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  • Title: Update on cardiac pacemakers: description, complications, indications, and followup.
    Author: Medina R, Michelson EL.
    Journal: Cardiovasc Clin; 1985; 16(1):177-213. PubMed ID: 3915711.
    Abstract:
    Great advances in pacemaker technology have produced devices capable of a vast array of physiologic adaptations formerly unimaginable, opening new possibilities in the pacemaker treatment of almost all rhythm disturbances. Nearly all units in use today are of the inhibited type, except for some antitachycardia applications. The AV-sequential mode (DVI) allows for preservation of AV synchrony, and the universal pacemaker (DDD) allows for a more physiologic response to a range of atrial rates. Programmability of numerous parameters has added a new dimension of adaptability to a variety of changing physiologic needs and pacemaker performance patterns, eliminating the need for surgical revision in many cases. The standard power source of today's pacemaker is the lithium chemistry cell, and the 5-year pacemaker is a reality, with 10 to 15 years of longevity distinctly possible in the near future. Almost all pacemakers use the transvenous route for access to the heart; new positive-fixation electrodes reduce displacement to a minimum; and new polyurethane or silicone-rubber leads have greatly simplified the techniques for implantation. Bipolar pacing systems are preferred, to avoid the oversensing of skeletal muscle interference--a problem that is especially important in triggered systems such as those used for antitachycardia applications. Threshold measurements are performed in millivolts at the time of implantation of most constant-voltage units, and current threshold measurements are useful for troubleshooting when failure to capture exists. Sensitivity parameters should be adjusted to sense the intracardiac signal; its amplitude should be determined in all cases, and measurement of the slew rate is useful when the amplitude is marginal. Recording of AV and VA conduction characteristics should be part of the routine implanting procedure, especially when simple blood pressure measurement during ventricular pacing indicates that this modality will be poorly tolerated and, therefore, implantation of a dual-chamber unit is contemplated. Different modalities of pacemaker malfunction have been reviewed, including the "cross-talk" phenomenon encountered with dual-chamber pacing. With the introduction of newer techniques, a host of pacemaker-mediated tachycardias have appeared, notably the "endless-loop" tachycardia of DDD pacemakers. This and other electrophysiologic phenomena of normal pacemaker function are bound to multiply as technology becomes more complex, but they should not be a problem if the programmable parameters are adapted to the electrophysiology of each particular patient.(ABSTRACT TRUNCATED AT 400 WORDS)
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