This study was approved by Ethics Committee of Xinhua Hospital Affiliated to Shanghai Jiao tong University School of Medicine (approval number: XHEC-D-2020-148) and performed in accordance with the Declaration of Helsinki.
Patients with chronic LBBB by Strauss criteria, optimal medical therapy-refractory New York Heart Association (NYHA) class III to IV heart failure(HF) symptoms and a baseline left ventricular ejection fraction (LVEF, calculated by Simpson method) ≤ 35% were enrolled in Shanghai Xinhua Hospital from April 1, 2019 to June 1, 2020.
Patients were excluded if they had a history of previous valve intervention, end-stage renal disease, previous heart transplantation, left ventricular assist device, metastatic cancer, moderate or severe valve disease, life-expectancy less than 1 year.
All patients submitted written informed consent and demonstrated an understanding of LOT-CRT as a nonstandard approach to achieve physiologic pacing, and their data were analyzed prospectively.
The RV defibrillator lead was first implanted in the RV to provide backup ventricular pacing should the patient develop transient complete atrioventricular block during the LBBAP lead placement. Subsequently, the LV lead was implanted in the standard fashion targeting sites with maximal LV delay. Then, LBBAP was performed using the Select Secure pacing lead. The fluoroscopy duration for the entire procedure, LBBAP lead implant and LV lead implant were separately recorded.
LBBAP lead implantation technique
As previously described [9-12], a Select Site C315 His sheath and a Select Secure 3830 pacing lead (Medtronic Inc, Minneapolis, MN, USA) were advanced to the implantation site. Right ventricular septal location for LBBAP is identified using the anatomical location and pacing localization in nine-grid system. Once this site is identified, the pacing lead is advanced deep into the septum while monitoring unipolar pacing impedance, electrogram characteristics and paced QRS morphology.
Additionally, the lead orientation can be displayed in various projections. During the initial LBBAP lead fixation, if the lead torques back, it will mean that the lead and sheath are not oriented orthogonal to the RV septum. Generally, the sheath and the lead are oriented such that the lead is pointing towards 12-1 O’clock direction right anterior oblique 30° view and 2-3 O’clock direction in left anterior oblique 30° view.
In addition to fluoroscopic views, significant rise in unipolar pacing impedance above 900 Ohms would suggest that the lead is directing to an oblique direction and need re-oriented. If several attempts were made to achieve LBBAP, prior sites were tagged in the mapping system or fluoroscopic view to prevent re-engaging in the same site. Once the lead position was finalized, 1-2 ml of contrast was injected through the delivery sheath to visualize the septal wall and the approximate depth of the lead under left anterior oblique fluoroscopic view.
Device Connection and Programming
In patients with normal sinus rhythm undergoing CRT-defibrillators, the LBBAP lead was connected to the pace-sense portion of RV port and a bipolar LV lead in the LV port. The pace-sense portion of the spliced ICD lead (DF-1) was capped. In patients with normal sinus rhythm undergoing CRT-pacemakers (P), the LBBAP lead was connected to the RV port and the LV lead to the LV port.
The pacing output required to maximally narrow the QRS (BBB correction threshold) and LBB capture threshold (without BBB correction) was assessed and recorded at a pulse width of 1.0 ms. The QRSd at baseline, during LBBAP, BVP (via RV defibrillator lead, when available) and LBB-Optimized LV pacing were measured on the EP recording system at 100 mm/s. The interval from the onset of QRS to the maximal deflection of LV electrogram (LVAT) during native LBBB pacing and during LBBAP was documented.
Patients were seen for routine clinical follow-up at standard time periods (every 3 months). Functional status was assessed by NYHA classification. Device thresholds were checked and adjusted as needed to maximize battery longevity. The pacing threshold, impedance and R wave amplitude were measured. According to previous literature, the high pacing threshold was defined as pacing threshold over 2.5 V/0.4 ms, increased threshold over 1.0 V compared with the baseline after the procedure and at follow-up. Echocardiographic indices, including LVEF, LV end-diastolic dimensions, pulmonary artery systolic pressure were recorded pre-implant and at follow-up.
Continuous variables were given as mean ± SD or median. Paired comparisons were made using a Student t test if the data were normally distributed, and with the Wilcoxon signed-rank test for nonparametric data. Paired categorical data (NYHA functional class) were compared using the Wilcoxon test. P ≦ 0.05 was considered significant.