J.W. van Keulen

Dynamics of the aorta before and after endovascular aneurysm repair: a systematic review.

OBJECTIVE An overview of the knowledge of thoracic (TAA), and abdominal aortic aneurysm (AAA) dynamics, before and after endovascular repair, is given. METHODS Medline, EMBASE and the Cochrane database were searched for relevant articles. After inclusion and exclusion, 25 relevant articles reporting on aneurysm dynamics remained, allowing for comparison. Results provided in the included studies were assumed (statistically) significant if they were larger than the repeatability of the used method. RESULTS The sample size of dynamic studies is limited and translational studies are missing. Magnetic resonance angiography (MRA) and computed tomographic angiography (CTA) were shown to have lower inter-observer variabilities than ultrasonography (US). The distension of several relevant stent-graft-landing zones during the cardiac cycle in both the abdominal and thoracic aorta are significant (mean diameter change of the AAA neck in the included studies ranged from 0.9 mm to 2.4 mm; mean area change of the thoracic aorta ranged from 4.8% to 12.7% at various levels). This distension remained preserved after stent-graft placement. Preoperatively, the renal arteries displace per heartbeat. Significant movement of the aorta in the anteroposterior (AP) and lateral direction, during the cardiac cycle, was observed. CONCLUSION The aorta exhibits a wide variety of morphologic changes throughout the cardiac cycle. CTA and MRA are reliable modalities to investigate aortic shape changes during the cardiac cycle. Significant changes per heartbeat are reported in the AAA neck and thoracic aorta. The renal artery displaces per heartbeat. The clinical relevance of dynamic imaging has not been proven yet, but dynamic changes of the aorta have to be taken into account in stent-graft selection and future stent-graft design.

Severe Proximal Aneurysm Neck Angulation: Early Results Using the Endurant Stentgraft System

OBJECTIVE Angulation of the proximal aneurysm neck has been associated with adverse outcome after EVAR. We aim to investigate the influence of angulation on early results when using the Endurant Stentgraft System. METHODS A retrospective analysis of a prospective multicentre database identified 45 elective patients treated with the Endurant stentgraft with severe angulation of the proximal neck, which were compared to a control group without significant angulation. Endpoints were early technical and clinical success, deployment accuracy and differences in operative details. RESULTS Mean age was 74 with 86.4% males. Mean infrarenal angle (β) was 80.8° ± 16 and mean suprarenal angle (α) was 51.4° ± 21. Patients in the angulated group had larger aneurysms (mean 309 cc vs. 187 cc), shorter necks (mean 27 mm ± 14 vs. 32.6 mm ± 13) and 74% (vs. 56%) were ASA III/IV. Technical success was 100%, with one patient requiring an unplanned proximal extension. No differences were found regarding early type-I endoleaks (0% vs. 0%), major postoperative complications (6.7% vs. 6.2%; p = 0.77) or early survival (97.8% vs. 96.9%, p = 0.79). Distance from lowest renal artery to prosthesis was 2.4 mm ± 2.7 vs. 2.3 mm ± 4.8, p = 0.9. Operative details were equivalent for both groups. CONCLUSIONS Treatment with the Endurant stentgraft is technically feasible and safe, with satisfactory results in angulated and non-angulated anatomies alike. No sealing length was lost in extremely angulated cases, confirming the devices high conformability. Mid- and long-term data are awaited to verify durability, but early results are promising and challenge current opinion concerning neck angulation.

Aortic Pulsatile Distention in Young Healthy Volunteers is Asymmetric : Analysis with ECG-gated MRI

