Implant procedure:
HBP was performed using the 3830 SelectSecure lead (Medtronic,
Minneapolis, MN) delivered through either the fixed curve (C315-HIS) or
deflectable curve (C304) sheath. Standard techniques for HBP were used,
including mapping for the distal His recording prior to fixation or
pace-mapping when the His recording was not located (infrequently). The
procedure was deemed successful if selective or nonselective His-bundle
capture was demonstrable. RV apical pacing leads were also implanted in
12% (6/50) of patients receiving HBP with the apical lead programmed to
pace 80 ms after His-pacing. At implant, pacing outputs were generally
programmed at 3.5 V at 1 ms and then adjusted based on the HBP capture
threshold (confirmed by 12 lead EKG morphology) during follow-up, such
that outputs were programmed to ~twice the capture
threshold for His-capture.
LBBAP was also performed using the above lead and sheaths. Standard
techniques were used, as previously described.15Briefly, the lead was advanced 2 cm distal to the His electrogram toward
the RV apex or on the basis of unipolar paced
morphology.20 With the sheath held flush against the
septum, the lead was rotated and advanced until the lead perforated the
RV septal myocardium. The paced QRS morphology and impedance was
continuously monitored and the lead rotated until the paced morphology
approximate a RBBB morphology. Contrast injection was performed in
select cases. At implant, outputs were generally programmed at 2-2.5 V
at 0.5 ms, and then adjusted only if needed during follow-up based on
threshold (confirmed by 12 lead EKG morphology) such that outputs were
programmed to ~ twice that of threshold.
Data Collection and Follow-Up :
Baseline demographic, clinical, electrocardiographic, and procedural
data were collected by chart review. Follow-up data from the first
post-procedure follow-up and from the most recent follow-up were
collected for all patients. Pacing threshold was defined as the lowest
voltage required to capture the conduction system with either selective
or nonselective morphology. Pacing parameters were recorded in detail
with 12-lead ECG performed during threshold testing. Pacing thresholds,
R-wave sensing and impedances were all carefully documented at implant
and in follow-up. Stimulus to peak R wave in lead V6 (RWPT) was defined
as the time in milliseconds between the pacing stimulus and the peak of
the R-wave in V6 on the surface electrocardiogram. Pacemaker stimulation
energy was analyzed as a function of voltage and pulse width (E =
V2t/R where E = energy, V = voltage, t = pulse width
and R = impedance).14 Though pulse widths of 0.4, 0.5
and 1 ms were used variably across the population, we were able to use
this method to adjust thresholds to reflect an amplitude measured at a
pulse width of 0.5 ms for consistency across all measurements (adjusted
pulse amplitude = sqrt[(recorded pulse
amplitude)2(recorded pulse width)/(0.5)]. For the
purpose of analysis, an ‘acceptable pacing endpoint’ (APE) included the
following parameters: sensing R-wave amplitude >5 mV,
pacing threshold <2.5 V @ 0.5 ms and impedance between 400 and
1200 Ohms. APE captures normal lead behavior as seen with legacy pacing.
Total fluoroscopy duration and procedure duration was obtained.
Follow-up for each patient stopped with any lead revision or generator
replacement.
Statistical Analysis :
Pre-procedural, procedural and follow-up data for patients who underwent
HBP were compared with patients who underwent LBBP. Continuous variables
were reported as mean +/- SD and compared with two-sample t-tests.
Categorical variables were reported as percentages and compared using
chi squared or two-tailed Fisher exact tests as appropriate. The
Kaplan-Meier method was used to generate failure curves for descriptive
purposes with censoring performed at either the date of loss of APE,
date of last follow-up, or date of death. All analyses were performed
with the use of Stata software version 16.1. Statistical significance
was defined by p-values <0.05.