Premature dissolution of the Agile patency device: implications for capsule endoscopy

Abstract

Background: The main risk of capsule endoscopy is retention of the capsule behind a stricture. Passage of an intact Agile patency device (Medtronic, Dublin, Ireland) through the small bowel is widely used to ensure luminal patency, although capsule retention has occurred in patients who have had a reassuring patency study. The device is designed to remain intact for at least 30 hours postingestion, such that loss of signal from the radiofrequency identification tag contained within, or absence of the device on radiological imaging, implies unimpeded intestinal transit.

Aim: To identify the rate of premature dissolution (<30 hours postingestion) of the Agile patency device.

Methods: Outcomes of all consecutive patients having an Agile patency device were analysed.

Results: Premature dissolution of the patency device occurred in 5 of 307 patients, an incidence of 1.3%. This was recognised by the detection of a persistent radiofrequency signal after radiological imaging had failed to identify the patency device, prompting a careful search for the radiofrequency tag on the CT scout film. The tag was difficult to detect because of an oblique lie making it appear smaller than its 13×3 mm size and confusion with intra-abdominal or other metallic fragments.

Conclusions: In the absence of radiological evidence of an intact Agile patency device, premature dissolution should be suspected in patients registering a persistent radiofrequency signal and confirmed by identifying the radiofrequency identification tag. Failure to do so might result in false reassurance that capsule endoscopy could be performed without risk of retention.

Keywords: diagnostic and therapeutic endoscopy; endoscopy; small bowel disease; small bowel enteroscopy.

Figure 1

Agile patency device showing the wax timer plugs at either end and compressed lactose content.

Figure 2

CT imaging of an intact patency device (containing the visible radiofrequency tag) shown in the descending colon (arrow).

Figure 3

CT scout film showing three sterilisation clips and the radiofrequency tag (arrow) lying just to the right of the patient’s midline.

Figure 4

CT scout film following a repeat study on the patient shown in figure 3 showing the intact patency device (containing visible radiofrequency tag) in the descending colon (arrow), three sterilisation clips and a central circular radio-opaque object.

Figure 5

A lateral view taken during the same examination shown in figure 4 demonstrating the intact patency device (arrow) and in which it is evident that the central ring-like opacity seen in figure 4 is an umbilical piercing on the abdominal wall.

Figure 6

CT scout film showing the radiofrequency tag in the patient’s left upper quadrant (arrow), a cholecystectomy clip in the right upper quadrant and an intrauterine coil device in the pelvis.

Figure 7

CT imaging showing the radiofrequency tag in the descending colon (arrow), which is separate from residual barium from the patency device (also present but less obvious in the scout film taken of the same patient shown in figure 6).

Figure 8

Suggested protocol for ensuring a patent small bowel lumen using the Agile patency device. In the absence of a radiofrequency (RF) signal 30 hours postingestion, capsule endoscopy can be performed. Should the signal remain, a scout film will allow targeting of a limited CT scan through the device. If a colonic location is confirmed, capsule endoscopy can proceed but further imaging may be needed to confirm and define a stricture should the device remain in the small bowel. If the scout film fails to identify a patency device, the RF scan should be repeated and if negative, capsule endoscopy could proceed. If the RF signal remains, evidence of the RF tag should be sought, premature collapse of the device suspected and repeat study considered.