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sheath was withdrawn to the right atrium and sensing and pacing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.