Takashi Shima, MD; Yoshio Ohnishi, MD; Tomoo Inoue, MD; Akihiro Yoshida, MD; Hiroki Shimizu, MD; Takeshi Itagaki, MD; Junichi Sekiya, MD; Kouhei Yamashiro, MD; Asumi Takei, MD; Kazumasa Adachi, MD; Mitsuhiro Yokoyama, MD

Abstract
Optimal pace mapping is a good predictor of the appropriate ablation site for idiopathic right ventricular tachycardia (VT) originating from the right ventricular outflow tract (RVOT). We studied the relationship between the RVOT pacing site and QRS morphology in the 12-lead ECG during pacing to find the optimal site more quickly. In 13 patients with idiopathic VT, pacing at 8 sites in the RVOT (free wall, septum, and anterior and posterior regions of upper and lower sites) was performed while 12-lead ECGs were recorded. The R-wave amplitude minus the S-wave amplitude in lead I (R_I-S_I) and aV_F (R_av_F-S_av_F) and the transitional zone index (TZI) were compared in the different pacing sites; TZI was defined to examine the transitional zone as a value. The R_I-S_I was smaller in the anterior region than in the other regions, and the negative R_I-S_I predicted that the pacing site was in the upper or lower anterior regions. The R_av_F-S_av_F was larger in the septum and anterior regions than in the free wall and posterior regions. The TZI was larger in the free wall region than in the septum. From the results, we constructed a flow chart that differentiates the origin of the arrhythmia in the RVOT and a directional guide that indicates the direction from the current mapping site for optimal pace mapping. The results provided an ECG guide for locating the focus of VT originating from the RVOT. These findings may systematically improve the mapping procedure.
(Jpn Circ J 1998; 62: 399-404)

Key Words: Pace mapping; Right ventricular outflow tract; Idiopathic ventricular tachycardia; Transitional zone index; Catheter ablation

Mailing address: Takashi Shima, MD, First Department of Internal Medicine, Kobe University School of Medicine, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe 650, Japan