Fourteen years of implanted pacemakers in children

Chronic Right Ventricular Pacing and Cardiac Performance:. The Pediatric Perspective

Cardiac stimulation from right ventricular apical or free-wall lead positions alters inter- and intraventricular impulse conduction and distorts biventricular contractility. This may contribute to eventual cellular remodeling and the development of histopathological changes which, over time, adversely affect left ventricular systolic and diastolic functions. This concept has especially important implications when pacemaker therapy is initiation in young patients. Recent studies demonstrating physiological benefits of right ventricular septal, outflow, or bundle of His pacing, in deference to the apical implant site, have gained interest to potentially prevent dysfunction and improve paced myocardial contractility. Pacing initiated in children can be expected to have more far-reaching consequences than pacing initiated in the elderly. Unfortunately, there have been limited clinical pediatric studies that evaluate precise site-specific lead locations. This current report presents a review of pacemaker applications in children, both with and without structural congenital heart defects, including the earliest applications in which patient survival was the prime concern, to more recent studies attempting to optimize physiological and histological parameters associated with pacemaker induced contractility. The past decade has seen direct evidence that right ventricular apical pacing in children contributes to adverse histological remodeling and eventual contractile dysfunction. More recent studies demonstrate that selective site pacing can be effectively applied to all children with and without structural congenital defects and shows promise in the prevention of previously documented adverse remodeling and deterioration of systemic ventricular contractility.

The Southern Thoracic Surgical Association 50th anniversary celebration: the impact of STSA pediatric cardiothoracic surgery manuscripts on surgical practice

BACKGROUND

Members of the Southern Thoracic Surgical Association (STSA) have presented important pediatric cardiothoracic surgery papers at the annual meetings over the last 50 years. In order to determine the influence of these presentations on the practice of surgery, a review was undertaken. Early papers were characterized by emerging advances in open-heart surgery, anatomic congenital heart studies, and electrophysiologic discoveries that extended life with pacemakers. Later years were characterized by innovative myocardial preservation methods, improved cardiopulmonary bypass techniques, expanded homograft availability, emphasis on accurate repairs, intraoperative transesophageal echocardiography, and cardiopulmonary transplantation.

METHODS

All but one of the scientific programs of the annual meetings (that of 1964) were located. The programs were reviewed and 180 presentations were identified on topics in congenital heart disease, pediatric thoracic disease, and pediatric thoracic wall abnormalities. Of those 180 oral presentations, 155 manuscripts (86%) were eventually published or in press and available for critical review and analysis. Manuscripts were grouped by diagnosis or therapeutic intervention. We determined a "cumulative citation frequency" (CCF), which measures the number of times an article is cited in the bibliography of related papers in the universe of participating journals. The selected manuscripts were compared with the historic landmark contributions and the existing trends at the time, and the number of articles both by individual authors and from institutions were tallied.

RESULTS

Grouping by authors and institutions showed that 100 of 155 pediatric cardiothoracic manuscripts (65%) originated from 13 institutions. The CCF for the 20 leading articles ranged from 26 to 93.

CONCLUSIONS

This historical STSA 50-year record of pediatric cardiothoracic advances was accomplished in a milieu of collegial respect and camaraderie. Our annual meetings over the years have provided a venue for thoracic surgeons to share their ideas, innovations, and scientific inquiry. These contributions have significantly affected the practice of pediatric cardiothoracic surgery. The STSA has worked for 50 years and we trust that it will work for another 50 years and beyond.

Long-term performance of bipolar epicardial atrial pacing using an active fixation bipolar endocardial lead

Bipolar epicardial leads are not yet widely available for atrial use. Since September 1986, we have used a bipolar active fixation endocardial lead (Cardiac Pacemakers model number's 4266, 4268, and 4269) as a bipolar epicardial atrial lead by attaching the corkscrew tip to the atrial surface and imbricating atrial tissue around the more proximal electrode. A total of 77 bipolar epicardial atrial leads have been implanted using this approach in 72 patients with congenital heart disease (ages 3 months to 38.7 years; mean 8.9 +/- 8.8 years). Indications for atrial pacing included AV block (n = 46), sinus node dysfunction (n = 17), and antitachycardial pacing (n = 9). Indications for epicardial pacing included the presence of an intracardiac right to left shunt (n = 33), concomitant cardiac surgery (n = 26), surgeon preference (n = 7), and lack of transvenous access to the atrial endocardium (n = 6). Follow-up (median 23 months; mean 28.0 +/- 23.1 months; range 1-78 months) data beyond 1 month postimplantation were available for 44 leads. Atrial sensing was > or = 2.0 mV for 26 leads (59%) with sensing possible at > or = 0.75 mV for 42 leads (95%). Threshold data were available at 5 V for 37 leads and at 2.5 V for 36 leads with mean pulse width thresholds measuring 0.21 +/- 0.33 ms and 0.34 +/- 0.34 ms, respectively. Two leads failed (high capture thresholds at 5 days [n = 1], lead fracture at 42 months [n = 1]; one of which was replaced. Four additional leads were replaced electively (marginal thresholds [n = 1], intermittent phrenic nerve stimulation [n = 1], damaged during subsequent surgery [n = 1], clinically irrelevant insulation break [n = 1]) concomitant with additional cardiac surgery. Until a commercially available lead is developed and released, improvisation with a bipolar active fixation endocardial lead as a bipolar epicardial atrial lead is a reasonable approach to providing bipolar atrial sensing and pacing in patients for whom endocardial pacing is contraindicated.

