Background: Verapamil-sensitive, idiopathic left ventricular tachycardia (ILVT) with right bundle branch block configuration and left-axis deviation has been suggested to originate from the left posterior fascicle. The purpose of this study was to determine how frequently potentials generated by the Purkinje fiber network (P potential) can be recorded preceding ventricular activation, and the role of the P potential in guiding radiofrequency catheter ablation.
Methods and results: Eight patients (mean age, 26 +/- 10 years) with ILVT (cycle length, 346 +/- 59 milliseconds) were studied. Right and left ventricular endocardial mapping during tachycardia identified earliest ventricular activation at the posteroapical left ventricular septum. In all patients, earliest ventricular activation during tachycardia was preceded by a distinct potential. This potential also preceded ventricular activation during sinus rhythm, consistent with activation of a segment of the left posterior fascicle (P potential). The earliest recorded P potential preceded the QRS during tachycardia by 15 to 42 milliseconds (mean, 27 +/- 9 milliseconds). The application of radiofrequency current at 1 to 4 sites (median, 1) eliminated ILVT in all eight patients. In the seven patients with P potentials recorded at multiple sites within the posteroapical septum, ablation was successful at the site of the earliest P potential and unrelated to the timing of ventricular activation. In the remaining patient, ablation was successful at a site recording a late P potential fusing with earliest ventricular activation. During follow-up (1 to 67 months; median, 10.5) ILVT recurred only in the latter patient. Pace mapping during tachycardia at the successful ablation site in four patients produced a similar QRS with stimulus-QRS interval equal to P-QRS interval during tachycardia. However, a similar QRS was obtained by pacing at nearby sites that recorded a later P potential.
Conclusions: These findings support the hypothesis that ILVT originates from the Purkinje network of the left posterior fascicle. A P potential can be recorded at the posteroapical left ventricular septum during ILVT, and ablation is successful at the site recording the earliest P potential. Pace mapping with similar QRS is not specific due to capture of the Purkinje fiber network at a site remote from the origin of the tachycardia.