Review for 10.1186/s12876-021-01689-6 (2021)

Reviewer’s report
Title: 
Utility and safety of a new uneven double-lumen sphincterotome in cases
of difficult biliary cannulation
Version: 
0 
Date: 
03 Sep 2020
Reviewer's report:
With great interest studied the new advancement in ERCP field in your study.
Very few published reports exist of usage of uneven cannula(PIOLAX in
Billroth anatomy, Haber RAMP catheter for intrahepatic duct cannulation).
Uneven sphincterotome (magictome) in your study may be a first report. Here
are the comments 
1. The main aim of various evolving instruments and techniques is to achieve
successful biliary cannulation(utility) which is the rate limiting step and thereby
reduce the complications such as pancreatitis(safety). In the present study,
authors failed to show any significant difference in cannulation success or
occurrence of PEP between the new instrument and conventional catheter.
2. It is a retrospective study with difference in time zone between groups (2013-
2018 vs 2018 -2020). With passage of time, there will be improvement in the
expertise of ERCPist and technician, refinement of instruments, emergence of
new definitions {difficult cannulation (5min,5 attempts)} and new data [PEP
prevention techniques(rectal indomethacin, PDstenting)]. It would be always
pertinent to include cases and controls in the same time zone to reduce these
biases.
3. There is enough evidence to show that cannulation with sphincterotome is
better than the catheter(cannula). Worldwide practices have been changed to
sphincterotome first approach except in selected situations where catheter is
used. Present study compared new kind of sphincterotome with conventional
catheter. It would have been fitting if comparision is between regular
sphincterotome and magictome in terms of cannulation success and cannulation
time. This would have made it possible to take up repeated studies on same
parameters.
4. Risk factors for PEP include more than one guidewire passage. In the present
study, another guidewire is passed which comes out of magictome at an
angle(not aligned to MPD axis) into the pancreatic duct which may significantly
increase PEP risk.
5. In recent Cochrane systemic review , it was shown that no improvement in
successful cannulation with double guidewire technique but there is increased
rate in PEP. Measure taken to prevent PEP in controls and cases have not been
discussed by the authors. 
6. Papillary edema with meddling of papilla has been mentioned by the authors
in the study as contributing to PEP. Even with shorter time, angulating the
magictome with it being fixed by pancreatic guidewire near ampulla did not
reduce PEP. PD stenting is one of the most studied measure in PEP prevention.
PD stent placement is left to the discretion of endoscopist and very few patients
received PD stenting.
7. In the present study, only significant difference authors found was the shorter
time of total biliary cannulation and shortened time from PD to CBD
cannulation. The minimum total biliary cannulation time by magictome was 6.5
min (>5min), which may explain the non reduction of PEP. More number of
guidewire passages or deep guidewire passage without loop into MPD have been
identified as risk factors for PEP and not indwelling time of pancreatic guidewire
as mentioned by the authors.
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