P1810Premature ventricular contractions originating from the left ventricle underneath the membranous septum: new insights into the electrophysiological characteristics and mechanisms

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Background: There is littile known about the features of focal ventricular arrhythmias originating from the left vetricle (LV) underneath the membranous septum. Objective; To investigate the electrophysiological characteristics and mechanisms of these ventricular arrhythmias. Methods; We studied five patients (five men, 72±4 years) with premature ventricular contractions (PVCs) originating from the LV underneath the membranous septum. Results; ECGs of these PVCs exhibited left bundle branch block QRS morphology and early precordial transition with QS pattern in lead V1 in all, and left superior (n=1) or inferior axis (n=4). In all patients, the earliest ventricular activation sites during PVCs were detected in the left ventricular septum and at the lower border of the low voltage zone (<1.0mV) underneath the noncoronary cusp. These sites were considered to be the left ventricle underneath the membranous septum. A high-frequency presystolic potential (PP) was recorded during PVCs, preceding the QRS by -45±28 ms (range; -10 to -80 ms). Moreover, the ventricular late diastolic potentials (LDP) were detected during sinus rhythm at these sites, and the morphologies of LDP and PP were identical. The intervals from the ventricular potentials to LDP and PP were equal (363±14 ms, range; 355 to 380ms). Therefore, it was considered that PVCs were induced at the time of intermittent conduction of PP to the ventricular potentials. Pacing from these sites reproduced an excellent match to the QRS complexes of PVCs in three patients. Radiofrequency delivery at these sites successfully eliminated PVCs in all patients. Conclusions; This study demonstrates that PP and LDP are critical potentials in PVCs originating from the LV adjacent to the membranous septum, and suggests that the mechanism of this PVCs is the intermittent conduction from the localized tissue to the interventricular septum.

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