were occluded at baseline). During the 5-year follow-up period (median follow-up, 24.7 months; range, 11.5-61.7 months), three patients required secondary treatment with hypogastric occlusion and graft extension to the external iliac. Thus, internal iliac flow was maintained in 98% of at-risk hypogastric arteries. There were no aneurysm-related clinical events, except for the three secondary treatments. Totally excluded iliac aneurysms did not change in diameter over time (P = .85), whereas untreated CIAs enlarged at a rate of 0.16 mm/y (95% confidence interval, 0.09-0.23; P < .0001). Partially excluded CIAs enlarged at a higher rate of 0.59 mm/y (95% confidence interval, 0.47-0.71; P < .0001). Enlargement ≥3 mm occurred only in partially treated CIAs larger than 3 cm.

CONCLUSIONS

EVAS was effective in treating aortoiliac aneurysms with preservation of internal iliac patency in most cases. Complete CIA exclusion prevented aneurysm enlargement over time, whereas partial exclusion did not prevent continued CIA enlargement, particularly in larger aneurysms.

Operative Repair for Aortic Aneurysms: The Gold Standard

Surgical treatment of abdominal aortic aneurysm (AAA) is being challenged by newer, minimally invasive therapies. Such new treatment strategies will need to prove themselves against concurrent results of standard operative AAA repair, within defined medical risk and aneurysm morphological categories. We review the natural history of AAAs, the medical risk levels for elective AAA repair, aneurysm morphology and its impact on operative mortality, the issue of high-risk patient treatment, and the current standard of care for AAAs based on single-center, multicenter, and population-based statistics. In good-risk patients, aneurysms > 5 cm in diameter are best treated by replacement with a prosthetic graft. Operative mortality should be < 5% and 1-year survival > 90%. Aortic endograft techniques must meet or exceed these standards if they are to supplant standard surgical repair.

Prevention of Spinal Cord Ischemia in an Ovine Model of Abdominal Aortic Aneurysm Treated with a Self-Expanding Stent-Graft

Purpose:

To present novel techniques to prevent spinal ischemia during aneurysm creation and chronic bifurcated stent-graft implantation in an ovine model of abdominal aortic aneurysm (AAA).

Method:

Experimental AAAs were created in 38 sheep. To prevent spinal ischemia, an internal aortic shunt was used during aneurysm creation. In the animals designated to receive bifurcated stent-grafts, a left external iliac-to-internal iliac bypass was performed to revascularize the caudal artery and prevent postdeployment spinal cord ischemia. Specimens were harvested at 1 week, 1, 3, and 6 months, and 1 year.

Results:

Aneurysms were successfully created without paralysis in 35 animals. Two died due to aspiration pneumonia. Of the 33 animals implanted with endografts, 16 (94%) of 17 with straight devices and 15 (94%) of 16 with bifurcated stent-grafts survived with well-functioning, patent stent-grafts. Paralysis developed in 2 animals after endografting due to technical failures.

Conclusions:

The use of an internal shunt during aneurysm creation and internal iliac-to-external iliac transposition prior to bifurcated stent-graft deployment prevented spinal ischemia in an ovine AAA model. Chronically deployed stent-grafts were well tolerated.

Treatment of Axillosubclavian Vein Thrombosis: A Novel Technique for Rapid Removal of Clot Using Low-Dose Thrombolysis

Purpose:

To report successful combined percutaneous mechanical thrombectomy and pharmacological lysis for axillosubclavian vein thrombosis, with rapid clot removal at a single setting using low-dose thrombolysis.

Case Reports:

Two consecutive patients presented with arm swelling; the diagnosis of axillosubclavian vein thrombosis was confirmed with duplex ultrasound. Both patients were treated percutaneously with the Solera mechanical thrombectomy device, after which 5 mg of tissue plasminogen activator were delivered within ∼10 minutes via the Trellis infusion catheter to remove any residual thrombus. Completion venography and serial duplex ultrasound scans in follow-up demonstrated widely patent axillosubclavian veins with no residual thrombus in both cases.

Conclusions:

Standard treatment of axillosubclavian vein thrombosis may require 12 to 36 hours, with multiple trips to the angiography suite. The novel technique combining mechanical thrombectomy and pharmacological lysis can be performed safely and successfully at a single setting with a small dose of the lytic drug.

