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Ebook Understanding intracardiac EGMs and ECGs: Part 2

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Nội dung chi tiết: Ebook Understanding intracardiac EGMs and ECGs: Part 2

Ebook Understanding intracardiac EGMs and ECGs: Part 2

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2t in the late nineteenth century, although by the early twentieth century the AV node and His bundle had been identified as the pathway that electrica

lly connected the atria to the ventricles. The concept that additional muscular connections between atria and ventricle existed was controversial unti Ebook Understanding intracardiac EGMs and ECGs: Part 2

l 1942, when Wood and colleagues described the first histologic evidence of three accessory pathways connecting the right atrium and right ventricle i

Ebook Understanding intracardiac EGMs and ECGs: Part 2

n a young boy who died suddenly. The properties of accessory pathways have fascinated electrophysiologists for many years, particularly after seminal

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2and electrophysiologyTire AV node generally forms the only connection between atrial and ventricular tissue, with the remainder of the atrial tissue a

nd ventricular tissue separated by the fibrous aimulus that forms the scaffolding for the mitral and aortic valves. This arrangement, along with the r Ebook Understanding intracardiac EGMs and ECGs: Part 2

efractory properties of the AV node and I lis bundle, reduces the likelihood of "feedback" between atrial and ventricular depolarization. There is a s

Ebook Understanding intracardiac EGMs and ECGs: Part 2

mall but definite incidence of sudden cardiac death in patients with accessory pathways, particularly in those patients with symptomatic arrhythmias (

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2f accessory pathways can vary significantly (Table 9.1). Most commonly accessory pathways are composed of tissue histologically and electrophysiologic

ally like atrial or ventricular tissue, with a rapid phase 0 upstroke and a plateau phase. Accessory pathways can usually conduct in both directions, Ebook Understanding intracardiac EGMs and ECGs: Part 2

from atrium to ventricle and from ventricle to atrium. However, some accessory pathways can only conduct in one direction, usually from ventricle to a

Ebook Understanding intracardiac EGMs and ECGs: Part 2

trium. These accessory pathways are often called "concealed," because their presence is not observed during sinus rhythm (no atrioventricular activati

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2y slowly, more like AV node tissue.Understanding intracardiac EGMs and ECGs. By Fred Kusumoto. Published 2010 by Blackwell Publishing. ISBN: 978-1-405

1 -8410-6107108 Part 2 Specific ArrhythmiasTable 9.1 Atrioventricular accessory pathway types.LocationECG characteristicsNormal conduction propertiesM Ebook Understanding intracardiac EGMs and ECGs: Part 2

anifestAccessory pathway conducts in both directions Delta wave and a short PR interval will be observed during sinus rhythm Supraventricular tachycar

Ebook Understanding intracardiac EGMs and ECGs: Part 2

dia is most common, although regular and irregular wide complex tachycardia may be observedConcealedAccessory pathway only conducts “backwards" from v

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2 pathway conducts only from the atria to the ventricles Short PR with a delta wave will be observed during sinus rhythmSlow conduction propertiesAnter

ograde onlyNormal ECG at baseline (slow conduction does not produce a delta wave) Present with wide complex tachycardiaRetrograde onlyPermanent juncti Ebook Understanding intracardiac EGMs and ECGs: Part 2

onal reciprocating tachycardia (PJRT) Incessant supraventricular tachycardiaECG findings in patients with accessory pathwaysECG during sinus rhythm (d

Ebook Understanding intracardiac EGMs and ECGs: Part 2

elta waves)The ECG is the single most important noninvasive tool for identifying the presence of an accessory pathway. Patients with accessory pathway

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2 simply mean that the presence of an accessory pathway can be identified because a portion of the ventricles is depolarized early or "preexcited" due

to accessory pathway depolarization. In these patients, the ventricle is activated by both the AV node and the accessory pathway, and the QRS morpholo Ebook Understanding intracardiac EGMs and ECGs: Part 2

gy can provide important clues for the location of the accessory pathway.Remember from Chapter 2 that ordinarily the AV node is characterized by slow

Ebook Understanding intracardiac EGMs and ECGs: Part 2

conduction, and the right and left ventricles depolarize almost simultaneously. In a patient with a right-sided accessory pathway connecting the right

