Exit block in pediatric cardiac pacing

Atrial undersensing secondary to quiet timer blanking in pediatric and congenital heart disease patients

BACKGROUND

Atrial undersensing despite normal atrial lead parameters and high amplitude electrograms has been described in adult patients as a consequence of atrial amplifier saturation. Repetitive inputs cause amplifier ringing and undersensing occurs as a consequence of quiet timer blanking. High amplitude ventricular electrograms can also result in atrial blanking secondary to cross-chamber effect. This has not been described in pediatric patients or epicardial pacing systems and specific risk factors are not known. We describe five cases of atrial undersensing in pediatric and congenital heart disease patients with epicardial dual-chamber systems and high ventricular lead outputs.

METHODS

This was a retrospective cohort study of all patients with dual-chamber pacing systems cared for at the Heart Institute at Children's Hospital Colorado.

RESULTS

Five cases of atrial undersensing with normal atrial lead parameters were found. All were epicardial systems with acceptable lead parameters at implantation and Medtronic (Medtronic, Inc., Minneapolis, MN, USA) generators with unipolar leads. Ventricular pacing outputs were elevated at presentation, median 5.5 V (5-7.5). Presenting symptoms were exercise intolerance (four) and detection on routine monitoring (one). Successful interventions included reduction in ventricular lead pacing output (one), programming of rate response (two), and implantation of an alternative generator manufacturer (two).

CONCLUSION

Atrial undersensing secondary to amplifier ringing and quiet timer blanking is an uncommon presentation but may be clinically important in patients with unipolar epicardial atrial leads and high pacing outputs from ventricular leads.

Thirty years of experience with epicardial pacing in children

Due to underlying cardiovascular anatomy and size, epicardial pacing may be the preferred method of pacing in small children. To assess long-term safety, we reviewed all epicardial pacemakers implanted in children between 1971 and 2001. We found that 122 patients, with a median age of 5.4 years, had a total of 181 pacemakers and 260 electrodes implanted over a total follow-up of 789 patient-years. Of the total, 12 patients died after the first implantation, with one death attributable to dysfunction of the pacemaker. Reintervention was required in 75 patients after 5.0 +/- 3.2 years, due to depletion of the battery in 45 patients (60%), fracture or dysfunction of electrodes in 27 patients (36%), and infection in 3 patients (4%). In univariate analyses, risk factors for reintervention were an approach via a median sternotomy, with a relative risk of 2.3 (p = 0.0087), and an indication for pacing other than atrioventricular block, with a relative risk of 1.7 (p = 0.0314). In multivariate analyses, the approach via the median sternotomy independently predicted the need for reintervention, with a relative risk of 2.1, and 95% confidence intervals from 1.1 to 4.1 (p = 0.0256). The longevity of the second pacemaker and/or its electrode, assessed in 26 patients, was 3.7 +/- 2.6 years, not shorter than the first implantation (p = 0.4037). We conclude that epicardial pacing is a reliable means of achieving permanent pacing in children, with low morbidity and mortality. A substantial proportion, nonetheless, requires reintervention within five years, warranting meticulous follow-up.

Transfemoral pediatric permanent pacing: long-term results

The femoral vein has been used as an alternative conduit to implant pacemakers in children of any weight. Such method associates endocardial pacing and good cosmetics. The aim of this study was to evaluate prospectively, since 1981, the long-term follow-up of 99 children, from newborn to 13 years old (average = 4.1 +/- 3.6 years, 56 girls), who underwent the implantation of pacemakers via the femoral vein. Atrioventricular block was present in 88% of patients, of congenital etiology in 39% and postoperative in 54%. Single chamber pacemakers were implanted in 92% of patients. During a mean follow-up of 5.3 +/- 5.0 years (maximum = 18.2 years), 5 patients died of cardiac causes, 4 of infection, 2 suddenly, and 3 of unknown causes. The 5-, 10- and 15-year actuarial survival rates were 83.7%, 75.7%, and 75.7%, respectively. Transfemoral leads were used for a mean of 48.9 +/- 44.0 months. Reasons for lead explantations were pacing failure in five patients, infection in eight, and elective in nine. The 2-, 5- and 10-year actuarial survivals of transfemoral leads were 87.6%, 73.8%, and 31.8%, respectively. The mean lead survival was 97 months. Overall, 105 reoperations were performed, 38 for battery depletion, 24 for body growth, 14 for infection or pocket revisions, and 27 for miscellaneous reasons. In conclusion, the durability and overall long-term performance of transfemoral leads were excellent.

