Clinical and electrophysiological characteristics of a transvenous atrial lead.

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Abstract
Despite some reports on the use of the atrial transvenous endocardial lead, Medtronic 6991, there is 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 4 wk 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 .+-. 0.9 mV after 1 wk. 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% 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 ms) at the time of electrode insertion. It increased to 2.7 .+-. 1.0 V after 4 wk. 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 h; apart from these 3, the electrodes were connected easily to the intended pacemakers and have functioned well during the observation period of between 2 and 24 mo. The transvenous endocardial atrial lead, Medtronic 6991, has attractive qualities. The electrophysiological data recorded are suitable for the pacemakers in use. This atrial lead seems promising and deserves further evaluation.

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