What are the Characteristics of the Ideal Endovascular Graft for Abdominal Aortic Aneurysm Exclusion?

Purpose:

To review the anatomic factors crucial to successful endoluminal abdominal aortic aneurysm (AAA) repair and propose an ideal endograft design for AAA exclusion.

Methods and Results:

The anatomic features of critical importance to endovascular AAA exclusion comprise remote arterial access, proximal and distal fixation sites, AAA morphology, and arterial wall pathology. When designing an aortic endograft, the major components to consider are stent selection, graft material, and the delivery system. The ideal endograft design must be sufficiently versatile to treat a broad range of patients. To meet this requirement, the endograft should display a high degree of dimensional adaptability. A modular bifurcated endograft design permits intraoperative customization to tailor the device to each patient's anatomy and pathology.

Conclusions:

The modular stent-graft concept addresses many of the important factors in the evolution toward an ideal aortic endograft. Extensive testing will be needed to determine if the bifurcated stent-graft described here is the optimal design for effective AAA exclusion.

Carotid Endarterectomy: The Gold Standard

Carotid endarterectomy has been firmly established as the gold standard of therapy for symptomatic and asymptomatic patients with severe carotid stenosis, provided surgical complication rates are within prescribed limits. The procedure-related risk of stroke/death should be < 3% in asymptomatic patients and < 6% in symptomatic patients. New investigational therapies such as balloon angioplasty and stenting for carotid stenosis should be evaluated against the same standard.

Coronary Computed Tomography Angiography Derived Fractional Flow Reserve and Plaque Stress

Fractional flow reserve (FFR) measured during invasive coronary angiography is an independent prognosticator in patients with coronary artery disease and the gold standard for decision making in coronary revascularization. The integration of computational fluid dynamics and quantitative anatomic and physiologic modeling now enables simulation of patient-specific hemodynamic parameters including blood velocity, pressure, pressure gradients, and FFR from standard acquired coronary computed tomography (CT) datasets. In this review article, we describe the potential impact on clinical practice and the science behind noninvasive coronary computed tomography (CT) angiography derived fractional flow reserve (FFR_CT) as well as future applications of this technology in treatment planning and quantifying forces on atherosclerotic plaques.

Human pluripotent stem cell tools for cardiac optogenetics

It is likely that arrhythmias should be avoided for therapies based on human pluripotent stem cell (hPSC)-derived cardiomyocytes (CM) to be effective. Towards achieving this goal, we introduced light-activated channelrhodopsin-2 (ChR2), a cation channel activated with 480 nm light, into human embryonic stem cells (hESC). By using in vitro approaches, hESC-CM are able to be activated with light. ChR2 is stably transduced into undifferentiated hESC via a lentiviral vector. Via directed differentiation, hESC(ChR2)-CM are produced and subjected to optical stimulation. hESC(ChR2)-CM respond to traditional electrical stimulation and produce similar contractility features as their wild-type counterparts but only hESC(ChR2)-CM can be activated by optical stimulation. Here it is shown that a light sensitive protein can enable in vitro optical control of hESC-CM and that this activation occurs optimally above specific light stimulation intensity and pulse width thresholds. For future therapy, in vivo optical stimulation along with optical inhibition could allow for acute synchronization of implanted hPSC-CM with patient cardiac rhythms.

Aortic neck enlargement after endovascular aneurysm repair using balloon-expandable versus self-expanding endografts

OBJECTIVE

This study evaluated changes in aortic neck diameter after endovascular aneurysm repair (EVAR) using a balloon-expandable stent (BES) endograft compared with a commercially available self-expanding stent (SES) endograft. We hypothesized that forces applied to the aortic neck by SES endografts may induce aortic neck enlargement over time and that such enlargement may not occur in aneurysm patients treated with a device that does not use a proximal SES.

METHODS

This was a retrospective quantitative computed tomography (CT) image analysis of patients treated with the Nellix (Endologix, Irvine, Calif) BES (n = 49) or the Endurant II (Medtronic, Minneapolis, Minn) SES (n = 56) endograft from 2008 to 2010. Patients with preimplant, postimplant, and at least 1-year serial CT scans underwent quantitative morphometric assessment by two independent vascular radiologists blinded to the outcome results. Changes in the infrarenal neck over time were compared with the suprarenal aorta for each patient.

