Apical rocking and septal flash revealed by an electrocardiographic parameter in the left bundle branch block
Authors: Andrei D O , Calin A , Calin C , Dragatoiu N C , Barbu F S , Oprean L V , Rosca M , Musat D L 
Published: January 2025

Abstract

Background
Assessing the relationship between electrical and mechanical dyssynchrony in patients with left bundle branch block (LBBB) remains a significant challenge for clinicians. Visual echocardiographic parameters, apical rocking (ApR), and septal flash (SF) are accurate markers of the contraction-and-stretch pattern in the septal and lateral wall in LBBB patients. Electrical activity of the LV apical septum and the LV lateral wall is ECG recorded by the aVL and aVF leads. An ECG parameter that integrates the electrical activation of these two contralateral LV walls could reveal subtle electrical features related to the uncoordinated contraction pattern in LBBB. To the best of our knowledge, no studies have examined the relationship between electrical and mechanical uncoordinated activation of the apical septum and lateral LV wall.

Purpose
This study aimed to assess the relationship between visual echocardiographic parameters of mechanical uncoordinated contraction pattern (ApR and SF) and ECG parameters of electrical intraventricular asynchrony in patients with LBBB.

Methods
We retrospectively included 157 consecutive patients with LBBB, in sinus rhythm, without significant coronary artery disease, and no more than mild organic valvular heart disease. The ApR and SF were echocardiographic visually assessed as a typical sequence of the septal-to-lateral apex motion for the ApR and the short leftward movement of the septum in early systole for the SF. We measured the following ECG parameters: LV activation times (LVAT), RR1 interval (as the longest interval from the first R wave to the last R1 wave) in lateral leads, intrinsicoid deflection (ID) in lateral and aVF leads, and a newly defined marker – the difference (Diff) between aVL and aVF ID’s (Diff_IDaVL_aVF). Based on the presence and absence of both ApR and SF (ApR_SF), the patients were divided into two groups: patients with (68.2%) and without (31.8%) ApR_SF.

Results
In the group of patients with ApR_SF, the LVAT, ID, and RR1 measured in lateral leads, and the Diff_IDaVL_aVF were significantly longer, but IDaVF was significantly shorter compared to the group of patients without ApR_SF (p&lt;0.05) (Table 1). In multivariable analysis, the Diff_IDaVL_aVF (p &lt; 0.001) was the only parameter independently correlated with the presence of ApR_SF (Table 2). On ROC analysis, the best cut-off of DIFF_IDaVL_IDaVF for predicting the presence of ApR_SF in LBBB patients was 46 ms (AUC of 0.92, sensitivity 86%, and specificity 80%) (Figure 2).

Conclusions
In LBBB, a simple ECG parameter incorporating the electrical activation of contralateral LV myocardial segments can provide insights into the myocardial contraction pattern in LBBB patients. A Diff_IDaVL_aVF longer than 46 msec identified LBBB patients with specific contraction patterns (ApR_SF). Considering ECG is the screening tool for LBBB diagnosis, these patients might benefit from early treatment to avoid a worse prognosis.