Papers by Efstratios Georgakarakos
Modeling and Computational Comparison of the Displacement Forces Exerted between the AFX Unibody Aortic Stent Graft and its Hybrid Combination with a Nitinol-based Proximal Aortic Cuff
Annals of Vascular Surgery, 2021
BACKGROUND The bifurcated AFX (Endologix, Inc, Irvine, CA, USA) aortic stent-graft is the sole un... more BACKGROUND The bifurcated AFX (Endologix, Inc, Irvine, CA, USA) aortic stent-graft is the sole unibody endograft for the management of Abdominal Aortic Aneurysms (AAA). In order to improve the AFX central sealing and clinical efficacy in challenging cases, a replacement of the central chromium-cobaltium AFX extension with a Nitinol-based proximal aortic cuff has been suggested. Yet, comparative data regarding the hemodynamic performance of this design is missing. Aim of this study was to compare the displacement forces (DF) acting on the hybrid AFX-Endurant design, with the classic AFX and Endurant endografts, in angulated and non-angulated cases based on patient-specific Computational Fluid Dynamics (CFD) simulations. METHODS 3D endograft models of 11 treated AAA cases were reconstructed from Computed Tomography Angiography (CTA) imaging data: 5 cases of AFX, 3 cases of the combination AFX-Endurant and 3 cases of the classic Endurant design. The DF on the main-body, the iliac limbs, and the entire stent-graft was calculated by processing the velocity and pressure fields generated by pulsatile CFD simulations. RESULTS The range of total DF (acting on the whole endograft structure) in the AFX, hybrid AFX-Endurant and Endurant group was 2.5-5.2N, 2.0-5.9N and 1.9-2.9N respectively, with the maximum total DF being lower for Endurant. The DF on the main-body of the classic and hybrid AFX cases were higher than the right and left iliac limbs (2.5-4.9N vs. 0.6-5.3N and 0.7-3.6N respectively). Conversely, the DF on the main-body of the Endurant cases was comparable to the force exerted on the right and left limbs. When separating the cases with respect to their neck angulation, the DF on all endograft parts (main-body, limbs) and on the endograft as a whole were lower for the hybrid AFX-Endurant group compared to the classic AFX and Endurant groups, for cases with almost straight neck. CONCLUSION The off-label use of the hybrid AFX-Endurant stent-graft does not seem superior to the conventional AFX or Endurant endografts in angulated cases but was associated with lower DF than AFX or Endurant in non-angulated cases. The clinical value and utility of these findings remain to be elucidated.
AORTA, 2014
Common practice in recanalization of a thrombosed prosthetic graft limb in an aortoiliac bypass f... more Common practice in recanalization of a thrombosed prosthetic graft limb in an aortoiliac bypass focuses on balloon-catheter thrombectomy and angiographic exploration followed either by open surgical revision or endovascular management. This report describes the technique of percutaneous endovascular recanalization of an early thrombosed aortic graft limb with stent placement and subsequent restoration of patency and adequate limb perfusion, which remains patent after one year. Percutaneous intervention with stent placement and angioplasty for early graft limb recanalization avoids femoral incisions, and complications or morbidity associated with open surgery, while permitting rapid mobilization of the patient.
An uncommon clinical presentation of acute limb ischemia: underscoring the role of perigenicular collaterals
Vascular, 2012
We present a case of atypical acute limb ischemia in a non-diabetic patient, with ankle-brachial ... more We present a case of atypical acute limb ischemia in a non-diabetic patient, with ankle-brachial pressure index of 0.6 and rest pain localized exclusively over the gastrocnemius muscle, sparing the foot. This uncommon presentation was attributed to an impaired perigenicular collateral network. Thrombolysis restored adequate perfusion only temporarily and was followed by thromboembolectomy. The ischemia presentation in our case underscores the importance of the adequacy of the perigeniculate collateral network for the perfusion of the tibial muscles and, especially, the gastrocnemius muscle.
