Junctional tachycardia is less common. Basic knowledge of arrhythmias and cardiac automaticity will facilitate understanding of this article.Īs discussed in Chapter 1 the atrioventricular node does not exhibit automaticity, meaning that it does not discharge spontaneous action potentials, at least not under normal circumstances. The most common rhythm arising in the AV node is junctional rhythm, which may also be referred to as junctional escape rhythm. In this article, you will learn about rhythms arising in, or near, the atrioventricular (AV) node. 4).Rhythms arising near the atrioventricular node: junctional rhythm (escape rhythm) and junctional tachycardia Hence, patients with WPW syndrome carry a small but definite risk of sudden cardiac death (Fig. Rarely, due to very high ventricular rates, it can degenerate in to ventricular fibrillation and cause sudden death. The ECG shows a wide QRS tachycardia that is very fast, has broad complexes with varying QRS durations (normal narrow and with varying degrees of fusion) and is irregular. However, when it occurs it can cause very rapid ventricular rates in WPW syndrome. AF occurs more commonly in patients with WPW syndrome than those without APs, though AP itself does not have any direct role in initiation or maintenance of AF. Fortunately, this comprises only 5% of all arrhythmias in patients with WPW syndrome. This sequential activation of the two ventricles results in wide QRS complexes during this arrhythmia that can be difficult to differentiate from ventricular tachycardia on ECG (Fig. The ventricular activation in this tachycardia is sequential – the ventricle (left or right) where the AP is inserted gets activated first followed by activation of the other ventricle. It is a very uncommon form of arrhythmia wherein the reentrant circuit is reverse of ORT, that is, the antegrade conduction is over AP and retrograde conduction is over the AV node–His- Purkinje system. Antidromic atrioventricular reentrant tachycardia (AVRT).ORT can also occur in patients with concealed APs that have no preexcitation on baseline ECG. Since the antegrade conduction is over normal His-Purkinje system, the ventricles are activated normally and hence it presents like a narrow QRS tachycardia (see Fig. In this arrhythmia, the reentrant circuit travels from atria to ventricles over the normal AV node–His-Purkinje system and retrogradely from ventricles to the atria over the AP. It is the most common type of arrhythmia in patients with WPW syndrome and presents as a type of PSVT. Orthodromic reciprocating tachycardia (ORT).The arrhythmias that can occur in patients with WPW syndrome include the following: Conduction time through the AP – slow conductingAP produce minimal preexcitation.Conduction time through the AV node–His-Purkinje system – enhanced AV nodal conduction results in less preexcitation whereas slow AV nodal conduction produces more preexcitation.Distance between the sinoatrial node and the atrial end of the AP – shorter the distance, more is the preexcitation.The degree of ventricular preexcitation during sinus rhythm depends on three factors (1): The APs that conduct only retrogradely do not produce ventricular preexcitation and are known as concealed APs. Most APs conduct in both directions and only antegradely conducting pathways are rare. In contrast to the AV node, these APs have the capability to conduct electrical impulses very rapidly either antegradely (from atrium to ventricle) or retrogradely (from ventricle to atrium) or in both directions. These provide an additional electrical connection between the atria and the ventricles apart from the normal AV node–His-Purkinje system and result in earlier depolarization of that part of the ventricle where they insert. The atrioventricular APs, also known as Bundles of Kent, usually connect the atria and the ventricles at the mitral or tricuspid annulus.
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