Case Presentation:
A 50-year male was referred for consideration of a redo ablation
procedure. 2 years before this referral, he was diagnosed with an
episode of pre-excited atrial fibrillation, and underwent an attempt at
a left lateral pathway ablation. The index attempt with radiofrequency
ablation did not eliminate the pathway and he was discharged on oral
flecainide. The procedure was also complicated by a right-sided deep
vein thrombosis and further attempts at a redo procedure were delayed.
However, he developed recurrent episodes of palpitations 2 years after
his index procedure. Hence, he was referred for a second attempt at
ablation. His baseline 12-lead ECG did not show any evidence of manifest
pre-excitation. During his EP study, pre-excitation was seen with atrial
extrastimuli and with shorter intervals, a narrow complex tachycardia
was induced (Figure 1). However, the atrial activation appeared to
alternate at times, despite the tachycardia being sustained.
What is the mechanism of the alternating atrial activation?