Ventricular activation during ventricular endocardial pacing: I. Electrocardiographic patterns related to the site of pacing

The QRS configuration produced by pacing at multiple left ventricular endocardial sites was evaluated in eight patients with (group 1) and six patients without (group 2) left ventricular wall motion abnormalities. Pacing was performed at a total of 122 sites, 4 to 13 sites in each patient. The QRS configuration resulting from apical pacing locations was compared with that at basal, septal to lateral and inferior to superior locations. Significant differences in QRS configuration during pacing from apical and basal locations were observed in electrocardiographic leads I, V₁, V₂ and V₆ (probability p] < 0.01). Specifically, a QS pattern in leads I, V₂ and V₆ was more characteristic of an apical pacing location (p < 0.001), and a monophasic R wave in leads V₁ and V₂ was more characteristic of a basal pacing location (p < 0.01). Significant differences in leads V₁ and V₂ were observed when septal and lateral pacing sites were compared (p < 0.001). A monophasic R wave in leads V₁ and V₂ was more characteristic of a lateral pacing location (p < 0.01); a QS complex in lead V₂ was more characteristic of a septal pacing location (p < 0.001). Pacing at superior sites usually produced an inferior axis and vice versa (p < 0.001). The electrocardiographic patterns produced by pacing at similar sites in patients in group 1 were less consistent than those in patients in group 2. The QRS complex during ventricular pacing was wider in patients in group 1 (159 ± 30 ms) than in patients in group 2 (132 ± 18 ms) (p < 0.001).It is concluded that the QRS configuration recorded with 12 lead electrocardiography during endocardial pacing can help locate the region of the pacing site in patients with and without organic heart disease, although precise localization is not possible.