Abstract
Background and aims
Pediatric pacing is usually performed as epicardial pacing in small children in need of pacemaker therapy. Epicardial pacing compared with transvenous pacing for pediatric complete atrioventricular block (CAVB) has different strengths and weaknesses. The epicardial left ventricular wall position of the lead has been considered superior, in terms of contraction pattern, compared to a transvenous right ventricular stimulation. We aimed to compare QRS duration and cardiac function before and after the switch from epicardial to transvenous pacing in a pediatric population.
Methods
Pediatric patients with congenital or acquired CAVB, who underwent a switch from epicardial-to transvenous pacing at our center from 2005 to 2021, were identified through the national ICD- and Pacemaker Registry. Data regarding clinical status, ECG, and echocardiography before and after the switch and at last follow-up were collected.
Results
We included 15 children. The median age at the switch was 6.7 (4.4–11.7) years with a median weight of 21 (15–39) Kg. The median QRS duration with the transvenous systems was 136 (128–152) ms vs. a QRS duration during epicardial stimulation of 150 (144–170) ms with a median difference in QRS duration of 14 (6–20) ms. Children with a post-surgical AV block had a broader QRS duration, both with epicardial and endocardial stimulation. Before the switch, there was one patient with impaired left ventricular function (LVF) but with normal left ventricular end-diastolic diameters. After the switch, one patient developed symptomatic LV dysfunction with the recovery of LVF at the last follow-up after being implanted with a cardiac resynchronization therapy device.
Conclusions
Our report of pediatric patients after switching from epicardial to transvenous pacing shows how transvenous pacing is not inferior to epicardial pacing in terms of QRS duration and no significant deterioration of cardiac function was detectable.
Keywords: Epicardial pacing, Transvenous pacing, Pediatric, Complete atrioventricular block
Graphical abstract
1. Introduction
Complete atrioventricular block (CAVB), congenital or acquired, is the main indication for pacemaker implantation in the pediatric population [1,2].
Two main strategies are used for permanent pacing therapy in pediatric patients:
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Epicardial pacing (epi) is preferred in small infants and/or in individuals with specific cardiac anomalies. In contrast to endocardial (endo) pacing, epi pacing is not associated with a risk of venous thrombosis, but it requires thoracotomy and is more prone to lead-related complications [3] and higher capture thresholds although new generation steroid eluting buttoned leads may lower and stabilize the capture thresholds.
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Endocardial pacing (endo) is minimally invasive, but long-term endocardial right ventricular (RV) pacing could increase the risk of heart dysfunction [[4], [5], [6]].
To our knowledge, no data are available on differences in QRS duration and echocardiographic parameters before and after a switch from epicardial to transvenous pacing in a pediatric population.
2. Methods
Using the Swedish national Pacemaker and implantable cardioverter-defibrillator (ICD) registry we identified all consecutive pediatric patients converted from an epicardial to an endocardial pacing system at our center between January 1, 2005 and March 1, 2021.
CAVB was defined as congenital (with or without the presence of maternal autoantibody) or acquired (if linked to congenital heart disease or cardiac surgery). Information on clinical characteristics, reasons for the switch, lead positions as well as pacemaker characteristics and complications were collected.
ECG tracings and echocardiographic images before and after the switch and at the last available follow-up were obtained.
To enable comparisons across age groups, end-diastolic dimensions were transformed to a body surface-related Z-score (LVEDD) and FS-values were transformed to an age-related z-score (FS) [7,8]. The Z-score describes how many standard deviations a given measurement lies above or below the specific reference population mean.
Categorical variables are described as absolute numbers and percentages. Continuous variables are reported as median (25°–75° percentile).
3. Results
Fifteen patients who had received an epicardial pacemaker for CAVB (60 % congenital, 40 % acquired) were converted to a transvenous system. The age at the first implant was 4.3 (1.2–16.1) months. The age at the switch was 6.7 (4.4–11.7) years with a weight of 21 (14.7–39) Kg. The main etiology of the CAVB was isolated congenital AV block with a positive test for exposure to maternal autoantibodies in 44 % of the cases (Table 1). Ventricular single chamber stimulation mode (VVIR) was used in the majority (80 %) of the epicardial systems. In the transvenous systems, the most frequent pacing mode was dual-chamber stimulation (DDD). The epicardial lead location was the RV wall in 60 %, and the LV-apex/anterior wall in 40 %. The right ventricle outflow tract and interventricular septum were the most common (73 %) locations for the endocardial leads. The endocardial leads were actively screwed in 80 % of cases with only 20 % of passive fixation (Table 2).
Table 1.
