1.General
The operation of LBBaP was attempted for thirty-one children (seventeen males and fourteen females) with a mean age of 3.2 ± 2.1 (range 0.7 ~ 7.0) years old, and weight of 14.1 ± 5.7 (range 7.0 ~ 28.0) kg. All patients were diagnosed as complete atrioventricular block. The median duration of bradycardia history in these patients was 1.5 (IQR 0.08–3.7) years. In these patients, the results of Holter before the pacemaker implantation showed that: the average of total heartbeat was 6.6 ± 0.8 thousand beats per 24 hours, and the average of heart rate was 47 ± 5 beats per minutes (bpm). Congential heart disease was presented in 35.5% of patients (11/31 cases), in which of eight patients underwent cardiac surgery previously (including: one case of atrial septal defect, five cases of ventricular septal defect, and two cases of complete endocardial cushion defect). Before pacemaker implantation, abnormal cardiac structure was still present in three patients (including: two cases of atrial septal defect and one case of patent ductus arteriosus). These three patients underwent transcatheter occlusion before pacemaker implantation. Twenty-seven patients (87.1%) were implanted with pacemaker for the first time, and four patients (12.9%) were received reoperation due to the previous epicardial pacemaker or electrode malfunction at this time. Before pacemaker implantation, left ventricular enlargement was seen in twenty-four patients (24/31, 77.4%) (echo-LVEDD Z score > + 2), and normal LVEDD (-2༜LVEDD Z score༜+2) was seen in other patients (7/31, 22.6%). Before pacemaker implantation, normal echo-LVEF was seen in all patients with the mean value of 68.1 ± 3.9%.
2.Pacemaker implantation
One patient was implanted with dual-chamber pacemaker (DDD) and thirty patients were implanted with single-chamber pacemaker (VVIR). The operation of LBBaP was succeeded in twenty-two patients with the success rate of 70.9% (22/31 cases). The operation of LBBaP had failed in nine patients, for these patients the right ventricular septal pacing (RVSP) was performed eventually. The comparison of baseline data and intraoperative parameters between the patients of LBBaP group and the patients of RVSP group was seen in Table 1. At baseline, there was no significant difference in terms of patients’ age, body weight and echo-indicators between two groups (P༜0.05). In patients of LBBaP group, the average age was 3.3 ± 2.1 (range 0.8 ~ 7) years old and the average body weight was 14.7 ± 6.0 (range 7.0 ~ 28.0) kg.
Table 1
The comparison of baseline data and intraoperative parameters between the patients of LBBaP group and the patients of RVSP group
|
LBBaP group(N = 22)
|
RVSP group
(N = 9)
|
P-value
|
Baseline Data
|
|
|
|
Age(years old)
|
3.3 ± 2.1
|
2.9 ± 2.0
|
0.578
|
Body weight(kg)
|
14.7 ± 6.0
|
12.6 ± 5.0
|
0.359
|
LVEDD Z score
|
3.0 ± 1.4
|
2.8 ± 1.6
|
0.672
|
LVEF (%)
|
68.5 ± 3.8
|
67.2 ± 3.4
|
0.367
|
LVESV index (ml/m2)
|
19.3 ± 4.6
|
20.7 ± 7.3
|
0.608
|
IVS (mm)
|
5.1 ± 0.8
|
5.0 ± 0.9
|
0.821
|
Intraoperatively parameters
|
Capture threshold of ventricular electrode (V)
|
0.5 ± 0.1
|
0.6 ± 0.1
|
0.418
|
R-wave amplitude of ventricular electrode (mV)
|
14.0 ± 3.8*
|
9.6 ± 4.7
|
0.015
|
Impedance of ventricular electrode (Ω)
|
728.1 ± 138.6
|
672.0 ± 107.0
|
0.286
|
Sti-LVAT(ms)
|
51.2 ± 7.8*
|
66.7 ± 8.0
|
0.000
|
QRS duration on ECG (ms)
|
100.9 ± 9.1*
|
114.2 ± 11.9
|
0.002
|
*The comparison between two groups when P༜0.05 was presented. LVEDD = left ventricular end-diastolic dimension. LVEF = left ventricular ejection fraction. LVESV = left ventricular end-systolic volume. IVS = thickness of interventricular septum. Sti-LVAT = the peak activation time of left ventricle. ECG = electrocardiogram |
In LBBaP group, the potential of left bundle branch was successfully recorded in 63.6% of patients (14/22 cases) during operation. In patients who received the operation of LBBaP successfully, the average of procedure time (calculated from the time when the guide wire passed across the tricuspid valve annulus to the time that the ventricular electrode was fixed) was 21.8 ± 13.3 minutes (min). The average of instant current of injury was 10.7 ± 3.9 mV. The average of fluoroscopic exposure dose was 3.6 ± 1.9 mGy, the fluoroscopic exposure time was 7.2 ± 3.2 min, the cumulative product of area and fluoroscopic exposure dose (DAP) was 564.7 ± 319.2 mGycm2. In the patients of LBBaP group, the average thickness of interventricular septum (measured by echocardiography preoperatively) was 5.1 ± 0.8 mm and the average depth which the ventricular electrode penetrating into the interventricular septum (measured by angiography during operation) was 7.7 ± 1.9 mm.
