Real-time intraoperative functioning lumen imaging probe during endoscopic per-oral pyloromyotomy (pop)

Fourteen patients with gastroparesis underwent POP with FLIP during the study period. Median age was 41 (IQR 16–67). Gastroparesis etiology was as follows: diabetic gastroparesis (6), idiopathic (7), and post-surgical (1). The median pre-procedure GCSI score was 3.1 with bloating as the most prominent reported symptom. Median post-procedure GCSI score at one month was 2.2 which demonstrated clinical improvement. Mean GCSI score improved from 2.97 to 2.28 after POP at a mean follow-up of 1 month.

The median pre-POP pyloric diameter was 13.2 mm. On average, patients demonstrated a significant increase in pyloric diameter of 1.4 mm (p = 0.0012) from a mean diameter of 13.9 mm to 15.3 mm at the time of the POP procedure. The average distensibility index (DI) significantly increased by 2.9 mm²/mmHg, from 6.2 mm²/mmHg to 9.1 mm²/mmHg at the time of POP (p = 0.007) [Table 1]. Technical success for POP was achieved in 14/14 (100%) of patients. Technical success for FLIP procedure was achieved in 12/14 (86%), where post-POP measurements were unable to be obtained due to catheter malfunction. Mean operative time was 36 min and mean length of hospital stay was 0.7 days (0–3 days). There were no perioperative complications. Follow-up scintigraphic gastric emptying studies were available in five patients. Overall, 4 out of 5 patients (80%) had improvement in scintigraphic gastric emptying compared to preoperative assessments. One patient (20%) had worsening GES despite improvement in gastroparesis symptoms as measured by GCSI. The follow-up gastric emptying study results after the POP procedure demonstrated an improvement from 46.3% to 32.4% (p < 0.007) [Table 2] [15].

Prior to the use of FLIP, improvement in the pyloric diameter after POP was largely based on visual cues and the ease of passage of the endoscope through the pylorus after pyloromyotomy. Real-time measurements of distensibility and pressure using FLIP, as represented by a topographical image displayed during the procedure, give instant feedback to the endoscopist that can be used during the procedure to evaluate the extent of the pyloromyotomy and to make appropriate adjustments at that time.

The results from the present study support that FLIP is safe and feasible, and a significant improvement in pyloric diameter and distensibility was seen in patients who underwent POP for gastroparesis of varying etiologies. This is consistent with previously reported use of this technology following POP or pyloric botulinum toxin injection [16]. Patients also experienced significant improvements in both gastroparesis symptoms and objective gastric emptying times, although the cohort size was too small to evaluate the relationship between improvement in distensibility and GCSI/GES measurements. We used a standardized approach in measuring distensibility via FLIP, which was done immediately before and after pyloromyotomy. Using a non-standardized approach for FLIP measurements, which were taken intraoperatively and up to 3 months post POP, Vosoughi and colleagues were able to demonstrate a correlation between higher distensibility indices/cross-sectional areas and clinical success after POP in a study of patients with gastroparesis. Additionally, post-POP cross-sectional area was predictive of clinical improvement with a high specificity (91%) and reasonable sensitivity (71%) [1]. A case series of four patients with pre and post POP FLIP procedures showed increased cross-sectional area was associated with clinical response at 3 months [1]. Finally, these investigators demonstrated that immediate post-POP evaluation of cross-sectional area and distensibility index was a better predictor of clinical success compared to measurements at 3 months. Performing the FLIP data at 3 months is reasonable; however, it requires an additional endoscopic procedure which is not part of our standard practice. In addition to being a better predictor of clinical success, immediate post-POP measurements with FLIP allows for real-time evaluation of extent of myotomy such that further myotomy can be performed and outcomes immediately evaluated. This pilot study aimed to assess safety and efficacy of this technology but real-time use of the FLIP technology can be used in the future to guide further myotomy as appropriate. It is likely the delta change in values of diameter and DI will be more valuable than absolute values with a target of delta change > 2 or DI greater than 10 if technically possible.