RESULTS

Follow-up extended to 4.8 years for the BES and to 4.6 years for the SES, with no significant difference in median follow-up time (34 months for BESs and 24 months for SESs; P = .06). There were no differences in preimplant neck diameter (25.2 ± 0.9 mm vs 25.7 ± 1.1 mm; P = .54) or length (27.7 ± 3.7 mm vs 23.6 ± 3.7 mm; P = .12) between BESs and SESs at baseline. After implantation, neck diameter increased by 1.1 ± 0.5 mm in BES patients and 2.6 ± 0.5 mm in SES patients (P = .07) compared with the preoperative diameter. At 3 years, neck diameter increased by 0.5 ± 0.9 mm in BES patients and by 3.8 ± 1.0 mm in SES patients (P = .0002) compared with the first postoperative CT scan. The annual postimplant rate of increase in the infrarenal neck diameter was fivefold greater in SES patients (1.1 ± 0.1 mm/y) than in BES patients (0.22 ± 0.04 mm/y; P < .0001). There were no significant differences in the diameter of the suprarenal aorta at baseline or at 3 years and no differences in the annual rate of change in suprarenal aortic diameter between BES and SES endografts.

CONCLUSIONS

EVAR using SES endografts resulted in progressive infrarenal aortic neck enlargement, whereas EVAR using BES endografts resulted in no neck enlargement over time. These data suggest that infrarenal neck enlargement after EVAR with SES endografts is likely related to the force exerted by SES elements rather than disease progression in the infrarenal neck.

Robust pluripotent stem cell expansion and cardiomyocyte differentiation via geometric patterning

Geometric factors including the size, shape, density, and spacing of pluripotent stem cell colonies play a significant role in the maintenance of pluripotency and in cell fate determination. These factors are impossible to control using standard tissue culture methods. As such, there can be substantial batch-to-batch variability in cell line maintenance and differentiation yield. Here, we demonstrate a simple, robust technique for pluripotent stem cell expansion and cardiomyocyte differentiation by patterning cell colonies with a silicone stencil. We have observed that patterning human induced pluripotent stem cell (hiPSC) colonies improves the uniformity and repeatability of their size, density, and shape. Uniformity of colony geometry leads to improved homogeneity in the expression of pluripotency markers SSEA4 and Nanog as compared with conventional clump passaging. Patterned cell colonies are capable of undergoing directed differentiation into spontaneously beating cardiomyocyte clusters with improved yield and repeatability over unpatterned cultures seeded either as cell clumps or uniform single cell suspensions. Circular patterns result in a highly repeatable 3D ring-shaped band of cardiomyocytes which electrically couple and lead to propagating contraction waves around the ring. Because of these advantages, geometrically patterning stem cells using stencils may offer greater repeatability from batch-to-batch and person-to-person, an increase in differentiation yield, a faster experimental workflow, and a simpler protocol to communicate and follow. Furthermore, the ability to control where cardiomyocytes arise across a culture well during differentiation could greatly aid the design of electrophysiological assays for drug-screening.

A computational framework for investigating the positional stability of aortic endografts

Endovascular aneurysm repair (Greenhalgh in N Engl J Med 362(20):1863-1871, 2010) techniques have revolutionized the treatment of thoracic and abdominal aortic aneurysm disease, greatly reducing the perioperative mortality and morbidity associated with open surgical repair techniques. However, EVAR is not free of important complications such as late device migration, endoleak formation and fracture of device components that may result in adverse events such as aneurysm enlargement, need for long-term imaging surveillance and secondary interventions or even death. These complications result from the device inability to withstand the hemodynamics of blood flow and to keep its originally intended post-operative position over time. Understanding the in vivo biomechanical working environment experienced by endografts is a critical factor in improving their long-term performance. To date, no study has investigated the mechanics of contact between device and aorta in a three-dimensional setting. In this work, we developed a comprehensive Computational Solid Mechanics and Computational Fluid Dynamics framework to investigate the mechanics of endograft positional stability. The main building blocks of this framework are: (1) Three-dimensional non-planar aortic and stent-graft geometrical models, (2) Realistic multi-material constitutive laws for aorta, stent, and graft, (3) Physiological values for blood flow and pressure, and (4) Frictional model to describe the contact between the endograft and the aorta. We introduce a new metric for numerical quantification of the positional stability of the endograft. Lastly, in the results section, we test the framework by investigating the impact of several factors that are clinically known to affect endograft stability.