OBJECTIVE Knowledge of aortic shape changes throughout the cardiac cycle can offer improved understanding of vascular pathophysiology and may have crucial impact on stentgraft design and EVAR durability. To understand underlying mechanisms of dynamic changes in aortic aneurysm (neck) morphology, the undiseased aorta has to be studied first. Objective is to visualize and characterize dynamic aortic shape changes in young healthy volunteers. MATERIALS AND METHODS Fifteen healthy volunteers (7 male, median age 24 year, range 18-28) were scanned using ECG-gated balanced gradient-echo MRI, with 16 reconstructed cardiac phases. Transverse scans were made perpendicular to the aorta: (A) above the aortic bifurcation, (B) infrarenal, (C) juxtarenal, (D) suprarenal and (E) above the celiac trunk. After aortic lumen segmentation, radial changes during the cardiac cycle were measured, from the center of mass, over 360 degrees, and plotted. An ellipse was fitted over the distention plots, yielding the direction (AP:0 degrees, Right: -90 degrees, Left: 90 degrees ) and magnitude of radius change over the major and minor axis. RESULTS Asymmetric distention was observed, with a variable rate per patient and level. Radius changes decreased from the proximal to distal aorta. Radius changes over the major axis ranged from 14% to 41%. At level A mean change in radius over the minor versus major axis was 1.4+/-0.2mm (17%) versus 1.6+/-0.2mm (20%), respectively. At B 1.7+/-0.4mm (22%) versus 2.0+/-0.4mm (25%), at C 1.7+/-0.4mm (22%) versus 2.2+/-0.4mm (27%) at D 2.0+/-0.4mm (25%) versus 2.4+/-0.5mm (30%) and at E 2.2+/-0.3mm (27%) versus 2.6+/-0.3mm (32%). Mean orientation of the major axis was (A) 0.8+/-23.3 degrees , (B) 1.8+/-31.3 degrees , (C) 14.0+/-15.5 degrees , (D) -28.8+/-48.0 degrees and (E) 18.4+/-22.2 degrees. CONCLUSIONS Aortic pulsatile distention in young healthy volunteers is asymmetric, with up to 41% radius change in the descending aorta. This study offers a frame of reference for dynamic imaging studies in patients with aortic pathology and provides a valuable non-invasive tool for future research into aortic distention, development and localization of vascular pathology.

Pulsatile Distension of the Proximal Aneurysm Neck is Larger in Patients with Stent Graft Migration

PURPOSE The proximal abdominal aortic aneurysm (AAA) neck expands significantly during the cardiac cycle, both before and after endovascular aneurysm repair (EVAR). Clinical consequences of this pulsatility were anticipated but have never been reported. This study investigated whether there is a relation between stent graft migration and preoperatively measured pulsatility of the proximal aneurysm neck. METHODS EVAR patients with a preoperative dynamic computed tomography angiography (CTA), an immediate postoperative, and a CTA at 3 years after EVAR were included. The preoperative dynamic CTAs consisted of eight images per heartbeat. Aortic diameter and area changes per heartbeat were measured at two levels: (A) 3 cm above and (B) 1 cm below the most distal renal artery. Postoperatively, the distance between the most distal renal artery and the most proximal stent graft ring was measured. Two patient groups were distinguished according to whether migration during follow-up occurred (group 1) or had not occurred (group 2). The aneurysm neck dynamics of the two groups were compared by using the t-test for unpaired data and multivariable logistic regression analyses were performed. Mean values are presented with the standard deviation. RESULTS Included were 26 patients (19 Talent, 6 Excluder and 1 Lifepath). Stent graft migration of > or =5 mm occurred in 11 patients (group 1). The pulsatility of the AAA neck in these patients was compared with the pulsatility in 15 patients with no graft migration (group 2). There were no significant differences in aortic neck characteristics (angulation, length and diameter) or degree of stent graft oversizing between the two groups. At level A in group 1 versus group 2, the diameter increase during the cardiac cycle was 2.0 +/- 0.3 versus 1.7 +/- 0.3 mm and the aortic area increase was 49 +/- 15 versus 33 +/- 12 mm(2). At level B in group 1 versus group 2, the diameter increase per heartbeat was 1.8 +/- 0.3 versus 1.6 +/- 0.4 mm, and the area increase was 37 +/- 10 versus 25 +/- 15 mm(2). The heartbeat-dependent diameter and area changes at both levels were significantly higher in group 1 compared with group 2. Multivariate regression analysis showed suprarenal aortic pulsatility was a significant predictor for stent graft migration after 3 years. CONCLUSION The preoperative heartbeat-dependent aneurysm neck distension is significantly associated with stent graft migration after 3 years. The aortic pulsatility in patients with stent graft migration is significantly higher than the pulsatility in patients without stent graft migration.

The Influence of Different Types of Stent Grafts on Aneurysm Neck Dynamics after Endovascular Aneurysm Repair

