A narrow QRS complex during a left bundle branch block morphology wide QRS tachycardia: A clue for manifest or bystander involvement of nodofascicular pathway?

Abstract

A 52-year-old man presented with repeated paroxysms of palpitations resulting from both a rapid narrow (NCT) and wide (WCT) QRS complex tachycardia. His WCT had a left bundle branch block (LBBB) pattern with a precordial transition at V5 and a cycle length (CL) of 440 milliseconds (Figure 1). His WCT terminated following intravenous adenosine. His physical examination was normal, and echocardiography revealed no evidence of structural heart disease. The electrophysiological (EP) study showed a normal atrial-His bundle interval of 84 milliseconds and an His bundle-ventricular (HV) interval of 47 milliseconds during sinus rhythm. During atrial extra stimulus (AES) testing, there was no evidence of preexcitation but a dual atrioventricular (AV) nodal physiology of the antegrade pathway with an atrial echo beat. Right ventricular (RV) pacing showed decremental ventriculoatrial (VA) conduction, with concentric earliest atrial activation recorded in the anteroseptal region. We can easily induce a typical slow-fast AV nodal reentrant tachycardia (AVNRT); but failed to induce the patient's clinical WCT by atrial and ventricular stimulations. Therefore, we decided to perform a slow pathway ablation. However, after slow pathway ablation from the inferoseptal region; the LBBB morphology with the inferior axis at CL of 470 milliseconds was reproducibly inducible by ventricular extra stimuli (VES) after a retrograde right bundle branch block (RBBB). A narrow QRS beat during WCT noted in Figure 2. What is the mechanism of the WCT? 2 | DISCUSSION The differential diagnosis of a regular WCT with a typical LBBB morphology is limited to six entities: NCT with fixed LBBB, NCT with functional aberrancy, preexcited antidromic reentrant tachycardias (ART) using the variants of accessory pathways (APs) (including atriofascicular [AF], nodoventricular [NV], nodofascicular [NF], and fasciculoventricular connections), NCT with a "bystander" variants of APs, myocardial ventricular tachycardia (VT) and bundle branch reentrant VT. 1-5 NF/NV pathways, depending on their level of takeoff relative to the area of physiologic delay, can be associated with either a short or normal PR interval; therefore they commonly present with minimal preexcitation. 6 While NF/NV pathways may participate as the retrograde limb of NCT, 7,8 antidromic/manifest NF/NV pathways can comprise the anterograde limb of WCT 1,6,9,10 or exist merely as bystanders. 11 As most of these pathways are rightsided, the QRS morphology during an ART is typically an LBBB morphology. 3,10 Recognition of a His bundle potential is important for the differentiation. A similar HV interval to sinus rhythm during WCT excludes the presence of bypass tracts. Very simply, the WCT with a

Termination, Advancement, and Delaying Responses to His Synchronous Premature Ventricular Contractions During Narrow QRS Tachycardia: What Are the Possible Mechanisms?

“…18 Furthermore, the ventricular overdrive suppression did not entrain the tachycardia but rather dissociated the ventricle from the ongoing tachycardia, ruling out the AVRT or nodoventricular pathway as a tachycardia mechanism ( Figure 6). 14,19,20 These results collectively seem sufficient to establish a diagnosis of atypical AVNRT. A longitudinal dissociation of one slow pathway or two separate slow pathways could explain the oscillation of two CLs.…”

A Wide QRS Tachycardia with Three Distinct Left Bundle Branch Block Morphologies in a Patient with Sinus Rhythm with Left Bundle Branch Block: What Is the Mechanism?

“…6 In the current case, both early and late atrial extrasystoles did not affect the morphology and cycle length of the ventricular electrograms during tachycardias. 7 , 8 Comparison of the QRS complexes between the tachycardia and those in sinus rhythm is also helpful as a QRS complex that is narrower during wide complex QRS tachycardia than during sinus rhythm establishes the diagnosis of VT ( Figure 2 ) . 9 – 11 …”

Erratum

“…In the current case, the ablation of not inferoseptal but the mid septal region of the slow pathway was curative. In most cases, the atrial insertion of the pathway was in or near the slow pathway region [1]. Current strategies for ablation involve initial radio- However, after ablation in the mid-septal region, close to the compact AV node, NF/NV pathway conduction was abolished, eliminating tachycardia.…”

“…Current strategies for ablation involve initial radio- However, after ablation in the mid-septal region, close to the compact AV node, NF/NV pathway conduction was abolished, eliminating tachycardia. We speculated that the radiofrequency application modified both slow pathway and NF/NV pathway connecting with a slow pathway which resulted in no inducibility of both tachycardias [1,16,31]. Because of the risk of AV block in this region, cryoablation would also be preferred [32,33].…”

“…When the article 1 was first published online, there is one missing sentence in the last paragraph of the article (However, after ablation in the mid‐septal region, close to the compact AV node, NF/NV pathway conduction was abolished, eliminating tachycardia).…”