Characteristics and results of epicardial pacing in neonates and infants

The results of epicardial pacing in infants with isolated congenital complete atrioventricular block (CAVB) are reported. Thirty-four patients, aged 1 day to 20 months (22 patients < 1 month), were paced between 1988 and 1998. Thirty had bradycardia < 50 beats/min with symptoms in 12 patients, and 4 patients were paced because of associated ventricular ectopy or prolonged QT interval. In thirty cases, the electrodes were implanted through a left thoracotomy and connected to an abdominal generator; in four, the subxyphoid approach was preferred. Twenty-two children had dual chamber units. There was no operative death, but three patients died later of cardiomyopathy. Seven infants were reoperated for electrode displacement, infection, exit block, and pacemaker sensitivity. Chronic ventricular thresholds ranged from 0.3 to 2 V except in one case (4 V) and proper atrial sensing was lost in two cases. All children are doing well and the generator has lasted at least 5 years in 16 cases. In conclusion, epicardial pacing in infants with CAVB can be done with satisfactory results. There was no mortality in relation with pacing and thresholds have improved with the use of steroid-eluting electrodes. The deep location of the generator prevents cutaneous erosion and allows implantation of large units with a longer life duration.

A comparison of steroid-eluting epicardial versus transvenous pacing leads in children

OBJECTIVE

To evaluate the acute and chronic performance of steroid-eluting (SE) epicardial (EPI) pacing leads as compared to SE transvenous (TV) pacing leads in children.

METHODS

From 1989 through 1997, 55 children with congenital heart disease received a total of 85 SE pacing leads, of which 38 were EPI and 47 TV. The mean age of children receiving EPI leads was younger than those receiving TV leads (7.7 months vs 15.1 years, p = 0.001), and they had shorter follow-up (17.2 months vs 36.2 months, p < 0.001). All leads were evaluated for acute and chronic sensing and capture thresholds, and impedance.

RESULTS

Acute and in particular chronic atrial and ventricular sensing and capture thresholds in SE EPI and TV leads were essentially equivalent. [table: see text]. The chronic impedance of TV leads (atrial 525 ohms, ventricular 520 ohms) was consistently higher than EPI leads (atrial 404 ohms, ventricular 386 ohms).

CONCLUSION

At intermediate follow-up, SE EPI leads are functionally equivalent to SE TV leads. We recommend the use of SE EPI leads as long as practically feasible prior to using the TV approach in children who will require a life-time of pacing.

Applications of pacing strategies in neonates and infants

Pacing in neonates and infants continues to be challenging due to size constraints, growth potential, and the need for life long pacing. Indications for permanent pacing in pediatric patients have been difficult to determine due to the lack of data from controlled studies and multicenter trials. Temporary pacing has been useful to restore cardiac output in pediatric patients quickly and efficiently. Methods of temporary pacing include transcutaneous, transesophageal, transvenous, and epicardial. Permanent pacemaker implantation can be accomplished by transvenous or epicardial approaches, but the use of transvenous pacing in neonates and infants offers no advantages over epicardial pacing. Transvenous pacing in infants is often prohibitive due to size and growth constraints as well as the subsequent risk of skin erosion and venous thrombosis. Smaller pulse generators, multiprogrammable features, and steroid-eluting epicardial leads are a few of the technological advances that have made pacing in neonates and infants easier and safer. Data supporting the use of pacing systems in very young patients are sparse. Pacing 'indications' should be viewed as guidelines until such data can be accumulated.

