Variegated left ventricular electrical activation in response to a novel quadripolar electrode: visualization by non-invasive electrocardiographic imaging.

Improving response to cardiac resynchronization therapy (CRT) remains challenging. Appropriate candidates may be identified by the presence of left ventricular (LV) conduction delay. An additional determinant may be the electrical effect elicited by LV pacing, which may vary among and within individuals. However, this is little explored, reflecting the lack of means for both easily altering lead position in any individual patient and of rapidly assessing its electrical effects. However, the advent of both multipolar LV electrodes and non-invasive single-beat electroanatomic mapping potentially resolves these challenges. These were investigated here. Results confirmed wide variations in electrical responses to LV pacing. In any individual patient, different pacing configurations elicited different electrical effects. Conversely, any one stimulation vector produced different effects in different patients. Thus, the reaction of electrical substrate to LV pacing is inconsistent. This observation introduces an added level of complexity in the understanding CRT electrical action. Attention to this factor may influence response to electrical resynchronization therapy.