The Bolton Treo endograft for treatment of abdominal aortic aneurysms: Just another trimodular platform?
Expert review of medical devices, Jan 19, 2017
The Treo abdominal aortic stent graft system (Bolton Medical, Barcelona, Spain) is a trimodular e... more The Treo abdominal aortic stent graft system (Bolton Medical, Barcelona, Spain) is a trimodular endovascular endoprosthesis recently introduced for the endovascular repair of abdominal aortic aneurysm (AAA). It presents some unique structural characteristics such as the combination of suprarenal and infrarenal fixation, variability of the main-body length, lock-stent mechanism in the iliac limbs to enhance their stability. Areas covered: This article discusses the technical features and clinical performance of Treo as well as the interesting hemodynamic consequences of its design. Expert commentary: The Treo aortic stent-graft provides accurate deployment, secure proximal seal and fixation as well as efficient conformability in angulated necks. Early results drawn from single-center studies are promising with acceptable technical and clinical success. Moreover, the custom-made solution provided with the Treo platform is one of the most intriguing challenges in current endovascular e...
The influence of intraluminal thrombus on abdominal aortic aneurysm wall stress
International angiology : a journal of the International Union of Angiology, 2009
The aim of this study was to examine the effect of intraluminal thrombus (ILT) on the peak wall s... more The aim of this study was to examine the effect of intraluminal thrombus (ILT) on the peak wall stress (PWS) in abdominal aorta aneurysm models (AAA). Anatomically correct patient specific AAA models were created by 3D reconstruction of in vivo acquired computed tomography images from 19 male patients. Patients were divided in two groups according to aneurysm peak transverse diameter, 5-7 cm (10 patients, ''intermediate'' group) and >7 cm (9 patients, ''large'' group), respectively. PWS was evaluated in the presence and absence of ILT. The percentage of PWS reduction (Delta PWS %) was estimated as a percentage of PWS value in the absence of ILT. Finite element analysis was used to numerically compute the wall stress distribution assuming a 2-mm thick hyperelastic AAA wall material model and a 120 mmHg systolic uniform wall loading. The thrombus was modeled as an isotropic, elastic, homogenous and incompressible material. The volume of ILT was estim...
European journal of vascular and endovascular surgery : the official journal of the European Society for Vascular Surgery, Jan 27, 2015
Existing guidelines suggest routine use of pre-operative color Doppler ultrasound (DUS) vessel ma... more Existing guidelines suggest routine use of pre-operative color Doppler ultrasound (DUS) vessel mapping before the creation of arteriovenous fistulae (AVF); however, there is controversy about its benefit over traditional clinical examination or selective ultrasound use. This was a systematic review and meta-analysis of randomized controlled trials (RCTs) comparing routine DUS mapping before the creation of AVF with patients for whom the decision for AVF placement was based on clinical examination and selective ultrasound use. A search of MEDLINE/PubMed, SCOPUS, and the Cochrane Library was carried out in June 2014. The analyzed outcome measures were the immediate failure rate and the early/midterm adequacy of the fistula for hemodialysis. Additionally, assessment of the methodological quality of the included studies was carried out. Five studies (574 patients) were analyzed. A random effects model was used to pool the data. The pooled odds ratio (OR) for the immediate failure rate w...
The inflatable-rings fixation mechanism of the Trivascular Ovation Stent Graft System: Every revolution comes at a price!
The Journal of cardiovascular surgery, Jan 20, 2014
Thrombus morphology may be an indicator for aneurysm expansion
The Journal of cardiovascular surgery, 2014
Studying the expansion of small abdominal aortic aneurysms: is there a role for peak wall stress?
