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A new method of evoked response detection, previously demonstrated in the ventricle, has been studied in the atrium at the time of routine pacemaker implant in 16 patients. The atrial evoked response was readily detectable in all patients due to excellent recovery from poststimulus polarization. In six patients, as experimental threshold-tracking pacemaker was used to automatically verify atrial capture and to generate strength-duration curves. It is concluded that this pacing technique is both simple and reliable, and that automatic atrial threshold tracking is feasible [ABSTRACT FROM AUTHOR]

Earlier work by the authors has shown that batch anaerobic digestionof waste milk and cattle slurry is feasible at COD loadings of up to293 kg COD m-3. Higher COD loadings were added to batch anaerobic digestion systems in an attempt to determine the maximum CODloading which could be applied without causing digester failure. Biogas methane concentration was found to give a good indication of the effect of the shock loading on the digestion system. COD removal was significantly reduced in digesters receiving the highest shock loading. Reduced NH4+- N and NH3 concentrations in this system suggested depressed biological activity. [ABSTRACT FROM AUTHOR]

Endocardial lead systems for implantable cardioverter-defibrillators utilize large (12F) rigid catheters with spring defibrillation electrodes, and lead system failure has been observed during long-term implant. We evaluated a novel flexible 8F braided electrode catheter for pacing and defibrillation in canine experiments. Active fixation and pacing were accomplished using a screw-in distal electrode, and defibrillation pulses were delivered through a braided electrode. Two braided electrode catheters were positioned in the right ventricular apex (6 cm2) and in the superior vena cava-right atrial junction (5 cm2), respectively. An elliptical 13 cm2 surface area patch electrode was positioned along the left lateral cardiac border. Ventricular fibrillation (VF) was induced and monophasic and asymmetric biphasic shocks (leading voltages 260 to 1000 V) were delivered via dual and triple electrode configurations in each animal using a prospective randomized crossover study design. Mean right ventricular pacing threshold was 0.5 +/- 0.2 mA, with a mean electrogram amplitude of 11.1 +/- 2.8 mV during sinus rhythm prior to fibrillation and defibrillation. Two hundred seven VF inductions (mean 30 +/- 4 per animal) were analyzed. The mean defibrillation threshold could be reduced to 8.0 +/- 3.2 joules with biphasic shocks from 12.9 +/- 5.1 joules obtained for monophasic shocks using a dual electrode system (p less than 0.004). Mean shock leading voltage was correspondingly reduced to 488 +/- 100 V from 691 +/- 154 V (p less than 0.0006).(ABSTRACT TRUNCATED AT 250 WORDS)

An overview of advances is presented. The focus is on automatic functions that have been developed to monitor the patient continuously and readjust the postventricular atrial refractory period, the atrioventricular (AV) delay, the ventricular refractory period, and the pacemaker stimulus intensity. The advent of automatic algorithms for the postventricular atrial refractory period may have broadened considerably the clinical application of dual chamber pacemakers. Automatic adjustment of the ventricular refractory period has been demonstrated in an implantable pacemaker and may eliminate the rhythm disturbance associated with inappropriate T-wave sensing. Automatic adjustment of the AV delay has been implemented, and there is evidence suggesting that improved hemodynamics may result. Automatic output regulation has emerged in an implantable pacemaker and promises to increase device longevity while providing important patient safety benefits.