Ebook Practical clinical electrophysiology: Part 2
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Ebook Practical clinical electrophysiology: Part 2
CHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2 the ventricular myocardium by an atrial impulse earlier than would be expected with normal atrioventricular (AV) conduction. A della wave is often seen on the surface electrocardiogram (ECG), which represents activation of the ventricle by an “accessory" pathway (AP) before activation by the conduc Ebook Practical clinical electrophysiology: Part 2ting system (see Fig. 9-1). Wolff-Parkinson-while (WPW) syndrome is defined as an AP-rncdiatcd tachycardia occurring in patients with ventricular prceEbook Practical clinical electrophysiology: Part 2
xcitation on a 12-lead ECG.APs occur when there is an incomplete segmentation of the embryologic cat diac tube and formation of the fibrotic AV7 ring CHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2hways 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 norma Ebook Practical clinical electrophysiology: Part 2l 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 "rEbook Practical clinical electrophysiology: Part 2
etrograde" from the ventricle to the atrium, and are clinically relevant only when they participate in a tachycardia. In fact a minority of APs only cCHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2in an “all or none” manner1191 20■ Practical Clinical ElectrophysiologyFIGURE 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 ventric Ebook Practical clinical electrophysiology: Part 2ular preexcitation or delta wave. (See color insert.)99% of the time. Approximately 1% of antegradely conducting AV pathways exhibit decremental conduEbook Practical clinical electrophysiology: Part 2
ction, the vast majority of which are light sided.APs can be located anywhere around the A-V ling except at the portion of the aortomitral continuity CHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2and the atrial insertion more lateral in inferior APs and the ventricular insertion site lateral and atrial insertion site septal in anterior and posterior APs. Less common variants of typical AV APs arc atriofas-cicular, nodofascicular, nodovcntricular, and fasciculovcntricular pathways, representi Ebook Practical clinical electrophysiology: Part 2ng AP conduction between combinations of the atrium, AV node, conducting system, and ventricle. These valiants are quite rare, but all except fasciculEbook Practical clinical electrophysiology: Part 2
oventricular pathways may participate in tachycardias.CLINICAL EVALUATIONThe first step in evaluating a patient who presents with preexcitation on an CHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2ion. Symptoms may include sustained palpitations or syncope. A history of syncope must be taken carefully to differentiate neurocardiogenic or vasovagal syncope fromWolff-Parkinson-White Syndrome and Variants ■121FIGURE 9-2. Precordial leads Vi -Vft and a rhythm strip of lead 2 are shown for a patie Ebook Practical clinical electrophysiology: Part 2nt with preexcitation through a left-sided accessory pathway. A: During atrial fibrillation (AF), overt preexcitation is seen with R-R intervals as shEbook Practical clinical electrophysiology: Part 2
ort as 200 msec are seen, which may provoke hemodynamic instability and cardiac arrest. B: After restoration of sinus rhythm, the same preexcitation pCHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2will often be preceded by palpitations and may even require urgent cardioversion or delibrillalion if rapidly conducted atrial fibrillation (Al ) is present (see Fig. 9-2). Many patients will never have symptoms related to an AP, and the management of these patients is controversial (see discussion Ebook Practical clinical electrophysiology: Part 2in the subsequent text). A family history of preexcitation or sudden cardiac death is important, as a familial association has been described. Tn addiEbook Practical clinical electrophysiology: Part 2
tion, the presence of congenital heal! disease should be ascertained. Ebstein anomaly is associated with right-sided APs, and when present the APs areCHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2d valve (TV) is the left AV valve.Asymptomatic PatientsThe evaluation of patients presenting without identifiable symptoms or history of syncope and preexcitation on an ECG is controversial. The two risks to such patients are the development of an AP-mediated supraventricular tachycardia (SVT) and t Ebook Practical clinical electrophysiology: Part 2he occurrence of AF with rapid conduction over the AP leading to ventricular fibrillation and/or cardiovascular collapse. The incidence of the latterEbook Practical clinical electrophysiology: Part 2
is extremely low (<0.02% per year), and while the magnitude of122■ Practical Clinical Electrophysiologythis outcome warrants further risk stratificatiCHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2nduct impulses rapidly from the atrium to the ventricle. If an AP is unable to conduct rapidly from the atrium to the ventricle, the risk of extremely rapid ventricular rates and ventricular fibrillation resulting from preexcited AF is low.It should be noted that APs have properties similar to myoca Ebook Practical clinical electrophysiology: Part 2rdium (see subsequent text), and that in a setting of high adrenergic tone their ability to conduct rapidly increases. Therefore, the first step in noEbook Practical clinical electrophysiology: Part 2
ninvasive testing is often exercise treadmill testing because it induces a rapid heart late in a setting of high adrenergic tone. If preexcitation is CHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2the ventricle during AF. Care must be taken in reviewing the ECGs during stress testing; however, as the heightened adrenergic tone also increases AV conduction down the normal conduction system, and a decrease but not complete absence of prccxcitalion may be observed. The abrupt loss of the della w Ebook Practical clinical electrophysiology: Part 2ave must be recognized to confirm that the refractory period of the AP is reached during routine exercise and is therefore unlikely to ever conduct ATEbook Practical clinical electrophysiology: Part 2
al a potentially lethal rale.Another noninvasive test that may be used to risk-stratify patients with asymptomatic prcexcilalion is a 24-houx Holler CHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2e to sustain rapid conduction din ing AF. Intravenous (IV) administration of procainamide (10 mg per kg over 5 minutes) has been used in the past to risk-stratify patients — disappearance of preexcitation with drug administration is associated with longer AP refractory periods. However, this test is Ebook Practical clinical electrophysiology: Part 2 rarely used in current clinical practice. The downside of these two tests is that neither evaluates the function of the AP in the setting of high catEbook Practical clinical electrophysiology: Part 2
echolamines, and therefore may underestimate the capacity of an AP to conduct r apidly.Patients who do not exhibit low-r isk characteristics on non inCHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2n patients with asymptomatic preexcitation and the comparably low' risks of electrophysiology study is warranted at this point in the clinical evaluation. Factors that often determine whether invasive evaluation is pursued include high-risk occupations such as commercial drivers and pilots and, more Ebook Practical clinical electrophysiology: Part 2 commonly, patient preference. Some authors argue that patients who arc asymptomatic and in the agc-group of 35 to 40 years represent a low-risk groupEbook Practical clinical electrophysiology: Part 2
and do not warrant electrophysiologic (EP) testing, but because AF may develop later in life and is the presenting arrhythmia in up to 20% of patientCHAPTERWolff-Parkinson-White Syndrome and VariantsVentricular prccxcitalion occurs in 0.1 to 3.1 out ol 1,000 people, and is defined as activation of Ebook Practical clinical electrophysiology: Part 2 older age-group with preexcited AF, suggesting that the AP docs not conduct at a rate conducive to the development of ventricular arrhythmia in this population. It should also beWolff-Parkinson-White Syndrome and Variants ■123noted that these same authors discount the utility of noninvasive testing Ebook Practical clinical electrophysiology: Part 2 and recommend F.p testing in all patients with asymptomatic preexcitation who arc younger than 35 years. The goals of EP testing are to evaluate theEbook Practical clinical electrophysiology: Part 2
refractory period of the AP and to assess for inducible AP-mcdiated tachyarrhythmias. Specific methods are discussed in subsequent text.Symptomatic PaGọi ngay
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