11 - Intraventricular conduction abnormalities

Abstract

Normally, the entire mass of ventricular myocardium is depolarized in about 80 to 100 milliseconds. The term “intraventricular conduction disturbances” (IVCDs) refers to abnormalities in the intraventricular propagation of supraventricular impulses resulting in changes in the morphology and/or duration of the QRS complex. These changes in intraventricular conduction can be fixed and present at all heart rates, or they can be intermittent (transient). The term aberration is used to describe transient bundle branch block (BBB) and usually does not include persistent QRS abnormalities caused by BBB, preexcitation, or the effect of drugs. Transient BBB can have several mechanisms, including acceleration-dependent block, pause-dependent block, and concealed conduction. Chronic IVCDs can result from either intrinsic conduction system degeneration or an extrinsic insult from a variety of cardiovascular diseases, and the prognosis of BBB is largely related to the presence, type, and severity of the underlying heart disease, and to the possible presence of other conduction disturbances. The ECG pattern of BBB can represent either complete block or conduction delay (relative to the other fascicles) that produces asynchronous ventricular activation without necessarily implying complete failure of conduction in the diseased fascicle. Therefore, an ECG pattern of complete BBB can have varying degrees or alternate with contralateral complete BBB pattern. In selected patients, invasive electrophysiological testing can be used to obtain information that could predict which patients are at risk for syncope, atrioventricular block, or sudden cardiac death from a ventricular tachyarrhythmia.