Permanent cardiac pacemakers: issues relevant to the emergency physician, Part I

Many people benefit from the implantation of cardiac pacemakers for management of certain cardiac dysrhythmias. These patients are seen regularly in the emergency department with a variety of pacemaker complications and malfunctions. The presence of a pacemaker may also affect management of unrelated medical problems. This two-part series reviews the medical issues related to patients with permanent pacemakers. Part I covers pacing modes and terminology, complications of the implant procedure, and the approach to a patient with a permanent pacemaker. Part II covers the causes, diagnosis and management of pacemaker malfunction; the pacemaker syndrome; the pacemaker Twiddler's syndrome; and other considerations in the paced patient including diagnosis of acute myocardial infarction, ACLS protocols, trauma, and sources of interference. Indications for permanent pacemaker implantation and temporary external pacing will not be covered.

Cardiac pacing in premature infants and neonates: steroid eluting leads and automatic output adaptation

BACKGROUND

Appropriate generator and lead selection as well as techniques of implantation are most important aspects of cardiac pacing in the extremely young patient. Here we report the clinical results using a new technique with automatic output adaptation based on evoked response in combination with steroid-eluting epicardial leads in small children.

METHODS

One neonate and 2 premature infants underwent permanent pacemaker implantation because of congenital high-degree atrioventricular block or postoperative complete heart block, respectively. Steroid-eluting epicardial leads and a multiprogrammable pacemaker with automatic output adaptation were used.

RESULTS

Intermuscular abdominal generator placement and epicardial suture-fixation of the bipolar lead through a subcostal approach was without complications. Serial follow-up examinations revealed safe and consistent pacemaker function up to 12 months after operation.

CONCLUSIONS

The technique represents an excellent alternative for permanent cardiac pacing in extremely small patients. We believe that it provides an increase in functional lifetime of the devices and delays the need for battery replacement with its associated complications in this young patient population.

Pacemaker therapy in premature children with high degree AV block

The smallest pacemaker pulse generator and a steroid-eluting bipolar epicardial lead were implanted in two premature children with symptomatic AV block. Stable capture threshold and high amplitude evoked response electrogram resulted in normal function of the pacemaker Autocapture algorithm, which adjusts output 0.3 V above the measured capture threshold. Autocapture had previously been used only with endocardial leads. Longer-term observation is required.

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.

Permanent left ventricular pacing with transvenous leads inserted into the coronary veins

This paper describes a preliminary experiment-conducted jointly by 2 centers-of permanent left ventricular pacing using leads inserted by the transvenous route and through the coronary sinus into the cardiac veins of the left ventricle free wall. The aim was to obtain permanent biventricular pacing in a totally endocavitary configuration in patients with severe LV dysfunction and drug-refractory heart failure. Two types of leads were used: nonspecific unipolar leads at the beginning of the experiment, followed by leads specifically designed to be used in the coronary sinus in a second step. The electrode could be fitted in an adequate location in 35 of the 47 patients (75.4%), with a 1.15 +/- 0.7 V acute pacing threshold and 11.8 +/- 5.7 mV R wave amplitude. The success rate was significantly higher with the specific electrodes (81.8% vs 53.3%, p < 0.001). The pacing and sensing thresholds upon implantation were not influenced by the type of lead or by the localization of the cardiac vein that was catheterized (great cardiac vein, lateral vein, postero-lateral or posterior vein, mid cardiac vein). In contrast, the pacing threshold was significantly lower (0.8 +/- 0.2 vs 1.8 +/- 0.8 V; p = 0.002) and the R wave amplitude tended to be greater (13.1 +/- 4.5 mV vs 9.3 +/- 6.5 mV; p = 0.07) when the tip electrode could be inserted distally into the vein, by comparison with a proximal site near the ostium. At the end of follow-up (10.2 +/- 8.7 months), 34 out of the 35 leads were still fully functional, with a chronic pacing threshold of 1.8 +/- 0.7 V and a R wave amplitude of 10.7 +/- 6 mV. To conclude, permanent LV pacing via the transvenous route is possible in most patients, with excellent safety and long-term results.