International angiology : a journal of the International Union of Angiology, 2011
The aim of this paper was to study the characteristics of three distending small abdominal aortic... more The aim of this paper was to study the characteristics of three distending small abdominal aortic aneurysms (AAAs), with an increase in maximal diameter from 5 to 5.5 cm or above. Peak Wall Stress (PWS) in the presence and absence of intraluminal thrombus (ILT) was evaluated in 3 cases of small AAAs (5 cm), at initial presentation and after their expansion, at maximum diameters ≥5.5 cm using finite element analysis. Furthermore, AAA sac volume (Vsac), the percentage volume of ILT (ILT%) and the percentage change of Vsac (ΔV%) and ILT (ILT%) were estimated and the location of PWS was recorded. Two AAA expanded from 5cm to 5.5 cm in a period of 6 months after initial presentation, with increase of sac volume by 20% and 30%, respectively. The third AAA expanded to a diameter of 6.5 cm after a follow-up period of 13 months, with a subsequent increase in sac volume of 78%. The expansion of AAA max diameter did not correlate with differences in peak wall stress (PWS) values at the initial...
Stroke, 2012
Background and Purpose— Microembolic signals (MES) on transcranial Doppler are an independent ris... more Background and Purpose— Microembolic signals (MES) on transcranial Doppler are an independent risk factor for recurrent stroke in patients with extracranial symptomatic/asymptomatic carotid artery stenosis (CARAS). Clopidogrel load (300 mg) combined with dual antiplatelet therapy has been shown to reduce MES in patients with symptomatic CARAS. We sought to determine feasibility of clopidogrel load in decreasing asymptomatic embolization in patients with symptomatic CARAS undergoing urgent carotid endarterectomy within the first 2 weeks from the index event. Subjects and Methods— Consecutive patients with symptomatic CARAS (70%–99%) and presence of MES on 1-hour baseline (<24 hours from the index event) transcranial Doppler monitoring of ipsilateral middle cerebral artery were treated with clopidogrel load followed by clopidogrel (75 mg)±aspirin (100 mg) during the elapsed time period between hospital admission and urgent carotid endarterectomy at 3 tertiary-care stroke centers. R...
Training to Measure Ankle-Brachial Index at the Undergraduate Level: Can It Be Successful?
The International Journal of Lower Extremity Wounds, 2013
We examined the effectiveness of teaching ankle-brachial index (ABI) measurement to medical stude... more We examined the effectiveness of teaching ankle-brachial index (ABI) measurement to medical students. ABI was estimated in 28 lower limbs by an experienced vascular surgeon. After a 2-week training course, 5 fourth-year students repeated the estimations and their results were compared with that of the trainer&amp;amp;amp;amp;amp;amp;amp;amp;#39;s. There was no difference in ABI values between trainees and trainer for subjects with mild-to-moderate peripheral arterial disease (PAD; 0.77 ± 0.22 vs 0.77 ± 0.19, respectively, P = .95). In the 4 normal limbs, ABI was 1.37 ± 0.12 and 1.16 ± 0.11, as measured by the trainer and the trainees, respectively (P &amp;amp;amp;amp;amp;amp;amp;amp;lt; .00001). In subjects with severe PAD, trainees tended to overestimate ABI (P = .0002) in the beginning of the educational process, but this was no longer the case at a later stage of the training with no difference in ABI values between the 2 examiner groups (P = .09). In conclusion, training of medical students in ABI measurement can be helpful toward accurate estimation of PAD and merits further practice.
Journal of endovascular therapy : an official journal of the International Society of Endovascular Specialists, 2017
To present early results with the Treovance aortic stent-graft in the treatment of abdominal aort... more To present early results with the Treovance aortic stent-graft in the treatment of abdominal aortic aneurysms (AAAs). Between October 2013 and January 2016, 35 consecutive AAA patients (mean age 74±7.7 years; 32 men) were treated with Treovance. The maximum diameter of the treated AAA was 60±9 cm. Nine (25%) patients presented with concomitant iliac aneurysms. Seven (20%) AAAs had infrarenal neck angulation >60°. The infrarenal neck length and diameter were 21.6±12.6 mm and 25.7±4.6 mm, respectively. Sixteen (45%) AAAs had a reversed tapered neck contour. Six (17%) and 9 (25%) patients showed severe or moderate iliac tortuosity, respectively. Primary endpoints were endoleak, reintervention, and aneurysm-related death. Primary technical success was 94% due to 2 intraoperative type Ia endoleaks, which were successfully treated with a proximal aortic extension (100% assisted primary technical success). Local dissection was encountered in 5 (7%) of 70 femoral artery access sites in 4...