Projected costs and consequences of computed tomography-determined fractional flow reserve

BACKGROUND

Randomized trials have shown that fractional flow reserve (FFR) guided percutaneous coronary intervention (PCI) improves clinical outcome and reduces costs compared with visually guided PCI. FFR has been measured during invasive coronary angiography (ICA), but can now be derived noninvasively from coronary computed tomography (CT) angiography (cCTA) images (FFRCT ). The potential value of FFRCT in clinical decision making is unknown.

HYPOTHESIS

Use of FFRCT can reduce costs and improve outcomes among patients with suspected coronary artery disease.

METHODS

We used clinical data from 96 patients in the DISCOVER-FLOW (Diagnosis of Ischemia-Causing Stenoses Obtained Via Noninvasive Fractional Flow Reserve) study and outcomes data from the literature to project the initial management costs and 1-year death/myocardial infarction rates associated with 5 clinical strategies: (1) ICA with PCI based on visual angiographic assessment, (2) ICA with FFRICA -guided PCI, (3) cCTA followed by ICA and PCI based on visual assessment, (4) cCTA followed by ICA with FFRICA -guided PCI, and (5) cCTA FFRCT and PCI of lesions with FFRCT ≤0.80.

RESULTS

The projected initial management costs were highest for the ICA/visual strategy ($10 702), and lowest for the cCTA/FFRCT /ICA strategy ($7674). The use of FFRCT to select patients for ICA and PCI would result in 30% lower costs and 12% fewer events at 1 year compared with the most commonly used ICA/visual strategy.

CONCLUSIONS

A strategy of using FFRCT to guide the selection of patients for ICA and PCI might reduce costs and improve clinical outcomes in patients with suspected coronary artery disease.

Computed fractional flow reserve (FFTCT) derived from coronary CT angiography

Recent advances in image-based modeling and computational fluid dynamics permit the calculation of coronary artery pressure and flow from typically acquired coronary computed tomography (CT) scans. Computed fractional flow reserve is the ratio of mean coronary artery pressure divided by mean aortic pressure under conditions of simulated maximal coronary hyperemia, thus providing a noninvasive estimate of fractional flow reserve (FFRCT) at every point in the coronary tree. Prospective multicenter clinical trials have shown that computed FFRCT improves diagnostic accuracy and discrimination compared to CT stenosis alone for the diagnosis of hemodynamically significant coronary artery disease (CAD), when compared to invasive FFR as the reference gold standard. This promising new technology provides a combined anatomic and physiologic assessment of CAD in a single noninvasive test that can help select patients for invasive angiography and revascularization or best medical therapy. Further evaluation of the clinical effectiveness and economic implications of noninvasive FFRCT are now being explored.

Label-free electrophysiological cytometry for stem cell-derived cardiomyocyte clusters

Stem cell therapies hold great promise for repairing tissues damaged due to disease or injury. However, a major obstacle facing this field is the difficulty in identifying cells of a desired phenotype from the heterogeneous population that arises during stem cell differentiation. Conventional fluorescence flow cytometry and magnetic cell purification require exogenous labeling of cell surface markers which can interfere with the performance of the cells of interest. Here, we describe a non-genetic, label-free cell cytometry method based on electrophysiological response to stimulus. As many of the cell types relevant for regenerative medicine are electrically-excitable (e.g. cardiomyocytes, neurons, smooth muscle cells), this technology is well-suited for identifying cells from heterogeneous stem cell progeny without the risk and expense associated with molecular labeling or genetic modification. Our label-free cell cytometer is capable of distinguishing clusters of undifferentiated human induced pluripotent stem cells (iPSC) from iPSC-derived cardiomyocyte (iPSC-CM) clusters. The system utilizes a microfluidic device with integrated electrodes for both electrical stimulation and recording of extracellular field potential (FP) signals from suspended cells in flow. The unique electrode configuration provides excellent rejection of field stimulus artifact while enabling sensitive detection of FPs with a noise floor of 2 μV(rms). Cells are self-aligned to the recording electrodes via hydrodynamic flow focusing. Based on automated analysis of these extracellular signals, the system distinguishes cardiomyocytes from non-cardiomyocytes. This is an entirely new approach to cell cytometry, in which a cell's functionality is assessed rather than its expression profile or physical characteristics.

