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.