Effect of abdominal aortic endoprostheses on arterial pulse wave velocity in an in vitro abdominal aortic flow model

In Vitro Geometry Analysis of Fenestrations in Endovascular Aneurysm Repair

PURPOSE

Changes in the flared end of balloon-expandable covered stent (BECS) may precede BECS-associated complications but are not regularly assessed with computed tomographic angiography (CTA) after fenestrated endovascular aneurysm repair (FEVAR). Validation of the flare geometric analysis (FGA) and assessment of intraobserver and interobserver variability are investigated in this study.

METHODS

Two series of 3 BeGraft BECSs (Bentley InnoMed GmbH, Hechingen, Germany) and 1 series of 3 Advanta V12 BECSs (Getinge AB, Göteborg, Sweden) were deployed in 3 side branches (45°, 60°, and 90° aortic branch angles) of an aorta phantom model. A standard post-FEVAR CTA scan was acquired. Computed tomographic angiography-derived measurements consisted of centerline reconstructions and placement of 3-dimensional coordinate markers by 2 observers in a vascular workstation. Flare geometric analysis calculates 3 BECS parameters: the circumferential flare-to-fenestration distance (FFD), which is the distance from the proximal end of the flare to fenestration, and diameters at the proximal end of the flare (Dflare) and at the fenestration (Dfenestration). Computed tomographic angiography-derived measurements were validated against microscopy measurements. Bland-Altman plots were used to determine the intraobserver and interobserver variability of the BECS parameters and intraclass correlation coefficient (ICC).

RESULTS

For each BECS, the FFD at 4 equidistant quadrants of the circumference, Dflare, and Dfenestration were calculated. The mean difference and repeatability coefficient (RC) of the validation were 0.8 (2.1) mm for FFD, 0.4 (1.0) mm for Dflare, and -0.2 (1.2) mm for Dfenestration. The mean intraobserver and interobserver difference (RC) was 0.5 (1.6) mm and 0.7 (2.6) mm for FFD, 0.1 (0.6) mm and 0.1 (0.7) mm for Dflare, and -0.1 (0.8) mm and -0.8 (1.0) mm for Dfenestration. The mean ICC of intraobserver variability was 0.86 for FFD, 0.94 for Dflare, and 0.78 for Dfenestration. The mean ICC of interobserver variability was 0.77 for FFD, 0.92 for Dflare, and 0.48 for Dfenestration.

CONCLUSION

This study showed that FGA of the flared ends of BECS can be performed with high accuracy in a phantom model, with good intraobserver and interobserver variability. Flare geometric analysis can be used to determine flare geometry of the BECS on standard post-FEVAR CTA scans.

Treatment Site Does Not Affect Changes in Pulse Wave Velocity but Treatment Length and Device Selection Are Associated With Increased Pulse Wave Velocity After Thoracic Endovascular Aortic Repair

Background: Endovascular treatment of aortic aneurysm is associated with an increase in pulse wave velocity (PWV) after surgery. However, the effect of different types of endovascular devices on PWV at different sites of the thoracic aorta remains unclear.

Objectives: The purposes of this study were (1) to investigate the changes in PWV after endovascular treatment of thoracic aortic aneurysm; (2) to evaluate whether there is a difference in the changes in PWV at different treatment sites; and (3) to evaluate the effect of treatment length on changes in PWV.

Methods: From July 2008 to July 2021, 276 patients underwent endovascular treatment of the true thoracic aortic aneurysm. Of these patients, 183 patients who underwent preoperative and postoperative PWV measurement within 1 year of surgery were included in the study. The treatment length index was calculated by treatment length divided by the height of the patients.

