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Biomedical subjects

J Merideth

Publications and source records attributed to J Merideth.

At least 19 recordsLinked to original sources
PubMed1986

The effects of magnetic resonance imaging on implantable pulse generators.

The effects of magnetic resonance imaging were assessed on four dual chamber and two single chamber pulse generators. The tests were performed with a resistive, water-cooled magnet operating at 0.15 T. The 6.4-MHz radiofrequency (RF) field was operated at a maximum power of 1,000 watts with a period adjusted from 130 to 500 ms. Reed switch closure occurred in all six pulse generators tested when placed near the entrance of the magnetic resonance imaging scanner, and the generators reverted to asynchronous operation unless programmed to the "magnet off" mode. None of the pulse generators exhibited any alterations in programmed parameters or in the ability to be reprogrammed after RF pulsing. When the RF field was turned on, there was no change in the asynchronous paced cycle length in four pulse generators; however, during RF scanning there was rapid cardiac stimulation at the RF pulse period in one single chamber and one dual chamber pulse generator.

Animals↗
PubMed1985

Bipolar tined polyurethane ventricular lead: a four-year experience.

With the advent of polyurethane as an insulating material for permanent pacemaker leads, concern has arisen over the integrity and long-term durability of polyurethane-insulated pacing leads. Specific concern has arisen over particular bipolar tined polyurethane ventricular leads. We have assessed our 4-year experience with this lead. This experience involves two groups of patients, those with leads manufactured before a certain date and those with leads manufactured at a later date. In the first group (judged to be at increased risk) the failure rate was 8.8%, and in the second group (judged not to be at increased risk) the rate was 3.9%. Lead failure occurred at an average of 17.5 months in the first group. Adequate follow-up on the second group is not available to determine whether or not the failure rate may eventually be as high as that in the early group. Actuarial analysis suggests that survivorship free of lead failure is probably not significantly different in the two groups. This experience points out the need for determining lead failure rates, identifying optimal lead design and configuration, and establishing a lead registry or mechanism by which the integrity of various pacing leads can be evaluated.

Electrocardiography↗
PubMed1984

Two decades of cardiac pacing at the Mayo Clinic (1961 through 1981).

Pacemaker procedures performed at the Mayo Clinic for the years 1961, 1971, and 1981 were reviewed to examine the changes that have occurred in a large pacemaker practice during the 2 decades since the advent of pacemaker therapy. Major changes in trends and practice have occurred; in addition to numerical growth, the indications for permanent pacing and the technologic alternatives available have expanded considerably. The increasing choices available today (in all areas of pacemaker practice) provide a challenging stimulus to physicians as they seek the best clinical options in patient care.

Cardiac Pacing, Artificial↗
PubMed1984

Apparent pacemaker failure due to reversion circuitry within the programming device.

While being evaluated for a recurrent tachyarrhythmia, a patient with a permanent pacemaker underwent reprogramming of the unit from the DVI to the VVI mode for assessment of the underlying rhythm. Subsequent reprogramming of the pacemaker to the DVI or DDD mode was impossible despite multiple attempts and the use of multiple programmers. The problem was considered to be a malfunction of the pacemaker circuitry, and plans were made for the pacemaker to be explanted and a replacement unit implanted. Before the procedure, the pacemaker company was notified of the explantation. We subsequently learned that a special programming sequence had to be carried out because of reversion circuitry present in the pacemaker but not described in the available literature. This report emphasizes the need for familiarity with each of the individual pacemakers being implanted and the need for the manufacturer to be as specific as possible given the complexity of current units.

Equipment Design↗
PubMed1982

Early follow-up of lead performance in atrioventricular sequential systems.

Recent developments in pacemaker technology led us to report our initial and follow-up assessment of atrioventricular (A-V) sequential systems in 50 consecutive patients. Primary indications for pacing were sinus node dysfunction or A-V block. Leads were introduced through the subclavian vein. Atrial J-tined leads (27 silicone, 19 urethane) were positioned in the atrial appendage or stump in 46 patients, and coronary sinus or Bisping leads were placed in 4 patients; all 50 patients had tined ventricular leads. A Medtronic 5992 generator was placed in 35 patients and an Intermedics 259-01 generator in 15. Median implantation time was 105 minutes. Complications requiring reoperation in 409 patient-months of follow-up included lead retraction (one patient), phrenic nerve stimulation (one), pseudofracture (one), and atrial lead-induced "cross talk" (one). Monthly telephone transmission confirmed atrial capture in 35 patients and loss of capture in 1; the remainder had no identifiable P wave. Ventricular capture was confirmed in all. Postimplant and follow-up checks showed good stability of lead positions. We conclude that these systems have a low incidence of problems in short-term follow-up.

