Case:
A 35 year-old-lady underwent EP study for recurrent narrow QRS
tachycardia (Fig 1A) terminating with adenosine. Baseline ECG showed no
pre-excitation (Fig 1B). EP study was performed with decapolar catheter
in coronary sinus (CS), quadripolar catheters placed in HRA (high right
atrium) and His; and one roving catheter in right ventricle (RV).
Baseline intervals: AH interval=76 ms, HV interval 34 ms. During
antegrade study AH jump, AV node duality and intermittent rate related
aberrancy (RRA) with unusual axis ( RBBB with right axis deviation, HV
34 ms) was noted. Retrograde study -VA conduction was concentric and
decremental (VAERP=270 ms), no VA jump. No sustained tachycardia could
be induced by standard protocols at baseline. On isoprenaline, a short
VA tachycardia (SVT1) with near simultaneous A and V activation [HV=34
ms, tachycardia cycle length (TCL)= 305 ms, Fig 1C) was induced with
atrial premature depolarisation (APD) and ventricular premature
depolarisation (VPD) with similar RRA (Fig 1C and 1D). Maneuvers
confirmed SVT1 to be slow-fast atrioventricular nodal reentrant
tachycardia (AVNRT) (VAV response, SA-VA=160 ms, cPPI-TCL=151 ms).
During programmed decremental APDs from CS to differentiate it from
junctional tachycardia (JT), faster SVT2 was induced with a longer VA
(Fig 2A and 2B). SVT2 had TCL of 260 ms after initial wobble, septal VA
= 140 ms. What could be the mechanism of SVT2 ?