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Ebook Practical clinical electrophysiology: Part 2

(BQ) Part 2 book "Practical clinical electrophysiology" presents the following contents: Wolff-ParkinsonWhite syndrome and variants, ventricular tachycardia, bradycardias, syncope, sudden death syndromes, implantable cardioverter defibrillator indications, permanent pacemakers, clinical managementof patients with implantable cardioverter defibrillators, noninvasive diagnostic testing, antiarrhythmic drugs. | Wolff-Parkinson- White Syndrome and Variants Ventricular preexcitation occurs in 0.1 to 3.1 out of 1 000 people and is defined as activation of the ventricular myocardium by an atrial impulse earlier than would be expected with normal atrioventricular AV conduction. A delta wave is often seen on the surface electrocardiogram ECG which represents activation of the ventricle by an accessory pathway AP before activation by the conducting system see Fig. 9-1 . Wolff-Parkinson-White WPW syndrome is defined as an AP-mediated tachycardia occurring in patients with ventricular preexcitation on a 12-lead ECG. APs occur when there is an incomplete segmentation of the embryologic cardiac tube and formation of the fibrotic AV ring during fetal cardiac development. The most common type of pathway is AV formed by myocardial tissue connecting the atrium and ventricle and most pathways are epicardial. AV pathways may be manifest which means that they conduct antegradely from the atrium to the ventricle and result in preexcitation which can be seen on the surface ECG or inapparent which means that preexcitation is not seen on the surface ECG or concealed because normal AV conduction activates the ventricle faster than the AP or because the AP does not conduct in an antegrade manner. These latter APs conduct only retrograde from the ventricle to the atrium and are clinically relevant only when they participate in a tachycardia. In fact a minority of APs only conduct in the antegrade manner preexcitation whereas the majority conduct in a retrograde direction. Pathways exhibiting antegrade conduction do so in an all or none manner 119 120 Practical Clinical Electrophysiology FIGURE 9-1. Diagram of antegrade conduction over both the normal atrioventricular AV conducting system and a left-sided accessory pathway. The amount of conduction over the accessory pathway corresponds to the degree of ventricular preexcitation or delta wave. See color insert. 99 of the time. Approximately 1 of .