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DELL'ORFANO, J., et al.: The Monolithic Fetal Pacemaker: Prototype Lead Design for Closed Thorax Deployment.Prenatal sudden cardiac death and hydrops fetalis are often due to complete heart block. However, no pacing modality exists for intrauterine application for fetal bradycardia. A prototype lead for a novel fetal pacemaker has been developed and used in a direct pacing model. It has been demonstrated that the lead can be safely and successfully deployed using a hypochondriac and transdiaphragmatic or subxiphoid approach. Pacing with ventricular capture was evident with the widening of QRS duration from50.2 ± 9.8to95.1 ± 12.8 ms (P = 0.0001). Further studies by echocardiogram revealed an increase in the pulse with pacing, confirming pacing. This study documents proof‐of‐concept for closed thorax over‐the‐wire deployment of a novel lead design applicable to fetal pacing. By combining the lead design with microcircuitry and a small power source, it is possible to create a monolithic fetal pacemaker system capable of being deployed in utero. (PACE 2003; 26[Pt. I]:805–811) [ABSTRACT FROM AUTHOR]

Pacemaker electrode surface modification by organosilane and organic self-assembled monolayer strategies creates a possible new variable in pacemaker electrode behavior. Because all of these chemical surface coatings are unstable at extremes of potential. the potential to which the electrode relaxes (between pacing pulses) becomes extremely important. The authors measured this potential for platinum (Pt) and gold (Au) relevant for their use as anode (or cathode) in a bipolar pacing system and from this potential the standard electrode potential, E° was determined. Thirty-Four determinations were made by a null current three-electrode potentiostatic technique of 2.45 mm² plutinum or gold electrodes implanted chronically in blood perfused muscle in a spontaneously breathing rat. Linear voltage sweeps were performed while monitoring current with voltage at null current determined repeatedly at varying scan rates and limits. Electrode potential varied between -388 ± 19 m V (vs Ag/Agt*)for platinum anti -388 ± 55 in V for gold electrodes. Hyteresis was observed in all sweeps (P < 0.008, Fisher's exact) and measured 61 ± 17 m V (anodic) and 25 ± 3 mV (cathodic) with steep dependence on polarity (P < 0.001, t-test). The findings were independent of the materials' electronic work function. E° versus normal hydrogen electrode (NHE) were thus -166 mV (platinum) and -166 mV (gold). Because the most common bipolar system uses platinum as anode, these results arc directly applicable to current pacing technology. Provided low thresholds are achievable with novel surface modified electrodes, the small range of variation of E°, and the particular mean value observed, are both compatible with function, provided care is used during electrode testing to avoid surface disruption. These results are significant also for biosensors that use similar surface modification methodologies. [ABSTRACT FROM AUTHOR]

The monophasic action potential (Franz) catheter is regarded as the criterion standard for high fidelity recording of a class of physiological signals. However, its signal modalation characteristics have never been reported. Broadband impedance spectroscopy was performed in perfused living rat heart in a three-electrode potentiostatic configuration to determine the filtering characteristics of the MAP and model Ag/AgCl electrode-tissue interfaces. The filter transfer function H(f) (attenuation [dB] vs log(f) [log(Hz)l) was derived for the frequency range 10 Hz-106 Hz. As a filter, the MAP interface is characterized by two ranges of filtering behavior. At high frequency the MAP interface is a high-pass filter with pass band frequency 54 kHz-549 kHz (median 321 kHz) and with --3 dB cutoff points ranging from 10 kHz to 302 kHz. In this high frequency range the transfer function is characterized by decreasing attenuation per decade. However, in the lower frequency range relevant to physiological signals (the monophasic action potential, 0.1-40 Hz), it is a severely attenuating nondiodic high-pass filter element with an average attenuation of 16.87 dB relative to passband. In this physiological range, rolloff is nonlinear with increasing attenuation per decade. While the MAP electrode and model Ag/AgCl electrodes are high-pass filters with robust transfer functions for high frequency signals in the living heart, the attenuation of signals in a frequency range relevant to in vivo physiological recording imparts extreme attenuation that may distort physiological signals unpredictably. This disadvantage may be mitigated by amplitude scaling to a calibrated pure tone signal within the physiological frequency band to recover a reproducible signal. [ABSTRACT FROM AUTHOR]