Implantable transvenous pacing leads: the shape of things to come.

With the dawn of a new millennium, physicians' demands for very thin transvenous leads able to be positioned in nontraditional sites like the Bachmann's bundle, the high and mid-right ventricular septum, and the His bundle have created new and exciting challenges for lead engineers. Bipolar leads can now be as thin and reliable as unipolar leads. Cathode electrodes are very small, porous, and demonstrate high impedance. To optimize stimulation thresholds, steroid-eluting passive- and active-fixation electrodes have become popular for use in the atrium and ventricle. To create thin lead body diameters, new insulation and conductor materials and lead body designs are necessary. Hybrid medical materials having the best features of silicone rubber and polyurethane will allow for reliable insulation. Conductor cables instead of helical coils permit strong thin diameter leads to be designed. Transvenous lead implantation using the traditional stylet may not be possible with thin diameter leads, necessitating the use of sophisticated workstations using steerable catheters to guide these new active-fixation leads to selective sites in the right heart. The pacing lead of the future may be very different from the one used today. Ironically, it will have features and implantation techniques similar to the transvenous leads designed prior to the use of the stylet. We are now approaching full circle in lead development, retracing the footprints of the early implanters of three and a half decades ago.