[Adjustment of double-chamber pacemakers in VDD mode by measurement of thoracic electric bio-impedance]

Abstract

An optimal atrioventricular interval (AVI) was sought in 6 patients with a double chamber pacemaker by an non-invasive technique: measurement of stroke volume by thoracic bioimpedance. This method proved to be easy and reliable in practice when there was only one pacing spike (VDD mode). It confirmed the existence of a variable optimal AVI according to individual patients: 250 ms (3 patients), 200-250 ms (1 patient), 150 ms (1 patient), 75-100 ms (1 patient). The value of optimal AVI is unpredictable since it depends upon individual electrophysiological and hemodynamic parameters. In a patient with severe mitral incompetence, Echo-Doppler provided evidence of end-diastolic ventriculo-atrial regurgitation at middle and long AVI, while a short AVI enabled elimination of end-diastolic regurgitation and a 15.45 per cent improvement in stroke volume. In two patients with a long optimal AVI (250 ms), a programmed short AVI (75 ms) paradoxically appeared to be more favourable than a middle AVI (150 ms).