Single-Lead DDD Pacing with Two Ring Electrodes in the Right Atrium and One Ring in the Superior Vena Cava

Dual-chamber (DDD) pacing for maintenance of atrioventricular (AV) synchrony generally requires the implantation of two leads, one in the right atrium and one in the right ventricle. During the early 1990's, the efforts were made to achieve DDD pacing using only one lead [1-3]. The idea was to use the electrical field generated between the floating ring electrodes located in the right atrium to stimulate the atrium and thereby treat bradycardia conditions in a manner that favors safe pacing (reduces the complication rate) and makes the pacemaker implantation easier. Different authors have searched for a suitable mechanism to perform DDD pacing using a single-pass lead; the proposed technical solutions met varying degrees of clinical success [4-13]. Verlato et al. reported on a multicenter study investigating clinical utility of the overlapping biphasic impulses (OLBI) delivered via floating atrial electrodes [14]. Atrial pacing was achieved in all patients in whom the floating electrodes were placed in the superior vena cava (SVC), 77.7% of patients experienced effective pacing with the electrodes floating in the upper atrium, 82.1% with the electrodes placed in the mid-atrium, and 50% of patients were successfully paced with the electrodes floating in the lower atrium. An explanation for these differences may be a lower capture threshold of cardiac cells in the sinoatrial area compared with other myocardial cells. The knowledge gained in the aforementioned study has incited the development of a single-pass lead with