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Letter by Dérimay et al regarding the article: “Coronary bifurcation bench test using multimodality imaging: Impact of stent strut link location on stent deformity and jailed side‐branch orifices during reproximal optimizing technique” by Kume et al

To the Editor: We read with great interest the experimental study by Kume et al., comparing the mechanical effects of the provisional stenting technique: re-POT sequence, according to the presence of a stent link at the side branch ostium. After analysis of four samples of stents (n = 24), authors concluded that the presence of a link at the ostium was not associated with a difference in term of elliptical deformation, global apposition and side branch obstruction. However, we think these conclusions should be taken with care. Indeed in this bench study, authors did not respect the physiological bifurcation geometry (HK-model) using a nonfractal bench (same diameter in proximal and distal part of the main axis). In this bench model, considering a main branch at 3.5 mm and a side branch at 2.5 mm, the mother vessel expected is 4.1 mm (vs. 3.5 mm). Authors recognized this limitation and so they limited there conclusions just to “the left main trunk with smaller diameters and non-left main trunk.” However, a physiological stepwise between proximal and distal diameter is present in all bifurcations. According to the Finet's law, the expected stepwise is greater than 0.5 mm in 90% of the bifurcations. So the difference of diameters between mother vessel and main branch needs to be taking into account systematically during the bifurcation revascularization, left main or not, and justify a specific proximal dilatation: the initial POT. As demonstrated by Finet et al., initial POT significantly decreased the proximal malapposition (expected by the fractal geometry) and also improved the SB ostium. In case of nonfractal bench, like in this study, initial POT cannot bring the maximum of benefits especially in the SB (key point of the analysis here). Indeed, in fractal bench after postdilatation by initial POT, the stent design will be optimize at the SB ostium by decreasing of the metallic obstruction and an increase of the distal cell usually preferred for the rewiring. In these conditions, it seems difficult in a nonfractal bench to analyze the potential impact of the link presence at the ostium. Moreover, in this study, the authors used exclusively noncompliant (NC) balloons for the POTs. Compliant or NC balloons are recommended for the POT by the European Bifurcation Club. However, during the POT, the objective is just to post dilate the stent greater than the mother vessel target diameter (stent artery ratio > 1). According to the mechanical properties of the balloon, the variation of diameters at increasing pressure is lower with a NC balloon than with a compliant one. So to use a NC balloon exposes to a higher risk of malapposition rate. In this study, the global malapposition rate after POTs was largely higher than in previous experimental or clinical studies (10% vs. 2% and 3%, respectively). These residual malappositions, clearly shown in Figure 5, were expected because a NC balloon 3.5 mm cannot reach 3.65 mm (the target). The manufacturer curves are realized in hot water without taking into account the stent resistance or the balloon friction force. Thus, in our opinion, it is difficult to conclude about the impact or not of the presence of a link at the ostium on the final mechanical result after re-POT sequence from a nonphysiological fractal bench and a suboptimal POT. It seems necessary to perfectly respect the physiology of the bifurcation to be closer of the in vivo condition. We look forward to reading Dr. Kume's response to the above.