Discussion
The main finding of the present study is that single-point LV pacing optimized by FOI enabled greater QRS shortening than MPP alone. Moreover, the use of SPP significantly prolonged the expected battery longevity compared with MPP. The addition of MPP to FOI optimization did not result in a significant additional reduction in the QRS duration. Finally, a high percentage of patients were not candidates for MPP because of high pacing thresholds or PNS.
Compared with conventional CRT, MPP via a quadripolar LV lead has demonstrated acute and long-term improvements in hemodynamic, clinical, and echocardiographic responses.2,3,14 However, most studies comparing MPP with standard single-point LV pacing neglect AV optimization.2,13 As shown in the BEST study,7,10 achieving fusion with intrinsic conduction through the FOI method maximized shortening of the QRS duration and, in turn, induced greater reverse LV remodeling upon follow-up. In the present study, an optimized single-point LV pacing strategy using the FOI method bested an MPP strategy programmed with a fixed AV interval of 130 ms, a wide anatomical LV1–LV2 distance, and minimal intraventricular delay (5 ms).4,5 Our findings are reinforced by a recent study published by O’Donnell et al.19 In this study assessing the ΔQRS duration immediately after implantation, the authors observed how automatic AV delay using SyncAV (SPP-SyncAV) showed a better response than that using MPP alone. Conversely, O’Donnell et al. found that the combination of MPP-SyncAV was slightly better than SPP-SyncAV (ΔQRS duration of 6 ms). In our study, adding MPP to FOI did not significantly shorten the QRS duration (only 2 ± 7 ms). Nevertheless, approximately 2/3 of the patients obtained the narrowest QRS with the MPP-FOI configuration. However, the lack of differences either in the biventricular activation times or mechanical asynchrony improvements by echo between SPP-FOI and MPP-FOI strategies, together with the high percentage of patients in whom MPP could not be chronically programmed and the faster battery drain, favors SPP programming as the initial approach.
Electrocardiographic imaging is a noninvasive technique capable of accurately detecting changes in activation patterns resulting from device optimization strategies.20 Ploux et al. found that the mean total activation time decreased in CRT responders regarding intrinsic rhythm, while it increased in nonresponders.20 In our study, a significant shortening of biventricular activation times (according to ECGI) was achieved with both FOI configurations (SPP-FOI and MPP-FOI) compared with non-paced rhythm. In addition, biventricular activation times correlated well with QRS duration. Therefore, both the ECG and noninvasive cardiac mapping data support the FOI method’s ability to obtain the shortest QRS duration and activation time, which are often associated with a better patient outcome.10,11,20
Two limitations warrant mentioning regarding MPP. First, the inability to program two LV vectors due to high pacing thresholds or PNS may be a relevant issue in a real-life setting. The MORE-CRT MPP-PHASE I study reported high MPP activation rates (approximately 97%). However, in that study, maximal anatomical separation between LV1 and LV2 was not sought, and the upper limit threshold was left to the physician’s discretion.4 In our study, the inability to use MPP chronically was very high (12/23 patients, 52%). We believe that these data, obtained using wide LV1-LV2 anatomical separation and low thresholds (≤ 3.5 V, as recommended),4,6 more closely reflect a real-life scenario. New studies evaluating MPP in this context could clarify this issue. Second, MPP programming with high-output pacing can significantly reduce battery longevity,5,6and the consequent need for device replacement is associated with potentially severe complications and carries an economic impact.21 This study is the first to assess battery life in patients with MPP activation, low pacing thresholds (≤ 3.5 V), and the D1/P4, D1/M3, and M2/P4 configurations only. We observed a significant difference in the estimated mean battery longevity of the MPP and single-point LV pacing devices of almost 2 years.
The clinical implications of our results are straightforward. Our data suggest that ECG-based optimization by FOI should be the preferable approach in patients undergoing CRT. The addition of MPP should be individualized and carefully evaluated since it may result in greater battery drainage without apparent clinical benefit.