Baseline characteristic.
| Characteristics | N = 15 (%) | Median (IQR) |
|---|---|---|
| Sex, Female | 6 (40) | |
| Age at switch (yrs) | 7.7 (4.4–11.7) | |
| Weight at Switch (kg) | 27.8 (14.7–39) | |
| Height (cm) | 126 (103–154) | |
| CAVB Etiology | ||
| Isolated Congenital Av Block | 9 (60) | |
| Ab + | 4 (44) | |
| AV Block CHD/Surgical Complication | 6 (40) | |
| AVSD | 3 (50) | |
| CoA/VSD | 1 (17) | |
| Fallot | 1 (17) | |
| TGA/VSD | 1 (17) | |
Values are presented as number of cases (%) or median with interquartile range (IQR).
CAVB, complete atrioventricular block; Ab, maternal autoantibody; AVSD, atrioventricular septal defect; CoA, coarctation of the aorta; VSD, ventricular septal defect; TGA, transposition of the great arteries.
Table 2.
Device data.
| Device Data | N = 15(%) |
|---|---|
| Epicardial Pacing Mode | |
| VVIR | 12 (80) |
| DDD | 3 (20) |
| Epicardial Ventricular Lead Position | |
| RV | 9 (60) |
| Anterior wall | 7 (78) |
| RVOT | 1 (11) |
| Apex | 1 (11) |
| LV | 6 (40) |
| Anterior wall | 4 (66) |
| Apex | 2 (44) |
| Transvenous pacing mode | |
| VVIR | 4 (27) |
| DDD | 11 (73) |
| Transvenous ventricular lead position | |
| Septum | 6 (40) |
| RVOT | 5 (33) |
| Apex | 4 (27) |
| Fixation | |
| Active | 12 (80) |
| Passive | 3 (20) |
Values are presented as the number of cases (%).
RV, right ventricle; LV, left ventricle; RVOT, right ventricle outflow tract.
The paced QRS duration with epicardial stimulation was 150 (IQR 144–170) ms vs. 136 (IQR 128–152) ms with the transvenous system with a median reduction of 14 (IQR 6–20) ms. The time interval between ECGs was 198 (23–926) days.
Children with acquired CAVB had a broader paced QRS duration both with epicardial (158 ms vs. 149 ms) and endocardial stimulation (148 ms vs. 132 ms) compared to congenital CAVB.
The epicardial wall of the LV showed the broadest paced QRS duration followed by the RV epicardial wall and both had a wider paced QRS compared to endocardial RV stimulation from the septum or apical position (Fig. 1).
Fig. 1.
Comparison of QRS duration between epicardial pacing from left ventricular wall (red), right ventricular wall (green), transvenous endocardial pacing from septum RVOT (blue) and transvenous endocardial pacing from ventricular apex (purple).
Based on the echocardiographic data available (Table 3), only one subject had LV function impairment (FS < −2 z-score) without volume abnormality (LVEDD >2 z-score) before the switch. One patient, with CAVB secondary to surgical intervention for great vessel transposition, developed heart failure with dilatative cardiomyopathy (LVDD z-score 3.48 and FS z-score −7.28) after the transvenous system implantation. Good response at follow-up was observed after cardiac resynchronization therapy system upgrading (LVDD z-score 1.71 and FS z-score 1.04). The median time with epicardial systems was 6.7 (2.6–11) years and in 8 cases the switch was concomitant to a scheduled exchange of the PM generator, in 6 cases related to lead failure, and in one case the switch was performed to restore atrioventricular synchronicity. The FU time with the endo system was 6 (2.5–11.7) years. During the time with the epicardial system, 5 generator exchanges were performed before the switch (in one case upgrading to a bicameral system was performed to achieve atro-ventricular synchronicity) and 8 leads failures were reported. After the switch to the endocardial system, 9 generator exchanges were performed (in one case upgrading to a bicameral system was performed to achieve atrioventricular synchronicity and in one case upgrading to a biventricular system was performed due to clinical deterioration) and 5 leads failures were reported (Fig. 2, Fig. 3 and Table 4).
Table 3.
Left ventricular function before and after the switch from the epicardial to the endocardial system and at the last available follow-up.
| Mean | S.D. | Min | Max | ||
|---|---|---|---|---|---|
| Epicardial system | LVDD cm | 3.69 | 0.62 | 2.64 | 5.08 |
| LVDD z-score | 0.08 | 1.11 | −2.25 | 1.46 | |
| FS z-score | 1.80 | 2.06 | −2.33 | 5.52 | |
| LVEF % | 68 | 4.64 | 60 | 75 | |
| Endocardial system | LVDD cm | 3.86 | 0.78 | 2.49 | 5.1 |
| LVDD z-score | −0.10 | 1.44 | −2.15 | 3.48 | |
| FS z-score | 0.03 | 3.22 | −7.28 | 4.35 | |
| LVEF % | 64 | 9,19 | 35 | 73 | |
| Follow-up | LVDD cm | 4.3 | 0.57 | 3.18 | 5.3 |
| LVDD z-score | −0.34 | 1.25 | −3.05 | 1.71 | |
| FS z-score | 0.61 | 1.16 | −2.19 | 2.16 | |
| LVEF % | 65 | 7,7 | 45 | 75 |
Values are presented as mean ± 1SD.
