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An unusual cause of a relatively narrow, wide complex tachycardia

  • Author Footnotes
    1 All authors have contributed to the work equally
    Anna Sarcon
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    1 All authors have contributed to the work equally
    Affiliations
    Division of Cardiology, Section on Electrophysiology, University of California San Francisco, San Francisco, California
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  • Author Footnotes
    1 All authors have contributed to the work equally
    Bing Liem
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    1 All authors have contributed to the work equally
    Affiliations
    Division of Cardiology, Section on Electrophysiology, University of California San Francisco, San Francisco, California
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  • Author Footnotes
    1 All authors have contributed to the work equally
    Melvin Scheinman
    Correspondence
    Address reprint requests and correspondence: Dr Melvin M. Scheinman, Division of Cardiology, University of California San Francisco, 500 Parnassus Avenue, Room E436, San Francisco, CA 94117.
    Footnotes
    1 All authors have contributed to the work equally
    Affiliations
    Division of Cardiology, Section on Electrophysiology, University of California San Francisco, San Francisco, California
    Search for articles by this author
  • Author Footnotes
    1 All authors have contributed to the work equally
Open AccessPublished:March 04, 2022DOI:https://doi.org/10.1016/j.hrthm.2022.03.001

      Keywords

      Case presentation

      An 11-year-old boy presented with palpitations but no evidence of any cardiac disease. The baseline electrocardiogram (ECG) recorded during sinus rhythm is shown in Figure 1A and the tachycardia in Figure 1B. What are the differential diagnoses of this arrhythmia?
      Figure thumbnail gr1
      Figure 1A: Normal sinus rhythm. B: Tachycardia with relatively narrow QRS and atrioventricular dissociation.
      ECG analysis of the baseline ECG in sinus rhythm is normal (Figure 1A). Figure 1B shows the tachycardia with a relatively narrow QRS with normal frontal axis; also note atrioventricular (AV) dissociation.

      Discussion

      The findings of relative narrow QRS with a typical right bundle branch block (RBBB) pattern is most compatible with supraventricular tachycardia with aberration. The presence of AV dissociation immediately excludes atrial tachycardia or an accessory pathway–mediated tachycardia. Of note, AV dissociation does not exclude nodoventricular (N-V) or nodo-fascicular (N-F) pathways. Therefore, these diagnoses are included after review of the ECG. Other likely possibilities include atrioventricular nodal reentrant tachycardia (AVNRT) with upper common pathway block to the atrium or junctional tachycardia. The patient underwent electrophysiological study, which revealed a negative H-V interval. A left heart examination showed that recordings from the proximal left posterior fascicle (LPF) preceded changes in ventricular response. In addition, during sinus rhythm, the left bundle branch potential proceeded that from the LPF; however, this relationship reversed during tachycardia. These findings prove that the tachycardia emanated from the fascicular system and excluded AVNRT and junctional tachycardia. The findings of electrophysiological study serve to exclude a concealed N-F or N-V pathway as well as a manifest right N-F pathway. However, in theory, this can be explained by a left-sided N-F pathway, which seems to be much less likely than the upper septal fascicular explanation. These diagnoses are clearly excluded by inscription of the negative H-V. Therefore, the most likely mechanism is upper septal fascicular tachycardia, which involves retrograde conduction over the septal fascicle and near simultaneous activation of the left anterior and posterior fascicles with slight delay in reaching the right bundle branch (Figure 2) accounting for the pattern of a relatively narrow QRS with an RBBB configuration. In this Case, efforts to map the left fascicular system resulted in bump conversion of the tachycardia, which rendered the tachycardia noninducible. The patient was treated with a calcium channel blocker.
      Figure thumbnail gr2
      Figure 2Left upper septal type ventricular tachycardia demonstrating simultaneous activation of the fascicular system and slow activation of the right bunch branch. AV = atrioventricular.
      Three types of fascicular tachycardias are recognized. The most common by far involves the LPF and manifests as a monomorphic wide complex tachycardia with RBBB and superior axis. Less common are fascicular tachycardias from the left anterior fascicle presenting as an RBBB pattern with right-axis deviation. Very uncommon are the upper septal fascicular tachycardias as described in our Case. These reentrant fascicular tachycardias often are responsive to calcium channel blockers.
      • Nogami A.
      Purkinje-related arrhythmias part I: monomorphic ventricular tachycardias.
      In summary, we present a very unusual cause of tachycardia that masquerades as a supraventricular tachycardia but actually emanates from the left ventricular fascicles.

      Reference

        • Nogami A.
        Purkinje-related arrhythmias part I: monomorphic ventricular tachycardias.
        Pacing Clin Electrophysiol. 2011; 34: 624-650