Active fixation lead with a dual-pitch, free spinning compound screw

摘要

An active fixation lead assembly including a dual-pitch screw mechanism and a free spinning mechanism, which provides an improved capability for firmly engaging a lead tip upon heart tissue while avoiding damage to the tissue due to overtorquing of the lead. The dual-pitch screw mechanism employs an extendable coupling screw, firmly attached to a helical fixation coil. The thread pitch of the extendable coupling screw is greater than the thread pitch of the helical fixation coil so that the coil portion will move through tissue faster per revolution than the coupling screw, thereby embracing the tissue more tightly against the lead and improving the electrical connection between the tissue and the electrode. Generally, the free spinning mechanism allows the fixation coil to rotate freely after the fixation coil has been fully extended. More particularly, the free spinning mechanism facilitates the use of a low level of torque to cause engagement of the coil with heart tissue so that a physician operator can feel the engagement of the heart tissue with the lead despite the large distance between the lead tip and a stylet knob.