Lesson Eighty-two Eccentric atrial activation during a narrow QRS tachycardia:what is the mechanism?

摘要

A 49-year-old woman presented with a 2-year history of recurrent palpitations and documented episodes of paroxysmal supraventricular tachycardia(SVT)terminated with adenosine.Resting 12-lead electrocardiogram(ECG)revealed normal sinus rhythm without preexcitation.She had a structurally normal heart on echocardiogram.After having obtained an informed consent,an electrophysiology study was performed using standard technique and a decapolar coronary sinus(CS)catheter was inserted with the distal pole positioned at the lateral mitral annulus(Figure 1A).Baseline measurements revealed a sinus cycle length of 804 milliseconds and an atrial-His(AH)interval and His-ventricular(HV)of 72 and 36 milliseconds,respectively.Incremental ventricular pacing showed eccentric retrograde atrial activation with earliest activation noted at CS bipolar pair 3-4.Although atrial activation was earlier on the more distal CS electrodes versus the His bundle electrode,the difference in activation between CS 3-4 and CS 4-5 was minimal(Figure 1B).The ventricular-atrial(VA)conduction was decremental.Programmed atrial extrastimulation established the presence of anterograde dual AV nodal physiology with an AH jump of 78 milliseconds.A narrow QRS complex tachycardia with a cycle length varying between 440 and 460 milliseconds was reproducibly induced with programmed atrial stimulation.The retrograde atrial activation sequence was eccentric and identical to that observed during ventricular pacing.Overdrive ventricular pacing during the tachycardia resulted in a VAV response(Figure 1B).Premature ventricular complexes(PVCs)introduced during SVT to scan diastole preexcited the atrium with a preexcitation index of 125 milliseconds.What is the mechanism of the tachycardia?