This article deals with several major issues of cardiac pacing: 1. An overview of cardiac stimulation; 2. Functional improvements in pacing; 3. The problems of sensing spontaneous cardiac events; and 4. Some technical aspects of pacemaker follow-up. The authors treat the first of these issues by an extended tutorial on action potential and its propagation, empirical theories of depolarization of a critical mass or volume of excitable heart muscle, bipolar and unipolar stimulation, and the relationship between threshold stimulation values time following electrode implantation. The second issue discussed traces the functional development of clinical pacing through several stages from asynchronous ventricular stimulation (the same rate of stimulation regardless of the spontaneous activity of the heart), to the presently most advanced dual-chamber demand pacing. The third issue discussed points out that the detection, by a pacemaker, of the spontaneous activity of the heart calls for electrical sensing circuits that are able to detect minute (1-10 mv) signals having spectra in the 10 to 100 Hz range, and maximum instantaneous rates of change of about 1 v/sec. The spectrum of a QRS complex (associated with ventricular depolarization) is significantly different from that of a T-wave (which occurs during ventricular repolarization), hence the two can be separated by a high-pass filter. The same is not quite true for differentiating between premature ventricular beats and normal ventricular events. Successfully identifying spontaneous atrial activity is often problematic when large ventricular complexes are also sensed by the atrial channel of a dual-chamber or an atrial pacemaker. On the third issue, it is pointed out that certain aspects, such as monitoring rate and pulse duration of follow-up, have become simpler with improvements in the quality of implants and the implantation process. Other aspects became more complex as the complexity of the pacing systems themselves has increased. Office vists allow the recording of stimulus-artifact waveforms and high-quality electrocardiograms. Time measurements can be performed but, in addition, the stimulus duration can be measured. Computerized data processing facilitates the identification of trends in changing parameters.
ASJC Scopus subject areas
- Biomedical Engineering