T wave polarity in the diagnosis of left bundle branch block in patients with heart failure and reduced ejection fraction caused by ischemic or non-ischemic cardiomyopathy

The diagnosis of left bundle branch block (LBBB) is of uttermost importance in patients with heart failure and reduced ejection fraction (HFrEF). Nevertheless, the definition of LBBB is still a matter of discussion. European guidelines on cardiac pacing and resynchronization therapy from 2021 include T wave polarity in the diagnostic criteria, not as an indispensable requirement but as a usual attribute. In the frontal plane, the T wave should be negative in lead I and aVL, and positive in aVR, so the axis should be approximately limited to 121-239°. However, an exact analysis of the T wave axis in LBBB has not been published yet.

The purpose of this study is to analyse the T wave axis in the frontal plane in HFrEF patients with and without LBBB. To better understand the potential contribution of the most frequent causes of HFrEF, we limited our study to patients with coronary artery disease (CAD) or non-ischemic cardiomyopathy (CMP).

All patients with an ejection fraction ≤40% caused by CAD or CMP undergoing an ICD implant procedure between the years 2013 and July 2023 in our centre were included in the study. The exclusion criteria were (1) coincidence of CAD and CMP, (2) upgrade from a pacemaker, (3) limited quality of ECG recording, (4) more than 1 ventricular premature beat in the recording, (5) right bundle branch block. LBBB was diagnosed according to the European guidelines considering only the subset of indispensable requirements regarding the duration, and morphology of the QRS. The T wave axis was measured by the premium ECG machines of one manufacturer before the implant procedure. Statistical analysis was made in R-software, axis expressed in degrees was compared using R package ‘circular’.

Among 667 patients included in the study, 182 men had CMP (93 with LBBB), 356 had CAD (109 with LBBB). CMP was the principal diagnosis in 71 women (45 with LBBB), CAD in 58 (24 with LBBB). The T wave axis was non-random (P<.001) with a mean angle 104°. The difference in the T wave axis was significant only in men with CAD (118° with LBBB vs 95° without LBBB, P<.001) and women with CMP (134° with LBBB vs. 58° without LBBB, P<.001). Regarding the criteria of LBBB, a significant difference in the proportion of patients with T wave axis supporting the diagnosis was only in men with CAD, where 52 of 109 (49%) with LBBB had the axis in the required range vs. 71 of 247 (29%) without LBBB (P<.001).

In patients with HFrEF caused by CAD or CMP, the impact of the T wave axis analysis on the diagnosis of LBBB is limited.