Extravascular implant tools that utilize a bore-in mechanism to safely access extravascular locations and implant techniques utilizing these tools are described. The bore-in mechanism may include a handle and a helix extending from the handle. The bore-in mechanism is used, for example, in conjunction with a tunneling tool to traverse the diaphragmatic attachments to access a substernal location. The tunneling tool may be an open channel tunneling tool or a conventional tunneling tool (e.g., metal rod).