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Patient selection: Insights from the
Patient selection: Insights from the PROTAGORAS 2.0 study regarding adequate preoperative sizing and planning
Stefano Fazzini highlights key findings of the recently-published PROTAGORAS 2.0 study, concluding “aortic stent graft oversizing should be considered the most important parameter for optimal ChEVAR [chimney endovascular aneurysm repair] planning”.
RECENTLY, THE CHEVAR
procedure was included in the European Society for Vascular Surgery (ESVS) 2019 guidelines for the treatment of juxtarenal abdominal aortic aneurysms (jAAA), as an alternative to fenestrated EVAR (FEVAR) in urgent settings and/or hostile anatomies (e.g. angulated aortic neck, narrow and calcified iliac access).
Despite the tremendous evolution of ChEVAR in the last decade, in terms of important publications (such as PERICLES and PROTAGORAS) and worldwide spread, the gutter-related endoleak (type Ia endoleak) is still considered the Achilles’ heel of the technique by many authors.
One of the reasons for this perception is the concerning results comparing ChEVAR with FEVAR, showing that the former has a higher rate of late type Ia endoleak. Some authors have suggested that new research should focus on improvements in the preoperative planning, in order to avoid significant divergent experiences with this approach.
As a bailout and not-standardised procedure, ChEVAR cannot be compared with FEVAR in terms of preoperative planning, because many challenging anatomical aspects must be taken into account with ChEVAR.
At the same time, physicians performing ChEVAR should be dealing with urgent cases and hostile anatomies.
The new era of the ChEVAR technique, named ‘standardisation’, could be realised by easy/customised planning and an ideal chimney–graft combination.
Most of the published data have been evaluated by in vitro experiences focusing on gutter-related endoleaks and chimney graft compression, which is supposed to influence flow profile and may induce a risk of stent thrombosis.
To overcome the technical bias of in vitro studies (silicon models with one standard chimney graft morphology), we decided to analyse a homogeneous cohort of patients with single/double chimney grafts involving only one device combination: the Medtronic Endurant stent graft combined with a balloon-expandable stent graft (Advanta V12, Getinge). This choice allowed us to evaluate many challenging anatomies, such as a hostile neck (reverse tapered, angulated) and access (narrowed and calcified).
We performed a computed tomography angiography (CTA)-based evaluation of a 10-year Münster experience with ChEVAR. With PROTAGORAS 2.0 (European Journal of Vascular and Endovascular
Surgery, article in press) for the first time, a single parallel graft combination was evaluated using late outcomes and CTA-based pre/postoperative imaging in order to identify significant predictors to optimise sizing and prevent persistent type Ia endoleaks and chimney grafts stenosis/ occlusion.
A recommended new range for main graft sizing, a new composite parameter (L-OS), and the concept of lost neck are the main elements of novelty for ChEVAR planning.
A central finding of this study was that a main graft oversizing between 30 and 40% (Figure 1) was significantly associated with a freedom from type Ia endoleak-related reintervention, without compromising primary chimney graft patency. Wide necks (>29mm) were significantly related to type Ia endoleaks having a mean oversizing of less than 20%; inversely, narrow diameters (<20mm) were significantly related to chimney graft stenosis/occlusion caused by excessive oversizing of more than 50%.
The mean diameter of sealing zone (three aortic cross-sections of total neck length) should be taken into consideration in order to select the aortic stent graft diameter (Figure 2). In contrast to the actual recommendations of 20–30%, the optimal main graft oversizing seems to be higher, at around 30%. In fact, oversizing of at least 30–35% should be used for single and double chimneys, respectively. Stefano Fazzini The turbulence of blood flow at the level of the gutters should induce a spontaneous resolution of flow, proportional to the length and inversely proportional to the gutter area. Despite this general belief, a total neck length >20mm could not guarantee the sealing of early and late endoleaks in this study, if the oversizing was not adequate.
In the present analysis, oversizing was the only significant independent parameter to prevent late type Ia endoleak. The presence of infrarenal neck was the only factor preventing type Ia endoleaks; in the case of no infrarenal neck, an oversizing of more than 35% would be needed to minimise the risk of persistent gutters.
Another novelty of our research was the presentation of a new composite parameter (L-OS: total neck length [mm] + oversizing [%]) in order to reflect more accurately the successful preoperative planning. It could be a useful tool for uncertain cases (the choice of stent graft sizing leading to a wide gap of oversizing, e.g. 32/36mm resulting in 23/38% oversizing for a neck diameter of 26mm) to find a compromise between a short neck and aggressive oversizing, single or double chimney grafts. An L-OS range of 55–65 was significantly related to freedom from persistent type Ia endoleak and primary chimney graft patency.
Considering that we treated 86% of hostile necks, the higher ranges (OS>35 and L-OS>60) could be indicated for double
Figure 1. Key parameters for sizing of ChEVAR procedures with single/double chimney grafts.
Figure 2. Aortic neck diameter is measured as the mean of three aortic cross-sections of the sealing zone (proximal, middle, distal segment). chimney grafts and hostile parameters as pararenal neck or infrarenal angulation >60 degrees (Figure 3).
An additional finding of the current study was the estimation of the lost neck, considering that the ideal and available total neck length is not always achieved; even in the case of very precise deployment, some amount of neck (mean of 3mm) could be lost during the procedure, caused by the presence of the sheaths in place and/or very angulated anatomy.
Finally, the association between these two devices, the most used in the published literature, seems to result in optimal clinical outcomes, combining the flexibility of Endurant stent grafts and high patency rate of Advanta V12. Our imaging-based analysis confirm the benefit of the high conformability at the level of the transition zone between the aortic neck and the proximal portion of the aneurysm, thanks to short M-shaped stents of Endurant stent grafts.
Our experience suggests that aortic stent graft oversizing should be considered the most important parameter for optimal ChEVAR planning. The total neck length seems not effective to guarantee the sealing without an adequate oversizing. In conclusion, as far as the usage of the Endurant stent graft and Advanta V12 is concerned, we advise an oversizing of 30–40% to avoid persistent type Ia endoleaks and likewise to ensure chimney graft patency. In case of double chimney grafts and/or hostile neck features, greater degrees of oversizing should be planned. A 20–25mm total neck length should be suggested considering the amount of lost neck, higher in angulated anatomies. The pararenal and wide necks seem to be the main risk factors for endoleaks.
Stefano Fazzini is a researcher and vascular surgeon in the Department of Vascular and Endovascular Surgery at “Tor Vergata” University of Rome in Rome, Italy.
Figure 3. The easy customisation for ChEVAR sizing. The main hostile neck parameters are considered pararenal, angulated (>60°), hostile shape (reverse tapered), and calcified (>50%) neck.
