Significance of late diastolic potential preceding purkinje potential in verapamil-sensitive idiopathic left ventricular tachycardia

Background-Verapamil-sensitive idiopathic left ventricular tachycardia (VT) is due to reentry with an excitable gap. A late diastolic potential (LDP) is recorded during endocardial mapping of this VT, but its relation to the reentry circuit and significance in radiofrequency (RF) ablation remain to be elucidated. Methods and Results-Sixteen consecutive patients with this specific VT were studied (12 men and 4 women; mean age, 32 years). In all patients, sustain ed VT was induced and during left ventricular endocardial mapping, LDP prec eding Purkinje potential (PP) was recorded at the basal (11 patients), midd le (3 patients), or apical septum (2 patients). The area with LDP recording was confined to a small region (0.5 to 1.0 cm(2)) in each patient and was included in the area where PP was recorded (2 to 3 cm(2)), The relative act ivation times of LDP, PP, and local ventricular potential (V) at the LDP re cording site to the onset of QRS complex were -50.4+/-18.9, -15.2+/-9.6, an d 3.0+/-:13.3 ms, respectively, The earliest ventricular activation site du ring VT was identified at the posteroapical septum and was more apical in t he septum than the region with LDP in every patient. In 9 patients, VT entr ainment was done by pacing from the right ventricular outflow tract while r ecording LDP. During entrainment, LDP was orthodromically captured, and as the pacing rate was increased, the LDP-to-PP interval was prolonged, wherea s stimulus-to-LDP and PP-to-V interval were constant. In 3 patients, the pr essure applied to the catheter tip at the LDP region resulted in conduction block between LDP and PP and in VT termination. RF energy application at t he LDP recording site successfully eliminated VT. Conclusions LDP was suggested to represent the excitation at the entrance t o the specialized area with a conduction delay in response to the increase in the rate within the critical slow conduction zone participating in the r eentry circuit of this VT. LDP can be a useful marker for successful RF abl ation for this VT.