COMPONENTS OF AN ICD SYSTEM An ICD consists of a pulse generator, a ventricular shocking or sensing lead, and sometimes an atrial lead. The ICD lead differs from a standard pacing lead in that it has coil electrodes, typically two, one in the superior vena cava-right atrium and one in the right ventricle; in addition, one or two small electrodes used for pacing and sensing are near the tip of the lead (Fig. 1). Shocks are delivered between the electrodes and the pulse-generator canister in different pathways, but most commonly with the right ventricle as cathode (negative) and the superior vena cava-right atrium coil and the pulse-generator canister as anode (positive). The shock pathways are programmable in various ways in different manufacturers’ devices.The most common variation is to reverse the polarity so that right ventricle is anode and the superior vena cava-right atrium-canister is cathode.