A comparison of two stab-on unipolar epicardial pacing leads in children

The Oscor MP52V and Medtronic 4951 leads have similar construction and intended application. To determine if one of these designs was more suited to pediatric pacing, we reviewed implant, 3 month, and 12 months follow-up thresholds for all 18 MP52V implants at our institution from December 1989 to April 1991 and compared them to the 4951 implants from January 1982 to October 1989. Lead survival for the MP52V implants was compared to the most recent 36 4951 implants. Patients ranged in ages from 2 days-16 years (median = 4 years) and required antibradycardia pacing for congenital or acquired heart disease. Patients were compared for weight and proportion of atrial leads in each group by t-test and Fisher exact tests respectively. Energy thresholds were assessed in microJ and compared by t-test. Lead survival was defined by abandonment or replacement for any reason. Kaplan & Meier survival curves were plotted and compared by Gehan's Wilcoxan Test. There were no significant differences between the MP52V and 4951 groups for age at implant (53 months vs 80 months) or proportion of atrial implants (5/18 vs 11/36). Lead survival was poor but did not differ significantly (70% vs 78% cumulative survival at 3 years), usually failing by exit block. Implant and follow-up thresholds did not differ significantly between leads. The MP52V did not provide significant improvement in performance over the 4951. New epicardial lead designs are needed to improve lead survival and thresholds in children.

Long-term performance of epimyocardial pacing leads in adults: comparison with endocardial leads

The long-term performance of epimyocardial pacing leads in children is well established, but few studies have analyzed the performance in adults. This issue has clinical relevance in view of the increased use of epimyocardial leads with implantable cardioverter defibrillator and antitachycardia pacing systems. We analyzed 93 epimyocardial pacing "systems" (121 leads: 65 unipolar, 28 bipolar) in adult patients (age 57 +/- 16 years), implanted since January 1980. Two different models were studied: Medtronic 4951 "Stab-on" (n = 35) and Medtronic 6917/6917A "Screw-in" (n = 58). A control group was created by randomly matching each epimyocardial system with two endocardial leads, according to age and year of implant. Epimyocardial and endocardial leads were followed-up for 44 +/- 35 and 43 +/- 35 months, respectively (P = NS). Freedom from failure for epimyocardial leads was 0.91 (95% Confidence Interval [95% CI] = 0.82 to 0.96) at 5 years, and 0.91 (95% CI = 0.69 to 0.98) at 10 years. No difference was found between the two analyzed models. Freedom from failure for endocardial leads was 0.97 (95% CI = 0.93 to 0.99) and 0.90 (95% CI = 0.61 to 0.97) at 5 and 10 years, respectively. Epimyocardial leads had a significantly poorer short-term survival than endocardial leads, secondarily to earlier "technique related" failures (P = 0.03; relative risk 3.0; Wilcoxon test). However, overall long-term performance was similar to endocardial leads. Epimyocardial pacing leads, meticulously implanted and tested, have a long-term performance similar to endocardial pacing leads.

Improved chronic epicardial pacing in children: steroid contribution to porous platinized electrodes

Although new "low threshold" epicardial electrodes combine steroid with a porous, platinized-platinum surface, the actual contribution of steroid elution has not been established. We evaluated this new electrode surface design with and without steroid in 13 children, ages 1-22 years. Both electrodes are unipolar and of similar surface area. The Medtronic Model 4951-P is a barb design for epimyocardial insertion without steroid while the Model 10295A is a steroid eluting, epicardial disk-shaped design. Both electrodes were implanted for atrial and ventricular pacing. At implant, sensed P and R waves, and pacing impedances were comparable between both electrodes. There were no significant differences between initial measured pulse width or calculated energy thresholds for the first 2 months following implant. Strength-duration curves for both electrodes at 1 month were comparable to implant values. After 2 months, the threshold of the nonsteroid electrode peaked and stabilized at a significantly higher (P less than 0.05) level than the more constant steroid eluting electrode. This difference continued for the first year following implant. We conclude that the new porous, platinized-platinum electrode design intrinsically limits initial electrode-tissue interface reactivity in children and improves epicardial pacing with low chronic threshold values. Steroid elution augments these intrinsic qualities by maintaining fibrous capsule stability with more constant low thresholds over time.

