Catheter ablation of ventricular premature depolarizations originating from the mid interventricular septum: Significance of electrocardiographic morphology for predicting origin

BACKGROUND Ventricular premature depolarizations (VPDs) orig-inating from the mid interventricular septum (IVS) adjacent to the atrioventricular annulus between the His bundle and the coronary sinus ostium (mid IVS VPDs) have not been characterized. OBJECTIVE The aim of this study was to investigate the electro-physiological characteristics of mid IVS VPDs. METHODS Thirty-eight patients with mid IVS VPDs were enrolled. VPDs were divided into different types according to precordial transi-tion of the electrocardiogram (ECG) and QRS morphology in lead V1. RESULTS Four types of VPDs were divided. The precordial transition zone appeared earlier and earlier from types 1 to 4. The notch in lead V1 moved gradually backward, and its amplitude gradually became higher, resulting in the transition from left to right bundle branch block morphology in lead V1 from types 1 to 4. Based on activation and pace mapping, ablation response, and 3830 electrode pacing morphology in the mid IVS, the 4 types of ECG morphology corre- sponded to an origin in the right endocardial side, right/mid intra-mural region, left intramural region, and left endocardial side of the mid IVS, respectively. An intramural origin was identified for 50% of VPDs. Eighty-nine percent of mid IVS VPDs could be eliminated. Bilateral ablation (waiting for delayed efficacy) or bipolar ablation was sometimes needed for intramural VPDs. CONCLUSION Mid IVS VPDs were found to have unique electro-physiological characteristics. The ECG characteristics of mid IVS VPDs were important in terms of prediction of its exact origin, the choice of ablation method, and the likelihood of treatment being successful.