Computational modeling of shear-based hemolysis caused by renal obstruction

As endovascular treatment of abdominal aortic aneurysms (AAAs) gains popularity, it is becoming possible to treat certain challenging aneurysmal anatomies with endografts relying on suprarenal fixation. In such anatomies, the bare struts of the device may be placed across the renal artery ostia, causing partial obstruction to renal artery blood flow. Computational fluid dynamics (CFD) was used to simulate blood flow from the aorta to the renal arteries, utilizing patient-specific boundary conditions, in three patient models and calculate the degree of shear-based blood damage (hemolysis). We used contrast-enhanced computed tomography angiography (CTA) data from three AAA patients who were treated with a novel endograft to build patient-specific models. For each of the three patients, we constructed a baseline model and endoframe model. The baseline model was a direct representation of the patient's 30-day post-operative CTA data. This model was then altered to create the endoframe model, which included a ring of metallic struts across the renal artery ostia. CFD was used to simulate blood flow, utilizing patient-specific boundary conditions. Pressures, flows, shear stresses, and the normalized index of hemolysis (NIH) were quantified for all patients. The overall differences between the baseline and endoframe models for all three patients were minimal, as measured though pressure, volumetric flow, velocity, and shear stress. The average NIH across the three baseline and endoframe models was 0.002 and 0.004, respectively. Results of CFD modeling show that the overall disturbance to flow caused by the presence of the endoframe struts is minimal. The magnitude of the NIH in all models was well below the accepted design and safety threshold for implantable medical devices that interact with blood flow.

Validation of a power law model in upper extremity vessels: potential application in ultrasound bleed detection

Vascular ultrasound can provide quick and reliable diagnosis of arterial bleeding but it requires trained and experienced personnel. Development of automated sonographic bleed detection methods would potentially be valuable for trauma management in the field. We propose a detection method that (1) measures blood flow in a trauma victim, (2) determines the victim's expected normal limb arterial flow using a power law biofluid model where flow is proportional to the vessel diameter taken to a power of k and (3) quantifies the difference between measured and expected flow with a novel metric, flow split deviation (FSD). FSD was devised to give a quantitative value for the likelihood of arterial bleeding and validated in human upper extremities. We used ultrasound to demonstrate that the power law with k = 2.75 appropriately described the normal brachial artery bifurcation geometry and adequately determined the expected normal flows. Our metric was then applied to three-dimensional (3-D) computational models of forearm bleeding and on dialysis patients undergoing surgical construction of wrist arteriovenous fistulas. Computational models showed that larger sized arterial defects produced larger flow deviations. FSD values were statistically higher (paired t-test) for arms with fistulas than those without, with average FSDs of 0.41 ± 0.12 and 0.047 ± 0.021 (mean ± SD), respectively. The average of the differences was 0.36 ± 0.12 (mean ± SD).

Computational analysis of stresses acting on intermodular junctions in thoracic aortic endografts

PURPOSE

To evaluate the biomechanical and hemodynamic forces acting on the intermodular junctions of a multi-component thoracic endograft and elucidate their influence on the development of type III endoleak due to disconnection of stent-graft segments.

METHODS

Three-dimensional computer models of the thoracic aorta and a 4-component thoracic endograft were constructed using postoperative (baseline) and follow-up computed tomography (CT) data from a 69-year-old patient who developed type III endoleak 4 years after stent-graft placement. Computational fluid dynamics (CFD) techniques were used to quantitate the displacement forces acting on the device. The contact stresses between the different modules of the graft were then quantified using computational solid mechanics (CSM) techniques. Lastly, the intermodular junction frictional stability was evaluated using a Coulomb model.

RESULTS

The CFD analysis revealed that curvature and length are key determinants of the displacement forces experienced by each endograft and that the first 2 modules were exposed to displacement forces acting in opposite directions in both the lateral and longitudinal axes. The CSM analysis revealed that the highest concentration of stresses occurred at the junction between the first and second modules of the device. Furthermore, the frictional analysis demonstrated that most of the surface area (53%) of this junction had unstable contact. The predicted critical zone of intermodular stress concentration and frictional instability matched the location of the type III endoleak observed in the 4-year follow-up CT image.

