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The design of a pacemaker which indicates the occurrence of significant bradyarrhythmia is described. Significant bradyarrhythmia is defined as either asystole for 6 seconds, bradycardia with three successive RR-intervals greater than 2 seconds each, or five or more RR-intervals of 2 seconds or more over a period of 25 seconds, but without three such intervals in succession. During bradyarrhythmia the generator initially stimulates at an interval of 2 seconds (30 per minute) and when the described criteria have been fullfilled the pacemaker automatically converts to a conventional ventricular inhibited pulse generator stimulating at a rate of 70 per minute.

The development of the carbon tip electrode and its low chronic threshold behavior are described. Compared to presently used electrode material, carbon tip electrodes result in lower chronic stimulation thresholds. In a group of 43 patients, chronic pulse generator output has been favorably reduced in association with this type of electrode. Thus the use of activated carbon tip electrodes may result in the routine implantation of low output pacemakers.

The spectral energy distributions of signals picked up by endocardial, atrial and ventricular electrodes have been investigated. The results show similar spectral distributions for P-waves and QRS-complexes with maximum spectral densities at frequencies between 10 and 30 Hz.

Pacemaker mediated re-entry tachyarrhythmias and their causes are discussed. Several methods to prevent these arrhythmias are presented. It is shown that the most efficient method incorporates a long refractory period of the atrial detection after ventricular depolarization. The benefits of a short A-V delay after atrial sensing are discussed.

Microprocessors have a major impact on cardiac pacemaker technology. The development of adaptive systems capable of responding to physiologic variables will ultimately improve the care of the individual patient. However, in order to minimize power drain, it will be necessary to incorporate certain functions into the hardware outside the microprocessor. In addition, specifically designed program languages may indeed become necessary.