PLEOMORPHIC VENTRICULAR-TACHYCARDIA ARISING FROM A NEW SITE DURING ANTIARRHYTHMIC DRUG-THERAPY

We analyzed the site of VT origin and the induction mode of VT in 9 pa tients who showed new VT morphologies with different bundle branch blo ck patterns after administering antiarrhythmic drug(s). In all patient s, VT exhibiting the clinical morphology was induced in the drug free state. (1) VT origin: In 6 patients, VTs showing LBBB pattern had a si te of origin at the right ventricular free wall, and VTs with RBBB pat tern originated from the left ventricular free wall. VT from the intra ventricular septum of the right ventricle showed RBBB pattern in two p atients and VT with LBBB pattern arose from the posteroseptum of the l eft ventricle in one patient. (2) VTs with new morphologies: After adm inistering drug(s), VTs with new morphologies were induced in 18 studi es and the mean cycle length of these VTs was not different from that in the control study. Among them, the induction mode was less aggressi ve in 4 of 7 drug studies and more aggressive in 1 study. (3) VTs with the same morphology: VTs with morphologies identical to those of the clinical VTs were induced in 15 studies. However, the drugs' effect wa s evident. The mean cycle length of these VTs was significantly prolon ged, and VTs were induced by less aggressive modes or at longer coupli ng intervals. In conclusion: (1) After administering drug(s), differen t electrophysiologic characteristics were observed between the VTs wit h new morphologies and the VTs with the same morphology. (2) If a new VT was induced by less aggressive modes after administering drug(s), t he drug(s) might act to facilitate inducibility: proarrhythmic effect.