Right bundle-branch block ventricular tachycardias: septal versus lateral ventricular origin based on activation time to the right ventricular apex.

BACKGROUND Identifying the septal versus lateral site of origin of ventricular tachycardia (VT) with a right bundle-branch block (RBBB)-type pattern and an R-S ratio >1 in lead V1 is difficult with the 12-lead ECG, especially in patients with prior apical infarction. METHODS AND RESULTS We prospectively evaluated 58 patients with VT. Sixteen patients had apical infarcts (group 1), 29 had nonapical infarcts (group 2), and 13 had no heart disease (group 3). QRS complex onset to activation at the right ventricular apex (stim-RVA) was measured during left ventricular (LV) apical septal and lateral pacing, and 47 RBBB-type VTs (QRS-RVA) were localized to the septal or lateral apex by using entrainment techniques. Pacing and VT site of origin were confirmed by electroanatomic mapping. The stim-RVA time was 59+/-16 ms for septal versus 187+/-24 ms for lateral sites in group 1, P<0.001; 70+/-14 ms for septal versus 169+/-19 ms for lateral sites in group 2, P<0.001; and 42+/-15 ms for septal versus 86+/-16 ms for lateral sites in group 3, P<0.005. The QRS-RVA time was 50+/-13 ms for apical septal VTs versus 178+/-21 ms for lateral VTs in group 1, P<0.001; 71+/-17 ms for apical septal versus 157+/-20 ms for lateral VTs in group 2, P<0.001; and 32+/-12 ms for septal versus 71+/-16 ms for lateral VTs in group 3, P<0.01. CONCLUSIONS The QRS-RVA differs for the VT site of origin from the LV septal versus lateral apex. These data prove useful in rapidly regionalizing the VT site of origin with a V1 R-S ratio >1, particularly in instances of an apical infarct, where surface ECG distinctions are less identifiable.