Pilot Study of Dynamic Cine CT Angiography for the Evaluation of Abdominal Aortic Aneurysms: Implications for Endograft Treatment

Polymer based endografts have improved rates of proximal aortic neck dilatation and migration

BACKGROUND

Proximal aortic neck dilatation (PND) affects a considerable proportion of patients undergoing endovascular aneurysm repair (EVAR) and is associated with increased rates of type I endoleak (EL1), migration, and reinterventions. Although there are numerous studies investigating PND following the placement of endografts that utilize self-expanding stent (SES) technology, there are few reports for patients treated with endografts that utilize polymer-filled rings. The purpose of this study is to examine PND and graft migration after EVAR with the Ovation stent graft.

METHODS

The study comprised patients who underwent EVAR as part of the prospective, international, multicenter Ovation stent graft trial. A clinical events committee adjudicated adverse events through 1 year, an independent imaging core laboratory analyzed imaging through 5 years, and a data safety and monitoring board provided study oversight. Neck diameter was measured at the level of the lowest renal artery. PND was defined as neck enlargement of 3 mm or more. Graft migration was defined as distal movement >10 mm or movement ≤10 mm when resulting in secondary intervention.

RESULTS

A total of 238 patients received this device during the study period. Patients were predominantly male (81%), with a mean age of 73 ± 8 years. Median follow-up was 58 months (IQR 36-60). Almost half the patients (110 patients, 46%) had challenging anatomy; defined as outside the instructions for use (IFU) with other commercially available stent grafts. 41 patients (17.2%) had a proximal neck length <10 mm and 93 (39%) had a minimum access vessel diameter <6 mm. The technical success rate was 100%. The 1-, 3- and 5-year overall survival rates were 96.6%, 86.2% and 74.9%, respectively. The immediate postoperative proximal neck diameter ranged from 16 mm to 31 mm with a mean of 22.4 ± 3 mm. During follow-up, ten patients (4.2%) developed PND. Freedom from PND estimates at 1, 3 and 5 years were 97.7%, 96%, and 93.6%, respectively. None of the patients developed endograft migration.

CONCLUSIONS

The use of the Ovation stent graft was associated with low rates of PND despite challenging neck anatomy in 17% of patients. No graft migration was observed. The design of this endograft may explain its superiority to SES in preventing neck dilatation and migration even in patients with challenging neck anatomy. This is important, as we continue to see significant late failures of EVAR due to proximal neck degeneration.

Toward Endografting of the Ascending Aorta: Insight into Dynamics Using Dynamic Cine-CTA

Purpose:

To evaluate pulsatility and movement along the ascending thoracic aorta using dynamic electrocardiographically-gated 64-slice cine computed tomographic angiography (CTA).

Methods:

Diameter and area change and center of mass (COM) movement of the ascending thoracic aorta was determined per cardiac cycle in 15 patients at surgically relevant anatomical levels: (A) 5 mm distal to the coronary arteries, (B) 5 mm proximal to the innominate artery, and (C) halfway up the ascending aorta. Additionally, COM movement was determined 1 cm (level P) and 2 cm (level Q) distal from the origins of the innominate, left carotid, and left subclavian arteries. Eight gated datasets covering the cardiac cycle were used to reconstruct images at each level perpendicular to the aortic lumen. The distance between important anatomical landmarks was determined.

Results:

All levels showed significant cardiac cycle—induced diameter and area changes (p<0.001), with the largest pulsatility 5 mm distal to the coronary arteries. Mean maximum diameter changes were (A) 17.4%±4.8% (range 7.5%–27.5%), (B) 13.9%±3.5% (range 10.6%–25.0%), and (C) 12.9%±3.4% (8.3%–19.6%). Mean area changes were (A) 12.7%±5.5% (range 4.3%–21.8%), (B) 7.5%±2.0% (range 4.1%–11.0%), and (C) 5.6%±2.2% (range 1.9%–11.4%). Mean maximum COM movements were (A) 6.1±2.0 mm (range 2.7–9.0), (B) 2.3±1.1 mm (range 1.1–5.6), and (C) 3.6±1.5 mm (range 1.4–6.5). Mean COM movements of the innominate, left carotid, and left subclavian arteries, respectively, were (P) 1.960.7 mm (range 0.9–3.7), 2.4±0.6 mm (range 1.4–3.3), and 1.9±0.6 mm (range 0.8–2.8), and (Q) 1.8±0.7 mm (range 0.8–3.5), 1.8±0.6 mm (range 0.8–2.7), 1.9±0.6 mm (range 1.1–3.4).

