Scientific letter Endocardial Pacing in Infants and Young Children Weighing Less Than 10 Kilograms

To the Editor,

Permanent pacemaker implantation is a challenge in pediatric patients, who account for less than 1% of all patients who undergo this procedure.¹ Widespread pacemaker use in children is limited by the absence of devices tailored to this population. Epicardial pacemaker placement used to be the preferred option for young patients, as the size of generators and endocardial leads were considered to be inappropriate and even dangerous for young children. Today, however, endocardial pacemakers are being increasingly used in the pediatric population as they offer several advantages, such as lower sensing and pacing thresholds and a reduced risk of lead fractures.²

We report our experience with permanent pacemaker implantation in patients weighing less than 10 kg at our hospital between January 2006 and March 2015. The procedure was performed in 25 patients with a median age of 17 months (range, 6-40 months) and a median weight of 7 kg (range, 4.4-10.0 kg). The indication for pacing in 22 (88%) of the patients was complete atrioventricular block (AVB) after surgery (Table). The AVB had occurred after closure of a ventricular septal defect in all cases except one. The median time between surgery and implantation was 23 days (range, 9-40 days). The pacing leads were inserted by puncturing the right (n = 15) or left (n = 10) subclavian vein. The atrial or ventricular leads, measuring 52 cm in length and 2 mm in diameter, were inserted through 7-Fr introducer sheaths. Bipolar active-fixation leads were used in all cases. For dual chamber pacemakers, a right atrial loop measuring approximately 4 to 6 cm in length was created (Figure). Details of the generator models, implantation sites, pacing mode, and electrical parameters during implantation and follow-up are given in the Table. The generator was placed in a subpectoral pocket. The implantation procedure was completed without complications in most of the patients. One patient developed supraventricular tachycardia without repercussions during fixation of the atrial leads. In another patient, the atrial lead needed to be replaced due to malfunction caused by dislodgement on day 2 after the procedure. Twenty-two of the patients (88%) were followed up for a median of 48 months (range, 1-102 months). Generator replacement due to battery depletion was necessary in 2 children and there was no evidence of venous thrombosis during replacement in either case. Leads were extracted due to pocket-site infection in 3 patients (12%) at 8, 25, and 27 months. There had been no evidence of hematoma at the implantation site in any of the cases. Once the infection had cleared, the lead was removed using an epicardial surgical approach and replaced in 2 patients and was repositioned percutaneously on the contralateral side in the third. All the patients, including those who required lead extraction, were in good clinical health.

Table.

Clinical and Electrical Characteristics of Permanent Endocardial Pacemaker Implantation in Young Children

Patient	Congenital heart disease	Generator	Implantation site		Pacing mode	Electrical parameters during implantation
			Atrium	Ventricle		Atrium			Ventricle			Heart rate, max/min (bpm)
						Sensitivity (mV)	Pacing treshold (mV)	Impedance (Ω)	Sensitivity (mV)	Pacing threshold (mV)	Impedance (Ω)
1	ASD+ VSD	St JudeMicrony II	------	Apex	VVIR	-------	-------	-------	N/A	N/A	N/A	185/90
2	CoAo + PDA + VSD	Guidant InsigniaI Entra	Posterior wall	Apex	DDDR	N/A	N/A	464	N/A	N/A	512	150/80
3	Double discordance + VSD	Vitatron	Posterior wall	Apex of LV	DDD	N/A	0.2	450	N/A	0.4	598	170/90
4	AVC defect	St. JudeMicrony II	-----	RVOT	VVIR	-------	-------	------	N/A	N/A	415	185/90
5	VSD + PDA	Guidant InsigniaI Entra	Atrial appendage	RVOT	DDDR	N/A	N/A	610	N/A	N/A	530	180/80
6	Supracardiac-type TAPVC in SVC	Guidant InsigniaI Entra	Posterior wall	Apex	DDD	3.5	0.4	420	3.5	0.4	430	180/90
7	Dextrocardia, situs inversus, DORV	Guidant InsigniaI Entra	Posterior wall	Apex	DDD	0.75	0.6	447	8.6	0.9	464	150/90
8	Structurally healthy heart	Guidant InsigniaI Entra	Posterior wall	Apex	DDDR	1.5		530	8.0		490	185/90
9	TGA + VSD + subpulmonary ring	Guidant InsigniaI Entra	Lateral wall	Apex	DDDR	2.0	1.0	400	10	1.25	700	185/110
10	VSD + PDA	Medtronic	Atrial appendage	RVOT	DDDR	0.19	2.4	866	15	2.1	952	180/80
11	VSD + PDA	Boston ScientificAltrua	Atrial appendage	RVOT	DDD	1.0	0.75	470	6.0	0.5	440	185/70
12	Structurally healthy heart + paralysis of right atrium	Boston ScientificAltrua	Posterior wall	RVOT	DDDR	N/A	N/A	420	8.5	N/A	480	185/90
13	VSD + PDA	Boston ScientificAltrua	Atrial appendage	RVOT	DDDR	2.0	1.6	610	15	1.2	530	180/70
14	VSD + PDA	Boston ScientificAltrua	Posterior wall	RVOT	DDDR	3.6	1.5	636	20.7	0.9	870	185/100
15	Juxtaposed atrial appendages	Medtronic	Interatrial septum	Apex	DDD	1.0	0.6	764	6.8	1.1	697	185/100
16	VSD + PDA	Boston ScientificAltrua	Atrial appendage	RVOT	DDDR	1.5	0.9	430	2.5	0.5	480	180/80
17	AVC defect	Boston ScientificAltrua	Lateral wall	RVOT	DDDR	1.2	0.5	780	7.0	0.8	640	185/100
18	ASD + VSD	Boston ScientificAltrua	Posterior wall	RVOT	DDDR	1.2	0.4	560	6.0	0.7	538	185/70
19	VSD	Boston ScientificAltrua	Roof	Apex	DDDR	0.75	0.8	413	2.5	0.4	445	180/80
20	VSD + PDA	Boston ScientificAltrua	Lateral wall	Apex	DDDR	0.75	1.2	534	2.5	1.2	568	180/80
21	Intracardiac-type TAPVC in coronary sinus + VSD	Boston ScientificAltrua	Atrial appendage	RVOT	DDDR	0.5	0.9	474	2.5	0.5	540	185/90
22	DORV	Boston ScientificAltrua	Roof	RVOT	DDDR	0.8	1.3	568	3.0	1.4	620	185/70
23	CoAo + VSD	Boston ScientificIngenio MRI	Atrial appendage	RVOT	DDDR	1.0	1.5	610	6.5	0.7	740	185/100
24	VSD	Boston ScientificIngenio MRI	Atrial appendage	RVOT	DDDR	0.75	0.6	468	2.5	0.8	534	185/90
25	ASD + DORV	Boston ScientificIngenio MRI	Atrial appendage	RVOT	DDDR	0.75	0.4	788	2.5	0.4	753	185/110

