Pulsatile Changes of the Aortic Diameter May Be Irrelevant Regarding Endograft Sizing in Patients With Aortic Disease

Abstract

Purpose:

Endovascular aortic repair has become the preferred elective treatment of infrarenal aortic aneurysms. Aortic pulsatility may pose problems regarding endograft sizing. The aims of this study are to determine the aortic pulsatility in patients with aortic disease and to evaluate the effect of pulsatility on the growth of aneurysms.

Materials and Methods:

In this retrospective study, analyses of computed tomography angiography (CTA) images of 31 patients under conservative treatment for small abdominal aortic aneurysms were performed. Reconstructions of the raw electrocardiography (ECG) gated dataset at 30% and 90% of the R-R cycle were used. After lumen segmentation, total aortic cross-sectional area was measured in diastole and systole in the following zones: Z0, Z3, Z5, Z6, Z8, and Z9. Effective diameters (EDs) were calculated from the systolic (ED_sys) and diastolic (ED_dia) cross-sectional areas to determine absolute (ED_sys – ED_dia, mm) and relative pulsatility [(ED_sys – ED_dia) / ED_dia, %]. Diameter of the aneurysms was measured on baseline images and the last preoperative follow-up study of each patient.

Results:

A total of 806 measurements were completed, 24 pulsatility and 2 growth measurements per patient. The mean pulsatility values at each point were as follows: Z0: 0.7±0.8 mm, Z3: 1.0±0.6 mm, Z5: 1.0±0.6 mm, Z6: 0.8±0.7 mm, Z8: 0.7±1.0 mm, Z9: 0.9±0.9 mm. Follow-up time was 5.5±2.2 years during which a growth of 13.42±9.09 mm (2.54±1.55 mm yearly) was observed. No correlation was found between pulsatility values and growth rate of the aneurysms.

Conclusion:

The pulsatility of the aorta is in a submillimetric range for the vast majority of patients with aortic disease, thus probably not relevant regarding endograft sizing. Pulsatility of the ascending aorta is smaller than that of the descending segment, making an additional oversize of a Z0 implantation questionable.

Clinical Impact

Endovascular aortic repair reqiures precise preoperative planning. Pulsatile changes of the aortic diameter may pose issues regarding endograft sizing. In our retrospective single-centre study, aortic pulsatility of patients with AAA was measured on ECG gated CTA images. Pulsatility values reached a maximum at the descending aorta, however absolute pulsatility values did not exceed 1 mm at any point along the aorta. Therefore, significance of aortic pulsatility regarding the sizing of EVAR prostheses is questionable. Correlation between pulsatility and AAA growth was not found.

Keywords

aorta aneurysm abdominal aneurysm computed tomography angiography endovascular aneurysm repair stent graft

Introduction

In the past 2 decades, endovascular aneurysm repair (EVAR) has grown from a promising alternative to open surgical repair (OSR) to the preferred elective treatment modality in most patients with infrarenal aortic aneurysm. Due to its considerably lower 30-day mortality than in cases treated with OSR, EVAR is always considered in patients with suitable aortic and side branch anatomy and adequate postoperative life expectancy.^1–6 Computed tomography angiography (CTA) imaging plays a crucial role in the diagnosis, preoperative assessment, and postoperative follow-up of patients with abdominal aortic aneurysm (AAA).^7–10

Electrocardiography (ECG) gating is a widely used technique to minimize motion artifacts on CTA images caused by pulsation.¹¹ Moreover, retrospective ECG-gating also permits the comparison between systolic and diastolic images of the aorta. Several studies including our previous research reported considerable data about pulsatile changes of the non-aneurysmatic aorta.^12–14 However, aortic pulsatility in patients with aneurysms has not been assessed yet. Pulsatility of aortic segments commonly used as EVAR landing zones may be a concern for complications such as endograft migration or endoleaks. Furthermore, as thoracic endovascular aortic repair (TEVAR) tends to increasingly involve the ascending aorta as landing zone, the change of diameter in this segment might also be noteworthy.

In this study, our primary objective was to measure aortic pulsatility in a cohort of patients with aortic disease using retrospective ECG synchronized CTA images. Our secondary goal was to determine whether aortic pulsatility has any effect on the growth rates of AAAs.

Materials and Methods

This is a single-center, investigator-driven retrospective study approved by the Semmelweis University Regional and Institutional Committee of Science and Research Ethics (95/2021). All procedures were carried out in accordance with the Declaration of Helsinki.

