Evaluation of cardiac synchrony in left bundle branch pacing: Insights from echocardiographic research

Figure 1. Flow chart of patients diagnosed with SSS who accepted pacing therapy in our study. 1 Reasons for exclusion: pacemaker replacements (n = 8), single chamber pacemaker implantations (n = 8) 2 ; Reasons for exclusion: intrinsic QRS > 120 ms, or were accordant with our exclusive criterions, or the patients refused to take part in the study (n = 42). LBBP, left bundle branch pacing; RVSP, right ventricular septum pacing; SSS, sick sinus syndrome

Figure 2. Comparison of QRSd of RVSP, LBBP with normal axis, and LBBP with left axis deviation. The 12‐lead surface ECGs of RVSP, LBBP with normal axis, and LBBP with left axis deviation in three patients. QRSd of RVSP mode was obvious wider than that in native‐conduction mode (A). QRSd of LBBP with normal axis (B) or with left axis deviation (C) was slightly wider than that in native‐conduction mode. ECG, electrocardiography; LBBP, left bundle branch pacing; QRSd, QRS durations; RVSP, right ventricular septum pacing; Stim‐LVAT, the interval from the pacing stimulus to the peak of the R‐wave

Figure 3. Comparison of LV mechanical synchrony between LBBP and RVSP groups. LV mechanical synchronization parameters (SDI or Tsd‐12‐LV) in LBBP capture were significantly shorter compared with RVSP capture mode (A). Similar LV synchrony was showed in native‐conduction (B, left) and LBBP capture modes (B, right) by color coded bull's eye maps in a patient with SSS. Poorer synchrony was showed in RVSP capture mode (C, right) compared with native‐conduction mode (C, left) in another patient with SSS. TDI showed that the time of peak myocardial contraction velocity in the LV segments was relatively concentrated in one LBBP patient (D, left) but was discrete in the other RVSP patient (D, right). LBBP, left bundle branch pacing; LV, left ventricular; RVSP, right ventricular septum pacing; SDI, systolic dyssynchrony index; SSS, sick sinus syndrome; Tsd‐12‐LV, the standard deviation of the time‐to‐peak contraction velocity in the 12 segments

Figure 4. The Stim‐LVAT of tip‐paced ECGs in patients with LBBP with and without LBB potential. One patient without LBB potential (A, left), had Stim‐LVAT of 68 ms (A, right). The other patient recorded with LBB potential (B, left), had Stim‐LVAT of 67 ms (B, right). ECG, echocardiography; LBB, left bundle branch; Stim‐LVAT, the interval from the pacing stimulus to the peak of the R‐wave

Figure 5. Comparison of QRSd (A) and Stim‐LVAT (B) between subgroups divided by paced QRS axis and LBB potential in LBBP group. LBBP, left bundle branch pacing; QRSd, QRS duration; Stim‐LVAT, the interval from the pacing stimulus to the peak of the R‐wave

Figure 6. Comparison of LV mechanical synchrony between subgroups divided by paced QRS axis and LBB potential in LBBP group. Subgroup of left axis deviation had slightly greater SDI and Tsd‐12‐LV than the normal axis subgroup, but without statistically significance (A,B).There were no differences in SDI or Tsd‐12‐LV between the potential+ and potential− subgroups (C,D). ECG, echocardiography; LBB, left bundle branch; LBBP, left bundle branch pacing; LV, left ventricle; SDI, systolic dyssynchrony index; Tsd‐12‐LV, the standard deviation of time‐to‐peak contraction velocity in LV 12 segments