Alto Deployment in Patients With Severe Tortuosity of the Proximal Aorta: An In Vitro Study

The Alto stent graft system accommodates various anatomies but presents unique challenges. In Japan, polymer filling failures occurred in 1.1% of cases, prompting an investigation into potential causes. It was hypothesised that polymer port location and proximal neck angulation contribute to these failures. The Alto device limits the suprarenal angle to <60° but does not specify the infrarenal neck angle. Because a 90° infrarenal angle is off label for many devices, the infrarenal angle was set at 90° for this study. The aim of this study was to identify the optimal port position for severe proximal aortic tortuosity and to determine the appropriate timing for stiff guidewire withdrawal.

An in vitro experimental system was set up using an artificial blood vessel bent at an aortic angle of approximately 90°, immersed in a warm bath (physiological saline at 36°C). Using this system, device outcomes were evaluated on the basis of the presence or absence of a guidewire and the placement position of the polymer port (greater curvature or lesser curvature) under fluoroscopy, performing one evaluation per experiment across a total of six patterns. When the polymer port was on the lesser curvature without a guidewire and nose cone facing downwards, the primary seal ring was incompletely filled, indicating minimal polymer injection. When the polymer was on the greater curvature without a guidewire and nose cone facing downwards, the polymer reached the primary seal ring but not the contralateral limb. However, port placement at the greater curvature with a guidewire allowed the polymer to reach the contralateral limb.

For the Alto system, aligning the polymer port with the greater curvature of the proximal aortic neck and straightening the aorta with an extra stiff guidewire in cases of severe tortuosity (approximately 90°) are key to ensuring complete polymer filling and preventing failure.