John Merideth

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.

The effects of magnetic resonance imaging on implantable pulse generators.

The efects 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 of” mode. None of the pulse generators exhibited any alterations in programmed parameters or in the ability to be reprogrammed after RF pulsing. When the HF 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.

Apparent interruption of atrial conduction pathways after surgical repair of transposition of great arteries

Abstract Apparent interruption of the atrial conduction (internodal) pathways after the Senning operation, the Mustard procedure or the creation of an atrial septal defect was sought in the hearts of 49 patients with transposition of the great arteries, and the findings were correlated with postoperative dysrhythmias. The results indicate that (1) extensive disturbance of the atrial septal connections between the sinus and atrioventricular nodes frequently is associated with serious dysrhythmia, and (2) disruption of the region of the middle atrial conduction pathway, especially when coupled with damage to another pathway, is frequently associated with dysrhythmia, most commonly nodal rhythm.

Prognosis of transient atrioventricular conduction disturbances complicating open heart surgery for congenital heart defects

Abstract Two patients who had open heart correction of ventricular septal defect and atrioventricular canal in 1956 and 1958, respectively, had recurrences of high degree heart block several years after an episode of transient dysrhythmia in the immediate postperfusion period. As a result of these observations, we chose to review our surgical experience during a period when adequate electrocardiographic observations and follow-up studies were available. A total of 911 patients less than 15 years of age had had open heart surgical correction of tetralogy of Fallot, ventricular septal defect or atrioventricular canal from 1960 through 1967. Of the 71 surviving patients who had transient complete heart block, second degree heart block, or atrioventricular dissociation immediately after surgery, 59 could be traced, and only 1 patient (with transient atrioventricular dissociation) had return of the dysrhythmia. During this period, 7 patients had persistent complete heart block after leaving the operating room, and electronic pacing was instituted. Five died within 24 hours after surgery, and the remaining 2 died soon after discharge. The study revealed that the risk of recurrence of transient postoperative high degree heart block or atrioventricular dissociation is low, and the prognosis for patients with sinus rhythm after such an episode is favorable.

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 Medtroric 5992 generator was placed in 35 patients and an Intermedics 259–01 generator in 15. Median implantation time was 105 minutes. Complications requiring reoperdtion in 409 patient‐nnonths 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 capturein 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 conch de that these systems have a low incidence of problems in short‐term followup. (PACE, Vol. 5, September‐October, 1982)

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 poIyurethane‐insuJated pacing leads. Specific concern has arisen over particular bipolar tined polyurelhane 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 al 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 no(to be at increased risk] the rate was 3.9%. Lead failure occurred at an average af 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 thai 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.

Management of cardiac tachyarrhythmias with cardiac pacemakers.

Cardiac pacemakers have been utilized in an increasingly larger variety of rhythm disturbances other than complete heart block. From our experience, we concur with others that temporary pacing may be effectively used for the suppression of cardiac tachyarrhythmias in acute situations.l.2 In view of this experience, it became apparent that certain patients with chronic, refractory tachyarrhythmias might be best managed with permanent cardiac pacing. This report concerns some aspects of our experience with the use of this technique.

An Evaluation of Long-term Stimulation Thresholds by Measurement of Chronic Strength Duration Curves

Successful long‐term cardiac pacemaker therapy requires both reliable generator output and stable, altainable chronic stimulation thresholds. Strength duration curves, which display cardiac stimulalion 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 lead implantation in 19 patients. We found that strength duration curves have 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.

Disturbances in Cardiac Conduction and their Management

A simple classification of atrioventricular block, criteria for diagnosis, and suggested therapy are discussed. The differences between Mobitz I and II second-degree A-V block are reviewed.Good management of patients who have bundle-branch or other forms of intraventricular block depends on informed judgment which includes consideration of (1) the effect of intraventricular conduction disturbances on the pumping action of the heart, and (2) the likelihood that a specific intraventricular conduction disturbance will be complicated by complete heart block.Evidence suggests that common forms of intraventricular disturbance, unlike ventricular fibrillation, do not alter significantly the pumping action of the heart. The role of intraventricular conduction disturbances in the genesis of ventricular fibrillation is assessed.We concluded that only when right bundle-branch block is combined with block of the anterior or posterior fascicle of the left bundle branch is complete heart block sufficiently imminent to warrant special concern. If bilateral block is associated with symptoms of episodic severe bradycardia, pacemaker therapy is indicated.

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.