ANALYSIS OF THE VENTRICULAR EVOKED-RESPON SE AS A FUNCTION OF PHYSICAL LOAD AND HEART-RATE FOR USE IN RATE-ADAPTIVE PACEMAKERS

The aim of this study was to evaluate the ventricular evoked response (VER) measured with unipolar fractally coated pacing leads for use wit h rate-responsive pacemakers. To this end, the morphology of the VER, its variation with pacing rate and various levels of physical loading, and the long-term stability of the signal were studied using the tele metric features of implantable pacemakers. Fractally coated electrodes were used in order to minimize the stimulation artefact, thus enablin g a reliable unipolar measurement of the VER. The VER shows uniform ba sic morphology, and remains virtually unchanged after 3 months; moreov er, frequency and load-dependent changes of VER morphology were identi cal for all patients. A special programming device has been developed to evaluate a rate adaptive algorithm for optimizing the pacing rate t o the current loading situation, and was successfully tested in two pa tients. The algorithm was shown to be capable of calculating a heart r ate adequate for haemodynamic demand.