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2depolarized early (Fig. 9.1). This leads to an absent isoelectric PR interval and an abnormal QRS complex that is wide and has a slurred upstoke or "d

elta" wave. The delta wave is caused by early activation of the right ventricle,Chapter 9 Accessory pathways 109Figure 9.1 Schematic showing the effec Ebook Understanding intracardiac EGMs and ECGs: Part 2

ts of a right-sided and a left-sided accessory pathway on the baseline surface ECG. Top: In the presence of a right-sided accessory pathway, a large p

Ebook Understanding intracardiac EGMs and ECGs: Part 2

ortion of the right ventricle is activated ver)' early (due to proximity of the accessor)' pathway to the sinus node), leading to the absence of an is

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2ion of the left ventricle leads to a prominent R wave in vr A short isoelectric PR segment is often observed before the delta wave because depolarizat

ion of the AV node occurs before depolarization of the accessory pathway. However, because of the rapid conduction properties of the accessory pathway Ebook Understanding intracardiac EGMs and ECGs: Part 2

a delta wave is still present.and the QRS complex is wide because the right ventricle depolarized by the accessory pathway proceeds by slower cell-to

Ebook Understanding intracardiac EGMs and ECGs: Part 2

-cell depolarization that does not use the specialized I lis-Purkinje tissue. Since the right ventricle is activated before the left ventricle, the ge

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2RS complex will be negative in Vj and positive in the lateral leads V5, V6,1, and aVL. From Fig. 9.1 it can be seen that the initial part of the QRS c

omplex is due to depolarization via the accessory pathway and the middle and later parts of the QRS are due to depolarization of both the accessory pa Ebook Understanding intracardiac EGMs and ECGs: Part 2

thway and the AV node. A 12-lead ECG from a patient with a rightsided accessory pathway is shown in Fig. 9.2. Notice that the p wave and QRS110 Part 2

Ebook Understanding intracardiac EGMs and ECGs: Part 2

Specific ArrhythmiasFigure 9.2 ECG from a patient with a right-sided accessory pathway. (Reprinted with permission from Kusumoto FM. ECG Interpretati

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2x in lead V1 is predominantly negative, because of early right-to-left depolarization of the right ventricle due to the right-sided accessor}’ pathway

.Patients with a left-sided accessory pathway will have a different ECC pattern. In this case a short isoelectric PR interval may be observed, since t Ebook Understanding intracardiac EGMs and ECGs: Part 2

he AV node will be depolarized before the accessory pathway (think of it "getting a head start"). I lowever, since the AV node has slow conduction pro

Ebook Understanding intracardiac EGMs and ECGs: Part 2

perties, depolarization via the accessory pathway still "beats" the AV node and a della wave and an abnormal QRS complex are still seen. In this case

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2lock pattern with a prominent positive QRS in Vị. Since the delta wave represents ventricular depolarization via the accessory pathway, careful analys

is of the delta wave can provide further clues for accessory pathway localization. If the accessory pathway is located al the lateral wall of the mitr Ebook Understanding intracardiac EGMs and ECGs: Part 2

al annulus, the delta wave will be negative in I and a VI. due to ventricular depolarization traveling away from this area (Fig. 9.3). If the accessor

Ebook Understanding intracardiac EGMs and ECGs: Part 2

y pathway is located more inferiorly and closer to the septum (Fig. 9.4) the delta waves will be negative in the inferior leads (II, III, andaVF)In pa

PART 2Specific ArrhythmiasCHAPTER 9Accessory pathwaysThe existence of multiple connections between the atrium and ventricle was first proposed by Kent

Ebook Understanding intracardiac EGMs and ECGs: Part 2onduction over the accessory pathway. Il has been suggested that some pathways are concealed because they are thinner and the voltage generated by acc

essory pathway depolarization is not sufficient to depolarize adjacent ventricular tissue. However, since the atria are thinner, retrograde depolariza Ebook Understanding intracardiac EGMs and ECGs: Part 2

tion of atrial tissue can still occur, and for this reason these patients still develop supraventricular tachycardia.

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