Effects of verapamil and lidocaine on two components of the re-entry circuit of verapamil-sensitive idiopathic left ventricular tachycardia

OBJECTIVES We characterized pharmacologically the slow conduction zone of v erapamil-sensitive idiopathic left ventricular tachycardia (ILVT) with rega rd to the late diastolic potential (LDP). BACKGROUND We showed that the slow conduction zone of ILVT could be divided into two components by LDP; that is, the distal component with a tachycard ia-dependent conduction delay property and the proximal one without it. METHODS Electrophysiologic studies were performed in eight consecutive pati ents. The LDP was recorded during left ventricular (LV) mapping during ILVT . Entrainment was performed from the right ventricular outflow tract while recording LDP. The effects of lidocaine (1 mg/kg body weight) and verapamil (0.5 or 1.0 mg) were examined during entrainment. RESULTS The LDPs preceding the Purkinje potential (PP) were serially record ed from the upper third to the middle of the LV septum along the narrow lon gitudinal line. The ventricular tachycardia (VT) cycle length increased, af ter lidocaine (p < 0.05), and further after verapamil (p < 0.05). The incre ments in the VT cycle length after administration of the drugs strongly cor related with those in LDP-PP (r> 0.9 for both drugs). The interval from the ventricular potential to LDP was unchanged after administration of the dru gs. In one patient, verapamil terminated VT by local conduction block betwe en LDP and PP. The LDP-PP measured during entrainment increased after lidoc aine, and further after verapamil, whereas the interval from the stimulus t o LDP remained unchanged. CONCLUSIONS The component distal to LDP is mainly calcium channel-dependent and partly depressed sodium channel-dependent. The proximal component is c onsidered to be sodium channel-dependent (normal). (J Am Cell Cardiol 2001; 37:1415-21) (C) 2001 by the American College of Cardiology.