Dual chamber pacing with a single-lead DDD pacing system

The successful application of single-lead VDD pacing during the last few ye ars hers generated the idea of single-lead DDD pacing: Preliminary data fro m several single-lead VDD studies attempting to pace the atrium by a floati ng atrial dipole are unsatisfactory, causing an unacceptably high current d rain of the device. We studied thefeasibility as well as the short- and lon g-term stability of atrioventricular sequential pacing, using a new single- pass, tined DDD lead. In eight consecutive patients (age 73 +/- 16 years) w ith symptomatic higher degree A V block and intact sinus node function, thi s new single-pass DDD lead was implanted in combination with a. DDDR pacema ker. Correct VDD and DDD function wets studied at implantation; at discharg e; and at 1, 3, and 6 months of follow-up. At implant, the atrial stimulati on threshold was 0.6 +/- 0.2 V/0.5 ms. During follow-up, the atrial pacing thresholds in different everyday positions averaged 2.1 +/- 0.5 V at discha rge, 2.9 +/- 0.5 V at 2 month, 3.8 +/- 0.4 V at 3 months, and 3.4 +/- 0.4 V at 6 months (pulse width always 0.5 ms). The measured P wave amplitude at implantation was 4.5 +/- 2.2 mV; during follow-up the telemetered atrial se nsitivity thresholds averaged 2.2 +/- 0.3 mV. Phrenic nerve stimulation at high output pacing (5.0 V/0.5 ms) was observed in three (38%) patients at d ischarge and in one (13%) patient during follow-up; an intermittent unmeasu rable atrial lead impedance at 3 and 6 months follow-up was documented in o ne (13%) patient. This study confirms the possibility of short- and long-te rm DDD pacing using a single-pass DDD lead. Since atrial stimulation thresh olds are still relatively high compared to conventional dual-lead DDD pacin g, further improvements of the atrial electrodes are desirable, enabling lo wer pacing thresholds and optimizing energy requirements as well as minimiz ing the potential disadvantage of phrenic nerve stimulation.