OBJECTIVE Dynamic imaging provides insight into aortic shape changes throughout the cardiac cycle. These changes may be important for proximal aortic stent graft fixation, sealing and durability. The objective of this study is to analyse the influence of different types of stent grafts on dynamic changes of the aneurysm neck. METHODS Pre- and postoperative electrocardiography (ECG)-gated computed tomographic angiography (CTA) scans were obtained in 30 abdominal aortic aneurysm (AAA) patients, 10 each from three different types of stent grafts (10 Talent, Endurant, and Excluder). Each dynamic CTA dataset consisted of eight reconstructed images over the cardiac cycle. Aortic area and radius changes during the cardiac cycle were determined at two levels: (A) 3 cm above and (B) 1 cm below the lowermost renal artery. Radius changes were measured over 360 axes, and plotted in a polar plot. An ellipse was fitted over the plots to determine radius changes over the major and minor axis for assessment of the asymmetric aspect and most prominent direction of distension. RESULTS Baseline characteristics did not differ significantly between the three groups. Preoperatively, the aortic area increased significantly (p < 0.001) over the cardiac cycle in all patients at both levels: (A) mean increase 8.3 +/- 4.1% (2.0-17.3%); (B) mean increase 5.9 +/- 4.2% (1.9-12.4%). The postoperative aortic area increase over the cardiac cycle did not differ significantly from preoperative increases: (A) mean increase 9.9 +/- 2.2% (4.4-20.0%); (B) mean increase 7.7 +/- 2.4% (3.8-12.4%). The difference between radius change over the major and minor axis was significant both pre- and postoperatively for all three stent grafts, indicating asymmetric distension. Suprarenal, the distension showed a tendency to right-anterior and infrarenal to left-anterior. The distension and direction of the aortic expansion was preserved after stent grafting. There were no differences between the three types of stent grafts regarding their impact on the aortic distension or direction of this distension. CONCLUSION The aorta expands significantly and asymmetrically throughout the cardiac cycle. After implantation of abdominal aortic stent grafts, the aortic distension and direction of distension remain equally preserved in all three groups. The three stent graft types studied seem to be able to adapt to the asymmetric dynamic aortic shape changes.

Abdominal stent-graft collapse due to progression of a Stanford type B dissection.

We present a 74-year-old man who was referred to our hospital with severe abdominal pain, oliguria, and laboratory findings compatible with early renal insufficiency due to progression of a Stanford type B aortic dissection. Two years earlier, the patient has undergone endovascular aneurysm repair (EVAR) to exclude a 5.4-cm abdominal aortic aneurysm with a Talent aortomonoiliac stent-graft (Medtronic CardioVascular, Minneapolis, MN, USA) and a femoral-femoral crossover bypass. One and a half years after this operation, he developed an acute type B dissection; the intimal flap originated just distal to the origin of the left subclavian artery and extended to just above the stent-graft at that time. The dissection was treated conservatively with antihypertensive agents; no progression of the dissection was seen in the following 6 months on computed tomographic angiography (CTA). Shortly after the current admission, an electrocardiographically-gated CTA obtained after prehydration revealed that the intimal flap of the dissection had progressed to several centimeters below the most proximal part of the stent-graft (Fig. 1) and had occluded the left renal artery. The most proximal ring of the stent-graft had collapsed and was broken (Fig. 2, Movie 1). Dynamic images, reconstructed with the use of CTA postprocessing software (3Surgery 4.0; 3Mensio Medical Imaging B.V., Bilthoven, The Netherlands), showed pulsatile flow in the false lumen, which extended into the aneurysm sac (Movie 2). The blood flow to the patient’s lower limbs was decreased as a result of the collapsed stent-graft. In addition, pulsatile compression of the true lumen was seen, caused either by the flow in the false lumen or movement of the intimal tear (Movie 2). This probably caused decreased blood flow through the superior mesenteric artery (SMA) and the aortic stent-graft. Since the patient had a celiac trunk stenosis and the inferior mesenteric artery had been overstented during the endovascular aneurysm repair 2 years earlier, the decreased blood flow in the SMA might have caused hypoperfusion of the intestines and subsequent abdominal pain. The patient was treated with a Relay NBS thoracic aortic stent-graft (Bolton Medical, Sunrise, FL, USA) to overstent the primary intimal tear; a balloon-expandable CP stent (NuMED, Hopkinton, NY, USA) was deployed proximal in the aortomonoiliac stent-graft to regain the original configuration of the abdominal stent-graft (Fig. 3). Following this procedure, the left renal artery regained its original configuration, renal function improved, and the abdominal pain disappeared.

Luminescence and energy migration characteristics of EuWO4Cl

Luminescence and energy transfer properties of EuWO/sub 4/Cl and Gd/sub 0.99/Eu/sub 0.01/WO/sub 4/Cl are reported. Emission due to a small amount of second phase has been observed for both samples. Energy migration among the Eu/sup 3 +/ ions has been observed for EuWO/sub 4/Cl. The temperature dependence of the migration rate can be explained assuming phonon-assisted energy transfer. The interaction between the Eu/sup 3 +/ ions is probably multipole-multipole in character.