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Conduction abnormalities after myocardial infarction

Authors
Peter J Zimetbaum, MD
Mark E Josephson, MD
Joseph E Marine, MD, FACC, FHRS
Section Editors
Bradley P Knight, MD, FACC
Bernard J Gersh, MB, ChB, DPhil, FRCP, MACC
James Hoekstra, MD
Deputy Editor
Gordon M Saperia, MD, FACC

INTRODUCTION

Electrical conduction abnormalities are well-recognized complications of acute myocardial infarction (MI). They are caused by either autonomic imbalance or ischemia and necrosis of the conduction system. The most common clinical consequence is bradycardia, which may or may not be symptomatic. Complete heart block with a slow escape rhythm is a potentially fatal event in this setting if not detected and treated. In addition, it is important to recognize which bradyarrhythmias are transient and which are likely to progress to irreversible and symptomatic high-degree atrioventricular block.

The major conduction abnormalities associated with acute MI will be reviewed here. Supraventricular arrhythmias, including sinus bradycardia, are discussed separately. (See "Supraventricular arrhythmias after myocardial infarction" and "Clinical features and treatment of ventricular arrhythmias during acute myocardial infarction".)

ANATOMY AND BLOOD SUPPLY OF THE CONDUCTION SYSTEM

After leaving the atrioventricular (AV) node, the bundle of His divides at the juncture of the fibrous and muscular boundaries of the interventricular septum into the right and left bundle branches (figure 1). The right bundle branch courses down the right side of interventricular septum near the endocardium in its upper third, deeper in the muscular portion of the septum in the middle third, and then again near the endocardium in its lower third. The right bundle does not branch throughout most of its course, but it begins to ramify as it approaches the base of the right anterior papillary muscle with fascicles going to the septal and free wall of the right ventricle. The apical free wall at the base of the right anterior papillary muscle is the earliest site of right ventricular activation.

The left bundle branch penetrates the membranous portion of the interventricular septum under the aortic ring. Shortly thereafter, it divides into several discrete branches [1-4]:

An anterior fascicle that crosses the left ventricular outflow tract and terminates in the Purkinje system of the anterolateral wall of the left ventricle.

              

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Literature review current through: Apr 2016. | This topic last updated: Apr 7, 2016.
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