Implant Procedure Description
All implants were performed under general anesthesia or conscious sedation. Antibiotic prophylaxis with 2g cefazolin or 1g vancomycin was used. Vascular access was obtained by fluoroscopic or ultrasound-guided direct puncture of the subclavian or axillary veins or via cephalic vein cutdown. A subcutaneous pocket was created in those patients without previous device.
Special attention was given to pre-implant evaluation of venous access and implant location. In patients with a previous atrial switch operation and those with dextrocardia, right-sided venous access was chosen for better sheath orientation against the interventricular septum. Electroanatomical mapping of the right atrium, right ventricle, and His bundle region was obtained with the EnSite Precision (Abbott, Abbott Park, Illinois) or Carto (Biosense-Webster, Irvine, CA) mapping system in selected patients in order to delineate the conduction system course and facilitate lead implantation in complex anatomy. All locations with His bundle recordings were tagged and the pacing lead was conected to the mapping system to guide the implantation process in these cases as previously described15.
For HBP, a standard C315 His sheath (Medtronic, Minneapolis, MI) was initially employed. A 3830 lead (Medtronic) was advanced and His bundle mapping was performed in an unipolar fashion. Unipolar electrograms obtained from the lead were displayed simultaneously in an electrophysiology recording system and in the pacing system analyzer. When a His deflection was identified, pacing at 5V at 1ms was performed to assess His bundle capture using a 12-lead ECG displayed at a sweep speed of 100 mm/s. If the patient had a previous device and no escape rhythm was present, pacemapping was used to identify an adequate position based on the 12-lead ECG morphology. If the His-bundle area could not be reached with the C315 His sheath, a deflectable C304 SelectSite sheath (Medtronic) or other delivery tools (including pre-shaped stylet directed active fixation leads) were attempted at the discretion of the implanting physician. Once the His bundle area was identified, the pacing lead was rotated clockwise 5-10 times. Then, the sheath was withdrawn to the right atrium and sensing and pacing parameters were tested with a threshold goal of ≤2.5 V at 1 ms was considered optimal. If stable sensing and pacing parameters were confirmed, the sheath was removed and the suture sleeve was sutured to the underlying muscle. The use of a backup ventricular pacing lead was not routinely employed and left at the discretion of the implanting physician.
LBBAP was attempted using the technique previously described by Huang and collegues16. Briefly, after the His bundle area was identified, the delivery sheath was advanced 1.5-2 cm towards the RV apex and ventricular pacing was used to identify a “w” pattern in V1 with a notch at the nadir of the QRS. At this point 5-10 rapid rotations were applied to the lead and pacing parameters and the paced QRS morphology were evaluated. Additional rotations were applied when necessary to achieve LBB capture and contrast injections were used to check the degree of penetration into the septum. HBP was initially attempted in all patients except in those with previous atrial switch surgery, where the His bundle is not accesible from the systemic venous atrium, and those in whom the implanting physician expected a low probability of HBP success due to suspected distal conduction system disease. In those cases LBBAP was the primary pacing strategy.