Ventricular pacing in children

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.

Implantation of transvenous pacemakers in infants and small children

A series of 14 infants and small children ranging from 7 months to 7 years in age (mean, 2.5 years) underwent implantation of transvenous pacemaker systems. Three factors are of utmost importance in children: small subclavian vein size, thin subcutaneous layer in the chest, and growth. A five-point protocol is followed strictly: (1) duplex assessment of upper veins, (2) use of active fixation leads, (3) use of short (36 to 45 cm) leads, (4) anchoring of pulse generator with nonabsorbable material to prevent migration, and (5) routine use of the "lateral approach" in children more than 2 years old when the pulse generator is implanted in the chest. Because lead diameters measure 2 to 2.3 mm, a one-lead system needs a vein diameter of 5 mm (cross-sectional area of 19 mm2). A two-lead system needs a vein at least 7 mm in diameter and a cross-sectional area of 38 mm2 to prevent vein occlusion. Therefore all children less than 3 years of age had the leads implanted via the internal jugular vein. In 50% of children between 4 and 7 years of age, the internal jugular system also was used. Children more than 7 years old have leads implanted via the subclavian veins. Duplex ultrasound assessment of the upper veins is important to decide route of implantation. Use of short leads is recommended to reduce bulk at the pulse generator site. The "lateral approach" prevents problems at the generator implantation site.

Pacemaker failure due to pocket emphysema

Pocket emphysema is an unusual cause of failure of a permanent pacemaker. Reported herein is temporary failure of a unipolar DDD pacemaker caused by pocket emphysema in a pediatric patient.

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.

Measurement of ventricular electrogram amplitude during intraoperative induction of ventricular tachyarrhythmias

Adequate sensing of ventricular tachycardia (VT) and ventricular fibrillation (VF) is necessary for proper functioning of an implantable cardioverter defibrillator (ICD). Several ICDs currently undergoing investigation have programmable fixed gain sensitivity for tachycardia detection. If intracardiac electrogram amplitude decreases below the programmed sensitivity during VT or VF, detection of a ventricular arrhythmia may be delayed or missed. The mean amplitude of intracardiac electrograms (ICEGM) recorded with bipolar epicardial or transvenous sensing leads was measured in 63 patients during induced VT and VF recorded in the operating room at the time of ICD implantation. The mean amplitude of the ICEGM during 41 episodes of VF in 15 patients decreased from 14.9 +/- 0.9 mV during sinus rhythm to 8.8 +/- 0.7 mV at 1 second, 9.7 +/- 0.7 mV at 5 seconds, and 9.4 +/- 0.7 mV at 10 seconds (p < 0.0001 vs sinus rhythm ICEGM) with endocardial leads. The mean amplitude of the ICEGM recorded during 173 episodes of VF in 43 patients with epicardial leads decreased from 10.4 +/- 0.3 mV in sinus rhythm to 7.8 +/- 0.3 mV at 1 second, 8.3 +/- 0.3 mV at 5 seconds and 8 mV at 10 seconds (p <0.0001 vs sinus rhythm ICEGM). The mean amplitude of epicardial and transvenous ICEGMs recorded during 34 episodes of monomorphic VT decreased from 18.5 +/- 1.8 mV (epicardial) and 14.4 +/- 2.0 mV (transvenous) during sinus rhythm (p = 0.15, epicardial vs transvenous) to 16.0 +/- 1.7 mV (epicardial) and 13.7 +/- 1.9 mV (transvenous) at 10 seconds (< 10% of baseline amplitude).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Sick sinus syndrome and diffuse impairment of the conduction system in a child: successful pacing with a steroid eluting endocardial pacing lead

A 9-year-old patient who had had a syncope was found to have atrial flutter in a resting electrocardiogram (ECG). Brief phases of sinus arrest had previously occurred after drug conversion to sinus rhythm. Structural heart disease was excluded by cardiac catheterization and angiography. Electrophysiologic study revealed a sick sinus syndrome, associated with diffuse impairment of the conduction system (supra-, infra-, and intrahisian block). Epimyocardial and an endocardial pacemaker implantation failed because of high stimulation threshold, after 3 years and 2 weeks, respectively. At the third implantation a steroid-eluting endocardial pacing lead was used and satisfactory pacing was still present 2 years later.

New technique for pacemaker implantation in the upper chest of children and women

A new lateral approach for implanting pacemaker generators in the chest of women and children is described. Using this technique, 83 women and 21 children were operated on with no early or late complications and with good cosmetic results up to 9 years after operation. This technique prevents formation of visible wide scars above the breast in women and prevents thinning or disruption of the chest incision in children. Ages of the women ranged from 19 to 56 years; children, 5 to 18 years. In 23 patients, this technique was used after wound complications had occurred 7 days to 3 years after use of the standard implantation technique.

