Fascicular Blocks: Update 2019.

Many advances in the knowledge of medical science are due to the observation of an unknown phenomenon that remains an open question. A plausible hypothesis must be demonstrated and proved through a scientific method in order to be accepted by the scientific community and the same results must be reached by following either the same or different techniques. The original case described by Rosenbaum MB et al., in this review triggered a series of anatomic and physiologic investigations with clinical and experimental observations that supported the trifascicular nature of the intraventricular conduction system of the heart and the concept of hemiblocks. The recognition and description of the left fascicular blocks made by the Argentinian School of Electrocardiology bridged an important gap in electrocardiography and many electrocardiograms that could not be explained until that moment could finally be understood. This review intends to redefine reliable criteria for the electrocardiographic and vectorcardiographic diagnosis of left fascicular blocks [hemiblocks]. The anatomy of the left bundle branch is also discussed to better understand the incidence, prevalence, clinical significance and main causes of left anterior and left posterior hemiblock either isolated or associated with right bundle branch block. This review offers the reader a reappraisal of the trifascicular nature of the intraventricular conduction system regarding the anatomy of the left bundle branch system and its pathophysiological and clinical significance.

The tetrafascicular nature of the intraventricular conduction system.

The existence of a tetrafascicular intraventricular conduction system remains debatable. A consensus statement ended up with some discrepancies and, despite agreeing on the possible existence of an anatomical left septal fascicle, the electrocardiographic and vectorcardiographic characteristics of left septal fascicular block (LSFB) were not universally accepted. The most important criteria requested to confirm the existence of LSFB is its intermittent nature. So far, our group has published cases of transient ischemia-induced LSFB and phase 4 or bradycardia-dependent LSFB. Finally, anatomical, anatomopathological, histological, histopathological, electrocardiographic, vectorcardiographic, body surface potential mapping, and electrophysiology studies support the fact that the left bundle branch divides into three fascicles or a "fan-like interconnected network."

Myotonic dystrophy and Brugada syndrome: A common pathophysiologic pathway?

Type 1 myotonic dystrophy (DM1) is a hereditary neuromuscular disease affecting multiple organs in human adults. Here we report a 42-year-old man diagnosed with DM1. Having a history of progressive muscular weakness and gradual loss of visual acuity, he was referred to us by his ophthalmologist for risk assessment of undergoing cataract surgery. Cardiology workup revealed type 1 Brugada ECG pattern, positive late potentials and inducible ventricular fibrillation in an electrophysiology study. Literature review revealed that those ECG changes may be observed in DM1, suggesting that DM1 and Brugada syndrome may share a common pathophysiologic pathway.