Demonstration of the reentrant circuit of verapamil-sensitive idiopathic left ventricular tachycardia: direct evidence for macroreentry as the underlying mechanism.

The exact reentrant circuit of verapamil-sensitive idiopathic left ventricular tachycardia (ILVT) remains unclear. This case report demonstrates the reentrant circuit of ILVT. A 20-pole electrode catheter was placed along the left posterior fascicle during electrophysiologic study. ILVT was reproducibly induced by programmed ventricular stimulation. During the tachycardia, sequential diastolic potentials bridging the entire diastolic period were observed in the recordings from the electrodes positioned from left ventricular mid-septum to inferoapical septum. The slow conduction zone appeared to be composed of a false tendon in this patient. Entrainment of the ILVT from the right ventricular outflow tract at a different pacing cycle length revealed that a dominant conduction delay occurred at the proximal site of the slow conduction zone. Entrainment studies from several sites on the left ventricular septum confirmed that these sites where sequential electrical activity was recorded were included within the reentrant circuit. However, the left posterior fascicle itself seemed to be a bystander. This report provides the direct evidence of macroreentry as the underlying mechanism of this ILVT, adjacent to the left posterior fascicle.