Developmental sequelae of fixed-rate ventricular pacing in the immature canine heart: an electrophysiologic, hemodynamic, and histopathologic evaluation

Permanent, fixed-rate ventricular pacing (VVI) is associated with hemodynamic deterioration in the adult with compromised myocardial function. The effects of this pacing mode on the intact, immature heart, however, are largely unknown. Twelve beagle puppies (age 3 to 4 months) were equally divided into paced and age-matched control groups. All underwent identical hemodynamic and electrophysiologic evaluations. Transepicardial atrioventricular block and pacemaker insertion were additionally carried out in the paced group. After 4 months of observation, repeat hemodynamic and electrophysiologic measurements followed by histopathologic examinations were done in all puppies. The paced group exhibited significant (p less than 0.05) elevations of right atrial and pulmonary artery pressures, alterations in sinus node function, and prolongation of ventricular refractory periods compared with the control group. Initiation of dysrhythmias by programmed electrical stimulation was observed only among the paced group of puppies. Histologic examination demonstrated myofibrillar cellular disarray, dystrophic calcifications, prominent subendocardial Purkinje cells, and an increase in variable-sized, disorganized mitochondria only in the paced specimens. These findings indicate that permanent, apically-initiated VVI pacing ultimately predisposes to adverse cellular changes associated with hemodynamic and electrophysiologic deterioration in the intact, developing immature canine heart.

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.

Concealed paroxysmal atrioventricular block: diffuse congenital atrioventricular conduction system disorder with nonpropagated His bundle depolarizations

A 2 1/2-year-old girl with bradycardia and left bundle branch block at birth began to experience "night cries" when deeply asleep. Electrophysiological study demonstrated congenital diffuse atrioventricular conduction disease with concealed paroxysmal atrioventricular block, nonpropagated His bundle depolarizations, severe sinus node abnormality, and a low atrioventricular junctional escape rhythm with probable reciprocation. After pacemaker implant, the "night cries" ceased.

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.

Surgical management of difficult pacing problems in patients with congenital heart disease

The child with congenital heart disease requiring permanent pacing presents a unique challenge with regard to the decision to pace, hardware, route, and unusual problems. Considerations of patient size, anatomy, insertion during and after complex intracardiac procedures, location of hardware, and unusual approaches are discussed including: placement of endocardial leads at open operation, closed transatrial endocardial technique, periprosthetic valvular endocardial placement, trans left superior vena cava placement and retromammary position via the axillary approach. Consideration of these unusual techniques may avoid frustration due to the complexities of the placement of pacing systems in these young patients.

Evaluation of pacemaker pulse generator and patient longevity in patients aged 1 day to 20 years

The longevity of pediatric patients requiring pacemakers and the survival rates of the implanted generators were evaluated. From January 1970 to December 1985, 96 patients aged 1 day to 20 years underwent 162 pulse generator implantation procedures. Indication for initial implantation was surgically induced heart block in 52 patients, sick sinus syndrome in 20, congenital complete heart block with symptoms of low cardiac output in 19 and tachydysrhythmia control in 5. Modal age at initial implantation was less than 1 year; median age was 5 years. During this period 90 generators were removed from service: 49 (54%) because of generator failure, 22 (24%) because the patient died, 12 (13%) because of elective upgrade at the time of lead failure or cardiac surgery, 5 (6%) because of generator pocket infection and 2 (2%) because of manufacturer's recall. Pulse generators were separated into 4 groups based upon generator technology. Group I (n = 16) were asynchronous units with mercury-zinc batteries; group II (n = 18) were single-chamber demand units with mercury-zinc batteries; group III (n = 14) were single-chamber demand units with rechargeable batteries; and group IV (n = 114) were single- or dual-chamber demand units with lithium batteries. Patient survival rate was 84% at 6 months and 70% by 109 months. There was no further decrease to the end of the study period. Six-month generator survival rate was 82% for all groups, mostly a reflection of patient deaths.(ABSTRACT TRUNCATED AT 250 WORDS)

Pacing in children and young adults with nonsurgical atrioventricular block: comparison of single-rate ventricular and dual-chamber modes