Steroid-eluting epicardial pacing leads in pediatric patients: encouraging early results

OBJECTIVES

This study evaluated the pacing and sensing characteristics of a new porous-tipped steroid-eluting epicardial lead in a group of pediatric patients.

BACKGROUND

Pacing in children may be complicated by small patient size, patient growth and the prevalence of structural congenital heart disease in children requiring pacing. Epicardial pacing has been associated with a high incidence of problems with sensing and capture, prompting the use of transvenous endocardial pacing when possible. In some children, epicardial pacing may still be desirable because of small patient size, potential for caval obstruction, previous cardiac surgery limiting transvenous access to the heart, or the need to repair congenital heart disease at the time of pacemaker insertion.

METHODS

Twelve patients aged 3 weeks to 18 years underwent placement of 23 epicardial pacing leads (8 atrial, 15 ventricular). Pulse width thresholds, sensing thresholds and lead impedance were measured weekly for 6 weeks, then at 3, 6, 12 and 18 months after pacemaker implantation. The median duration of follow-up was 12 months.

RESULTS

Ventricular pulse width thresholds did not change over time, whereas atrial pulse width thresholds improved significantly. At 6 months, the mean pulse width threshold at 2.5 V for the atrial and ventricular leads was 0.10 +/- 0.03 and 0.19 +/- 0.09 ms, respectively. The thresholds were slightly lower at 12 and 18 months. At the most recent follow-up, all atrial leads sensed appropriately at 2.5 mV and all ventricular leads at 5 mV.

CONCLUSIONS

These encouraging early results suggest that steroid-eluting epicardial pacing leads may be an attractive option for children needing epicardial pacing. Their excellent pacing and sensing characteristics may allow reliable dual-chamber pacing in infants who are too small for transvenous pacing.

Conjoined subrectus pocket for permanent pacemaker placement in the neonate

We present a method of pacemaker implantation in neonates using a subxyphoid epicardial lead and subrectus placement of the pulse generator. This method is simple and safe and carries minimal morbidity.

Is Epicardial Dual Chamber Pacing a Realistic Alternative to Endocardial DDD Pacing? Initial Results of a Prospective Study

Seventeen patients, in whom an epicardial (n = 7) or a transvenous DDDM pacemaker system had been implanted between June 1988 and October 1990, were followed up for pacemaker and lead related complications, pacemaker longevity, and electrophysiological lead parameters. The mean follow-up interval was 18 +/- 12 months, maximum 34 months. There were no differences in chronic atrial and ventricular sensing thresholds between epicardial and endocardial stimulation, nor were there any differences concerning lead related complications between the two pacing modalities. However, atrial as well as ventricular chronic stimulation thresholds were significantly higher with epicardial stimulation resulting in a twofold increase in atrial energy consumption and a threefold increase in the ventricular energy consumption. Thus, in one patient with an epicardial DDD system, the pacemaker had to be replaced prematurely because of battery depletion. It is concluded that epicardial DDD stimulation can be reliably performed as far as atrial and ventricular sensing is concerned, but that the energy requirements of available myocardial leads are not satisfactory for making optimal use of modern pacemaker capability.

Permanent cardiac pacing in children: morbidity and efficacy of follow-up

The data from 50 permanently paced children [mean standard deviation follow-up 5.3 +/- 3.7 years] were reviewed, with special attention being paid to the cause of complications and the efficacy of follow-up. The 5-year survival (SD) of the patients was 78 +/- 6%; mortality was mainly due to the underlying cardiac disease. The 5-year survival (SD) of the pacing systems was 48 +/- 8%. Surgical interventions were necessary every 4.9 patient years. Of these interventions, 58% were caused by lead-related problems. Epicardial leads showed significantly more exit blocks and high thresholds than endocardial leads. Endocardial leads, therefore, should be used at a younger age than is now the current practice, from 5 years of age onwards, for example. If epicardial leads are used, the pacemaker must have a high output facility. Since exit block occurred only within the first 3 months after implantation, we suggest frequent transtelephonic monitoring during the first 3 months. Holter monitoring appeared to be the most effective and sensitive method of detecting malsensing and should be performed regularly.