Results: Five different types of endovascular devices were used (Najuta, Kawasumi Laboratories, Inc., Tokyo, Japan; TAG, W.L. Gore & Associates, Inc., AZ, USA; Relay, Bolton Medical, Inc., FL, USA; Talent/Valiant, Medtronic, MN, USA; and Zenith, Cook Medical, IN, USA). There was no significant change in PWV in patients receiving Najuta (Before: 2,040 ± 346.8 cm/s vs. After: 2,084 ± 390.5 cm/s, p = 0.14). However, a significant increase was observed in other devices: TAG (Before: 2,090 ± 485.9 cm/s vs. After: 2,300 ± 512.1 cm/s, p = 0.025), Relay (Before: 2,102 ± 465.3 cm/s vs. After: 2,206 ± 444.4 cm/s, p = 0.004), Valiant (Before: 1,696 ± 330.2 cm/s vs. After: 2,186 ± 378.7 cm/s, p < 0.001), and Zenith (Before: 2,084 ± 431.7 cm/s vs. After: 2,321 ± 500.6 cm/s, p < 0.001). There was a significant increase in PWV in patients treated from aortic arch (Before: 2,006 ± 333.7 cm/s vs. After: 2,132 ± 423.7 cm/s, p < 0.001) and patients treated from descending thoracic aorta (Before: 2,116 ± 460.9 cm/s vs. After: 2,292 ± 460.9 cm/s, p < 0.001). Multivariate analysis showed that treatment site was not an independent factor associated with changes in PWV. However, Najuta (Coef −219.43, 95% CI −322.684 to −116.176, p < 0.001) and treatment index (Coef 147.57, 95% CI 24.826 to 270.312, p = 0.019) were independent factors associated with changes in PWV.

Conclusion: Najuta did not show a significant increase in PWV, while other commercially available devices showed a significant increase. The treatment site did not have a different effect on PWV. However, the treatment length was an independent factor associated with an increase in PWV.

Determination of aortic pulse transit time based on waveform decomposition of radial pressure wave

Carotid-femoral pulse transit time (cfPTT) is a widely accepted measure of central arterial stiffness. The cfPTT is commonly calculated from two synchronized pressure waves. However, measurement of synchronized pressure waves is technically challenging. In this paper, a method of decomposing the radial pressure wave is proposed for estimating cfPTT. From the radial pressure wave alone, the pressure wave can be decomposed into forward and backward waves by fitting a double triangular flow wave. The first zero point of the second derivative of the radial pressure wave and the peak of the dicrotic segment of radial pressure wave are used as the peaks of the fitted double triangular flow wave. The correlation coefficient between the measured wave and the estimated forward and backward waves based on the decomposition of the radial pressure wave was 0.98 and 0.75, respectively. Then from the backward wave, cfPTT can be estimated. Because it has been verified that the time lag estimation based on of backward wave has strong correlation with the measured cfPTT. The corresponding regression function between the time lag estimation of backward wave and measured cfPTT is y = 0.96x + 5.50 (r = 0.77; p < 0.001). The estimated cfPTT using radial pressure wave decomposition based on the proposed double triangular flow wave is more accurate and convenient than the decomposition of the aortic pressure wave based on the triangular flow wave. The significance of this study is that arterial stiffness can be directly estimated from a noninvasively measured radial pressure wave.

Validation of Central Pressure Estimation in Patients with an Aortic Aneurysm Before and After Endovascular Repair

PURPOSE

The aim of this study was to investigate if non-invasive central pressure estimations are accurate in patients with an abdominal aortic aneurysm, before and after endovascular repair. Secondary evaluation was if measurement-accuracy was dependent on anatomical characteristics.

METHODS

Procedural invasive and non-invasive pressure-measurements were performed simultaneously both before and after endovascular repair in 20 patients with an infrarenal abdominal aortic aneurysm. Invasive catheter measurements were performed in the abdominal aorta. A tonometric device was used to perform non-invasive pressure-wave-analysis at the radial artery. A generalized transfer-function was used to generate an ascending aortic waveform for both measurements, allowing for direct comparison.

RESULTS

Pre-treatment the mean differences between methods were - 5.5 mmHg (p = .904), - 11.8 (p < .001), and - 7.2 mmHg (p = .124) for central systolic, diastolic, and mean pressure, respectively. The accuracy was dependent of aneurysm sac volume and intraluminal thrombus volume. Post-treatment limits of agreement were smaller for all pressure parameters compared to pre-treatment. The mean differences were 6.5 mmHg (p = .007), - 6.4 (p < .020), and 1.6 mmHg (p = .370) for central systolic, diastolic, and mean pressure, respectively.