Computed Tomography Imaging and Image Analysis

Readily available images were analyzed of consecutive patients who underwent systolic and diastolic phase CTA as part of routine AAA surveillance. The cohort selected for our study consisted of patients who underwent at least 2 aortic CTA examinations at least 4 years apart. The computed tomography (CT) scans used for the study were conducted in the time period between November 24, 2005, and June 12, 2020.

CTA examinations used for pulsatility measurements were performed with a 256 slice multidetector scanner (Philips Brilliance iCT; Koninklijke Philips N.V., Best, The Netherlands). Acquisitions of the whole aorta and ilio-femoral arteries were taken from the level of the thoracic inlet to the level of the symphysis (tube voltage 100 kV). Intravenous nonionic iodinated contrast agent (Io-meron 400, Bracco Ltd, Milan, Italy) was administered into an anterocubital vein through a 18 g cannula using a dual-syringe power injector at a 4 to 5 mL/s flow rate. A retrospective ECG gated helical protocol was used for the scans, optimalized for multi-phase imaging of the aorta with the minimalization of motion artifacts due to the pulsiatile movement of the aorta. This method allowed us to acquire a relatively motion-free image of the aorta in both systolic and diastolic phases. Iterative reconstructions (iDose, Koninklijke Philips N.V., Best, The Netherlands) were performed with a 1 mm slice thickness and 1 mm increments for every 10% of the cardiac cycle, providing us with 10 series of images per patient. The acquired image data were then transferred to a dedicated workstation for further analysis.

Vessel segmentation and cross-sectional area measurements were performed by a board-certified radiologist experienced in cardiovascular imaging (D.M.F.). 3mensio Vascular (Pie Medical Imaging BV, Maastricht, The Netherlands) software was used for the evaluation of the CTA series. Automatic lumen segmentation was conducted by placing markers into the aortic root, aortic bifurcation, and common femoral arteries. In the cross-sectional plane, an ellipsoid contour was drawn manually along the outer wall of the aorta. Effective aortic diameter was derived. Two measurements with a 1 cm distance from each other were accomplished in the following positions: Z0 (distal end of the ascending aorta 1 cm proximal to the brachiocephalic trunk orifice), Z3 (distal to the left subclavian artery origin), Z5 (10 cm proximally to celiac trunk orifice), Z6 (at the celiac trunk orifice), Z8 (distal to the renal orifices), and Z9 (the largest diameter of the infrarenal aneurysm). Every measurement was performed on a systolic series at 30% of the cardiac cycle and on a diastolic phase at 90% (Csobay-Novák, Fontanini and Szilágyi). Positions along the centerline were identical in both phases. Twenty-four measurements were accomplished on each patient resulting in a total of 744 regarding pulsatility (Figure 1).

Absolute pulsatility is defined as the difference between systolic and diastolic effective diameters (EDs) of the vessel (mm; ED_sys – ED_dia). Relative pulsatility (%) is defined as the ratio of absolute pulsatility and diastolic ED [(ED_sys – ED_dia) / ED_dia].

Expansion rate assessment of the AAAs was conducted on the patients’ CTA studies performed independently from our research, including primary diagnostic and follow-up studies for AAA surveillance. Aneurysm diameter measurements were performed by a board-certified radiologist experienced in cardiovascular imaging (D.M.F.).

Statistical Analysis

Continuous variables are expressed as mean±SD or median with interquartile ranges, and categorical variables are expressed as numbers and percentages. Normality of continuous parameters was tested with Kolmogorov-Smirnov test. Paired t-test was performed to compare systolic and diastolic measurements. Absolute and relative pulsatility values along the aorta were compared using 1-way, repeated-measure analysis of variances (ANOVA). Pearson correlation was performed to assess correlation between different continuous variables. A 2-sided p<0.05 was considered to be significant in all analyses. SPSS (IBM, Armonk, NY, USA version 27.0) was used for all calculations.

Results

A total of 806 measurements on 31 patients (25 men, median age 73 years) were performed for pulsatility evaluation and growth rate assessment. Patient demographics are displayed in Table 1.

Table 1.

Demographic Data.

