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An under-recognized cause for syncope

Published:December 20, 2016DOI:https://doi.org/10.1016/j.ejim.2016.12.008

      1. Indication

      A 74-year-old male presented with history of recurrent syncope and fall that once caused scalp-injury. The episodes were sudden and lacked any prodrome. He regained consciousness spontaneously. Clinical examination was unremarkable, and there was no neck vessel bruits or carotid sinus hypersensitivity. There was no postural hypotension and the Tilt-table-test was negative. His Electrocardiogram showed right bundle branch block and a normal PR and corrected QT intervals (Panel A). His neurological evaluation including magnetic resonance imaging of the brain and cerebral vessels was normal. A video- electroencephalogram documented a syncopal episode during which there were no epileptiform discharges but bradycardia was noted. A Holter recording (shown in Panel B) clinched the diagnosis (Fig. 1).
      Fig. 1
      Fig. 1The electrocardiogram (A) and the Holter tracing (B).
      What is the diagnosis?

      2. Diagnosis

      The Holter revealed multiple episodes of asystole due to paroxysmal phase-4 atrioventricular (AV) block (PAVB). There was an abrupt AV block that lasted for a variable duration after premature ventricular beats (PVBs), and was associated with presyncope. PAVB is characterised by an abrupt change from the normal AV conduction to complete AV block that is initiated by a pause [
      • Lee S.
      • Wellens H.J.
      • Josephson M.E.
      Paroxysmal atrioventricular block.
      ]. It is under recognized because of lack of any evidence of abnormal AV conduction in between the episodes. There may be evidence of diseased distal conduction system in the baseline ECG, which commonly shows right bundle branch block. PAVB is a disorder of the His-Purkinje system (HPS) due to a phase-4 block in the His bundle or in the bundle branches after a pause [
      • Motte G.
      • Desoutter P.
      • Olive B.
      • Bodereau P.
      • Welti J.J.
      Paroxysmal block in phase 4 of the bundle of His.
      ]. The pause is usually secondary to premature beats, but can also be a sinus pause. During a pause, the HPS fibres spontaneously depolarize (but not up to the threshold potential) and become unresponsive to subsequent impulses due to sodium channel inactivation. This persists till an appropriately timed escape beat, sinus beat, or a premature beat resets the membrane potential to its resting value. During a clinical episode a precordial thump can thus be lifesaving as it can trigger an extra-systole and resume AV conduction. A Permanent pacemaker implantation is the definitive step in the management.

      References

        • Lee S.
        • Wellens H.J.
        • Josephson M.E.
        Paroxysmal atrioventricular block.
        Heart Rhythm. 2009; 6: 1229-1234
        • Motte G.
        • Desoutter P.
        • Olive B.
        • Bodereau P.
        • Welti J.J.
        Paroxysmal block in phase 4 of the bundle of His.
        Arch Mal Coeur Vaiss. 1977; 70: 797-807