These tracings demonstrate the different potential benefits of implanting a quadripolar LV lead. Indeed, in this patient, the implantation procedure was difficult since the targeted veins were of small caliber, the stimulation thresholds were variable, and a phrenic stimulation was present at the apical-lateral region. It seems essential to avoid the configurations associated with phrenic nerve stimulation (often poorly tolerated by the patient). Pacing thresholds ranged from a very satisfying value (<1Volt at 0.4 ms) to thresholds close to the maximal capacity of the device. It seems clear that the impact on the battery longevity will be highly variable depending on the chosen configuration. The third criterion is the optimal site of pacing for hemodynamic and clinical benefits. The four electrodes on quadripolar leads are relatively spaced: in this patient, the distal tip electrode (LV1) was positioned in an apical-lateral region while the proximal electrode (LV4) was positioned in the basolateral region. Electrocardiographic changes from one configuration to another are only slightly visible on the derivation used for the evaluation of the pacing threshold. In contrast, the 12-lead electrocardiogram found significant changes in the appearance of the paced QRS depending on the chosen configuration. The electrical activation being different, it seems plausible that the degree of response differs according to the chosen configuration. This reflects the difficulties found today to define what is an optimal site of pacing. In the absence of validated tool for defining a site as optimal, this criterion is rarely the criterion of choice between the different configurations.

In this patient, the selected configuration was LV1 / RV coil which allowed to obtain a satisfactory threshold value with no phrenic nerve stimulation. In case of no response to resynchronization, the choice of an alternative configuration to promote a better response remains empirical today.