Did balloon catheter have superior efficacy to the basket catheter?

We read with great interest the recent article by Ishiwatari et al. [1]. The authors concluded that the balloon catheter is recommended as the first-line device in endoscopic treatment of patients with four or more bile duct stones. It is an interesting study. Nevertheless, several issues seem worthy of comment.

First, their study was a noninferiority trial, which is generally analyzed using both intention to treat (ITT) analysis and per protocol analysis [2]. Unfortunately, the approach used in their study was per protocol analysis, which revealed superiority of the balloon over the basket (P  = 0.037). However, there were no significant differences between the two groups by ITT analysis (P = 0.134). Although some might argue that ITT analysis is overly conservative, most would agree that a positive outcome of an ITT analysis in a superiority trial is convincing.

Second, the authors performed subgroup analysis for the possible factors affecting the technical difficulty of endoscopic retrograde cholangiopancreatography (ERCP). However many subgroup analyses are undertaken in a clinical trial, the chance of finding a false-positive result (Type I error) by random chance alone increases if the significance level or threshold is kept the same (traditionally a P value of 0.05). Unfortunately, the authors did not adjust the threshold of significance for subgroup analyses or use an interaction test [3] [4].

Finally, 35 % of procedures were performed by trainees, who may be more skilled with the balloon catheter than with the basket catheter. These could make the balloon catheter treatment effect appear stronger.

To summarize, this study suggests that complete endoscopic treatment with a single catheter is more likely when choosing a balloon catheter over a basket catheter for extraction of bile duct stones of ≤ 10 mm. Well-designed, unbiased prospective international studies based on a larger sample size are still needed. We believe that our remarks will contribute to more accurate elaboration of the results presented by Ishiwatari et al. [1].

^* These author contributed equally to this work.

• References

• 1 Ishiwatari H, Kawakami H, Hisai H. et al. Balloon catheter versus basket catheter for endoscopic bile duct stone extraction: a multicenter randomized trial. Endoscopy 2016; 48: 350-357
• 2 Jones B, Jarvis P, Lewis JA. et al. Trials to assess equivalence: the importance of rigorous methods. BMJ 1996; 313: 36-39
• 3 Assmann SF, Pocock SJ, Enos LE. et al. Subgroup analysis and other (mis)uses of baseline data in clinical trials. Lancet 2000; 355: 1064-1069
• 4 Yusuf S, Wittes J, Probstfield J. et al. Analysis and interpretation of treatment effects in subgroups of patients in randomized clinical trials. JAMA 1991; 266: 93-98