Intravascular guidewire and microcatheter system

An intravascular system, comprising:

• a catheter device:
• wherein the catheter device is configured for navigation through a vessel that comprises one or more curves with a radius of curvature of 10 mm or less, wherein a ratio of an inner diameter of the vessel to an outer diameter of the catheter device, for at least a portion of the vessel, is about 300% to about 800%;
• wherein the catheter device comprises an inner shaft that includes a plurality of gaps formed in the inner shaft the inner shaft including a bending stiffness profile with a bending stiffness slope defined by a change in bending stiffness over a length of the catheter device;
• wherein the catheter device comprises an outer member that includes a transition section where a first polymer transitions to a second polymer of different hardness;
• and
• wherein the inner shaft comprises a length that crosses the transition section, and wherein a size and/or spacing of the plurality of gaps are configured so that the bending stiffness slope of the inner shaft at the length that crosses the transition section is less steep than the bending stiffness slopes proximal and distal of the length that crosses the transition section;
• and
• a guidewire device configured for navigation through the vessel,
• wherein the catheter device and the guidewire device are configured to enable the catheter device to advance over the guidewire device in response to a push force of 50 g or less applied to the catheter device.