The underdilation of nitinol stents at TIPS implantation: Solution or illusion?

PURPOSE: This study investigates the behaviour of self-expanding nitinol stents at the time of TIPS-implantation and thereafter.

METHODS: Hundred consecutive patients with cirrhosis receiving a TIPS revision were included. The smallest stent diameter was measured radiologically immediately after implantation and before shunt revision. Accuracy of the measurement was assessed by comparing the nominal stent diameter with the largest stent diameter measured at the time of revision.

RESULTS: Pearson correlation between largest measured and nominal diameters was excellent (r=0.952, p<0.001) showing that measurements are accurate. At TIPS implantation all stents were markedly underdilated reaching only 76-92% of their nominal diameter. Smallest measured diameters were similar (8mm) irrespective of the nominal diameter (8, 9, 10mm) of the stent. In addition, smallest diameters of 10mm stents were similar irrespective whether 8, 9 or 10mm balloons were used. During a mean follow-up of 12.7±17.8months (median 3 months, range 1-81) stents expanded by 0.5-1.6mm dependent on the nominal stent size (8, 9, 10mm) and the grade of primary underdilation. No significant difference was found between Viatorr and bare stents.

CONCLUSIONS: At TIPS-implantation, the compliance of the surrounding tissue predominantly determines the stent diameter. The nominal size of the stent or the dilatation balloon has little influence. Accurate adjustment of a desired pressure gradient is, therefore, not possible. During follow-up, stents expand towards their nominal diameter questioning the usefulness of underdilation.