I. Right Bundle Branch Block
II. Left Bundle Branch Block
GLOSSARY
heart failure failure of the heart to the pump sufficient blood
from the chambers into the aorta; inadequate supply blood
reaches organs and tissues. hypertrophy increase in thickness of muscle. myocardial infarction death of an area of heart muscle due to
blockage of a coronary artery by blood clot in and atheroma;
medical term for a heart attack or coronary thrombosis. sudden cardiac death death from cardiac causes that occurs
instantaneously or within the hour of the onset of symptoms;
the hallmark features are an instantaneous and unexpected
time and mode of cardiac death.
EACH CONTRACTION OF THE HEART IS PRECEDED by excitation waves of electrical activity that originate in a unique pacemaker called the sinoatrial (SA) node, which provides individuals with an automatic, infinitesi¬mal current that sets the electrical activity and contractions of the heart. The electrical discharge from the SA node passes across the atrium and reaches the atrioventricular (AV) node, see Fig. 1. From the AV node the current is conducted to the ventricle through two bundles, a large left bundle and a thinner right bundle (see the chapter Anatomy of the Heart and Circulation).

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• I. RIGHT BUNDLE BRANCH BLOCK
  The right bundle branch is the continuation of the penetrating AV bundle and runs as a single discrete bundle beneath the endocardium of the ventricular septum to the base of the anterior papillary muscle. The bundle then runs in the moderator band to form a rich anastomos¬ing network of conducting fibers throughout the right ventricle. The subepicardial location and discrete nature of the bundle branch of the rim of the right ventricular outflow makes it vulnerable to trauma from catheters. Because of its discrete nature, the bundle is easily damaged by several diseases including focal hypoplasia that causes congenital right bundle branch block, anteroseptal myo-cardial infarction that commonly affects the ventricular septum, and right ventricular hypertrophy associated with diffuse subendocardial fibrosis.
• II. LEFT BUNDLE BRANCH BLOCK
  Left bundle branch block (LBBB) is common after age 60 and is due to a block of the conduction in the bundle that receives impulses from the atrium and conducts the electrical current through the left ventricle (Fig. 1). The ECG is typical, and the physician makes the diagnosis only after looking at the ECG.
• BIBLIOGRAPHY
  Hiss, R. G., and Lamb, L. E. Electrocardiographic findings in 122,043

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