Conclusion:

The dynamics of the ascending thoracic aorta and the arch vessels are impressive, showing a wide range of 3-dimensional motions. Future ascending arch branched and fenestrated thoracic endograft designs must consider this active local environment, as it may have implications for durability, sealing, and ultimate clinical success.

Through-Plane Movement at Multiple Aortic Levels on Dynamic Computed Tomography Angiography Is Limited in Patients With an Abdominal Aortic Aneurysm

PURPOSE

To analyze the movement of the aorta in the craniocaudal direction (through-plane movement) during the cardiac cycle at several levels to determine any potential impact on endovascular aneurysm repair (EVAR) of abdominal aortic aneurysm (AAA).

METHODS

For this study, 30 patients (median age 73.0 years; 27 men) with an infrarenal AAA were randomly selected from a prospectively maintained EVAR database. All patients had undergone preoperative electrocardiogram-gated computed tomography angiography consisting of 8 phases. After semiautomatic segmentation, a 3-dimensional location probe was placed in the center of the aorta (center point) on the orthogonal slices at 12 different levels along the aorta and iliac arteries for all 8 phases. Movement of the center point during the cardiac cycle was analyzed for each level. Values are given as the median and interquartile range (IQR).

RESULTS

The median through-plane movement of all levels was 3.0 mm (IQR 2.8-3.2) and appeared to be lower in the region of the celiac and renal arteries: 2.6 mm (IQR 1.7-3.1) at 3 cm proximal to the most distal renal artery and 2.4 mm (IQR 1.9-2.9) at 1 cm distal to the most distal renal artery, respectively. The thoracic part of the aorta showed the largest through-plane motion: 4.1 mm (IQR 2.7-4.6).

CONCLUSION

This study quantifies aortic through-plane motion in the craniocaudal direction. Since through-plane movement appears to be limited, findings of previous studies investigating pulsatile in-plane distension seem to be representative for aortic distension.

Aortic-neck dilation after endovascular abdominal aortic aneurysm repair (EVAR): can it be predicted?

PURPOSE

This study was performed to evaluate whether dynamic computed tomography (CT) can provide functional vessel information predicting outcomes of aortic neck in patients undergoing endovascular aneurysm repair (EVAR) of an abdominal aortic aneurysm (AAA).

MATERIALS AND METHODS

Twenty patients with and 20 without AAA were enrolled. Electrocardiographically (ECG)-gated data sets were acquired with a 64-slice CT scanner. Axial pulsatility measurements were taken at three levels: 2 cm above the highest renal artery; immediately below the lowest renal artery; 1 cm below the lowest renal artery. Three independent readers performed the measurements. Systolic and diastolic blood pressures were measured in the brachial artery to calculate arterial-wall distensibility expressed as pressure strain elastic modulus (Ep). Cross-sectional area change, wall distensibility and Ep value were statistically compared.

RESULTS

No significant differences were found in terms of Ep values in the suprarenal and juxtarenal level. In the AAA group, a significantly higher value was obtained at the infrarenal level. A subgroup of patients with AAA (45%) had a significantly higher Ep value at the infrarenal level.

CONCLUSIONS

Dynamic CT provided insight into the abdominal aorta pathophysiology. Identifying patients with higher infrarenal distensibility could change selection of graft size to improve proximal fixation.

Imaging of the thoracic aorta

Three-dimensional vascular imaging techniques offer a significant advantage over traditional imaging techniques. Spatial resolution of current state-of-the-art allows sufficient depiction of anatomical detail. Pre-operative planning of complex endovascular procedures is facilitated by state-of-the-art imaging. Cone-beam CT holds great promise in guiding complex endovascular procedures.

Pulsatility in the iliac artery is significant at several levels: implications for EVAR

PURPOSE

To evaluate the pulsatility of the iliac arteries and compare their distension at several levels that might influence preoperative stent-graft sizing and the long-term durability of stent-graft sealing and fixation.

METHODS

Preoperative dynamic computed tomographic angiography (CTA) scans of 30 patients (24 men; median age 75 years, range 60-85) with an abdominal aortic aneurysm and patent iliac arteries were included. The CTAs consisted of 8 images per heartbeat. Bilateral diameter and area changes per heartbeat were measured semi-automatically in the common iliac artery (CIA) at 3 levels: (A) 0.5 cm after the aortic bifurcation, (B) in the middle of the CIA, and (C) 0.5 cm proximal to the iliac bifurcation. Pulsatility was defined as the largest difference in area and average diameter change over 180 axes per heartbeat. Pulsatility at the 3 levels was compared, and the intraobserver variability of the method was calculated according to Bland and Altman.

