Fascicular Blocks: Update 2019

Intermittent isolated anterior displacement of QRS complex - Differential diagnosis

BACKGROUND

The proposed criteria for diagnosis of left septal (middle) fascicular block (LSFB) appear to be conflicting. Moreover, it has been claimed that isolated anterior displacement (AD) of QRS complex could be a manifestation of a conduction delay of the right bundle branch, besides of LSFB. The purpose of the present study was to better define the etiology of AD through an analysis of the case reports dealing with intermittent AD, published up to now.

METHODS

PubMed search was performed to include all case reports dealing with intermittent AD occurring spontaneously, with an available 12‑lead electrocardiographic recording. Pertinent data were extracted from the papers for further analysis.

RESULTS

Eighteen case reports were found in the literature; in all cases intermittent AD was attributed to LSFB. In all cases AD was associated to changes of initial QRS forces, characterized by disappearance of septal q waves (in I and V6) and/or appearance of a small q wave in leads V1-V3. Morphology of terminal QRS forces, analysed for the first time, was unchanged in 90% of cases. Some Isolated ADs observed during induction of premature atrial extra-stimuli and recorded by vectorcardiographic tracing and some electrocardiographic leads were attributed to a conduction delay of the right bundle branch. In this case, initial QRS forces did not change and terminal QRS forces shifted to the right.

CONCLUSIONS

In the presence of intermittent isolated AD, a differential diagnosis between LSFB and a conduction delay of the right bundle branch appears to be possible by the analysis of initial and terminal QRS forces. Instead, the diagnosis of permanent LSFB remains a challenge.

Left Ventricular Summit-Concept, Anatomical Structure and Clinical Significance

The left ventricular summit (LVS) is a triangular area located at the most superior portion of the left epicardial ventricular region, surrounded by the two branches of the left coronary artery: the left anterior interventricular artery and the left circumflex artery. The triangle is bounded by the apex, septal and mitral margins and base. This review aims to provide a systematic and comprehensive anatomical description and proper terminology in the LVS region that may facilitate exchanging information among anatomists and electrophysiologists, increasing knowledge of this cardiac region. We postulate that the most dominant septal perforator (not the first septal perforator) should characterize the LVS definition. Abundant epicardial adipose tissue overlying the LVS myocardium may affect arrhythmogenic processes and electrophysiological procedures within the LVS region. The LVS is divided into two clinically significant regions: accessible and inaccessible areas. Rich arterial and venous coronary vasculature and a relatively dense network of cardiac autonomic nerve fibers are present within the LVS boundaries. Although the approach to the LVS may be challenging, it can be executed indirectly using the surrounding structures. Delivery of the proper radiofrequency energy to the arrhythmia source, avoiding coronary artery damage at the same time, may be a challenge. Therefore, coronary angiography or cardiac computed tomography imaging is strongly recommended before any procedure within the LVS region. Further research on LVS morphology and physiology should increase the safety and effectiveness of invasive electrophysiological procedures performed within this region of the human heart.