ECG characteristics of "true" left bundle branch block: Insights from transcatheter aortic valve-related LBBB and His-Purkinje conduction system pacing-correctable LBBB.

Background: Left bundle branch block (LBBB) pattern on the electrocardiogram includes patients with both complete conduction block in the His-Purkinje system as well as nonspecific left ventricular conduction delay without discrete block.
Objective: The purpose of this study was to characterize electrocardiographic morphological features of LBBB patterns in patients with (1) LBBB after transcatheter aortic valve replacement (TAVR) and (2) LBBB correctable by conduction system pacing (CSP).
Methods: Consecutive patients with post-TAVR (n = 123) or CSP-correctable LBBB (n = 58) from 2 centers were included in this retrospective evaluation. QRS durations as well as detailed morphological features, including notching and slurring, of QRS complexes in leads I, aVL, V ₁ , V ₂ , V ₅ , and V ₆ and in all 3 inferior leads were recorded.
Results: The mean age of the entire cohort was 78.3 ± 10.1 years, with 48% of the cohort being male (87/181). In the CSP-correctable group (n = 58), 14 (24.1%) underwent His-bundle pacing and 44 (75.9%) left bundle branch area pacing. A total of 17 of 181 (9.4%) of the combined cohort failed to completely meet the Strauss criteria. QRS morphology in lead V ₁ /V ₂ was always either rS or QS, and there were no q/Q waves noted in lead V ₅ /V ₆ . Although dominant R waves were seen in leads I and aVL of 176 of 181 (97.2%), q/Q waves were present in only 21 of 181 (11.6%). Importantly, notched or slurred QRS complexes were identified in at least 1 lead of 4 leads I, aVL, V ₅ , and V ₆ in 181 of 181 (100%).
Conclusion: Strauss criteria and QRS notching are highly prevalent in LBBB after TAVR and in LBBB correctable by CSP.
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