Patient characteristics	N=31
Age, years	73 (70–77)
Male sex	25 (80.6)
Body mass index (kg/m²)	26.9 (24.7–29.8)
Actively smoking	9 (29.0)
Any smoking history	27 (87.1)
Hypertension	28 (90.3)
Hypercholesterolemia	24 (77.4)
Diabetes mellitus	8 (25.8)
Chronic obstructive pulmonary disease (COPD)	17 (54.8)
Coronary artery disease	22 (30.1)
Peripheral artery disease	8 (25.8)
Chronic kidney disease	13 (41.9)
History of malignancy	5 (16.1)

Continuous data are presented as median (interquartile range); categorical data are number (%).

Maximal systolic diameters proved to be significantly higher than diastolic measurements in all positions: Z0: 34.82±2.96 mm versus 34.62±2.78 mm, Z3: 30.73±4.40 mm versus 30.31±3.27 mm, Z5: 28.53±2.97 mm versus 28.31±4.07 mm, Z6: 27.02±3.76 mm versus 27.00±3.22 mm, Z8: 23.97±4.61 mm versus 23.43±4.47 mm, Z9: 40.55±7.33 mm versus 39.90±7.33 mm, respectively, all p<0.001.

Average absolute and relative pulsatility values were calculated from the dual measurements. Absolute pulsatility values did not differ significantly between the measured positions; their mean values were as follows: Z0: 0.7±0.8 mm, Z3: 1.0±0.6 mm, Z5: 1.0±0.6 mm, Z6: 0.8±0.7 mm, Z8: 0.7±1.0 mm, Z9: 0.9±0.9 mm, p=0.62 (Figure 2).

Although relative pulsatility values displayed a tendency of decreasing along the descending and abdominal aorta, their difference along the aorta was not significant. The calculated values were Z0: 2.3%±2.3%, Z3: 3.6%±2.1%, Z5: 3.6%±2.5%, Z6: 3.2%±2.5%, Z8: 2.9%±4.4%, Z9: 2.2%±2.2%, p=0.18 (Figure 3). Both absolute and relative pulsatility of the aorta reached its maximum at Z3 (1.0 mm, 3.6%).

In the process of aneurysm growth rate evaluation, maximum diameters of the AAA were registered on the baseline and latest preoperative follow-up images. The mean time elapsed between the 2 examinations was 5.5±2.2 years. During the time of follow-up, the maximum diameter of the aneurysm showed growth in every patient. The mean absolute diameter of the aneurysms has changed from 41.6±7.3 mm to 52.8±11.3 mm during the examined time interval. The mean extent of aneurysm growth was 13.4±9.1 mm amid the observed period, equivalent to a mean yearly growth rate of 2.5±1.6 mm, assuming a constant growth rate. When assessing the correlation of absolute aortic pulsatility values in each position and the growth rate of the aneurysms, no significant associations were found: Z0: r=–0.30, p=0.90; Z3: r=0.15, p=0.50; Z5: r=0.19, p=0.39; Z6: r=0.06, p=0.81; Z8: r=0.09, p=0.69; Z9: r=0.14, p=0.54. Similar tendencies could be documented for relative pulsatility values: Z0: r=–0.02, p=0.90; Z3: r=0.18, p=0.42; Z5: r=0.20, p=0.38; Z6: r=0.05, p=0.81; Z8: r=0.08, p=0.72; Z9: r=0.17, p=0.46.

Discussion

In this study, systolic-diastolic differences of the aortic diameter were measured along the course of the vessel. Our results show that absolute aortic pulsatility is in a submillimetric range in most measuring points, thus relative pulsatility does not exceed 5% at any of the examined locations. The maximal extent of aortic pulsatility was detected at position Z3 on the proximal third of descending aorta. Furthermore, the study’s results did not show correlation between pulsatile changes of the aortic diameter and the growth rate of the observed aneurysms.

Parodi et al¹⁴ found that there was a significant difference between systolic and diastolic diameters on multiple points of the descending aorta, thus suggesting the use of systolic CTA images for stent graft sizing. Theoretically, planning based on diastolic images of the aorta could lead to undersizing of the stent grafts, which may pose the risk of complications such as type Ia endoleaks or distal migration.¹⁵ This is particularly important as diastolic phase images are routinely used for preoperative EVAR and TEVAR planning, being less compromised by motion artifacts.¹⁶

Our previous studies showed that pulsatility is significant neither in an elderly patient cohort with no relevant aortic disease nor in the thoracic aortic segment of younger patients.^12,13 The analyzed elderly cohort did not suffer from AAA; however, with a median age of 74 years, it was heavily affected with aortic wall atherosclerosis. Aortic pulsatility was not clinically considerable in this population, with the highest value in Z3.¹²

As our previous study suggested that younger individuals might have a higher risk of a potential undersize, our following research targeted a younger population. This study resulted in elevated aortic strain compared with the elderly atherosclerotic population; however, the extent of pulsatility on the descending aorta was also not relevant regarding TEVAR sizing.

