ATRIAL STIMULATION BY MEANS OF FLOATING ELECTRODES - A MULTICENTER EXPERIENCE

It is well established that single lead VDD pacing is a physiological, reliable, and easy to use mode of pacing. The major limitation of VDD pacing is the need of a normal sinus node function, confirming its indication to patients with isolated atrioventricular conduction disturbances. The Phymos 830 pacing lead was originally designed for VDD pacing in association with the Phymos MPS pulse generator; it has a floating atrial dipole with an interelectrode distance of 3 cm; the distal electrode is 11, 13, or 15 cm proximal to the tip. As a result of the incidental observation of atrial captures occurring at very low pulse amplitudes delivered from the floating dipole of this lead. a 13-center Italian study was initiated to test the systematic feasibility of this type of atrial pacing. Pacing parameters were set and strength-duration curves were acquired with the PSA Master 470 external device. The investigation was performed at pacemaker implant in 114 patients in the supine position. The tip of the electrode was positioned at the right ventricular apex and the atrial dipole at the site of the highest endocavitary signal. Atrial bipolar pacing was performed with the proximal electrode as the cathode, Stable atrial capture was obtained in 108 of 114 patients (94.7%); pacing threshold was < 3.5 V with a pulse width of 1 msec in 85 of 108 patients. Results of voltage threshold were: 2.99 +/- 1.25 and 2.59 +/- 1.13 V at pulse widths of 0.5 and 1 msec, respectively. The mean value of atrial pacing impedance (5 V, 1 msec) was 601.2 +/- 221 Ohm; the mean value of the endocavitary signal amplitude was 1.53 +/- 0.48 mV. During deep breathing loss of capture was observed in only 8.3% of patients; these patients regularly had an atrial pacing threshold higher than 3.5 V. Diaphragmatic stimulation occurred in 19.2% of patients at an output of 5 V and 1 msec. Our results suggest that stable atrial pacing is possible with floating electrodes in a high percentage of patients; in 85/114 patients (74.5%) atrial capture was reliable at a satisfactory mean pacing threshold. This experience shows that single lead DDD pacing is possible and may be reliable in acute conditions; and supports the availability of this pacing mode in selected patients. It can be considered a starting point for improvements in techniques and materials.