MEASUREMENT AND ANALYSIS OF MONOPHASIC AC TION-POTENTIALS USING FRACTALLY COATED LEADS .2.

The monophasic action potential (MAP) represents a summed signal forme d by overlapping action potentials of myocardial cells close to the ti p of the lead. Analysis of the MAP therefore provides detailed informa tion about the electrophysiological effects of autonomous nervous and pharmacological influences on the myocardium, for example adrenergic o r cholinergic stimulation of the heart. All known MAP recordings were obtained with Ag/AgCl electrodes, which, thanks to their low polarizat ion properties, ensure reliable MAP measurement. Owing to their toxici ty and inadequate long-term stability, however, Ag/AgCl electrodes can not be implanted. With the aim of making MAP measurement available for implantable devices, fractally coated leads were therefore developed. The aim of the present study was to evaluate the in vivo measurement of fractally coated leads which are characterized by negligible polari zation, low impedance over a wide frequency range, high biocompatibili ty and good long-term stability. In addition, as a result of their ext remely high Helmholtz capacities (up to 50 mF/cm(2)), fractally coated leads permit stimulation and virtually undisturbed recording of MAP w ith the same pair of electrodes. For the evaluation of MAP measurement s with fractally coated leads, a quadrupolar catheter enabling simulta neous MAP recardings with 2 Ag/AgCl electrodes and 2 fractally coated leads was devised. The stimulation pulses were always applied via the fractally coated leads. With both types of electrode, with spontaneous excitation and stimulation, the well-known MAP morphology, with ampli tudes of between 10 and 25 mV in the ventricle, and between 5 and 10 m V in the atrium, was seen. To analyse the influence of the autonomous nervous system on the MAP, sympathetic and parasympathetic influences were simulated by pharmacological stimulation of beta-adrenergic recep tors (Orciprenaline) and pharmacological blockage of cholinergic recep tors (atropine). In addition, MAPs were recorded under defined conditi ons of psychological stress. The stress, medication and ratedependent changes in MAP duration and amplitude reflect the corresponding change s in the underlying transmembrane action potentials and reveal excelle nt correlation between the two electrode types (r>0.99). MAPs measured with fractally coated leads are thus equal to those recorded with Ag/ AgCl electrodes in all points. In contrast to Ag/AgCl electrodes, howe ver, the biocompatibility and long-term stability of fractally coated leads render them suitable for implantation. Fractally coated leads th erefore meet an important requirement for the long-term monitoring of MAPs.