Comparing our current results with our previously reported findings, patients treated with AAA show similarly low aortic pulsatility to the non-aneurysmatic population, rarely exceeding 1 mm. It is important to note that the highest absolute and relative pulsatility was measured in Z3 in both aneurysmatic and non-aneurysmatic patients.^12,13 This implies that pulsatile changes of the ascending aorta are lower than the values registered on the proximal descending aorta; thus, the regular endograft oversizing should not be further increased with a Z0 proximal fixation zone.^15,17 This is becoming increasingly important as the endovascular repair of the aortic arch is getting widely accepted and available. There is a slight difference between the approach of the 2 major manufacturers of such branched devices regarding the sizing for the proximal landing zone, with Terumo Aortic recommending a somewhat heavier oversize (15%–20%) in Z0 compared with other aortic segments, while Cook Medical generally recommends the same degree of oversize (15%–20%) throughout the aorta (Niewijk E., Trompler J., written personal communication, 6.12.2021). It is also worth mentioning that the dilated portion of the aorta did not show any relevant changes compared with other segments.

Prediction of AAA growth is a profoundly researched subject, mostly due to the well-established connection between the maximum aneurysm diameter and the odds ratio for rupture, which is a life-threatening complication of AAAs.^3,6,18–21 Knowing the significance of this matter, we attempted to reveal correspondence between aortic pulsatility measurable on consequent follow-up CTA studies and the expansion rate of the aneurysms. Although every patient’s AAA showed growth during the examined follow-up period, no statistically significant association was found between aortic pulsatility values and the growth rate of an aneurysm.

Study Limitations

Although CTA is the preferred imaging modality for preoperative assessment of the aorta in patients treated for AAA, direct visualization of the vessel wall itself can be oftentimes limited on CT images. Hence, in the absence of landmarks such as atherosclerotic or thrombotic changes, the contour of the contrast agent-filled lumen is the only measurable boundary between the aorta and adjacent tissues, therefore identification of the exact location along the aorta to measure the diameter in the same position in 2 phases within an R-R′ cycle can be challenging. However, the spatial (0.625 mm) and temporal (0.270 seconds) resolution of the used CT equipment ensures that 2 images in identical table positions in different phases are more than likely to represent the same spot along the centerline. Moreover, the aforementioned Lin analysis of interobserver and intraobserver variabilities has proven the reliability of the method adopted for image evaluation.

It is also worth mentioning that the relatively small cohort on which this retrospective study was conducted gives room for further investigations on the subject involving a larger number of patients.

Conclusion

This study demonstrates that aortic pulsatility in patients with aortic disease usually does not exceed 1 mm, with a resulting relative pulsatility value below 5%. This implies that the regularly used 10%–20% oversizing in EVAR planning may be sufficient and a possible application of systolic instead of diastolic phase images for stent graft sizing is most likely unnecessary. As pulsatility is the highest on the descending aorta, further increase in oversize for a Z0 landing zone may be questionable.

Aortic pulsatility does not appear to correlate with long-term growth rate of aneurysms; consequently, this parameter is not likely to become a predictor of AAA expansion.

Footnotes

Acknowledgements

The author would like to thank Eric Niewijk from Terumo Aortic and Jürgen Trompler from Cook Medical for their help regarding this manuscript.

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Csaba Csobay-Novák—training, consultation, and proctoring for W. L. Gore & Associates, Cook Medical, Terumo Aortic, and Medtronic. Other authors have no competing interests.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Project no. NVKP_16-1–2016-0017 (“National Heart Program”) has been implemented with the support provided from the National Research, Development and Innovation Fund of Hungary, financed under the NVKP_16 funding scheme. The research was financed by the Thematic Excellence Programme (2020-4.1.1.-TKP2020) of the Ministry for Innovation and Technology in Hungary, within the framework of the Therapeutic Development and Bioimaging thematic programmes of the Semmelweis University.

ORCID iDs

Daniele Mariastefano Fontanini

Csaba Csobay-Novák

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