A new lead for transvenous atrial pacing and sensing. Clinical and electrophysiological experiences.

The Medtronic 6961 lead has been used in 14 patients for transvenous atrial sensing and/or pacing. This lead is furnished with small tines of silicone rubber at the distal end. The conductor coil material is space wound for flexibility. Thus, the lead lacks intrinsic elasticity and can be fastened within the right atrial appendage without a preformed J-shape. The clinical experiences with the lead are encouraging. The lead is easier to introduce and position in the right atrial appendage than the previously used tined J-shaped leads (Medtronic 6991). The small size of the new lead makes the choice of vein less critical and a normally-sized external jugular or cephalic vein permits the use of the same vessel for a second ventricular lead. By means of a lead extension wire, consecutive determinations of the P-wave amplitude, stimulation threshold of the right atrium, electrode resistance, and P/QRS-ratio were made for four weeks following electrode insertion. The mean P-wave amplitude at insertion was 4.9 +/- 1.5 mV (mean +/- SD). There was a significant decrease to a lowest mean level of 309 +/- 1.1 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 of the P-wave amplitude of +/- 12%. The P-wave amplitude was influenced by body position and maximal breathing movements to a minor extent. The threshold of stimulation was 0.9 +/- 0.4 V after one week. Later there was a small decrease in the threshold which, however, still remained significantly higher than at the time of insertion. The total resistance of the electrode system was about 700 ohms and P/QRS-ratio about 4 +/- 3. During an observation time ranging from 4 to 11 months there were no electrode dislocations. The electrodes were connected to the intended pacemakers without complications. In conclusion, the transvenous endocardial atrial lead, Medtronic 6961, shows attractive and promising qualities. The electrophysiological data recorded are suitable for the pacemakers in use. The electrode definitely deserves further evaluation.