RESULTS

The mean area increases in the CIAs at levels A, B, and C were 12.5% (16.3 mm²), 11.2% (13.6 mm²), and 9.6% (12.6 mm²), respectively, and the mean iliac diameter increases were 9.2% (1.1 mm), 8.5% (1.0 mm), and 8.1% (1.0 mm). The iliac distension was statistically significant at all levels. The iliac distension at level A was statistically significantly larger than the distension at level C. The intraobserver variability was 13.3 mm² for area and 0.6 mm for diameter measurements.

CONCLUSION

The pulsatility in the iliac arteries is statistically significant at several levels relevant to endovascular aneurysm repair. The distension of the iliac artery possibly decreases more distally, which might encourage the extension of stent-grafts to the internal iliac artery.

Fluoroscopic Roentgen stereophotogrammetric analysis (FRSA) to study three-dimensional stent graft dynamics

We report the clinical feasibility of fluoroscopic Roentgen stereophotogrammetric analysis (FRSA), a validated method to quantify real time three-dimensional (3D) dynamic motion of stent grafts and the first clinical results after abdominal and thoracic endovascular repair (EVAR). Stent graft motion was measured at 30 (stereo) frames per second, during the cardiac cycle and in the patient after abdominal EVAR, due to respiratory action. Translational motions of the center of mass, diameter change, and rotational and axial motion could be measured. Quantification of 3D motion was not available until now. FRSA can provide crucial information on the forces exerted on stent grafts and will, therefore, provide essential information for improvements in stent graft design.

Dynamic Cine-Computed Tomography Angiography Imaging of Standard and Fenestrated Endografts: Differing Effects on Renal Artery Motion

Different endograft configurations (fenestrated, transrenal, infrarenal) may varyingly affect aortic side branch movement. Renal artery motion was evaluated with 64-slice dynamic cine-computed tomography angiography before and after endovascular aneurysm repair in 16 patients (46 renal arteries). Center-of-mass displacement of the renals was determined per heartbeat for before repair for 3 different endografts; differences were compared, with significance at P < 0.5. Preoperative renal artery motion is significant (1.2 [SD 0.5] mm, range, 0.6-2.). Neither transrenal nor infrarenal endografts alter renal artery motion compared with before repair ( P < .05). Renal artery motion after fenestrated endovascular repair with renal stents reduces motion to 25% of the preoperative value (0.3 [SD, 0.1] mm, range, 0.2-0.5 mm; P = .01). Endograft implantation without stented side branches does not change renal artery motion, potentially allowing significant movement of the renal artery relative to the fenestration. Routine stenting of fenestrations limits postoperative renal artery motion to 0.3 mm, thereby preventing significant branch movement in relation the fenestration.

Current state of dynamic imaging in endovascular aortic aneurysm repair

Dynamic imaging, in which the time dimension has a specific function in data (image) interpretation, is becoming increasingly important when contemplating endovascular aneurysm repair. Clinical parameters and complications, including proper sizing, successful aneurysm sac exclusion, optimal stent-graft design, endoleaks, graft migration, and stent fracture are beginning to be better understood through dynamic magnetic resonance, ultrasound, and dynamic computed tomography. The current practice using static 3-dimensional reconstructions for the planning and follow-up of aortic aneurysm endograft treatment will most likely evolve, and the use of dynamic aortic imaging will continue to increase. Validation of these imaging modalities in larger scale trials is needed.

Assessment of three-dimensional stent-graft dynamics by using fluoroscopic roentgenographic stereophotogrammetric analysis

OBJECTIVE

To validate the use of fluoroscopic roentgenographic stereophotogrammetric analysis (FRSA) for its feasibility and accuracy for measuring the three-dimensional dynamic motion of stent grafts.

