A variably expanding balloon catheter comprises a sequentially stepped outer shell when fully inflated, such as three sequentially increasing steps followed by three sequentially decreasing steps. For example, a balloon catheter comprises a sequentially stepped outer shell, when fully inflated, such that a first section of the outer shell is constrained to a first diameter by the sequentially stepped outer shell, and a second section, adjacent to the first section and attached to the first section by a step transition. The step transition provides a discontinuous change in diameter from the first diameter to the second diameter along a length of the balloon catheter, which may be abrupt.