Background
The incidence of congenital complete atrioventricular block in a normal
heart (CCAVB) is 0.5-1/15.000 births (1) and is due to failure of
atrio-ventricular (AV) nodal conduction with preservation of the His
Purkinje system.
The implantation of a pacemaker is recommended for symptomatic patients
and for asymptomatic patients with ventricular dysfunction or at risk of
syncope and sudden death; nonetheless, right ventricular (RV) pacing can
have detrimental effects on cardiac function (2-4). Left ventricular
(LV) remodeling can occur, and be associated to exercise
intolerance/heart failure in up to 20% of adult patients (5),
congestive heart failure being observed in 7-10% of patients paced
because of CCAVB (3, 4).
While RV pacing- associated cardiomyopathy benefits from CRT, its
indication is less clear in pediatric than in older patients, owing to
the low prevalence of dilated cardiomyopathy (4). Since the His-Purkinje
system is preserved in CCAVB patients, it can be expected that His
bundle pacing (HBP) would be a suitable treatment for CCAVB patients
with RV pacing–associated LV dysfunction, and could become the gold
standard for CCAVB in the future.
Case 1. An 18-years old girl with a history of CCAVB had a VVIR
pacemaker implanted at 9. Elective replacement was indicated after 9
years of 90% VVIR pacing; echocardiographic evaluation showed slightly
increased LV volume (LVEDVi=86 ml/m2 and LVESVi=50
ml/m2) with a mildly depressed LVEF (42%) and
moderate mitral and tricuspid regurgitation. The 12-lead ECG showed
sinus rhythm with complete atrioventricular block and a
ventricular-paced QRS (duration 164 ms, Fig. 1, panel A). While in need
to open the pocket for device replacement, we planned an upgrade to
triple-chamber pacemaker with HBP to improve cardiac function by
restoring the physiologic atrioventricular, interventricular and
intraventricular synchronicity. An active-fixation atrial lead was
advanced in the right atrium and a SelectSecure 3830 pacing lead was
delivered by a Medtronic C315His catheter (Medtronic Inc, Minneapolis
MN) (Fig.1). Selective HBP was achieved at 1.5 V@1.0 ms pacing
threshold. The 3 leads were connected to a Serena CRT-P (Medtronic Inc,
Minneapolis MN); SelectSecure was connected into the LV port.
Atrioventricular physiologic pacing (DDD, lower rate 40 bpm and upper
rate 170 bpm) with selective HBP was programmed in LV-only mode, with a
QRS duration and morphology identical to the native QRS at a sensed AV
interval of 100 ms (Fig. 1, panel C). At 9-month follow-up the HBP
threshold was stable (1.5 V@1.0 ms), with 100% of pacing in DDD mode.
Echocardiography showed reverse remodeling: LVEDVi=65
ml/m2, LVESVi=32 ml/m2, LVEF= 50%,
mitral and tricuspid regurgitation decreased to mild (Table).
Case 2. A 16-years old male with CCAVB was implanted at 5 with
a VVIR pacemaker; in 2019 the device reached replacement indication.
Echocardiography showed mildly reduced LVEF (44%), LVEDVi=92
ml/m2and LVESVi=48 ml/m2, mild
aortic regurgitation. Paced QRS was 147 ms (Fig 2, panel A) while the
intrinsic junctional rhythm at 33 bpm had a QRS duration of 104 ms.
Upgrading with an active fixation right atrial lead and a SelectSecure
3830 pacing lead (Medtronic Inc, Minneapolis MN) was achieved, with a
selective HBP threshold as 0.75 V@0.6 ms (fig. 2, panel D. Physiologic
HBP was delivered by a Serena CRT-P programmed as in the former patient.
At 9-month follow-up a significant improvement of ventricular function
was observed: LVEDVi=76 ml/m2; LVESVi=32
ml/m2; LVEF=57% (Table). HBP threshold increased at
1.5V@0.6ms, showing minimal para-Hisian capture at 3V@0.6ms (Fig.2,
panel B).