A prospective comparison of physiologic response to single-rate ventricular and dual-chamber atrioventricular pacing was conducted in 14 pediatric patients (age 1 to 24 years, median 14) with symptomatic nonsurgical second- or third-degree atrioventricular block. All patients were studied acutely during cardiac catheterization before and after 1 hour of both pacing modes. Following pacemaker implant, eight patients were reevaluated after 1 month of each mode with symptom questionnaire, resting ECG, resting echocardiogram, and Doppler cardiac output measurement at rest and at peak treadmill exercise. Cardiac outputs (mean +/- standard error) increased acutely (n = 14) with both ventricular (32 +/- 12%) and dual-chamber (39 +/- 10%) pacing over intrinsic rhythm values (p less than 0.01 in both). During chronic pacing (n = 8), symptoms were reported only with the ventricular mode. Dual-chamber synchronous pacing was associated with improved mean resting shortening fraction and cardiac output, slower mean resting sinus rate (89 +/- 5 compared to 73 +/- 4 bpm (p less than 0.02), and a 23% increase in mean excerise cardiac output (4.2 +/- 0.4 compared to 3.4 +/- 0.3 L/min/m2) compared to single-rate ventricular pacing. Exercise-induced dysrhythmias occurred only with ventricular pacing. This study demonstrates that pediatric patients with nonsurgical atrioventricular block can compensate for loss of atrioventricular synchrony at rest but exhibit improved cardiac function with chronic dual-chamber atrioventricular compared to single-rate ventricular pacing.

Pacing in children

Fourteen children had a permanent pacemaker implanted between May 1967 and July 1983. Postoperative complete heart block was the indication in nine cases, congenital complete heart block in three, and sick sinus syndrome in two. Two patients died, one suddenly and one after aortic valve replacement. A total of 48 pulse generators were implanted; five patients were given an isotopic pacemaker. Twelve patients had epicardial leads implanted initially, and two received a transvenous endocardial system. The lead system implanted initially remained without malfunction in only seven patients. In the other seven patients 20 lead malfunctions occurred. Psychological maturity and physical development seemed to be normal in all 14 children. Improvement in equipment and technique will improve the outlook for paced children in the future.

Myopotential inhibition of unipolar pacing in children

Myopotential inhibition of unipolar demand pacing systems has been shown to be a frequent occurrence in adults with transvenous pacing systems in which the pulse generators are implanted adjacent to the pectoralis muscle. To evaluate this problem in children, most of whom have epimyocardial systems and abdominal wall generator implants, 50 patients underwent electrocardiographically monitored exercise and 24-hour ambulatory electrocardiograph monitoring. Patients' ages at the time of study ranged from less than one year to 18 years, and weights ranged from less than 5 kg to 63 kg. Sixteen different models of pulse generators from five manufacturers were involved. Pacing modes were VVI, DVI, AAI, VDD, and DDD. Forty-seven patients had epimyocardial systems. None of the patients was symptomatic as a result of myopotential inhibition. Only three patients (6%) had any evidence of myopotential inhibition and all three demonstrated this inhibition on both monitored exercise and ambulatory electrocardiograph. The inhibition was eliminated by reprogramming the sensitivity levels of the three generators without compromising R-wave sensing. Thirteen of the remaining 35 patients with multiprogrammable generators had induction of myopotential inhibition when exercised after temporary programming to maximal sensitivity settings. Myopotential inhibition of unipolar demand pacing appears to be less frequent and less problematic in the pediatric population, even though they are physically quite active. It is not clear whether this is a function of patient size or the abdominal wall position of the pulse generator.(ABSTRACT TRUNCATED AT 250 WORDS)

Advances in the management of cardiac arrhythmias in children

The authors discuss several recent developments in the diagnosis and management of cardiac arrhythmias in the young, focusing on areas in which the greatest progress has been made so that the pediatrician can incorporate these developments into his practice and participate more fully in the management of the patient requiring tertiary care.

Experience with a new epimyocardial pacing lead in children

A new permanent epimyocardial Medtronic 4951 "stab-in" or "fishhook" pacing electrode was implanted in 16 children. Identical technique, with particular attention to the direction of the coronary circulation, was utilized to implant the leads. There were 10 atrial implantations (5 active, 5 redundant) and 18 ventricular implantations (15 active, 3 redundant). Pacing modes were VVI (12), VDD (1), DVI (2), and DDD (1). Experience with the lead covers 280 patient months (3 days to 21.8 months, mean 14 months). Patients were followed monthly via telephonic transmission. With the exception of the single patient who expired three days after implantation, each patient has returned for follow-up analysis including chronic threshold determinations using the programming capabilities of the pulse generators. Only one lead required more than the minimum obtainable voltage output from the pulse generator to effect capture. No other lead required more than 5.0 volts at 0.5 ms pulse width. There have been no lead fractures or dislodgements. In this evaluation the Medtronic 4951 lead performed well in both atrium and ventricle in a group of children with diverse cardiac pathology. The small diameter of the lead and the low profile of the electrode are advantageous for use in pediatric patients.