A wide QRS tachycardia with the short and long ventriculoatrial interval in the presence of an atriofascicular pathway: What is the mechanism?

Abstract

A 58-year-old man with no structural heart disease presented with recurrent episodes of paroxysmal palpitation. In the electrophysiology laboratory, during the introduction of the venous sheaths and catheters, the patient had spontaneous sustained wide complex tachycardia (WCT) with left bundle branch block (LBBB) morphology. The responses to septal refractory atrial premature complexes (APC) from the lateral right atrium (Figure 1), and ventricular premature complexes (VPC) (Figure 2) were consistent with the atriofascicular (AF) accessory pathway (AP). However, during WCT, a transient atrioventricular (AV) block (Figure 3) with short and long ventriculoatrial (VA) intervals (Figure 4) was also observed. What could be the mechanism of this WCT without 1:1 AV conduction (Figure 3) and change in the VA interval (Figure 4) in a patient with an overt AF pathway?