Case report
A 77-year-old woman with ischemic cardiomyopathy was referred for radiofrequency catheter ablation (RFCA) for recurrent ventricular tachycardia (VT). Mapping was performed during atrial fibrillation paced at 60 per minute by the implanted cardioverter defibrillator because of hemodynamically unstable VT. RFCA was performed by targeting local abnormal ventricular activity (LAVA)1 using a 3.5-mm-tip open-irrigated catheter equipped with three microelectrodes (MEs: Qdot MicroTM; Biosense Webster, Diamond Bar, California). While mapping the left ventricle, the standard bipolar electrode detected LAVA, whereas the MEs did not detect the corresponding signals (Figure 1). What is the mechanism underlying these apparently paradoxical electrograms?