SIMULTANEOUS RECORDINGS OF THE MONOPHASIC ACTION-POTENTIAL WITH SILVER CHLORIDE-COATED AND IR-COATED ELECTRODES

Ag/AgCl and Ir-coated Electrodes allow the recording of the monophasic action potential (MAP) due to their electrical proper ties like non-p olarisability. This study investigates the correlation of MAP recorded with both types of electrodes Iii 20 mongrel dogs (18 +/- 6 kg) an Ag /AgCl and an Iv-coated catheter (Ir) were placed endocardially in the apex of the right ventricle. The effects of isoproterenol and verapami l were investigated during spontaneous rhythm mad stimulation simultan eously recorded with both types of electrodes in 10 dogs without AV-no de ablation. The correlation at different heart rates were investigate d in IO other dogs with complete AV-block. The morphology and amplitud es of MAP were comparable (AgCl: !15; +/- 7 mV; Ir : 13 +/- 8 mV). Fol lowing mt i.v. bolus of 2 mu g/kg isoproterenol the spontaneous rate i ncreased (175 +/- 18 to 245 +/- 25 bpm). During stimulation with 250 m s cycle length the duration shortened (MAPd90. AgCl: 160 +/- 11 to 130 +/- 12 ms; Ir: 154 +/- IS to 128 +/- 15 ms). The alterations reversed after 20 min. An i.v. bolus of 0.2 mg/kg verapamil decreased the spon taneous rate (167 +/- II to 104 +/- 23 bpm) and lengthened the MAPd90 (AgCl: 182 +/- 14 to 220 +/- 13 ms; Ir: 174 +/- 16 to 216 +/- 21 ms) a t 300 ms stimulation. The correlation between the MAPd90 of both lend types was r=0.98 during all measurements. Under the effect of beta-ago nist and Ca2+-antagonist medication MAP shaved a strong correlation re corded with both types of electrodes. Thus, both leads allow the recor ding of MAP but only the Ir-electrodes with their long-term stability ape implantable and allows us to control the effects of drugs with imp lantable devices.