Electrophysiological characteristics and ablation of ventricular arrhythmias originating from the intramural basal inferior septum

Aims The electrocardiographic and electrophysiological characteristics of ventricular arrhythmia (VA) arising from the intramural basal inferior septum (BIS) have not been specifically addressed to date. The aim of the current study was to characterize intramural BIS-VA and distinguish it from those with endocardial origins besides clarifying the anatomical configurations of the pyramidal space.Methods and results Fifty-five consecutive patients undergoing catheter ablation of VAs from BIS were identified and divided into three groups: the left ventricular (LV)-BIS group (n = 28), right ventricular (RV)-BIS group (n = 8), and intramural group (Intra, n = 19). Compared with the LV-BIS and RV-BIS groups, patients in the Intra group presented with no adequate earliest activation time at the two-sided BIS and epicardial coronary system [right: 7.79 +/- 2.38 vs. left: 7.16 +/- 2.59 vs. the middle cardiac vein (MCV): 6.26 +/- 1.73 ms, P = 0.173] and poor-matched pacing-produced QRS at each site. Under the intracardiac echocardiography view, the pyramidal base was the broadest part of the septum and served as the division of the two-sided BIS. Focal ablation yielded promising acute-term and long-term procedural success in the LV-BIS and RV-BIS groups. But for the Intra group, VAs disappeared only after stepwise ablation successively targeted early preferential exit. After follow-up, three patients in the Intra group had recurrent VA, and all of them were treated well by a redo procedure or drug therapy.Conclusion Intramural VAs were relatively common in the BIS region in our series. Intra-procedural mapping was important to distinguish the intramural VAs from other VAs by comparing the local activation time and pacing mapping. Procedural success could be achieved by stepwise ablation on the counterpart sides of the BIS and within the MCV. Graphical Abstract