Physiological and electrical characteristics of the porous endocardial electrode.

The principal complications in pacemaker therapy involve electrode-tissue instability. A new porous electrode has been devised that allows tissue ingrowth into the electrode interior, improving electrode biocompatibility and resulting in reduced dislodgment incidence, lower pacing thresholds, and improved sensing. Electrode porosity reduces polarization impedance permitting small-electrode design for both improved pacing longevity and optimal sensing function.

The porous endocardial electrode.

The permanent endocardial electrode has exhibited the problems of dislodgement, excessive threshold rises and loss of sensing. These failure modes are addressed with a new electrode incorporating a porous body of Pt-Ir fibers with a fiber diameter of 20 micrometers and an overall density of 10%. Porous electrodes have the advantages of utilizing the electrode interior both for tissue ingrowth to improve anchoring and for electrolyte penetration which improves R wave amplitude and reduces polarization losses. A series of 20 porous electrodes was compared with 17 solid electrodes of similar dimension. Electrodes were implanted in dogs in the apex of the right ventricle, and were subsequently followed up to 210 days. Comparison of the electrode data revealed that the porous electrodes had a 40% reduction in chronic voltage thresholds and had an overall dislodgement rate of 10%, compared to 53% for the solid electrodes. Histological examination revealed tissue ingrowth throughout the electrode interior and a fibrotic capsule about half the thickness of the solid electrodes. R wave stability was enhanced with the porous electrode due to improved anchoring, reduction in slew rate changes and less R wave attenuation. Assuming results are translatable to humans, the porous electrode will provide a greater pacing safety margin when used with a standard demand pacemaker, or improved longevity with the same safety margin as solid electrodes if used with a programmable pacemaker. The incidence of dislodgement and sensing failure will also be diminished with the porous electrode.

Comparison between mercury and lithium chemical systems for pacemaker energy source applications.

Over the past decade several types of chemical systems have been developed as energy sources for implantable pacemakers. The most widely used system is the mercuric oxide-zinc cell. Historically, mercury-zinc systems were the first to be used to power an implantable pacemaker; they have undergone several developments and modification in order to improve their performance characteristics. Recently, several new power sources have been designed and developed exclusively for implantable pacemakers, the most promising of which are chemical systems based upon lithium metal as anode material. This paper reviews the basic chemical, physical, and electrical characteristics of mercuric oxide-zinc and lithium based systems and evaluates their suitability for pacemaker applications based upon analysis of their inherent characteristics.

A method for the in vitro measurement of tensions of blood gases with a mass spectrometer.

A specially designed cuvette with an in vivo catheter allows the in vitro measurement of gas tensions in heparinized samples of blood with a mass spectrometer. Approximately 1.5 cc of blood is required, half of which is used to clear the dead space of the cuvette. The partial pressures of oxygen (P-o2) and of carbon dioxide (Pco2) of arterial and venous samples obtained from the catheterized femoral arteries and veins of 10 mongrel dogs were measured with the mass spectometer and with a conventional pH/gass analyzer. Good agreement was obtained between the two methods. The range of validation for P-o2 was between 35 and 100 mmHg; for P-co2 it was between 20 and 88 mmHg. Depletion, temperature control, flow dependency, and calibration problems are discussed.