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).