![]() The following factors are important differences between AVNRT and AVRT : In contradistinction to ORT resulting in NCTs, antidromic AVRT has anterograde conduction over the accessory pathway and retrograde conduction over the AV node-His bundle resulting in WCTs. In tachycardia, retrograde conduction over the accessory pathway is fast and yields a short RP tachycardia. This type is not apparent by analysis of the ECG during sinus rhythm because the ventricle is not pre-excited and the accessory pathway is said to be “concealed”. This pattern is also known as orthodromic reciprocating tachycardia (ORT). We have reviewed ECG findings of the NCTs and WCTs in order to reduce the possible diagnostic errors on the ECGs.ĪV reentrant tachycardia (AVRT) involves reentry between the atria and ventricles with use of the AV node-His bundle conduction as the anterograde and slow pathway and an accessory conduction as the retrograde and fast pathway. The accurate, rapid diagnosis in patients with these tachycardias still remains a significant clinical dilemma, because the published numerous ECG algorithms and criteria are complicated and difficult to recall in urgent clinical situations. Because administration of medications based on misdiagnosis of these tachycardias can be harmful and sometimes fatal, diagnosis of these tachycardias is critical. The WCTs can be VT or supraventricular tachycardia (SVT) with right or left bundle branch block (BBB) or right or left accessory pathway ( Table 1, ). The NCTs are typically of supraventricular origin above or within the His bundle, although rarely narrow complex ventricular tachycardias (VT) have been reported in the literature in which early activation of the His bundle can also occur in high septal VT, resulting in relatively narrow QRS complexes of 110–140 ms ( Table 1, ). Among these tachycardias with a heart rate greater than 100 beats per minute (bpm), the narrow QRS complex tachycardias (NCTs) are defined by the presence in a 12-lead electrocardiogram (ECG) of a QRS complex duration less than 120 ms and the wide QRS complex tachycardias (WCTs) are defined by the presence in a 12-lead ECG of a QRS complex duration more than 120 ms ( Figure 1). Although such tachycardias often occur in patients with a normal heart, they may cause bothersome symptoms and rarely represent life-threatening conditions. Differential diagnosis and treatment of tachycardias is a common dilemma encountered by physicians or cardiologists.
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