The implantable cardioverter-defibrillator lead: principles, progress, and promises

Abstract

The prognostic benefit of the implantable cardioverter-defibrillator (ICD) has been well established in multiple settings and its use is consequently widespread. Modern-day ICD systems use transvenous high-voltage leads to act as the interface between the heart and the generator, allowing for the sensing of a cardiac activity and the delivery of both bradycardia and tachycardia therapy, including high-voltage, high-current shocks. The ICD lead is in many ways the most fragile and critical component of the ICD system, and is subjected to more stress than any other implanted medical device. It has similar components to a pacing lead including tip and ring electrodes, fixation mechanism, conductors, insulators, and connector pins. In addition, it also contains the high-voltage shock coils that allow the delivery of defibrillation therapy to the cardiac tissue. The materials used to manufacture each of these components have undergone little evolution from their initial pacing lead-derived origin, but promising progress in this area is now occurring and better conductors and insulators have been developed. Lead body design continues to be multiluminal rather than coaxial, but various iterations of this basic paradigm continue to be investigated. In addition to miniaturization of the entire ICD lead, new industry standard lead connectors will also be introduced to reduce complexity and pocket bulk. However, long-term failure rates have been considerable, with lead failure related to both conductor and insulator malfunction. It is hoped that recent improvements in an ICD lead design and manufacture will result in a good functionality with a reliable long-term performance.