Comparison of Different Pacemakers with Holter Functions

Summary

The advent of small memory chips with very low power consumption, coupled with advances in radiofrequency telemetry, has enabled implantable cardiac pacemakers to become diagnostic as well as therapeutic devices.

Different types of devices are available. The simplest type merely indicates whether or not a bradycardia or tachycardia has occurred or has been treated. This may be indicated by the amplitude of a marker pulse, by the number of pulses on magnet application or on the magnet rate of the pacemaker. Some pacemakers are capable of counting paced and sensed beats over a given time period instead of, or as well as, indicating bradycardia or tachycardia. The most complex Holter functions currently available in an implantable device, in addition to the above features, allow the construction of a histogram of spontaneous heart rates, as well as being able to count premature beats or to give information about sensed tachycardias. Typical “random access memory” store is 256 bytes (8 bit), although such pacemakers require up to 2 kbytes of “read only memory” to control the pacing and diagnostic functions. An external microprocessor based device is then required to interpret, structure and present all the information that is telemetered out.

Increasing electronic sophistication will permit increased data storage and more versatile data processing, and although devices capable of storing short durations of electrographic waveforms will shortly become available, the future lies in improved “front-end” processing enabling the efficient storage of preprocessed data.

There is no reason why an implantable device without pacing functions should not be used for arrhythmia monitoring in certain selected patients, perhaps using subcutaneous electrodes. Finally, implantable ambulatory monitors could be used for other physiological variables, for example, systemic or pulmonary artery pressure, or concentrations of oxygen, glucose or other biological substances, depending on the sensor used.

Supported by the British Heart Foundation