METHODS

A digital biplane fluoroscopy setup was calibrated (Siemens Axiom Artis dBc). Stereo images were acquired of a static aortic model with a stent graft in different axial positions, imposed by a micromanipulator. The three-dimensional measurement error of FRSA was determined by comparing FRSA measurements with the micromanipulator. An aortic model with a stent graft was constructed and connected to an artificial circulation with a physiological flow and pressure profile. Markers were added to the spine (tantalum spherical markers; diameter 1 mm) and stent (welding tin; diameter 1 mm). The three-dimensional measurement precision was determined by measuring the position of a single (stable) spine marker during two pulsatile cycles. Finally, three-dimensional stent marker motion was analyzed with a frame rate of 30 images per second, including three-dimensional marker position (change), diameter change, and center of circle position change.

RESULTS

The mean error of FRSA measurement of displacement was 0.003 mm (SD, 0.019 mm; maximum error, 0.058 mm). A very high precision of position measurement was found (SD, 0.009-0.015 mm). During pulsatile motion, the position (changes) of the markers could be assessed in the x, y, and z directions, as well as the stent diameter change and center of circle position change.

CONCLUSIONS

FRSA has proven to be a method with very high accuracy and temporal resolution to measure three-dimensional stent-graft motion in a pulsatile environment. This technique has the potential to contribute significantly to the knowledge of stent-graft behavior after endovascular aneurysm repair and improvements in stent-graft design. The technique is ready for clinical testing.

Long-Term Single-Center Results with Aneurx Endografts for Endovascular Abdominal Aortic Aneurysm Repair

PURPOSE

To evaluate the long-term single-center results with the AneuRx stent-graft in endovascular abdominal aortic aneurysm (AAA) repair (EVAR).

METHODS

Between December 1996 and August 2003, 212 patients (197 men; mean age 71.3+/-7.0 years) were treated with the AneuRx stent-graft for an infrarenal AAA. Postoperatively, patients were enrolled in a fixed surveillance protocol, and data were prospectively captured into a database.

RESULTS

Graft deployment was successful in 98.6% (209/212). Thirty-day mortality was 2.4%. Median hospital stay was 4.3+/-5.5 days. Median follow-up was 52.0 months (range 1-109); only 1 patient was lost to follow-up. At 9 years, patient survival was 56% and freedom from secondary interventions was 48%. In 68% of cases, these reinterventions were needed for a fixation-related complication, and most of these complications (75%) encompassed the area of the proximal aneurysm neck. Primary clinical success was 37% at 9 years. After secondary interventions, the assisted primary clinical success improved to 73% at 9 years. Freedom from aneurysm-related death was 97% at 1 year and 90% at 9 years.

CONCLUSION

As an alternative to open repair, EVAR with the AneuRx device has low perioperative mortality. Reinterventions are mostly due to fixation-related complications. While the overall mortality risk in this population was 5% per year, annual aneurysm-related death was only 1%. The focus should be on surveillance and reducing the rate of long-term complications, which might be possible with improved proximal stent-graft fixation.

Use of dynamic computed tomography to evaluate pre- and postoperative aortic changes in AAA patients undergoing endovascular aneurysm repair

PURPOSE

To utilize dynamic computed tomographic angiography (CTA) on pre- and postoperative endovascular aneurysm repair (EVAR) patients to characterize cardiac-induced aortic motion within the aneurysm neck, an essential EVAR sealing zone.

METHODS

Electrocardiographically-gated CTA datasets were acquired utilizing a 64-slice Philips Brilliance CT scanner on 15 consecutive pre- and postoperative AAA patients. Axial pulsatility measurements were taken at 2 clinically relevant levels within the aneurysm neck: 2 cm above the highest renal artery and 1 cm below the lowest renal artery. Changes in aortic area and diameter were determined.

RESULTS

Significant aortic pulsatility exists within the aneurysm neck during the cardiac cycle. Preoperative aortic area increased significantly, with a maximum increase of up to 12.5%. The presence of an endograft did not affect aortic pulsatility (p=NS). Postoperative area also changed significantly during a heart cycle, with a maximum increase of up to 14.5%. Diameter measurements demonstrated an identical pattern, with significant pre- and postoperative intracardiac pulsatility within and above the aneurysm neck (p<0.05). An increase in maximum diameter change up to 15% was evident.

CONCLUSION

Patients undergoing EVAR experience aortic diameter changes within and above the aneurysm neck. The presence of an endograft does not abrogate this response to intracardiac pressure changes. Static CT imaging may not adequately identify patients with large aortic pulsatility, potentially resulting in endograft undersizing, stent-graft migration, intermittent type I endoleaks, and poor patient outcomes. The current standard regime of 10% to 15% oversizing based on static CT may be inadequate for some patients.