In the nine patients who had failed LBBaP, it was difficult to screw the ventricular electrode into the interventricular septum. Additionally, the electrode was unable to be placed in the region of left bundle branch. In three of these patients were diagnosed as congenital heart disease and they underwent cardiac surgery previously (two patient received the surgery of endocardial cushion defect correction, and one patient received the surgery of ventricular defect repairation).
The postoperative QRS duration in patients of LBBaP group was significantly narrower than that of RVSP group: 100.9 ± 9.1 vs. 114.2 ± 11.9 ms (P = 0.002). The comparison of postoperative echocardiographic image and ECG between one patient with LBBaP and another patient with RVSP was seen in Fig. 3.
In all over patients, no surgery related complications such as myocardial perforation, electrode malfunction, electrode dislodgement, pocket hematoma and venous thrombosis had occurred.
3.Follow-up
3.1 Complications and the pacing parameters
For all patients, the median time of follow-up was 12 (IQR 6–15) months. The pacing mode of VVIR was adopted for the patients with single-chamber pacemaker (30 cases) and the pacing mode of DDD was adopted for the patient with dual-chamber pacemaker (1 case). The average percentage of ventricular pacing was 96.0 ± 2.5%. The lower limit of pacing frequency was set as 70 (IQR 60–70) bpm, and the upper limit of pacing frequency was set as 140 (IQR 130–140) bpm. During follow-up, no complications (e.g., electrode perforation, electrode malfunction, pocket infection) had occurred.
In the patients of LBBaP group, the capture threshold and the R-wave amplitude of ventricular electrode maintained well during follow-up. The impedance had decreased obviously than baseline. The comparison of capture threshold of ventricular electrode between baseline and last time of visit was as follows: 0.58 ± 0.13 vs. 0.70 ± 0.25 V (P = 0.054). The comparison of R-wave amplitude of ventricular electrode between baseline and last time of visit was as follows: 14.0 ± 3.8 vs. 16.5 ± 4.5 mV (P = 0.072). The comparison of impedance of ventricular electrode between baseline and last time of visit was as follows: 728.1 ± 138.6 vs. 552.5 ± 74.0 Ω (P = 0.000).
During follow-up, the average capture threshold of ventricular electrode in patients of LBBaP group was obviously lower than that of RVSP group. Additionally, the R-wave amplitude in patients of LBBaP group was better than that of RVSP group. At last time of follow-up, the comparison of capture threshold between LBBaP group and RVSP group: 0.70 ± 0.25 vs 1.39 ± 0.94 V (P = 0.011). The change trend of pacing parameters in patients of two groups during follow-up was shown in Fig. 4.
3.2 Cardiac function
All the patients of LBBaP group had maintain a well cardiac function during follow-up, the echo-LVEDD Z score and LVESV index were significantly decreased than that of baseline. Additionally, the ehco-LVEF in patients of LBBaP group maintained normal during follow-up. The comparison of echo-indicators between baseline and last time of visit was shown in Fig. 5.
At last time of follow-up, the comparison of echo-LVEDD Z score in patients of LBBaP group and the patients of RVSP group was as follows: 0.5 ± 1.2 vs. 1.1 ± 0.7 (P = 0.220). The average of echo-LVEF in patients of LBBaP group was better than that of RVSP group was as follows: 66.1 ± 3.3 vs. 63.1 ± 2.2% (P = 0.025). The change tendency of echo-indicators in patients of LBBaP group and RVSP group during follow-up was shown in Fig. 6.
3.3 Assessment of cardiac synchrony
At baseline, there was no significant difference in terms of cardiac synchrony parameters in patients of LBBaP group and the patients of RVSP group: GLS (-24.3 ± 1.8 vs. -22.7 ± 3.0%), Ts-SD (41.8 ± 9.5 vs. 49.3 ± 10.4 ms), MDT (147.6 ± 49.1 vs. 169.2 ± 51.6 ms), and IVMD (40.8 ± 33.1 vs. 20.0 ± 14.1 ms), all of P value༞0.05.
Postoperatively, the average of Ts-SD, MDT and IVMD in patients of LBBaP group were all better than that of RVSP group (Fig. 7).