Richard V. Calfee

Clinical use of an implantable automatic tachycardia-terminating pacemaker

A significant fraction of patients with supraventricular and ventricular tachycardia remains a therapeutic problem despite improvements in diagnostic testing, new drugs, and improved techniques for the evaluation of the efficacy of drug therapy. Pacing provides an alternative in selected patients. Pacing techniques may be used for arrhythmia suppression or termination and in rare instances may allow the substitution of a more easily managed arrhythmia. We have permanently implanted a new programmable, automatic tachycardia-terminating pacemaker in patients with drug-refractory supraventricular tachycardia. Following pacemaker implantation, successful tachycardia termination has been documented by ambulatory monitoring. Because of changing requirements for effective termination, we feel programmability is mandatory for successful long-term efficacy. We conclude that pacemaker therapy of supraventricular trachyarrthythmia with the automatic antitachycardia terminating pacemaker is safe, effective, and well tolerated.

A Voluntary Standard for 3.2 mm Unipolar and Bipolar Pacemaker Leads and Connectors

In response to concerns over proliferation of new and different technologies in leads and lead connectors, a voluntary standard for 3.2 mm unipolar and bipolar pacemaker leads and connectors has been established. One major difficulty overcome in the process was the design of the voluntary standard. The greatest controversy centers around the design for the sealing mechanism for the connection of the pacemaker to the leads. Some suggest that the sealing mechanism should be in the form of seal rings on the lead; others believe that it is preferable to have the seal rings inside the pacemaker cavity. The new voluntary standard finally agreed upon represents a compromise position. It is a standard that appeals to future development since it favors leads smaller than those in current distribution, and provides for backward compatibility with existing leads. In addition, it allows each manufacturer as much design flexibility as possible. It is hoped that this voluntary standard will be universally accepted throughout the industry.

Therapeutic Radiation and Pacemakers

The article by Adamec, et al., in this issue of PACE regarding therapeutic radiation effects on pacemakers brings to light a problem which, although rare, is of clinical significance when it occurs and is probably occurring more frequently than in the past due to changes in both the practice of pacemaker medicine and the evolving trends in pacemaker electronics. High energy radiations such as x-rays, gamma rays, electrons, protons, neutrons, and cosmic particles can have profound effects on the operating characteristics of semiconductor devices. The magnitude of the radiation-induced changes in device characteristics depends not only on the type of radiation and total dose of radiation, but also on the type of device and on the specifics of device fabrication. Smaller devices in dense circuits tend to be more susceptible to radiation degradation. Since the trend in pacemaker electronics is toward larger scale integrated circuits, which combine more functions into smaller areas with less power consumption, radiation-induced problems are becoming less rare. The effects of radiation on materials are divided into two broad categories: (1) structural changes in the arrangements of atoms in the crystal and/or incorporation of new species of atoms (due to nuclear transmutation) and (2) effects due to the ionization of atoms by the radiation. This latter category may be further divided into two subgroups: [1) permanent effects which persist after the ionizing radiation source is removed and (2) transient effects which rapidly decay when the radiation source is removed. Transient effects are very similar in kind to the effect of light on a photographic light meter; the meter reading drops to zero when the light source is removed. Because of the requirement for low power consumption and high reliability ih pacemaker electronics, most modern pacemakers utilize

The treatment of ventricular tachycardia using an automatic tachycardia terminating pacemaker.

Implanted cardiac pacemakers may be used in the management of selected patients with ventricular tachycardia unresponsive to other forms of medical and surgicaJ therapy. We would like to report the successful treatment of such a patient utilizing a new multiprogrammable automatically activating ventricular burst pacemaker. Thorough electrophysiologic study preceded implantation, and was instrumental in choosing an effective terminating technique, in identifying the need for adjunctive drug therapy, and in testing the safety and efficacy of the implanted system. (PACE, Vol. 4, September‐October, 1981)

Pacemaker-Mediated Tachycardia: Engineering Solutions

This discussion summarizes the interaction of refractory periods and upper rate behaviors in modern dual‐chamber demand (DDD) devices, the data regarding and nine events initiating VA conduction and engineering solutions proposed and/or implemented to address the problem of pacemaker‐mediated tachycardia (PMT). Among the causes of PMT are premature atrial depolarization, loss of atrial capture, a return to the demand mode after asynchronous magnet mode pacing, programming from a mode that does not guarantee AV synchrony to a mode in which atrial tracking can occur, noise, certain situations involving Wenckebach behavior, loss of sensing, and the inability of a rate‐smoothing algorithm to allow a rapid change in ventricular rate. Engineering solutions to prevent the occurrence of PMT include a programmable postventricular atrial refractory period (PVARP), differential AV delay, adaptive AV delay, and the ability to discriminate between P waves of atrial origin and those resulting from retrograde conduction from the ventricle. Features such as the ability to lengthen the PVARP for one cycle after exiting the magnet or noise reversion modes or programming to a new mode, lengthen the PVARP for a single cycle following a PVC or revert to DVI pacing for one cycle following a PVC have been developed to recognize initiating events. A third solution. a tachycardia termination algorithm, can recognize and terminate PMT; varying the AV delay to determine whether P waves move in a corresponding manner and using a metabolic sensor to confirm the need for a fast heart rate are other possibilities in the detection of PMT. Diagnostic data features may also be used to evaluate the appropriateness of programmed settings. This discussion concludes that PMT is no longer a significant clinical entity when more advanced DDD pacemakers are utilized.

New Developments for Upper Rate Response in DDD Pacing

Although widely accepted as an effective method of dealing with rapid atrial rates in a DDD pacemaker, Wenckebach‐type and multiblock‐type upper rate behaviors may exacerbate pacemaker‐mediated tachycardia through AV dissociation. In addition, pathologic atrial rates (e.g., atrial fibrillation, atrial flutter, automatic atrial tachycardia, etc.) frequently result in ventricular pacing at inappropriately high rates. New, more sophisticated algorithms available in todays microprocessor‐based DDD pacing systems provide the capability to discriminate successfully a normal atrial rate response to exercise from a pathologic atrial rate. These and other improved capabilities allow the clinician to provide safe rate‐responsive pacing to patients in whom rate‐responsive pacing was previously contraindicated.

A packaged solution to the problems of testing arrhythmia control devices at implant.

A composite implantable arrhythmia control device (ACD) implements the functions of a bradycardia pacemaker, an antitachycardia pacemaker, a cardioverter, and a defibrillator in an integrated fashion. Given this broad spectrum of functionality, the implant testing for these devices can become a formidable endeavor requiring a large ensemble of expensive, complex support equipment, and a significant amount of time. However, if this procedure is not carried out correctly, the device might later fail to defibrillate. This article presents a unique packaging system for an ACD that allows the device to be used while it is still in its sterile package. The device may then be used during implant testing as the defibrillation test unit. This collapses the amount of support equipment that is required to just the ACD, its programmer, and an optional switch box. By providing additional support specifically for implant testing through the ACD programmer, implant testing may be reduced to a quick, easy‐to‐manage procedure. Since the device used during implant testing is the same device that will be implanted, this packaging system offers the further advantage that the physician can be confident that, once implanted, the ACD will function correctly.