Pacemakers in children: an update

This report reviews recent pacemaker technological advances as they apply to infants, children, and adolescents. Indications for pacemaker implantation in children have evolved since the 1984 Joint Task Force Guidelines. Recent data show that pacemaker implantation should be strongly considered in patients who have (1) asymptomatic congenital complete AV block with a mean heart rate less than 50 beats/min or other evidence of junctional instability; (2) congenital AV block with long QT interval; or (3) congenital long QT syndrome with bradyarrhythmias, or when conventional beta-blocker therapy is unsuccessful. Permanent pacemaker implantation is not necessarily an effective prophylactic measure against sudden death in patients following their operation who are receiving drug therapy for atrial tachyarrhythmias, and so is not absolutely indicated. New developments in lead technology have made transvenous lead systems more feasible for pediatric use. Because epicardial leads are required for small infants and for cosmetic reasons in some older children, design improvements are needed to enhance epicardial lead performance. Rate-responsive pacing is an acceptable alternative to dual-chamber pacing for augmenting exercise tolerance, and for children with sinus node dysfunction it is the preferred pacing mode. Pacemakers with automatic antitachycardia capabilities and with noninvasive electrophysiology features are valuable in children with atrial tachyarrhythmias. New data suggest that chronic atrial pacing also may be effective in controlling atrial tachyarrhythmias. New developments in pacemaker systems for the young parallel those for the older population, but differences between adult and pediatric patients demand ongoing increased participation by pediatric cardiologists.

Comparison of two myoepicardial pacemaker leads: follow-up in 80 children, adolescents, and young adults

Although several types of commercially available epicardial leads exist, few postimplantation data have been reported. To compare "screw-in" (6917-35) leads with "stab-on" leads (4951-35) from the same manufacturer, we reviewed the records of 80 young patients (age 8 days to 29 years) who underwent ventricular epicardial pacemaker implantation from 1973 to 1986. Follow-up for the 57 patients with the 6917-35 model ranged from 3 months to 17 years (median 6.5 years) and for the 23 patients with the 4951-35 model 9 days to 4.25 years (median 2.0 years). Actuarial life table analysis revealed significantly (P less than 0.001) fewer 4951-35 leads were functioning at each of 1-5 years after implant, compared to the 6917-35 leads. Analysis of available threshold pulse width data revealed no difference (P = 0.08) acutely (6 weeks after implant), but a significantly (P = 0.05) higher mean threshold for the 4951-35 leads was found chronically. No significant correlation was found for lead failure with age, underlying heart disease, lead site (i.e., left or right ventricle), or surgical approach. Using the sutureless, stab-on technique, the 4951-35 lead is associated with higher thresholds and lower survival rate when compared to the 6917-35 lead.

Epicardial ventricular pacemaker electrode longevity in children

While epicardially implanted electrodes remain the most widely used in children for ventricular pacing, their expected longevity remains unknown. The longevity of 126 such electrodes implanted from January 1970 through December 1985 was evaluated in 81 children followed up for 1 to 192 months (median 63). Age at initial implant was 1 day to 18 years. Each child had from 1 to 5 electrodes implanted; 85 electrodes were of the sutureless helical type and 41 were of the suture-fixated type. Electrode failure, defined as loss of capture with a high pacing threshold found at operation or sensing failure, occurred in 38 electrodes from 1 to 157 months postimplant (median 37). Mode of failure was high threshold with high impedance (n = 15), low impedance (n = 6), complete inability to pace (n = 8), sensing failure (n = 2) or high threshold with no measure of impedance (n = 7). Actuarial life table analysis of electrode longevity showed a 88 +/- 3% (standard error of the estimate) survival rate at 6 months with no significant decrease until 53 months (75 +/- 5%, p less than 0.05). There was then a gradual steady decrease to 49 +/- 7% by 101 months. From 101 to 157 months no significant decrease occurred. Survival rate decrease was greatest within the first 6 month period postimplant (-12%). Electrodes surviving to 6 months are highly likely to survive until 53 months. Of those surviving to 53 months, 74% should survive to 120 months.

Symptomatic sinus bradycardia in infants with structurally normal hearts

Sixteen infants, ages 6 weeks to 23 months, were evaluated because of syncopal attacks (n = 6), apneic episodes (n = 3), or a combination of syncope, apnea, or "convulsions" (n = 7). Comprehensive metabolic and neurologic investigations yielded negative results in 15 infants; in one, an abnormal EEG was recorded. Severe sinus bradycardia, complete sinus arrest, junctional escape rhythm, or ventricular escape rhythm was found in four patients, and permanent multiprogrammable pacemakers were implanted. Follow-up for 6 to 24 months with ventricular demand pacing showed complete cessation of attacks in two infants and marked improvement in two.

