Electrocardiographic manifestation of the middle fibers/septal fascicle block: a consensus report

Alternating anterior and posterior fascicular block and left septal fascicular block

Electrocardiogram of a patient affected by hypertensive cardiomyopathy showed an anterior fascicular block pattern and in right precordial leads an anterior displacement of QRS complex, characterised by a well evident jump of r wave from V1 to V2. Lead V2 showed qR morphology with embryonic q wave and very tall R wave. Septal q waves were not present in leads I and aVL. A subsequent electrocardiogram showed a posterior fascicular block pattern and the same findings in right precordial leads. Septal q waves were not present in inferior leads. Other causes of anterior displacement of QRS complex were ruled out by clinical/instrumental investigation. These findings are highly suggestive of left septal (middle) fascicular block coexisting with anterior and posterior fascicular block.

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.

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.

Left bundle branch block and the evolving role of QRS morphology in selection of patients for cardiac resynchronization

BACKGROUND

The clinical significance of left bundle branch block (LBBB) has recently expanded with the discovery of a strong association with better outcomes in patients receiving cardiac resynchronization therapy.

METHODS

Several milestones have contributed to the current understanding on the role of LBBB in clinical practice.

RESULT

Sunao Tawara described the arrangement of components of what he called the cardiac conduction system from the atrioventricular node to the terminal Purkinje fibers that connect to the working myocardium, and his hypotheses on how it functions remain current. Mauricio Rosenbaum and colleagues developed the bifascicular model of the left-sided conduction system that explains the characteristic electrocardiographic changes associated with propagation disturbances in its components. Andrés Ricardo Pérez-Riera and others have disputed the bifascicular model as oversimplified and have emphasized the role of the left septal fascicle. Marcelo Elizari and colleagues have explained the importance of masquerading bundle branch block. Elena Sgarbossa and colleagues developed a scheme to recognize ST elevation myocardial infarction in patients with left bundle branch block which remains current after more than 20 years. Enrique Cabrera and others identified electrocardiographic signs of remote myocardial infarction.

CONCLUSION

Substantial progress has been made in the understanding of LBBB, yet its role in clinical practice continues to evolve and important gaps remain to which research should be directed.

Intraventricular Delay and Blocks

From the atrioventricular node, electrical activation is propagated to both ventricles by a system of specialized conducting fibers, His Purkinje System (HPS), guaranteeing a fast, synchronous depolarization of both ventricles. From the predivisional common stem, a right and left branch separate, subdividing further in a fairly predictable fashion. Synchronous ventricular activation results in a QRS with specific characteristics and duration of less than 110 milliseconds. Block or delay in any part of the HPS changes the electrocardiographic (ECG) morphology. This article discusses the use and limitations of standard ECG in detecting abnormal ventricular propagation in specific areas of the HPS.

Transient left septal and anterior fascicular block associated with type 1 electrocardiographic Brugada pattern

The left septal fascicular block (LSFB) or blockage of the middle fibers of the left bundle branch is probably caused mainly by - in the developed world - the proximal obstruction of the left anterior descending artery (LAD) before its first anterior septal perforator branch (S₁). The association of transient LSFB and left anterior fascicular block (LAFB) - left bifascicular block - and the electrocardiographic type 1 Brugada pattern (BrP) has not been described in the literature yet.

Unusual conduction disorder: left posterior fascicular block + left septal fascicular block

A 44-year-old man with aortic valve insufficiency and stenosis underwent aortic valve replacement depicting interesting ECG changes. This unique case is discussed, contributing to the understanding of a trifascicular left intraventricular conduction system.

Prognostic significance of the absence of normal septal Q waves before aortic valve replacement

PURPOSE

Aim of this study was to investigate the prognostic significance of absence of septal Q waves in patients scheduled for aortic valve replacement.

MATERIAL AND METHODS

Sixty-one patients who underwent isolated aortic valve replacement for aortic stenosis were retrospectively evaluated. Septal Q waves were defined as Q waves of<2mm in amplitude and<40ms in width and absence of septal Q waves was defined as simultaneous loss of Q waves from at least three of the leads I, aVL, V5 and V6. Septal Q waves were absent in 17 patients (Group AQ, 27.8%) and were present in 44 patients (Group PQ, 72.1 %) preoperatively. Newly developed AV block>1st degree and newly developed left bundle branch block were primary endpoints.

RESULTS

Preoperatively, absence of normal septal Q waves was significantly associated with increased risk of postoperative AV block (HR: 11.18, range 1.37-91.21, 95% CI, p=0.02) whereas it was not associated with increased risk for newly developed LBBB (HR: 3.15 0.62-15.83, 95% CI, p=0.16).

CONCLUSION

Absence of normal septal Q waves in the preoperative ECG may predict further delay in conduction which might develop in the early postoperative course of aortic valve replacement.

Right bundle branch block and middle septal fiber block with or without left anterior fascicular block manifested as aberrant conduction in apparent healthy individuals: Electro-vectorcardiographic characterization

BACKGROUND

Right bundle branch block (RBBB) evident in the precordial ECG leads may be associated with evidence of left bundle branch involvement in the limb leads. Any of the components of the left bundle can be involved, and this complex interventricular conduction abnormality has previously been described in patients with underlying heart disease.

OBJECTIVES

To analyze the electro-vectorcardiographic manifestations of RBBB with left middle septal fiber block (LMSFB), with or without left anterior fascicular block (LAFB) in premature atrial beats of patients without apparent structural heart disease.

METHODS

Twelve patients (8 men/4 women; mean age: 32±8years) with premature atrial contractions with this conduction abnormality were included. Surface 12 simultaneous lead ECG recordings and the corresponding vectorcardiographic loops were analyzed.

RESULTS

The QRS complexes with RBBB and also LMSFB persisted for between 150 and 190ms. There were no q waves in lead I. The maximum spatial vector (72-86ms) was directed posteriorly, superiorly, and leftward, and the terminal forces were oriented anteriorly, inferiorly and rightward. In 10 patients, small q waves were apparent in leads V1-V2 and the frontal QRS axis was -60° and -70°, with the 46ms vector located at -50°±5. All of these patients most probably had LAFB in addition to LMSFB. In two patients, the initial electrical forces were directed anteriorly, inferiorly, and leftward, and the 46ms vector axis in the frontal plane was 6° and 11°, respectively, indicating absence of LAFB.

CONCLUSIONS

The combination of RBBB and LMSFB occurring in patients without apparent structural heart disease may be related to the simultaneous occurrence of block of conduction through these components of the Purkinje network. The anterior fascicle of the left bundle may also be involved.