Left posterior fascicular block
- William H Sauer, MD
William H Sauer, MD
- Associate Professor of Medicine
- University of Colorado School of Medicine
In the discussion that follows, it is assumed that the reader understands the general concepts of cardiac vectors, asynchronous activation of the ventricles (delayed as in fascicular or bundle branch block, or early as in pre-excitation), and the effects that asynchrony has on the duration, morphology, and amplitude of the QRS complex. (See "ECG tutorial: Physiology of the conduction system" and "General principles of asynchronous activation and preexcitation".)
FASCICLES OF THE LEFT BUNDLE BRANCH
The classic hypothesis proposed by Rosenbaum and his coworkers was that the left bundle branch divides into two fascicles of rapidly conducting Purkinje fibers (ie, phase 0 dependent on the rapid inward sodium current) (figure 1) . These fascicles primarily affect the direction of depolarization:
●The left anterior fascicle crosses the left ventricular outflow tract and terminates in the Purkinje system of the anterolateral wall of the left ventricle.
●The left posterior fascicle appears as an extension of the main bundle and fans out extensively posteriorly toward the papillary muscle and inferoposteriorly to the free wall of the left ventricle.
In addition, a third fascicle, called the left septal or median fascicle, is found in nearly 65 percent of people [2,3]. This fascicle runs to the interventricular septum, and can arise from the common left bundle or from the anterior, posterior, or both fascicles.To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:
- Rosenbaum M, Elizari MV, Lazzari JO. The Hemiblocks. Tampa Tracings, Tampa 1970.
- Demoulin JC, Kulbertus HE. Histopathological examination of concept of left hemiblock. Br Heart J 1972; 34:807.
- Uhley HN. Some controversy regarding the peripheral distribution of the conduction system. Am J Cardiol 1972; 30:919.
- Myerburg RJ, Nilsson K, Gelband H. Physiology of canine intraventricular conduction and endocardial excitation. Circ Res 1972; 30:217.
- Durrer D, van Dam RT, Freud GE, et al. Total excitation of the isolated human heart. Circulation 1970; 41:899.
- Willems JL, Robles de Medina EO, Bernard R, et al. Criteria for intraventricular conduction disturbances and pre-excitation. World Health Organizational/International Society and Federation for Cardiology Task Force Ad Hoc. J Am Coll Cardiol 1985; 5:1261.
- Surawicz B, Childers R, Deal BJ, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Endorsed by the International Society for Computerized Electrocardiology. J Am Coll Cardiol 2009; 53:976.
- Cinca J, Mendez A, Puig T, et al. Differential clinical characteristics and prognosis of intraventricular conduction defects in patients with chronic heart failure. Eur J Heart Fail 2013; 15:877.
- Godat FJ, Gertsch M. Isolated left posterior fascicular block: a reliable marker for inferior myocardial infarction and associated severe coronary artery disease. Clin Cardiol 1993; 16:220.
- Madias JE, Knez P. Transient left posterior hemiblock during myocardial ischemia-eliciting exercise treadmill testing: a report of a case and a critical analysis of the literature. J Electrocardiol 1999; 32:57.
- Lin D, Hsia HH, Gerstenfeld EP, et al. Idiopathic fascicular left ventricular tachycardia: linear ablation lesion strategy for noninducible or nonsustained tachycardia. Heart Rhythm 2005; 2:934.