CONCLUSION

In untreated AAA's the accuracy of non-invasive central pressure estimation was acceptable (mean difference between 5 and 10 mmHg) when compared to invasive pressures, but dependent of AAA characteristics. After EVAR the accuracy of central pressure estimation improved (reduction of 75% of the mean difference between pre and post measurements) TRIAL REGISTRATION NUMBER: NCT03469388; 3-5-2018.

Influence of shape-memory stent grafts on local aortic compliance

The effect of repair techniques on the biomechanics of the aorta is poorly understood, resulting in significant levels of postoperative complications for patients worldwide. This study presents a computational analysis of the influence of Nitinol-based devices on the biomechanical performance of a healthy patient-specific human aorta. Simulations reveal that Nitinol stent-grafts stretch the artery wall so that collagen is stretched to a straightened high-stiffness configuration. The high-compliance regime (HCR) associated with low diastolic lumen pressure is eliminated, and the artery operates in a low-compliance regime (LCR) throughout the entire cardiac cycle. The slope of the lumen pressure–area curve for the LCR post-implantation is almost identical to that of the native vessel during systole. This negligible change from the native LCR slope occurs because the stent-graft increases its diameter from the crimped configuration during deployment so that it reaches a low-stiffness unloading plateau. The effective radial stiffness of the implant along this unloading plateau is negligible compared to the stiffness of the artery wall. Provided the Nitinol device unloads sufficiently during deployment to the unloading plateau, the degree of oversizing has a negligible effect on the pressure–area response of the vessel, as each device exerts approximately the same radial force, the slope of which is negligible compared to the LCR slope of the native artery. We show that 10% oversizing based on the observed diastolic diameter in the mid descending thoracic aorta results in a complete loss of contact between the device and the wall during systole, which could lead to an endoleak and stent migration. 20% oversizing reaches the Dacron enforced area limit (DEAL) during the pulse pressure and results in an effective zero-compliance in the later portion of systole.

Computational Fluid Dynamic Analysis Supports the Hemodynamic Stability of Hybrid Combinations With the AFX Bifurcate and Nitinol-Based Proximal Segments in Solutions of Failed Endovascular Aneurysm Repair

Hybrid endograft combinations of two or more different types of covered stents are rarely reported to treat complex abdominal aortic aneurysm cases or primary and secondary endoleaks. Clinical and laboratory data regarding the clinical efficacy and mechanical stability of such combinations are lacking. Based on a recently published case report, we describe and comment on the hemodynamic profile of a representative simulated hybrid case of AFX and Nitinol-based proximal cuff and support the stability of this combination in non-angulated cases.

Changes in Noninvasive Arterial Stiffness and Central Blood Pressure After Endovascular Abdominal Aneurysm Repair

Purpose:

To evaluate the impact of elective endovascular aneurysm repair (EVAR) on the carotid-femoral pulse wave velocity (cfPWV) and central pressure waveform, through 1-year follow-up.

Materials and Methods:

A tonometric device was used to measure cfPWV and estimate the central pressure waveform in 20 patients with an infrarenal abdominal aortic aneurysm scheduled for elective EVAR. The evaluated central hemodynamic parameters included the central pressures, the augmentation index (AIx), and the subendocardial viability ratio (SEVR). AIx quantifies the contribution of reflected wave to the central systolic pressure, whereas SEVR describes the myocardial perfusion relative to the cardiac workload. Measurements were performed before EVAR, at discharge, and 6 weeks and 1 year after EVAR.

Results:

CfPWV was increased at discharge (12.4±0.4 vs 11.3±0.5 m/s at baseline; p=0.005) and remained elevated over the course of 1-year follow-up (6 weeks: cfPWV = 12.2±0.5 m/s; 1 year: cfPWV = 12.2±0.7 m/s, p<0.05). After an initial drop in systolic central pressure at discharge, all the central pressures increased thereafter up to 1 year, without significant differences compared with baseline. The same was observed for the AIx and SEVR.

