Effects of verapamil and lidocaine on two components of the re-entry circuit of verapamil-senstitive idiopathic left ventricular tachycardia.
OBJECTIVE
We characterized pharmacologically the slow conduction zone of verapamil-sensitive idiopathic left ventricular tachycardia (ILVT) with regard 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 tachycardia-dependent conduction delay property and the proximal one without it.


METHODS
Electrophysiologic studies were performed in eight consecutive patients. 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 recorded from the upper third to the middle of the LV septum along the narrow longitudinal line. The ventricular tachycardia (VT) cycle length increased after lidocaine (p < 0.05), and further after verapamil (p < 0.05). The increments in the VT cycle length after administration of the drugs strongly correlated 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 drugs. In one patient, verapamil terminated VT by local conduction block between LDP and PP. The LDP-PP measured during entrainment increased after lidocaine, and further after verapamil, whereas the interval from the stimulus to LDP remained unchanged.


CONCLUSIONS
The component distal to LDP is mainly calcium channel-dependent and partly depressed sodium channel-dependent. The proximal component is considered to be sodium channel-dependent (normal).
Tsuchiya
T
T
Cardiovascular Center, Saiseikai Kumamoto Hospital, Kumamoto City, Japan. tsuchit@mvc.biglobe.ne.jp
Okumura
K
K
Honda
T
T
Iwasa
A
A
Ashikaga
K
K
D000293:Adolescent; D000328:Adult; D002037:Bundle-Branch Block / Q000188:drug therapy* / Q000503:physiopathology; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography / Q000187:drug effects*; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007262:Infusions, Intravenous; D008012:Lidocaine / Q000008:administration & dosage* / Q000009:adverse effects; D008297:Male; D011690:Purkinje Fibers / Q000187:drug effects / Q000503:physiopathology; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000188:drug therapy* / Q000503:physiopathology; D017180:Tachycardia, Ventricular / Q000188:drug therapy* / Q000503:physiopathology; D014700:Verapamil / Q000008:administration & dosage* / Q000009:adverse effects
D015222:Sodium Channels; D008012:Lidocaine; D014700:Verapamil