SUMMARY Despite some reports on the use of the atrial transvenous endocardial lead, Medtronic 6991, there is still very little information on the electrophysiological properties of the lead. A lead extension wire was connected to the atrial lead, passed subcutaneously, and brought through the abdominal skin. P wave amplitude, threshold of stimulation, and electrode resistance were repeatedly determined through the atrial lead during four weeks after the electrode insertion in 17 patients. Mean P wave amplitude at insertion was 3-7 ± 1 0 (mean ± SD) mV. It decreased significantly to a lowest mean level of 2-3 ±09 mV after one week. From that time there were only small variations. In the supine position and with normal breathing there was a spontaneous variation in the P wave amplitude of ± 15 per cent. P wave amplitude was only to a minor extent influenced by body position and maximum breathing movements. The threshold of stimulation was 1-7 ±0-7 V (impulse duration 0 5 mi) at the time of electrode insertion. It increased to 2 7 ± 1 0 V after four weeks. The electrode resistance varied about 600 ohms.A total of 28 patients received an atrial transvenous endocardial lead. Three electrode dislocations occurred, all during the first 24 hours; apart from these three, the electrodes were connected easily to the intended pacemakers and have functioned well during the observation period of between two and 24 months. In conclusion, the transvenous endocardial atrial lead Medtronic 6991 has shown attractive qualities. The electrophysiological data recorded are suitable for the pacemakers in use. So far this atrial lead seems promising and deserves further evaluation.Despite the increasing number of patients with pacemakers, there has not been a corresponding increase in the use of atrial synchronous and atrial inhibited pacing. In Sweden not more than 1 per cent of initially implanted pacemakers are atrial synchronous (Karlof and Lagergren, 1973; Edhag, 1977). Many patients would, however, improve haemodynamically with an atrial inhibited or atrial synchronous pacemaker (Lagergren et al., 1966;DeSanctis, 1971;Furman, 1973). The reason for the limited use of atrial pacing is probably the lack of an electrode which combines a simple technique of introduction with long-term reliability. Recently promising results have been reported by the use of a transvenous J-shaped atrial tined lead (Smyth et al., 1976;Kleinert et al., 1977). These reports deal with the technique of introduction and electrophysiological characteristics of the lead at the time of electrode insertion.The present investigation was undertaken to study the electrophysiological characteristics of the Received for publication 17 April 1979 atrial electrode by means of repeated measurements throughout a period of four weeks after the introduction of the electrode. The report also contains information about our present clinical experience with the electrode.
Subjects and methods
PATIENTSThe subjects consisted of 28 patients; pertinent data from these are pres...