CONCLUSION

The region of larger intermodular stresses and highest frictional instability correlated with the zone where a type III endoleak developed 4 years after thoracic stent-graft placement. Computational techniques can be helpful in evaluating the risk of endograft migration and potential for modular disconnection and may be useful in improving device placement strategies and endograft design.

Evaluating Design of Abdominal Aortic Aneurysm Endografts in a Patient-Specific Model Using Computational Fluid Dynamics

Computer modeling of blood flow in patient-specific anatomies can be a powerful tool for evaluating the design of implantable medical devices. We assessed three different endograft designs, which are implantable devices commonly used to treat patients with abdominal aortic aneurysms (AAAs). Once implanted, the endograft may shift within the patient’s aorta allowing blood to flow into the aneurismal sac. One potential cause for this movement is the pulsatile force experienced by the endograft over the cardiac cycle. We used contrast-enhanced computed tomography angiography (CTA) data from four patients with diagnosed AAAs to build patient-specific models using 3D segmentation. For each of the four patients, we constructed a baseline model from the patient’s preoperative CTA data. In addition, geometries characterizing three distinct endograft designs were created, differing by where each device bifurcated into two limbs (proximal bifurcation, mid bifurcation, and distal bifurcation). Computational fluid dynamics (CFD) was used to simulate blood flow, utilizing patient-specific boundary conditions. Pressures, flows, and displacement forces on the endograft surface were calculated. The curvature and surface area of each device was quantified for all patients. The magnitude of the total displacement force on each device ranged from 2.43 N to 8.68 N for the four patients examined. Within each of the four patient anatomies, the total displacement force was similar (varying at least by 0.12 N and at most by 1.43 N), although there were some differences in the direction of component forces. Proximal bifurcation and distal bifurcation geometries consistently generated the smallest and largest displacement forces, respectively, with forces observed in the mid bifurcation design falling in between the two devices. The smallest curvature corresponded to the smallest total displacement force, and higher curvature values generally corresponded to higher magnitudes of displacement force. The same trend was seen for the surface area of each device, with lower surface areas resulting in lower displacement forces and vise versa. The patient with the highest blood pressure displayed the highest magnitudes of displacement force. The data indicate that curvature, device surface area, and patient blood pressure impact the magnitude of displacement force acting on the device. Endograft design may influence the displacement force experienced by an implanted endograft, with the proximal bifurcation design showing a small advantage for minimizing the displacement force on endografts.

A matrix micropatterning platform for cell localization and stem cell fate determination

To study the role of cell-extracellular matrix (ECM) interactions, microscale approaches provide the potential to perform high throughput assessment of the effect of the ECM microenvironment on cellular function and phenotype. Using a microscale direct writing (MDW) technique, we characterized the generation of multicomponent ECM microarrays for cellular micropatterning, localization and stem cell fate determination. ECMs and other biomolecules of various geometries and sizes were printed onto epoxide-modified glass substrates to evaluate cell attachment by human endothelial cells. The endothelial cells displayed strong preferential attachment to the ECM patterned regions and aligned their cytoskeleton along the direction of the micropatterns. We next generated ECM microarrays that contained one or more ECM components (namely gelatin, collagen IV and fibronectin) and then cultured murine embryonic stem cell (ESCs) on the microarrays. The ESCs selectively attached to the micropatterned features and expressed markers associated with a pluripotent phenotype, such as E-cadherin and alkaline phosphatase, when maintained in growth medium containing leukemia inhibitory factor. In the presence of the soluble factors retinoic acid and bone morphogenetic protein-4 the ESCs differentiated towards the ectodermal lineage on the ECM microarray with differential ECM effects. The ESCs cultured on gelatin showed significantly higher levels of pan cytokeratin expression, when compared with cells cultured on collagen IV or fibronectin, suggesting that gelatin preferentially promotes ectodermal differentiation. In summary, our results demonstrate that MDW is a versatile approach to print ECMs of diverse geometries and compositions onto surfaces, and it is amenable to the generation of multicomponent ECM microarrays for stem cell fate determination.