The study will include patients fulfilling our inclusion criteria.
Inclusion Criteria:
1. Pediatric patients aged \<18years old.
2. Congenital complete atrioventricular block, atrioventricular block as a complication after heart surgery, and symptomatic bradycardia associated with channelopathies.
3. Indications for permanent pacemaker implantation followed contemporary guideline-based recommendations.
4. Pediatric patients had previous right ventricular lead implantation and deterioration of LV systolic function.
Exclusion Criteria:
1. Patients will not attend for follow up after implantation.
2. Patients have critical systematic illness which may interfere with cardiac function assessment.
3. Patients have poor echocardiographic window.
All patients will be subjected to:
A. Full history taking: including age, sex, history of DM, HTN, history of CHD or any previous cardiac intervention, symptoms of heart failure, dizziness or syncope and history of any previous arrhythmia.
B. Full Physical examination:
* General examination Systolic and diastolic blood pressure and heart rate assessment.
* Local Cardiac examination. C. Laboratory investigations: Pre-operative (CBC - INR - Urea - Creatinine - Serum Electrolytes K, Na, Mg).
D. Standard 12 lead ECG. E. Echocardiography (TTE): For cardiac dimensions (IVS thickness, right side dimensions, left ventricular end- systolic and diastolic diameters), LV systolic function, degree of tricuspid regurgitation if present and any other structural abnormality detected.
F. LBBAP implantation technique:
-All patients will undergo implantation of permanent pacemaker either single or dual chamber under fluoroscopic guidance according the EHRA procedural recommendations.
G. Intraprocedural 3D-TEE during implantation:
\- 3D-TEE will facilitate accurate lead positioning through direct visualization of the interventricular septum then the investigators will measure interventricular septum (IVS) length, the angle of lead with the IVS, depth of lead in IVS (the distance from lead tip to the RV subendocardial region), the distance from lead tip to the LV subendocardial region, the distance from the lead tip to tricuspid valve annulus and the distance from the lead tip to RV apex.
H. Electrocardiographic features measured during lead implantation:
* The investigators will measure QRS duration \& morphology and LVAT duration, notice occurrence of LBB potential and/or fixation beats or not, differentiate selective versus non selective pacing during decremental pacing.
* Also, the investigators will measure lead current of injury COI and impedance during implantation.
* Calculation of total time of the procedure and fluoroscopic only time.
I. Follow up of the cases:
After one week and then after 3months by:
* Assessment of programming parameters (threshold, impendence and sensitivity) and ECG features (V6 RWPT, QRS during\& morphology).
* TTE for detection of lead complications, worsening of tricuspid regurgitation and any change of left ventricular function.