Epicardial corkscrew lead fracture: an underreported cause of pacing failure?

Three children with a pacemaker sustained similar lead fractures within a two-year period. Each fracture occurred in the corkscrew portion of a Medtronic Model 6917 epicardial lead. All patients were boys. The leads had been in place for 12, 45, and 43 months prior to fracture. None of the patients had sustained major trauma. Fracture of the corkscrew lead has been considered an uncommon complication. However, three lead fractures in the corkscrew area in a population of 60 children followed at this institution indicate that this may be a more common cause of pacemaker-system malfunction than previous data suggest. A plea is made for reporting all pacing failure to the manufacturer.

Ventricular pacing in children

Ventricular pacing was performed in forty-one children ranging from one day to twenty years of age (median age = 10). Weight of the recipient at implant ranged from 2 kg. to 86 kg. Indications included presyncope, syncope, dyspnea on exertion, congestive heart failure, postoperative infra-Hisian heart block, and inadequate cardiac rate during pharmacotherapy. Four patients died during follow-up, but no deaths were attributable to pacemaker management. In contrast, 66% of the patients required more than one pacemaker related-operative procedure, and 43% of leads implanted failed by 48 hours. Indications for permanent cardiac pacing in this population at this time are symptomatic congenital AV block, symptomatic sinus node disease, and AV block in the postoperative period. Technological developments which might reduce complications seen in this population and electrophysiologic techniques which may better define indications for pacing in children are also reviewed.

Electrophysiologic residua and sequelae of surgery for congenital heart defects

Postoperative arrhythmias may occur in any patient who undergoes intracardiac surgery for a congenital heart defect. The correction of certain intracardiac heart defects predisposes to a large incidence of cardiac arrhythmias. Ventricular arrhythmias and conduction disturbances are seen after correction of tetralogy of Fallot, ventricular septal defect and atrioventricular canal defect. Supraventricular arrhythmias and sinus nodal dysfunction may be seen after surgery for transposition of the great arteries or atrial septal defect. The identification, evaluation and treatment of these patients are discussed.

Cardiac pacing in children

Twenty patients aged between 12 months and 13 years underwent permanent pacemaker implantation. The main indication for pacing was post-surgical atrioventricular block. The complication rate was high and related mainly to infections and lead system problems. The use of small multiprogrammable pacemakers is expected to reduce the reoperation rate for system malfunction and elective replacement. Newer methods of electrode insertion and active fixation devices in smaller diameter leads make endocardial pacing a practical alternative to epicardial pacing in the larger child who did not require a pacing system at the time of surgery.

Comparison of the sutureless and suture-type epicardial electrodes in pediatric cardiac pacing

Fourteen consecutive patients with the suture-type electrode (Group 1) were compared with the previous 14 patents having the sutureless electrode (Group 2). five patients in Group 1 had had failure with the sutureless electrode, for a total of 23 patients. In Group 1, no exit block was encountered. One patient had sensing problems corrected simply by increasing the pacer rate. One patient had generator failure and another, lead fracture. In 5 patients in Group 2, exit block developed early (less than 6 months after implantation); 3 patients had the problem twice, making a total of eight early failures. Two patients had late exit block (more than 6 months after implantation). Improved results with the suture-type electrode can probably be explained by its smaller head, larger surface area, ease of placement in a small space, and control of direction and depth of implantation.

Changing indications for pacemakers in children

Permanent pacemakers were implanted in 50 children. Indications were symptomatic sinus node dysfunction in 34 (68%), surgical block in 9 (18%), and congenital block in 7 (14%). Twenty-three (68%) of the 34 children with sinus node dysfunction had undergone prior cardiac operations. Only 4 of the 50 patients (8%) had electrode problems after a mean pacing time of 29.5 months (range, 1 to 96 months). All 35 of the mercury-cell pulse generators used in 28 patients ceased to function after an average useful life of 20.8 months (range, 1 to 51 months). The lithium-powered units in the 45 survivors all show satisfactory pacing after 5 to 44 months (mean, 28.1 months). With improved pacemaker technology, longer survival after complex repairs, and better monitoring techniques, the indications for cardiac pacing in children have broadened. Surgical block now is an indication in only a small fraction of the pediatric pacemaker population. Sinus node dysfunction accounts for an ever-increasing majority of the pacemakers we currently implant in children.

Pacemaker implantation in infants and children: a simplified approach

A technique for epicardial pacemaker implantation is described. A single incision is utilized through which the electrode and power pack are implanted. Twelve infants and children were operated on in the last four years using this procedure. The marked improvement in cosmetic appearance and the relative ease in module replacement are major advantages of this method.

The recessed chest wall pacemaker pocket

Recurrent pouch problems led to the development of a recessed chest wall pacemaker pocket. Segments of the seventh and eighth ribs were resected in the mid-axillary line resulting in a "tailor-made" space suitable for generator implantation. Follow-up at one year has proven the chest wall to be a satisfactory alternative site for a pacemaker pocket.