Commentary: DynaCT and Its Use in Patients with Ruptured Abdominal Aortic Aneurysm

DynaCT is an on-table angiographic computed tomography (CT) modality that is able to acquire cross-sectional images similar to CT angiography (CTA). DynaCT can therefore be used instead of completion angiography after endovascular aneurysm repair (EVAR) to possibly detect complications that are missed by uniplanar angiography. Moreover, as Nordon et al. ¹ describe in this issue of the Journal, there might be a role for DynaCT in acquiring images that can be used for the evaluation of a patient's anatomy, thereby assessing his or her suitability for EVAR.

DynaCT could in that way be of particular use to patients with a ruptured abdominal aortic aneurysm (AAA) and, especially, hemodynamically unstable patients. EVAR decreases the mortality rate of patients with ruptured aneurysms compared to open repair. ² The problem with EVAR in the acute setting, however, is the need for preoperative cross-sectional images. The acquisition of CTA images, which are generally used, is time-consuming, and requires patients to be transferred, which might possibly reduce their survival rate.

DynaCT allows the acquisition of crosssectional images in a hybrid operating theatre, thereby preventing unnecessary patient transfers. The decision to perform an EVAR or an open aneurysm repair could thus possibly be made in the operating room. Whether

DynaCT is of actual benefit, however, depends on its ability to acquire satisfactory images that allow for adequate investigation of the patient's anatomy. Moreover, the images should permit reliable diameter and length measurements before stent-graft sizing can be performed based on these images.

The study by Nordon et al., ¹ as well an earlier study by Eide et al., ³ showed that DynaCT can be used to reliably perform diameter measurements. Nevertheless, Dyna-CT has some drawbacks.

First, DynaCT has a lower resolution than CTA, and the image quality of CTA is considerably higher. This lower resolution might be especially problematic in patients with a ruptured AAA, the very patients who would probably benefit most from preoperative on-table cross-sectional imaging.

Second, DynaCT has a field of view of only 30×25 cm. This is, as is shown in the Nordon study, inadequate to simultaneously visualize all vessels that are important for EVAR. Moreover, patients requiring emergent therapy for pathology of larger volume or length, such as thoracic or thoracoabdominal aneurysms or thoracic dissections, cannot be assessed by DynaCT.

Third, the DynaCT image underestimates aortic diameters, which in the dynamic aortic environment might lead to stent-graft sealing and fixation-related problems. ⁴ Nevertheless, it is possible that these perioperative measurements of aortic diameters are accurate. A lower blood pressure, induced by anesthesia, possibly results in lower aortic diameters. This process, although magnified, has been reported in patients with hypovolemic shock. ⁵

Fourth, DynaCT underscores the calcification of vessels. Severely calcified access vessels may be hard to pass with the delivery system, and calcification of the proximal aneurysm neck influences the possibility, success, and durability of EVAR. Inadequate assessment of calcifications can therefore be harmful.

Fifth, in a considerable number of cases, inadequate information on anatomy was obtained. That would be disastrous for EVAR planning in acute cases, and these patients would have only the option of open repair left. Considering that a significant portion of the patients with a ruptured AAA may be considered “fit for EVAR” but “unfit for open repair,” this would introduce a new (ethical) problem as the patient is already in theatre, possibly already under general anesthesia, when this essential information becomes available.

Nevertheless, and despite these drawbacks, we believe the findings of Nordon and colleagues ¹ are important. We agree that DynaCT can indeed become useful in the acute care of AAA patients. Certainly, the DynaCT system continues to evolve, and the time consumed in acquiring the reconstructions is decreasing steadily. DynaCT has already shown its use as a completion imaging modality after EVAR. Moreover, diameter measurements with the DynaCT have now been proven to be reliable.

In conclusion, we believe that DynaCT is a very promising technique that will likely become available for many centers in the near future. It will allow the acquisition of cross-sectional images of ruptured AAAs with only minimal time delay in the future. By doing this, DynaCT might eventually decrease mortality rates for patients with ruptured AAA. Future results of DynaCT are therefore awaited with much interest.