The current status of single lead dual chamber sensing and pacing

The use of single lead, atrial synchronous ventricular (VDD) pacing in pati ents with high grade atrioventricular (AV) block and normal sinus node func tion is an acceptable alternative to dual chamber (DDD) pacing. Implantatio n and follow up procedures are simplified, and cost is usually reduced by m ore than the cost of an additional atrial lead. With the use of either diag onally arranged dipole or closely spaced ring electrodes, reliable atrial s ensing can be achieved using differential atrial amplifier and high atrial sensitivity. Also oversensing is infrequently observed using provocation te sts and dynamic recordings, clinical undersensing is unusual and minimized by programming to the highest atrial sensitivity. However, as atrial pacing is not possible, loss of AV synchrony and rate response may occur for unre cognized or progressive sinus node disease and lower rate limit. The develo pment of single lead dual chamber pacing system may overcome this limitatio n. Recent studies have demonstrated that atrial pacing can be effective eit her with the use of a special pacing lead configuration or via floating atr ial electrode with a novel stimulation method. Overlapping Biphasic Impulse (OLBI) can reduce atrial pacing threshold. Early clinical experience sugge sted that this new pacing method can provide effective and reliable atrial pacing with a relatively low incidence of diaphragmatic pacing. Thus the pr oblem of atrial sensing is solved with a single pass lead but farther long term evaluation is required to assess the efficacy and feasibility of new i nstrumentation for single lead dual chamber pacing.