Results from the use of a preshaped lead for single-pass VDD/DDD stimulation

Main criticisms about single-pass VDD stimulation in patients with AV block and normal sinus node function concern atrial undersensing in a lead with floating atrial electrodes, and loss of AV synchrony if sinus node dysfunction develops after implantation. We evaluated the concept of a preshaped single-pass lead designed to place the atrial ring electrodes in a constant position close to, or in contact with, the atrial wall. A preshaped lead (Model 2775, Medtronic Inc.) was implanted in 14 patients and followed for up to 2 years. Mean P wave amplitudes (PWAs) were 3.1 mV at implantation, 1.2 mV at predischarge, and 1.3 mV after 12 months. In all patients, minimal PWAs were well above maximal atrial sensitivity of the pacemaker in all body positions during the complete follow-up; atrial undersensing was not observed. Effective atrial stimulation was possible in all patients at implantation (mean stimulation threshold 2.5 V at 0.50 ms), in 11 patients on the first day after implant (mean stimulation threshold 0.22 ms at 5.0 V), in 10 patients after 1 month (mean stimulation threshold 0.57 ms at 5.0 V), and in 10 patients after 1 year (mean stimulation threshold 0.65 ms at 5.0 V). Intermittent phrenic nerve stimulation could be provoked in six patients. In conclusion, the concept of a preshaped single-pass lead facilitated implantation, improved atrial sensing performance, and allowed atrial stimulation in some patients. Still, further improvements are necessary to decrease the atrial stimulation thresholds to acceptable values in all patients.