Figure Nº3 Electrophysiology study
A) Atrial pacing at 810 ms. The second and the fourth beats have 2:1 AV response (blue arrows). Note that both extrasystolic beats have proximal to-distal His-RBB activation and the same HV interval as sinus rhythm. Also, the second extrasystolic beat has RBBB + LAFB (annotated✚) consistent with the clinical arrhythmia. The third beat fails to conduct to the ventricle (red crossed arrow), possibly due to retrograde concealed penetration of the fast pathway by the preceding beat. The 5th beat is conducted with an abrupt prolongation in the AH interval, reflecting a change from fast to very slow AV nodal pathway conduction (green arrow) HBE= His bundle electrogram; HRA=high right atrium; RVA= Right ventricular apex; CS= coronary sinus
B) Atrial extrastimulus pacing 900/810ms: Double response is observed with consistent AH2 interval during extrastimulus testing (blue arrows) HBE= His bundle electrogram; HRA=high right atrium; RVA= Right ventricular apex; CS= coronary sinus