Fast Approximate Quantification of Endovascular Stent Graft Displacement Forces in the Bovine Aortic Arch Variant.

PURPOSE: Displacement forces (DFs) identify hostile landing zones for stent graft deployment in thoracic endovascular aortic repair (TEVAR). However, their use in TEVAR planning is hampered by the need for time-expensive computational fluid dynamics (CFD). We propose a novel fast-approximate computation of DFs merely exploiting aortic arch anatomy, as derived from the computed tomography (CT) and a measure of central aortic pressure. MATERIALS AND METHODS: We tested the fast-approximate approach against CFD gold-standard in 34 subjects with the "bovine" aortic arch variant. For each dataset, a 3-dimensional (3D) model of the aortic arch lumen was reconstructed from computed tomography angiography and CFD then employed to compute DFs within the aortic proximal landing zones. To quantify fast-approximate DFs, the wall shear stress contribution to the DF was neglected and blood pressure space-distribution was averaged on the entire aortic wall to reliably approximate the patient-specific central blood pressure. Also, DF values were normalized on the corresponding proximal landing zone area to obtain the equivalent surface traction (EST). RESULTS: Fast-approximate approach consistently reflected (r2=0.99, p<0.0001) the DF pattern obtained by CFD, with a -1.1% and 0.7° bias in DFs magnitude and orientation, respectively. The normalized EST progressively increased (p<0.0001) from zone 0 to zone 3 regardless of the type of arch, with proximal landing zone 3 showing significantly greater forces than zone 2 (p<0.0001). Upon DF normalization to the corresponding aortic surface, fast-approximate EST was decoupled in blood pressure and a dimensionless shape vector (S) reflecting aortic arch morphology. S showed a zone-specific pattern of orientation and proved a valid biomechanical blueprint of DF impact on the thoracic aortic wall. CONCLUSION: Requiring only a few seconds and quantifying clinically relevant biomechanical parameters of proximal landing zones for arch TEVAR, our method suits the real preoperative decision-making process. It paves the way toward analyzing large population of patients and hence to define threshold values for a future patient-specific preoperative TEVAR planning.

The Modified Arch Landing Areas Nomenclature (MALAN) Improves Prediction of Stent Graft Displacement Forces: Proof of Concept by Computational Fluid Dynamics Modelling.

OBJECTIVE: To assess whether the Modified Arch Landing Areas Nomenclature (MALAN), which merges Ishimaru's map with the Aortic Arch Classification, predicts the magnitude of displacement forces and their orientation in proximal landing zones for TEVAR. METHODS: Computational fluid dynamic (CFD) modelling was employed to prove the hypothesis. Healthy aorta CT angiography scans were selected based on aortic arch geometry to reflect Types I to III arches equally (each n = 5). CFDs were used to compute pulsatile displacement forces along the Ishimaru's landing zones in each aorta including their three dimensional orientation along the upward component and sideways component. Values were normalised to the corresponding aortic wall area to calculate equivalent surface traction (EST). RESULTS: In Types I and II arches, EST did not change across proximal landing zones (p = .297 and p = .054, respectively), whereas in Type III, EST increased towards more distal landing zones (p = .019). Comparison of EST between adjacent zones, however, showed that EST was greater in 3/II than in 2/II (p = .016), and in 3/III than in 2/III (p = .016). Notably, these differences were related to the upward component, that was four times greater in 3/II compared with 2/II (p < .001), and five times greater in 3/III compared with 2/III (p < .001). CONCLUSION: CFD modelling suggests that MALAN improves discrimination of expected displacement forces in proximal landing zones for TEVAR, which might influence clinical outcomes. The clinical relevance of the finding, however, remains to be validated in a dedicated post-operative outcome analysis of patients treated by TEVAR of the arch.

The Modified Arch Landing Areas Nomenclature predicts proximal endograft failure after thoracic endovascular aortic repair.

OBJECTIVES: Our goal was to assess the value of the Modified Arch Landing Areas Nomenclature (MALAN) for thoracic endovascular aortic repair (TEVAR), in which each landing area (LA) is identified by a proximal landing zone and the type of arch (e.g. 0/I), as predictors of postoperative proximal endograft performance. METHODS: A multicentre retrospective analysis was performed of patients treated with arch TEVAR (i.e. proximal landing zone 0-3) for various indications between 2007 and 2017. Patients were stratified by the MALAN classification into hostile LAs (i.e. 2/III and 3/III) and favourable LAs (i.e. 0/I-III, 1/I-III, 2/I-II and 3/I-II). Outcome criteria included composite proximal endograft failure (including type Ia endoleak, persistent false lumen perfusion at the level of the most proximal communication between the lumina in aortic dissections, endograft migration and retrograde dissection) and deaths from all causes. Competing risk analyses were performed. RESULTS: A total of 359 patients (hostile LAs 133; favourable LAs 226) were identified. The median age was 71.0 (62.0-77.0); 78.3% were men. Proximal endograft failure occurred in 28/133 patients (21.1%) in the hostile LA group and in 12/226 (5.3%) in the favourable LA group. On multivariate analysis, hostile LAs were independently associated with proximal endograft failure (P < 0.0001). There was no other independent risk factor. Favourable LAs were associated with an increased mortality rate (P = 0.006), which could be attributed to the proximal LA subgroup (i.e. 0/I-III and 1/I-III) (P < 0.0001), in addition to age (P < 0.0001). CONCLUSIONS: The MALAN classification identifies hostile proximal landing zones for TEVAR, namely 2/III and 3/III LAs, which are associated with dismal proximal endograft performance. The MALAN appears to be an intuitive and valuable tool to improve the preoperative decision-making process.

The Modified Arch Landing Areas Nomenclature identifies hostile zones for endograft deployment: a confirmatory biomechanical study in patients treated by thoracic endovascular aortic repair†.

OBJECTIVES: Our goal was to confirm whether the Modified Arch Landing Areas Nomenclature (MALAN) for thoracic endovascular aortic repair, in which each landing area is described by indicating both the proximal landing zone (PLZ) and the type of arch (e.g. 0/I), identifies unfavourable landing zones for endograft deployment in diseased aortas. METHODS: Preoperative computed tomography angiography scans of 10 patients scheduled for thoracic endovascular aortic repair for aneurysm or penetrating ulcer of the arch and with a potential hostile PLZ were reviewed. Five had proximal deployment planned in MALAN area 3/III and 5, in MALAN area 2/III. The angulation of each PLZ was calculated. Computational fluid dynamics modelling was used to compute magnitude and orientation of pulsatile displacement forces in each PLZ. Normalized values based on PLZ areas (i.e. equivalent surface traction) were calculated. Results were compared to those obtained in healthy controls stratified by the MALAN. RESULTS: Angulation was severe (>60°) in MALAN areas 3/III and 2/III, which was consistent with the findings obtained in healthy controls. Increased magnitude (P = 0.021) and unfavourable orientation (i.e. orthogonal to the longitudinal aortic axis) of equivalent surface traction (P = 0.011) was also found in these areas compared to the adjacent ones, following the same pattern seen in the controls. Adverse events related to proximal endograft performance were reported in 3/10 cases. CONCLUSIONS: This study confirms in diseased aortas initial proof-of-concept findings on the predictive value of the MALAN to identify landing areas with a geometric and haemodynamic environment hostile for thoracic endovascular aortic repair. These adverse biomechanical features may entail an increased risk of dismal endograft performance.