A catheter introducer system is provided with a catheter sheath having a valve providing for a friction fit around a catheter. The friction fit is selectively adjustable to vary between a first configuration for longitudinal movement of the catheter through the valve and a second configuration for holding the catheter longitudinally in place. The valve may include a chuck to grip the catheter radially. The chuck may include an annular base and an opposed annular clamp, and a washer disposed between the base and the clamp. At least one of the base and the clamp may include a beveled surface that forces the washer radially inwardly as the base and the clamp are drawn together. The system also includes one or more dilators layered within the sheath. One or more of the dilators may include a preformed arcuate portion configured to access a targeted branched vessel. The layered dilators and sheaths are typically softer and more hydrophilic proceeding from the innermost dilator out to the sheath. The dilator may be reinforced by a wire embedded in the body of the dilator. The distal tip of the sheath may be stiffened by a ring affixed adjacent the distal end. The sheath may include in the innermost dilator a trocar formed of a flexible, hollow outer wire and an inner stiff needle, which can extend beyond the wire for piercing and be withdrawn to relax the wire for advancement of the dilator.La présente invention concerne un système dintroduction de cathéter qui comprend une gaine de cathéter comportant un interrupteur de flux servant à produire un ajustement serré autour dun cathéter. Lajustement serré est sélectivement réglable pour passer dune première configuration permettant le mouvement longitudinal du cathéter à travers linterrupteur de flux et une seconde configuration permettant de retenir le cathéter longitudinalement en place. Linterrupteur de flux peut comprendre un mandrin servant à saisir le cathéter de manière radiale. Le mandrin peut comprendre une base ann