Patient	Electrical parameters during follow-up
	Atrium			Ventricle			Pacing %		AV interval
	Sensitivity (mV)	Pacing threshold (mV)	Impedance (Ω)	Sensitivity (mV)	Pacing threshold (mV)	Impedance (Ω)	Atrial	Ventricular	SAV	PAV
1	-----	-----	-----	N/A	N/A	N/A	NF	NF	NF	NF
2	N/A	N/A	N/A	N/A	N/A	N/A	NF	NF	NF	NF
3	1.75	2.5	650	N/A	0.75	450	29	99	NA	NA
4	-----	-----	-----	N/A	N/A	N/A	-----	NA	-----	-----
5	1.2	3.25	310	8.6	5.0	380	6	100	NA	NA
6	N/A	N/A	N/A	N/A	N/A	N/A	NF	NF	NF	NF
7	2.0	0.1	470	N/A	2.5	500	57	100	NA	NA
8	4.2	1.75	470	N/A	1.5	520	0	100	150	80
9	N/A	N/A	N/A	N/A	N/A	N/A	13	98	NA	NA
10	4.0	1.75	460	7.7	5.1	383	21	100	80	140
11	2.0	0.05	370	N/A	0.05	410	0	100	NA	NA
12	2.5	1.16	490	4.4	4.1	490	100	73	NA	NA
13	0.75	0.75	460	N/A	2.5	420	1	99	NA	NA
14	N/A	2.0	410	N/A	1.75	520	97	100	NA	150
15	1.4	1.25	522	N/A	1.25	470	1	100	120	150
16	2.4	1.24	610	N/A	1.25	480	4	100	NA	NA
17	2.2	1.75	420	N/A	1.5	420	19	100	NA	NA
18	0.5	1.5	420	N/A	1.5	420	14	100	NA	NA
19	N/A	2.0	380	N/A	1.75	410	2	100	NA	NA
20	1.0	1.25	530	N/A	1.75	430	40	100	NA	NA
21	0.32	8.75	560	6.5	1.5	440	14	92	NA	NA
22	2.4	1.25	410	N/A	1.25	460	57	100	NA	NA
23	1.9	1.25	400	N/A	1.5	460	11	100	NA	NA
24	0.9	6.25	N/A	12	2.0	N/A	7	2	NA	NA
25	N/A	N/A	N/A	N/A	N/A	N/A	56	100	80	160

ASD, atrial septal defect; AVC, atrioventricular canal; bpm, beats per minute; CoAo, coarctation of the aorta; DORV, doublet outlet right ventricle; LV, left ventricle; N/A, not applicable; NA, not available; NF, not followed up; PAV, paced AV; SAV, sensed AV; PDA, patent ductus arteriosus; RVOT, right ventricular outflow tract; SVC, superior vena cava; TAPVC, total anomalous pulmonary venous connection; TGA, transposition of the great arteries; VSD, ventricular septal defect.

Figure.

Two-year-old patient weighing 9 kg with congenital atrioventricular block. Note the position of the leads in both the atrium and at the right ventricle apex (A). The same patient aged 8 years old and weighing 25 kg (B). Note the minimum displacement of the leads despite the significant somatic growth.

A number of factors need to be considered when placing an endocardial pacemaker in young children. Lead displacement caused by growth can interfere with pacing, requiring the insertion of new leads within a relatively short period. Use of a longer atrial lead can prevent this from happening. Gheissari et al.³ calculated that a right loop of 8 cm would allow a child to grow for 6 to 12 years without the need for reoperation and that approximately 10 mm of lead per year should accommodate for somatic growth. Other authors, however, have warned that a surplus lead of this length could be displaced into the right ventricular outflow tract, possibly causing lung failure.⁴ In our experience, a loop length of approximately 4 to 6 cm is adequate. We have detected no problems to date, although we acknowledge that larger series and longer follow-up times are necessary. Another important issue with pacemaker placement in young children is the thinness of the subcutaneous tissue layer, as the generator tends to exert tension against the tissue and can cause lesions. This increases the risk of infection and the need for extraction, as has been previously indicated.⁵ The use of subpectoral pockets has been associated with a lower risk of infection in such cases.⁶ Subpectoral placement is preferred not only for cosmetic reasons but also because of the greater protection provided by the pectoral muscle in young patients.

In conclusion, although patients require close lifetime follow-up due to the risk of venous thrombosis and the possible need for lead extraction, we consider that endocardial pacing in pediatric patients weighing less than 10 kg is a reasonably safe and effective option in hospitals with experience.