Annals of vascular surgery, Jan 25, 2016
Ovation aortic stent-graft system is a new device for the endovascular treatment of Abdominal Aor... more Ovation aortic stent-graft system is a new device for the endovascular treatment of Abdominal Aortic Aneurysms achieving fixation via a 35-mm long, rigid anchored suprarenal stent and sealing stent at the infrarenal level by a means of a polymer-filling pair of inflatable O-rings, which cause narrowing of flow lumen and regional stenosis. Thus, concerns have been raised regarding hemodynamic consequences associated with this new design. Our preliminary report showed no significant increase of aortic pulse wave velocity (aPWV) immediately after implantation of the ovation in 3 patients. We studied further the hemodynamic implications of the Ovation implantation in 6 patients for a follow-up of 6 months. A brachial cuff-based automatic oscillometric device (Mobil-O-Graph; IEM, Stolberg, Germany) was used to perform noninvasively pulse wave analysis and stiffness estimation. Measurements were held preoperatively in 6 patients treated for abdominal aortic aneurysm, at the end of the fir...
Computer methods in biomechanics and biomedical engineering, Jan 22, 2016
Endovascular aneurysm repair (EVAR) of abdominal aortic aneurysms results in redirection of blood... more Endovascular aneurysm repair (EVAR) of abdominal aortic aneurysms results in redirection of blood through the deployed endograft (EG). Even though EVAR is clinically effective, the absolute flow restoration is not warranted. Our purpose was to compare the physiological with the post-EVAR infrarenal flow conditions. We developed patient-specific models based on computed tomography data of five healthy volunteers and ten patients treated with the Endurant(®) stent-graft system. Wall shear stress (WSS), helicity, pressure and velocity fields were calculated using computational fluid dynamics. The results showed a decrease of peak WSS on the part of the EG that resides in the iliac arteries, compared to the physiological value (p = 0.01). At the abdominal part, the average helicity seems to increase after EVAR, while at the iliac arteries part, the intensity of helical flow seems physiological. Pressure drop and peak velocity in the iliac arteries part are lower than the physiological v...
La Radiologia medica, Jan 23, 2016
To investigate if the routine use of an aortic balloon within 15-30 min after Ovation stent graft... more To investigate if the routine use of an aortic balloon within 15-30 min after Ovation stent graft ring inflation would resolve any inflow stenosis, which may reach 60 %, at the level of the sealing rings. Moreover, we estimated the potential hemodynamic compromise in these patients during rest and exercise. Following 3-dimensional reconstruction of AAA models, cross-sectional area of the infrarenal aorta just proximal the sealing mechanism (A aort, R aort, respectively) and internal area at the site of stenosis (A int, R int, respectively) were measured for 83. Forty-nine patients were managed without and 34 with an aortic balloon use. Pressure drop during rest and exercise was estimated. Technical success was 98 % and there were no perioperative deaths, one type-I endoleak, and 12 (14.5 %) type-II endoleaks. Median A int and R int were significantly reduced compared to A aort [55 % reduction, 143 (range 28-380) mm(2) vs 314 (range 177-531) mm(2), P value <0.001] and R aort [42 %...
