Four out of the 22 eligible patients were excluded from the study according to the exclusion criteria. Consequently, 18 patients were eligible for CRT. During follow-up, one patient lost to follow-up in group 2. So out of the 18 eligible patients, only 17 patients enrolled the study (9 cases in group 1, 8 in group 2). Among 9 patients in group1, 1 patient failed to complete LBBAP and transferred into group 2. In the end, 8 patients (47.1%) were defined as group 1; 9 patients (52.9%) were defined as group 2 (Fig. 1).
All patients had had at least 1 HF hospitalization 3 months before LBBAP implantation. Entresto (sacubitril/valsartan), β-blockers, and loop diuretics were prescribed to all patients.
Among the 17 patients, nine (52.9%) were male. All patients had cardiomyopathy (7 non-ischemic and 10 ischemic), and 6 patients had paroxysmal atrial fibrillation. Hypertension was present in 8 patients. Frequent ventricular premature contraction (VPC) (> 1,000 per 24 hours) were found in 5 patients. The mean age was 69.1 ± 6.4 years, and the baseline characteristics of the patients were provided in Table 1. At baseline, the two groups were matched for age, gender, hypertension, diabetes mellitus, ICM, paroxysmal atrial fibrillation as illustrated in Table I (all P > 0.05).
The echocardiographic indices, including LVEF, LVEDD, and NYHA classification, NT-proBNP were shown in Table 3. Both groups did not show significant difference (all P > 0.05). The baseline LVEF and the baseline QRSd with LBBB (Fig. 2a) were 33.9 ± 3.9% and 168.2 ± 18.9 ms, respectively.
CRTDs were implanted in 15 patients (Fig. 3A, 3B), and CRTPs were implanted in the remaining 2 patients (Table 2). One in every group, both groups did not show difference in CRTP implantation(P > 0.05). The operation duration was 135 ± 26 min. The duration of X-ray fluoroscopy was 25.2 ± 7.1 min.
In group 1, LBBAP was successfully achieved in 8 patients. Another one failed and transferred into group 2. So the acute success rate was 87.5%. In group 2, CS lead was successfully implanted in all 9 patients. The acute success rate was 100%. Compared with group 2, the operation duration and the duration of X-ray fluoroscopy in group 1 all increased, but the later was not significantly (P > 0.05)(Table 2).
Both the LBBAP and CS capture thresholds remained stable during procedure (1.3 ± 0.6 V at 0.4 ms vs. 1.6 ± 0.7 V at 0.4 ms). Bipolar LBBAP resulted in partial but significant narrowing of the QRSd (BBB correction) in 5 patients.
Both groups did not show difference in CS pacing lead, RV defibrillator lead parameters, such as R-wave amplitude, threshold, and impedance and so on (Table 2).
ECG characteristics and pacing parameters
Individual electrocardiographic responses to RV, LV, and LBBAP at the time of implantation were shown in Table 2. Among the 17 patients, the baseline QRSd was 168.1 ± 18.9 ms (Fig. 2a). At baseline, the two groups were matched for QRSd (158.0 ± 13.0, vs. 176.7 ± 19.7, P > 0.05) as illustrated in Table 3.
In group 1, after unipolar LBBAP, 8 patients demonstrated a right bundle branch block (RBBB) pattern with a paced QRSd of 123.0 ± 5.7 ms (P = 0.001 vs. baseline) (Fig. 2b). LBB potential could be recorded in 5 patients from the LBB lead (62.5%). The LVAT for all LBBAP patients was 72.5 ± 9.4 ms, and the R wave amplitude, pacing impedance, and unipolar pacing capture threshold were 9.9 ± 7.2 V, 678 ± 102 Ω, and 0.84 ± 0.17 V/0.4 ms, respectively.
In group 1, BVP resulted in significant reduction of the QRSd from 158.0 ± 13.0 ms at baseline to 132.0 ± 4.5 ms (P = 0.019) (Fig. 2c). Compared with BVP, unipolar LBBAP resulted in further reduction of the QRSd to 123.0 ± 5.7 ms (P = 0.006 versus baseline and P = 0.021 versus BVP). However, LOT-CRT resulted in a significantly greater reduction of the QRSd to 117.0 ± 6.7 ms (P < 0.01 versus baseline, BVP, or bipolar LBBAP).
In group 2, BVP resulted in significant reduction of the QRSd from 176.7 ± 19.7 ms at baseline to 143.3 ± 8.2 ms (P = 0.011). However, compared with LOT-CRT, BVP has no any advantage in reducing QRSd(P > 0.05, Table 3).
The mean follow-up time was 300 ± 185 days. At baseline, the two groups were matched for follow-up time (296 ± 201, 305 ± 190, P > 0.05). Among all 9 patients, CS lead parameters were stable during follow-up. In group 1, the LBBAP capture threshold, R-wave amplitude, and lead impedance were 0.74 ± 0.25 V, 13.36 ± 5.23 mV, and 533.73 ± 32.31 Ω during the 3-month follow-up (all P > 0.05, respectively, between the time of device implantation and the follow-up visit). In group 2, the RV lead parameters were also stable during follow-up. No patients showed signs of dislodgement, loss of capture, infections, embolism, or stroke associated with the implantation. The ventricular pacing rate was 95%. There were 8 VT/VF episodes treated with antitachycardia pacing and/or shock that had an electrogram available for adjudication (3 in group 1, 5 in group 2). However, the rate of VT/VF therapy was not statistically different (P = 0 .175) between two groups.
Transthoracic echocardiogram (Fig. 3) evaluation data at baseline and at the 1-month and 3-month follow-ups were available in all 17 patients receiving successful CRT. As shown in Table 3, the symptoms and the median NYHA classification score improved significantly, with the latter decreasing from 3.36 ± 0.50 to 2.45 ± 0.52 (P = 0.016). LVEF (33.9 ± 3.9% vs. 45.4 ± 8.7%, P = 0.002) and NT-proBNP (2937 ± 1646 vs. 1832 ± 1541, P = 0.014) were brought a corresponding improvement at the follow-up visit significantly. LVEDD (65.1 ± 9.1 mm vs. 58.7 ± 10.2 mm, P = 0.319) was improved at the 3-month follow-up visit, but not significantly (P > 0.05).
As compared to the base line, patients in group 1 showed significant improvement in LVEF and NT-proBNP levels, while patients in group 2 showed non-significant changes in these parameters (Table 3).