Study Limitations
Our study has several limitations. First, there were no specific recommendations for MPP programming and were left to the physician’s discretion. Second, an important limitation of the study was the number of patients involved and the length of the follow-up that limits the identification of additional potential advantages of MPP further than 6 months. Third, the main limitation of the study, inherent to any registry, is the absence of a randomized comparator group of conventional biventricular pacing. Consequently, it cannot be concluded the superiority of any strategy for CRT. However, the better clinical outcomes observed in the group of patients treated with MPP merits to be analysed in future trials. Fourth, it was observed a benefit when programming MPP with the widest pacing electrodes. However, we did not address the percentage of cases in which it is possible to program MPP following this strategy. In our study, it was selected in 31% of patients, value similar to that observed in the MORE CRT MPP study (29%) or in the MPP IDE study (23%). We do not know if this programming was not possible in the remaining cases and factors as phrenic stimulation or unacceptable pacing thresholds limited the selection of the widest electrodes for MPP. If we accept that MPP could improve the results of CRT only when the selected pacing poles are enough separated it will be desirable to define the percentage of cases in which this is possible. Finally, we did not address the impact of MPP over device battery longevity that is an important issue when considering early activation of MPP.