Conclusion:

Endovascular aortic aneurysm repair caused an increase in pulse wave velocity compared with baseline, which remained elevated through 1 year follow-up, which may be related to an increased cardiovascular risk. However, no differences in central pressure, augmentation index, and subendocardial viability ration were observed during follow-up.

Changes in Noninvasive Arterial Stiffness and Central Blood Pressure After Endovascular Abdominal Aneurysm Repair

PURPOSE

To evaluate the impact of elective endovascular aneurysm repair (EVAR) on the carotid-femoral pulse wave velocity (cfPWV) and central pressure waveform, through 1-year follow-up.

MATERIALS AND METHODS

A tonometric device was used to measure cfPWV and estimate the central pressure waveform in 20 patients with an infrarenal abdominal aortic aneurysm scheduled for elective EVAR. The evaluated central hemodynamic parameters included the central pressures, the augmentation index (AIx), and the subendocardial viability ratio (SEVR). AIx quantifies the contribution of reflected wave to the central systolic pressure, whereas SEVR describes the myocardial perfusion relative to the cardiac workload. Measurements were performed before EVAR, at discharge, and 6 weeks and 1 year after EVAR.

RESULTS

CfPWV was increased at discharge (12.4±0.4 vs 11.3±0.5 m/s at baseline; p=0.005) and remained elevated over the course of 1-year follow-up (6 weeks: cfPWV = 12.2±0.5 m/s; 1 year: cfPWV = 12.2±0.7 m/s, p<0.05). After an initial drop in systolic central pressure at discharge, all the central pressures increased thereafter up to 1 year, without significant differences compared with baseline. The same was observed for the AIx and SEVR.

CONCLUSION

Endovascular aortic aneurysm repair caused an increase in pulse wave velocity compared with baseline, which remained elevated through 1 year follow-up, which may be related to an increased cardiovascular risk. However, no differences in central pressure, augmentation index, and subendocardial viability ration were observed during follow-up.

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

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.

Effect of endoprostheses on pulse wave velocity and its long-term outcomes after thoracic endovascular aortic repair

BACKGROUND

The purpose of this study was to evaluate the changes in pulse wave velocity and left ventricular dimensions in patients undergoing stent-graft treatment for aortic arch aneurysm.

METHODS

From July 2008 to February 2019, 86 patients underwent thoracic endovascular aortic repair of an aortic arch aneurysm. Changes in pulse wave velocity (PWV), echocardiogram findings, and long-term outcomes were compared between endoskeleton type (n = 60) and exoskeleton type stent-graft (n = 26).

RESULTS

There was no significant difference in patient demographics except for diabetes which was more observed in endoskeleton type (p = 0.017). There was a significant increase in PWV in exoskeleton type after surgery, which further progressed at a median follow-up of 32 months (before: 2047 cm/s vs. after: 2259 cm/s vs. follow-up: 2486 cm/s, p = 0.010, p = 0.017). No significant difference was observed in endoskeleton type (before: 1980 cm/s vs. after: 2058 cm/s, vs. follow-up: 2042 cm/s, p = 0.25, p = 0.34). Echocardiogram performed at a median period of 46.3 months, revealed a significant increase in left ventricular diastolic volume (LVDV) (before: 107.4 ± 20.6 ml vs. follow-up: 127.7 ± 27.5 ml, p = 0.003) and decrease in e' (before: 5.5 ± 1.78 cm/s vs. follow-up: 4.7 ± 1.72 cm/s, p = 0.012) in exoskeleton type, while no significant change was observed in endoskeleton type (LVDV: before: 102.6 ± 32.3 ml vs. follow-up: 96.9 ± 35.4 ml, p = 0.74; e': before: 4.4 ± 1.21 cm/s vs. follow-up: 4.8 ± 1.40 cm/s, p = 0.68). At the median period of 61.3 months, there was no significant difference in long-term mortality (p = 0.89). However, the endoskeleton type was associated with a lower incidence of a cardiac event (p = 0.034) and cerebrovascular event (p = 0.029).

CONCLUSION

Types of endoprosthesis might affect differently on physiological changes and its accommodated risk factors after surgery.