An apparatus for the injection of therapeutic and other agents at a target site within a patient's body. A catheter including a first elongated shaft having a distal end and a proximal end and a lumen extending therebetween. The catheter also including a second elongated shaft slidingly disposed in the first elongated shaft, the second elongated shaft having a distal end and a proximal and a lumen extending therebetween. The catheter further including a third elongated shaft disposed in and attached to the second elongate shaft, the third elongated shaft to move in a one-to-one relationship with the first elongated shaft and the second elongated shaft to maintain a predetermined needle deployment length as each are subjected to various bend configurations.