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R V Calfee

Publications and source records attributed to R V Calfee.

10 recordsLinked to original sources
PubMed1991

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.

Electric Countershock↗
PubMed1988

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.

Algorithms↗
PubMed1987

Improved defibrillation thresholds with large contoured epicardial electrodes and biphasic waveforms.

A reduction in the shock strength required for defibrillation would allow use of a smaller automatic implantable cardioverter-defibrillator and would reduce the possibility of myocardial damage by the shock. Most internal defibrillation electrodes require 5 to 25 J for successful defibrillation in human beings and in dogs. In an attempt to lower the shock strength needed for defibrillation, we designed two large titanium defibrillation patch electrodes that were contoured to fit over the right and left ventricles of the dog heart, covering areas of approximately 33 and 39 cm2, respectively. In six anesthetized open-chest dogs, the electrodes were secured directly to the epicardium and ventricular fibrillation was induced by 60 Hz alternating current. Truncated exponential monophasic and biphasic shocks were given 10 sec later and defibrillation thresholds (DFTs) were determined. The DFT was 159 +/- 48 V, 3.2 +/- 1.9 J (mean +/- SD) for 10 msec monophasic shocks and 106 +/- 22 V, 1.3 +/- 0.4 J, for biphasic shocks with both phase durations equal to 5 msec (5-5 msec). The experiment was repeated in another six dogs in which the electrodes were secured to the pericardium. The mean DFT was not significantly higher than that for the electrodes on the epicardium: 165 +/- 27 V, 3.1 +/- 1.2 J for 10 msec monophasic shocks and 116 +/- 19 V, 1.6 +/- 0.5 J for 5-5 msec biphasic shocks. Low DFTs were also obtained with biphasic shocks in which the duration of the first phase was longer than that of the second.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

A central venous temperature sensing lead.

Pacemaker rate responsiveness derived from changing central venous blood temperature requires the development of sensor leads that are stable and reliable. The relevant characteristics of one such design are described. Temperature response time, data acquisition time, temperature sensitivity, and long-term sensor shunt impedance have been studied both in vitro and in vivo. These parameters are analyzed with respect to the intrinsic temperature signal and to pacemaker implementation problems.

Blood↗
PubMed1986

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.

Electrodes, Implanted↗
PubMed1983

Dual-chamber committed mode pacing.

The proliferation of dual-chamber pacemakers has resulted in several different modalities of DVI pacing. A distinction is made between "committed" and "non-committed" modes, and the differences are presented. In addition, a new hybrid mode has been developed which has been termed "semi-committed" and is currently being introduced. The semi-committed mode divides the AV interval into an early non-physiologic interval and a later "physiologic" interval which enables inhibition of ventricular output following a sensed ventricular event.

Atrioventricular Node↗
PubMed1981

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 surgical 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.

Aged↗