At the present time, the relatively high atrial stimulation threshold and the low and often unstable P wave amplitude are the main concerns in atrial pacing. As a further contribution to the solution of this problem we used a screw-in atrial lead in 16 patients. During the implantation, atrial mapping was performed in order to establish the position with the best electrical performance. The acute threshold for voltage at a pulse duration of 1 ms averaged 0.49 +/- 0.18 Volt. The acute peak-to-peak P wave amplitude averaged 4.6 mV +/- 1.3. No complication occurred at the time of the implantation. Follow-up periods averaged 12 months. No dislocation or bleeding was observed during a follow-up period of up to 28 months. Using this lead together with intraoperative atrial mapping, it is possible to achieve an acute strength-duration relationship in the atrium at a level similar to that in the ventricle. The results of this study demonstrate that intraoperative mapping is an important stein in enhancing the safety margins and long-term performance of atrial pacing.

Electrode fracture is a serious late complication of pacemaker implantation. This complication was observed in 33 patients within 3 years whereby the interval between electrode implantation and fracture was on average 35 (12--113) months. The cause lay partly in the electrodes themselves--in all cases singly wound spiral electrodes--and partly in technical deficiencies in the extrathoracic loop formation. Attention is drawn to the fact that fracture has never occurred in the Elema electrode type 588 used routinely by the authors.