Adult↗
PubMed1982

The clinical and electrophysiologic characteristics of patients with accelerated atrioventricular nodal conduction.

The clinical and electrophysiologic features of 42 patients found to have rapid atrioventricular (AV) nodal conduction during electrophysiologic study are described. The distinctive clinical feature of these patients was the high incidence of supraventricular tachycardias, which were rapid and had been poorly responsive to conventional antidysrhythmic treatment. Abnormalities of both AV nodal conduction and AV nodal refractoriness were present. Medical management and late follow-up were characterized by inconsistent control of rhythm. In four patients, control of the tachycardia was finally achieved by successful ablation of an accessory extranodal pathway that participated in macro-reentry paroxysmal supraventricular tachycardia. In a fifth patient, the tachycardia was controlled with the use of a patient-activated radiofrequency atrial-stimulating pacemaker. Although the existence of shortened AV nodal conduction time and refractoriness may not cause supraventricular rhythm disturbances, symptoms are aggravated by resultant rapid ventricular rates. Treatment for patients with this anatomic-functional substrate must be highly individualized and be based on electrophysiologic investigation. Newer treatment modalities with investigational medications, pacing techniques, and surgical approaches may play an important role in the management of these patients.

Adolescent↗
PubMed1981

Permanent pacemaker infections: characterization and management.

From January 1974 to June 1980, a total of 46 patients were treated for infections involving permanent pacing systems. Demographic characteristics, types of infecting organisms, specific clinical features, significance of an infected foreign body and various medical and surgical treatment methods are described. Likely infecting organisms depend on the mode of presentation and the time course of the infection. Optimal treatment for the large majority of patients requires removal of the entire infected pacing system. In a subgroup of patients, a short course of antibiotic therapy followed by one stage surgery involving implantation of a new pacing system and concurrent explanation of the infected pacemaker was used safely with excellent results.

Adult↗
PubMed1981

An evaluation of long-term stimulation thresholds by measurement of chronic strength duration curve.

Successful long-term cardiac pacemaker therapy requires both reliable generator output and stable, attainable chronic stimulation thresholds. Strength duration curves, which display cardiac stimulation thresholds as a function of impulse duration, provide needed data to evaluate more thoroughly acute and chronic lead thresholds. We measured chronic strength duration curves at the time of generator replacement in 47 patients with three different types of lead systems of variable geometry and surface area and compared these curves with acute strength duration curves measured at the time of initial implantation in 19 patients. We found that strength duration curves has a characteristic shape; however, chronic strength duration curves were shifted upward and to the right of acute strength duration curves, regardless of electrode tip surface area or geometric design. Our data suggest that variable pulse width exceeding 1 ms may not significantly reduce stimulation thresholds.

Aged↗
PubMed1981

Infected epicardial pacemaker systems. Partial versus total removal.

Nine patients with infected epicardial pacemakers are described. All of the patients had infection localized to the generator pocket. Staphylococcus epidermidis, the most common organism isolated, was found in seven (77.8%). Conservative nonsurgical treatment was initially attempted in five patients. This failed in all and necessitated subsequent operation. At the time of the initial operation, lead transection and partial removal of the system was performed in seven patients. In four of them (57%), persistent infection necessitated further operation and complete extraction to eradicate the infection. In contrast, in all six patients (100%) in whom total removal was achieved (two at the time of initial operation and four at the time of subsequent operation), there was successful resolution of the infection. Therefore, complete extraction of the entire pacing system should be carried out, whenever possible, to achieve the greatest likelihood of eradicating the infection.

Aged↗
PubMed1980

The value of redundancy in chronic bipolar pacemaker electrode systems.

Bipolar pacing systems, because of the presence of two intracardiac electrodes, provide lead redundancy. This allows conversion of bipolar to unipolar pacing or the reversal of lead polarity. During a 3-year period, this redundancy was utilized in 34 (13.7%) of 248 patients with chronic bipolar lead systems during follow-up pacemaker surgery. Of the 34 patients, elective pulse generator change was the most frequent indication for surgery (23 patients) and in this group redundancy was used most often to select the lead configuration with the highest R-wave amplitude and lowest stimulation threshold, or to solve the problem of weld defects of the connector pins or frayed insulation. The remaining 11 patients underwent surgery for pacemaker system malfunction and in this group redundancy was used to avoid the need for lead repositioning or placement of a new catheter system. Lead redundancy in those patients in whom bipolar pacing has been selected provides flexibility at the time of additional pacemaker surgery, and its use may obviate the need for a change in catheter system when stimulation thresholds are excessive, wire fraction is irreparable, or bipolar sensing signals are inadequate.

Electrodes, Implanted↗