Case Presentation
A 26-year-old man presented to emergency department with acute onset
palpitations with a history of such episodes since two months. The
electrocardiogram revealed a regular short RP narrow QRS tachycardia at
the rate of 145 beats per minute. The echocardiogram showed a left
ventricular ejection fraction of 0.25 during tachycardia but was normal
during sinus rhythm. He underwent an electrophysiology study which
revealed eccentric activation in the coronary sinus during right
ventricular pacing and during tachycardia (Figure 1) ,
suggestive of a retrograde conducting concealed left free wall accessory
pathway (AP). The mitral annulus was mapped via the transseptal route
and the AP was localized to the left anterolateral mitral annulus.
Radiofrequency energy was delivered during entrainment of the
orthodromic tachycardia by left ventricular (LV) lateral wall pacing(Figure 2 left panel) . A sudden change in QRS morphology was
seen during energy (Figure 2 right panel) , coincident with
elimination of accessory pathway conduction (Figure 3 left
panel) . What is the mechanism?