ABC | Volume 115, Nº1, Suplement, July 2020

Case Report Pérez-Riera et al. Transient left anterior fascicular block Arq Bras Cardiol 2020; 115(1Suppl.1):1-5 Figure 2 – A) ECG performed 30 days before: left atrial enlargement, prominent anterior QRS forces in V2 with qRs pattern in V1-V2, R wave voltage in V2 >15 mm (23 mm), prolonged R-wave peak time in right precordial leads (≥35 ms), ST-segment elevation in aVR (≥1 mm), minimal ST-segment depression in the inferior leads and from V3 to V6; these discrete alterations could raise the suspicion of LMCA disease and some degree of LSFB. Note: this ECG was considered “normal” by the clinician!! B) Coronary angiography in right anterior oblique cranial projection: this view shows a critical sub-occlusion of the LMCA (arrow) in the middle portion. Figure 3 – Outline showing the initial ventricular activation in cases of LSFB. Left His system with its three divisions, in a left sagittal projection. The LAF ends at the base of the ALPM of the mitral valve. The LPF ends in the base of the PMPM of the mitral valve. Since the activation vectors dependent on the anterosuperior (A) and posteroinferior (B) fascicles go in opposite directions, they cancel each other, with minimal predominance of LPF. This phenomenon explains the frequent initial q wave in the right precordial leads in the presence of LPFB. Note the absence of the first 1 AM vector, dependent on LSF. LBB: left bundle branch; RBB: right bundle branch; LAF: left anterior fascicle; LPF: left posterior fascicle; LSF: left septal fascicle; LSFB: left septal fascicular block. 3