A sheath assembly includes a first sheath, a second sheath, and an attachment mechanism. The first sheath includes a first sheath inner surface defining a first sheath lumen extending along a first sheath central longitudinal axis between a first sheath first end portion and a first sheath second end portion. The second sheath includes a second sheath inner surface defining a second sheath lumen extending along a second sheath longitudinal axis between a second sheath first end portion and a second sheath second end portion. The attachment mechanism couples the second sheath to the first sheath. The attachment mechanism includes an attachment mechanism step-up dilation. At least a portion of the attachment mechanism is asymmetrical, at the attachment mechanism step-up dilation, about the first sheath central longitudinal axis.