Routine use of FLIP during POP could help to identify which patients may have the greatest clinical improvement based on their baseline pyloric measurements. Previous studies have demonstrated that higher pre-POP distensibility indices were associated with 1-year clinical success and improvement in abdominal pain [1, 17]. Routine use of FLIP may help to establish a goal range of improvement in pyloric distensibility, where measurements below this threshold could indicate a need to perform a more extensive pyloromyotomy. In at least one patient the results of the FLIP technology were used in real time to perform a more extensive myotomy which demonstrated noticeable change in the distensibility index. A change in the DI appears to be more valuable than the actual recorded value. The degree of improvement in distensibility may also predict clinical response, which warrants further study with larger cohorts. This may be the case, as low pyloric compliance has been shown to correlate with worse gastroparesis symptoms [11]. In our patient group, four out of five patients who had a follow-up gastric emptying scintigraphy demonstrated objective improvement in gastric emptying times which is consistent with previous studies demonstrating an improvement rate of 78.3% [15]. The ability to see measurements using the FLIP technology in real time and to understand the correlation to clinical outcomes will allow this technology to be used to ensure the adequacy of myotomy and to make appropriate changes at the time of the procedure.

There are several technical considerations regarding endoscopic placement of the FLIP catheter at the pylorus. First, the catheter relies on the communication of a series of electrodes which can be compromised by manipulation during the procedure. Post-POP FLIP measurements were not able to be obtained in two patients, likely due to disruption of the electrodes that occurred during placement into the stomach. Additionally, the catheter tends to lose tensile strength with manipulation, making positioning more difficult during post-POP measurements. This challenge was mitigated by eventually switching to a therapeutic videogastroscope with a 6 mm working channel to reduce manual manipulation of the catheter. Alternatively, if this is not available, a raptor forceps may be used to drag the catheter alongside the scope into the duodenum but this is more technically challenging and causes greater catheter manipulation. Second, the device employs a balloon at the tip of the catheter with a preselected volume of 40 mL, which is thought to be optimal for the pylorus [18]. The pylorus can be quite narrow in some gastroparesis patients and inflating the balloon within the pyloric channel appeared to dilate the muscle in some cases, leaving a visibly larger channel when the balloon was removed. The pre-POP diameter and distensibility may be underestimated if the balloon is causing a degree of pyloric dilation or relaxation, and attempts at using a smaller volume of 30 cc did not produce similar quality topographic images of the pylorus [19]. Additionally, there is a theoretical risk of pyloric trauma which may obscure tissue planes making POP more challenging, although we did not experience this in our series. Ultimately, the risk of catheter malfunction is a real possibility. To mitigate this risk one may first trial the technology on a model or use it while supervised by a proctor or company representative. We identified a learning curve that improved considerably after five uses of the catheter. We recommend using the technology at least 5 times to lessen the learning curve and consider being proctored with initial uses. Additionally, it is preferable to use a therapeutic endoscope which will allow passage of the FLIP catheter directly through the channel into the duodenum. If this is unavailable, a raptor grasper may be used but requires grabbing the tip of the catheter and dragging it alongside the endoscope into the duodenum. In our experience this was more likely to cause catheter malfunction than with the therapeutic endoscope. Also, we recommend obtaining the FLIP measurements prior to placing clips which may cause damage to the balloon on the catheter.

There are several limitations to this study. First, the study was conducted at a single, tertiary care institution with very high volume of POP procedures, which may limit generalizability. Second, data were gathered prospectively although the analysis was completed retrospectively. Lastly, the small sample size resulted in lack of statistical power to perform an in-depth analysis of subgroups of gastroparesis, including comparisons of improvement in pyloric distensibility with improvements seen in GCSI scores and gastric emptying. Additionally, gastroparesis patients may use different medications to help with symptomatic relief including but not limited to anti-emetics and pro-motility agents. The use of these medications prior to and after the POP procedure has been shown to decrease demonstrating symptomatic release in previously published studies; however, the use of these medications was not tracked in this study evaluating EndoFLIP at the time of POP but would be beneficial to evaluate in future studies. Despite these limitations, this series described a real-time intraoperative FLIP protocol to evaluate improvements in pyloric diameter and distention in patients undergoing POP.

FLIP is a novel technology that may be used to provide objective measures of pyloric physiology in real time before and after POP. Data from our study suggest improvements in pyloric distensibility occur immediately after POP. Larger studies with long-term follow-up are needed to elucidate correlations between an increase in pyloric diameter/distensibility and the improvement in symptoms and gastric emptying times. Such data may be used in real time to ensure adequate pyloromyotomy and to predict the response to POP in patients with medically refractory gastroparesis.