Z-score= (X-μ)/σ: X = observed measurement, μ = expected measurement, σ = standard deviation.
LVDD, left ventricular diastolic diameter; FS, fractional shortening; S.D., standard deviation; LVEF, left ventricular ejection fraction.
Fig. 2.
Graphical view of the interventions and time with epicardial (red) and endocardial (blue) systems in the 15 patients. The patients with the lowest age at first implantation are at the bottom of the graph.
Fig. 3.
Rate of unscheduled intervention due to leads or systems failure for epicardial (red) and endocardial (blue) systems.
Table 4.
Procedures and leads revisions or failures by system (epicardial, endocardial).
| Epicardial system | Endocardial system | |
|---|---|---|
| First implant procedure | 15 | 15 |
| Generator replacement | 5 | 9 |
| Lead revision/failure | 8 | 5 |
| Upgrade to bicameral system | 1 | 1 |
| Upgrade to biventricular system | 0 | 1 |
4. Discussion
Unlike in adults, the decision regarding the type of pacing (epi vs endo) in the pediatric setting is complicated by the numerous variables that must be considered, along with limited evidence-based data [9,10]. Furthermore, the possible risk of long-term detrimental effects on cardiac function should be considered due to the long life expectancy. Our study describes ECG changes and LVF related to switching from epicardial to endocardial pacing. Although ECG and echocardiographic parameters are surrogate outcomes, it has been shown their role as independent predictors of worse prognosis [11,12,15] and CRT trials have shown a strong interaction between QRS duration and clinical primary outcomes [13]. Therefore our study aims to increase the insight for decision-making in pediatric pacing.
To our knowledge, this is the first study focusing on a cohort of pediatric patients before and after the switch from an epicardial pacing system to a transvenous pacing system.
Single chamber pacing (VVI) was the dominant mode in the epi group whereas DDD pacing was more common in endo pacing. The ventricular epicardial pacing lead was frequently located in the anterior wall of the RV which is easier accessible through the usual surgical approach with a lower sternotomy approach albeit the LV apex/lateral wall has been shown best preservation of ventricular function [14]. Other than AV-synchrony and pacing location, a recent study reported how QRS duration is independently associated with ventricular dysfunction irrespective of location or age at device implantation [15].
Our results showed a shorter QRS duration for endocardial pacing (from a septal/RVOT position or apical position) compared both with epicardial LV and RV stimulation. As expected the QRS duration was broader in the group with acquired CAVB but, consistently with the finding above, endo pacing achieved tighter QRS. In terms of pacing location, other studies hypothesized less intraventricular dyssynchrony when the LV apex or LV free wall are sites of pacing [16]. In our study, the endocardial (septal) activation had a similar or even shorter QRS duration compared to both epicardial left ventricle and right ventricle pacing sites.
Echocardiographic data concerning LVF showed similar values in the two pacing systems. Only one patient, operated for great vessel transposition at 4 months of age, developed LV dysfunction after the switch to a transvenous system and was upgraded to a CRT system. Since the low event rates of ventricular dysfunction, inference on clinical outcomes associated with the type of pacing and the QRS duration was not possible.
Pacemaker implantation at a younger age is challenging also due to the associated risk of device failure and complications. During our study, 35 interventions were performed without acute complications, 15 for system switch and 14 for generator replacement and upgrading to bicameral system pacing. Out of thirteen reinterventions related to lead/system failure, 6 were lead revisions not associated with generator replacement. These data are in line with other system survival analyses [10].
5. Limitations
The retrospective study design as well as a small and heterogeneous study group are important limitations and do not allow drawing conclusions from subgroup comparisons, especially regarding postoperative CAVB vs. non-surgical CAVB. The results have to be considered descriptive and used as hypothesis generators. The echocardiographic data were limited to M-mode measurements therefore LV dyssynchrony could not be assessed. The QRS width is a surrogate outcome and does not allow inference on direct clinical outcomes.
6. Conclusion
In a pediatric population with CAVB the switch from epicardial pacing to transvenous endocardial pacing results in shorter QRS duration. Further clinical studies are desirable to better understand the implications of pacing site on functional and clinical outcomes in the pediatric population.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Footnotes
Peer review under responsibility of Indian Heart Rhythm Society.
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