Wagner_Marriot's Practical Electrocardiography, 12e

CLINICAL PERSPECTIVE

Atrial

AVN: AV node HB: His bundle RBB: right bundle brunch KB: Kent bundle LBB: left bundle branch

muscle

AVN

KB

AV connective tissue

HB

Ventricular muscle

LBB

RBB

F I G U R E 7 . 1 .

Normal and accessory AV conduction system. Solid bar, nonconducting struc-

tures. AV, atrioventricular.

Ventricular preexcitation refers to a congenital cardiac abnormality where part of the ventricular myocardium receives electrical activation from the atria before the impulse arrives via the normal AV conduction system. A schematic illustration of the anatomic relationship between the normal AV conduction system and the accessory AV conduction pathway provided by the bundle of Kent is displayed in Figure 7.1. Nonconducting struc- tures, which include the coronary arteries and veins, valves, and fibrous and fatty connec- tive tissues, prevent conduction of electrical impulses from the atrial myocardium to the ventricular myocardium. AV myocardial bundles commonly exist during fetal life but then disappear by the time of birth. 3 When even a single myocardial connection persists, there is the potential for ventricular preexcitation. In some individuals, evidence of preexcitation may not appear until late in life; whereas in others with lifelong evidence of ventricular preexcitation on the electrocardiogram (ECG), the WPW syndrome may not occur until late in life. Conversely, infants with the WPW syndrome may outgrow any or all evidence of this abnormality within a few years. 4

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CHAPTER 7: Ventricular Preexcitation