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 patients who showed new VT morphologies with different bundle branch block patterns after administering antiarrhythmic drug(s). In all patients, VT exhibiting the clinical morphology was induced in the drug free state. (1) VT origin: In 6 patients, VTs showing LBBB pattern had a site of origin at the right ventricular free wall, and VTs with RBBB pattern originated from the left ventricular free wall. VT from the intraventricular septum of the right ventricle showed RBBB pattern in two patients and VT with LBBB pattern arose from the posteroseptum of the left ventricle in one patient. (2) VTs with new morphologies: After administering drug(s), VTs with new morphologies were induced in 18 studies and the mean cycle length of these VTs was not different from that in the control study. Among them, the induction mode was less aggressive 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 was evident. The mean cycle length of these VTs was significantly prolonged, and VTs were induced by less aggressive modes or at longer coupling intervals.

(1) After administering drug(s), different electrophysiologic characteristics were observed between the VTs with new morphologies and the VTs with the same morphology. (2) If a new VT was induced by less aggressive modes after administering drug(s), the drug(s) might act to facilitate inducibility: proarrhythmic effect.