Re-entrant tachycardia using two bypass tracts and excluding AV node in short PR interval, normal QRS syndrome.

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Abstract
In patients with the short PR interval, normal QRS complex syndrome, paroxysmal tachycardias are usually the result of cirus movement involving the AV node and a partial or complete AV nodal bypass. Patients 2 with this syndrome suffered distressing rapid paroxysms of tachycardia and also evidenced concealed direct VA [ventriculoatrial] connection. In both patients, tachycardia was initiated with critical AV prolongation distal to the His bundle, in response to programmed atrial premature stimuli. The constancy of the atrial echo timing from the onset of QRS complex with a varying HV [His-Purkinje] interval is evidence for involvement of ventricles in the re-entry pathway. In both patients the appearance of left bundle-branch block during tachycardia was associated with appropriate prolongation of tachycardia cycle length consistent with the presence of a direct VA connection. The short AH [atrial-His] interval during tachycardia and the absence of critical AH prolongation suggests the participation of a rapidly conducting pathway in the anterograde limb of the tachycardia circuit.