Novel approach to discriminate left bundle branch block from nonspecific intraventricular conduction delay using pacing-induced functional left bundle branch block

Conduction time from left bundle branch pacing to the left ventricular lateral wall in two patients in whom cardiac resynchronization therapy pacemaker was implanted

The efficacy of left bundle branch pacing (LBBP) as cardiac resynchronization therapy (CRT) has been reported, but LBBP may not always improve conduction disturbance in the left ventricle (LV). To evaluate LV electrical conduction delay during LBBP, we measured conduction time from the pacing at left bundle branch to LV lead sensing (LBBP-LV) in two patients in whom left bundle branch-optimized cardiac resynchronization therapy (LOT-CRT) was attempted. Case 1 was a 77-year-old female with dilated cardiomyopathy (DCM) and left bundle branch block. The QRS duration during LBBP was 160 ms and the interval between the stimulus artifact and peak of the R wave in lead V6 (Stim-V6RWPT) was 74 ms. LBBP-LV at the LV mid-lateral wall and LV mid-posterolateral wall were 112 ms and 102 ms, respectively. Case 2 was a 75-year-old female with DCM and nonspecific intraventricular conduction delay. The QRS duration during LBBP was 156 ms and Stim-V6RWPT was 66 ms. LBBP-LV at the LV mid-anterolateral wall, LV mid-lateral wall, and LV mid-posterolateral wall were 96 ms, 107 ms, and 121 ms, respectively. In conclusion, LBBP-LV at the LV mid-lateral area was relatively long. If LBBP does not improve LV conduction disturbances, LOT-CRT may be more effective.

Learning objective

The efficacy of left bundle branch pacing (LBBP) for cardiac resynchronization therapy (CRT) has been reported. However, if the conduction time from pacing to the left ventricular (LV) lateral area during LBBP is long, LBBP may not improve LV conduction disturbance, resulting in ineffective CRT. In such cases, more effective CRT would be expected with LV lead implantation at the area of the LV conduction delay during LBBP.

Simple electrophysiological predictor of QRS change induced by cardiac resynchronization therapy: A novel marker of complete left bundle branch block

BACKGROUND

QRS complex shortening by cardiac resynchronization therapy (CRT) has been associated with improved outcomes.

OBJECTIVE

We hypothesized that the absence of QRS duration (QRSd) prolongation by right ventricular mid-septal pacing (RVP) may indicate complete left bundle branch block (cLBBB).

METHODS

We prospectively collected 12-lead surface electrocardiograms (ECGs) and intracardiac electrograms during CRT implant procedures. Digital recordings were edited and manually measured. The outcome measure was a change in QRSd induced by CRT (delta CRT). Several outcome predictors were investigated: native QRSd, cLBBB (by using Strauss criteria), interval between the onset of the QRS complex and the local left ventricular electrogram (Q-LV), and a newly proposed index defined by the difference between RVP and native QRSd (delta RVP).

RESULTS

One hundred thirty-three consecutive patients were included in the study. Delta RVP was 27 ± 25 ms, and delta CRT was -14 ± 28 ms. Delta CRT correlated with native QRSd (r = -0.65), with the presence of ECG-based cLBBB (r = -0.40), with Q-LV (r = -0.68), and with delta RVP (r = 0.72) (P < .00001 for all correlations). In multivariable analysis, delta CRT was most strongly associated with delta RVP (P < .00001), followed by native QRSd and Q-LV, while ECG-based cLBBB became a nonsignificant factor.

CONCLUSION

Baseline QRSd, delta RVP, and LV electrical lead position (Q-LV) represent strong independent predictors of ECG response to CRT. The absence of QRSd prolongation by RVP may serve as an alternative and more specific marker of cLBBB. Delta RVP correlates strongly with the CRT effect on QRSd and outperforms the predictive value of ECG-based cLBBB.

A new electrocardiographic definition of left bundle branch block (LBBB) in patients after transcatheter aortic valve replacement (TAVR)

BACKGROUND

Current LBBB definitions cannot always distinguish LBBB from left ventricular conduction delay. Only patients with LBBB are expected to normalize with His bundle pacing. Patients who develop new LBBB immediately post transcatheter aortic valve replacement (TAVR) provide an excellent model to define electrocardiogram (ECG) features of LBBB. We sought to describe their ECG features and develop a new ECG definition of LBBB.

METHODS

We screened ECGs from 264 consecutive patients who underwent TAVR at the University of Ottawa Heart Institute. Patients with a baseline QRS of ≤100 ms who developed QRS ≥120 ms immediately after TAVR were included. Two electrocardiologists reviewed all ECG independently. Baseline demographics and echocardiographic data were retrospectively collected.

RESULTS

36 patients were included in the analysis. The median age was 85.5 years (IQR, 81.8-89 years) and 52.8% were males. The minimum QRS duration was 126 ms. The median QRS axis was -18° (IQR, -40-4.5°), which is 18.5° leftward compared to the median QRS axis before TAVR. Fourteen patients (38.9%) had left axis deviation. All patients had a notched/slurred R wave in at least one lateral lead and an R wave duration of ≤20 ms in V1 when present.

CONCLUSION

We developed a new ECG definition of LBBB that includes 2 novel findings: notching/slurring of the R wave in at least one lateral lead and an R wave ≤20 ms in V1. Further larger studies are warranted to confirm these findings.