Implantable Cardioverter-Defibrillator Leads

Abstract

The transvenous defibrillation lead was a critical technological step that enabled widespread adoption of implantable cardioverter-defibrillator (ICD) therapy. This lead is the most vulnerable component of the ICD system. It must remain chemically inert in a hostile biological environment, withstand flexing for hundreds of millions of cardiac cycles, and retain electrical integrity during shocks that would trip a household circuit breaker. Reliability issues concerning leads have led to the rethinking of lead design, reexamination of preclinical testing, implementation of algorithms that warn of lead failure and reduce inappropriate shocks, design of leads that can be extracted more easily, and development of a totally subcutaneous ICD system. The present review summarizes clinical aspects of defibrillation leads and reviews diagnostic and therapeutic approaches to lead failure. Please see the online-only Data Supplement for a brief summary of the engineering of lead design. ### Structural Overview Right ventricular (RV) defibrillation leads comprise a distal tip electrode with a fixation mechanism that anchors the lead to the heart, proximal terminals that connect to the generator, and a lead body that connects the two (Figure 1A). The lead body consists of a flexible insulating cylinder with 3 to 6 parallel longitudinal lumens through which conductors run from the proximal terminals to small pace-sense electrodes and larger shock coil electrodes. This multilumen design (Figure 1B) permits more conductors in smaller-diameter leads than older coaxial designs.1 The subcutaneous ICD uses a parasternal electrode in which the larger shock coil is straddled by 2 small sensing electrodes (Figure 1C). Figure 1. Structure of true bipolar leads in which the active fixation screw acts as the distal pace-sense electrode. A , Top , Dual-coil active fixation lead with DF-1/IS-1 terminal pins. Bottom , Single-coil active fixation lead with DF-4 terminal pins. B , Cross section of multilumen, dual-coil, true bipolar lead (Durata, …