Annals of Vascular Surgery, 2016
Aim: To present our preliminary experience with the recently introduced Treovance aortic stent-gr... more Aim: To present our preliminary experience with the recently introduced Treovance aortic stent-graft device (Bolton Medical, Barcelona, Spain) in the treatment of abdominal aortic aneurysm (AAA). Methods: Eight patients underwent treatment of an infra-renal AAA (mean maximum diameter 56.4±6.8mm) with the Treovance device. Iliac tortuosity was considered mild, moderate, or severe when ≥1 angulation of 45-90⁰, 1 angulation ≥90⁰, or ≥2 angulations ≥90⁰, respectively, were present. Results: Mild angulation of the infra-renal neck (10-45°) was present in 7 patients, whereas the remaining patient had severe infra-renal neck angulation (65°). Three patients had severe iliac tortuosity. Primary technical success was achieved in all but 1 patient in whom a type Ia endoleak was identified on completion angiogram. The endoleak was successfully treated with a proximal aortic cuff. A femoral access complication occurred in 1 patient. Mean follow up was 6.8 months (range 1-12). No device-related serious adverse events or rupture occurred during the given follow-up period. The only type II endoleak identified resolved spontaneously within 12 months. Conclusion: The Treovance abdominal stent-graft system, seems to guarantee an accurate, safe and effective deployment in AAA even through angulated and tortuous iliac vessels. Although our preliminary results are promising, follow-up data are needed to establish the durability of this new-generation endovascular device in standard or challenging anatomies.
Endovascular treatment of complex abdominal and thoracoabdominal type IV aortic aneurysms with fenestrated technology
The Journal of cardiovascular surgery, Jan 4, 2016
The establishment use of fenestrated and branched devices to treat complex aortic aneurysms as a ... more The establishment use of fenestrated and branched devices to treat complex aortic aneurysms as a first-line management option has been previously reported. This article reviews the current literature of the use of fenestrated devices to treat complex abdominal and thoracoabdominal type IV aortic aneurysms as a first-line management option. A literature search was performed. This review particularly focuses on all the aspects of the use and results of fenestrated stent-grafts (SGs) in patients with complex abdominal and type IV thoracoabdominal aortic aneurysms and summarizes the available evidence. The use of fenestrated SGs for complex aortic aneurysm disease has grown enormously the last years. SGs with fenestrations, scallops and occasionally branches have to be customized to each patient's anatomy and precisely deployed in vivo. Bridging covered stents between the main graft and the target vessels eventually exclude the aneurysm preserving blood flow to vital organs. Multipl...
Medical Hypotheses, 2016
Chronic total occlusion of the infrarenal aorta (CTOA) is a rare disease, characterized by severe... more Chronic total occlusion of the infrarenal aorta (CTOA) is a rare disease, characterized by severe impairment of limb perfusion. It is advocated that revascularization may improve survival rates, presumably due to improved cardiovascular performance; however no experimental or clinical data exist to identify a clear causative correlation and provide a relevant pathophysiologic background. Therefore we conducted a pilot study based on pulse wave analysis to detect the hemodynamic changes immediately after revascularization, in a group of six consecutive patients with CTOA. All patients were subjected to noninvasive measurements 1 day before surgery and at the end of the 1st postoperative month. Pulse wave analysis was performed noninvasively with a novel validated brachial cuff-based automatic oscillometric device. All patients had markedly preoperative high Augmentation Index (adjusted at heart rate 75 beats/ min, AI@75). The AI@75 decreased from 46 ± 6.6 preoperatively to 24 ± 5.7 (p 0.0002). Wave reflection magnitude decreased from 72.3 ± 5.2% to 63 ± 6.7% (p 0.02). Cardiax index increased from 2.8 ± 1.2 to 3.4 ± 1.2 l/min  1/m 2 (p 0.41). Pulse wave velocity remained practically unchanged postinterventionally. These findings show that central aorta hemodynamics can be improved immediately following revascularization procedures in patients with complete occlusion of the entire length of the infrarenal aorta and can constitute the background of improved postoperative life-expectancy.
Hellenic journal of cardiology : HJC = Hellēnikē kardiologikē epitheōrēsē
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Papers by Efstratios Georgakarakos