Ventricular dyssynchrony in left bundle branch area pacing assessed by ultra-high-frequency electrocardiogram and speckle-tracking echocardiography

Background Ultra-high-frequency electrocardiogram (UHF-ECG) is a unique technique that allows instantaneous dyssynchrony analysis with real-time visualisation. It has an emerging role in refining patient selection for cardiac resynchronisation therapy and in evaluating electrophysiological differences between conduction system pacing modalities, including left bundle branch area pacing (LBBAP). In this latter setting, data on electrical and mechanical dyssynchrony coupling assessed by UHF-ECG and speckle-tracking echocardiography are still lacking. Purpose To detect the early effects of LBBAP on the spatiotemporal distribution of ventricular electrical depolarisation and to assess the level of ventricular dyssynchrony. Methods We conducted a single-centre prospective study and enrolled patients receiving LBBAP. UHF-ECG was recorded at three-month follow-up from eight precordial leads during intrinsic rhythm and in unipolar and bipolar configuration; ventricular dyssynchrony index (VDI) was defined as the difference between the earliest and latest local activation time across precordial leads. Transthoracic echocardiography with speckle-tracking strain analysis was performed at baseline in spontaneous rhythm and after three months, when left ventricular mechanical activation and synchrony were assessed by global longitudinal strain (GLS) and left ventricular time-to-peak strain dispersion (LV-TPSD). Paired comparisons were used to evaluate changes in VDI, GLS and LV-TPSD, and correlations were analysed between VDI and echocardiographic measures. Results Twenty-three patients with LBBAP underwent UHF-ECG (for baseline characteristics, see Figure 1); strain analysis was available in 22. At three-month follow-up, VDI values were very similar in unipolar and bipolar configurations and strongly associated (ved16: r = 0.94; ved18 ≈ 0.90; mvd16 ≈ 0.90; mvd18 ≈ 0.97; all p < 0.01), indicating that changing pacing polarity did not materially modify the ventricular activation pattern captured by UHF-ECG. GLS did not change significantly from baseline spontaneous rhythm to bipolar pacing (−15.6 ± 4.3% vs −14.4 ± 3.9%, p = 0.20). Posterolateral LV TPSD (LV-PL-TPSD) decreased (66.1 ± 49.3 ms to 40.5 ± 32.7 ms, p = 0.035), whereas global LV-TPSD showed a modest reduction that did not reach statistical significance (74.8 ± 38.4 ms to 58.9 ± 49.3 ms, p = 0.16; Figure 2). No clear linear relationship was observed between VDI and changes in GLS or LV-TPSD in this small cohort. Conclusion Electrical dyssynchrony quantified by UHF-ECG VDI was similar with unipolar and bipolar programming, indicating no relevant effect of pacing polarity on ventricular activation. At three months, LBBAP preserved LV GLS and significantly reduced LV-PL-TPSD, suggesting an early improvement in mechanical synchrony driven by a more homogeneous lateral wall contraction.Figure 1.Baseline characteristicsFigure 2.