Electrocardiographic optimization
Measurements of the QRS duration during intrinsic rhythm and with the
three pacing configurations were recorded in the 32 patients. The
results are plotted in Figure 2 . Compared to MPP, SPP-FOI and
MPP-FOI achieved greater QRS shortening: the ΔQRS with SPP-FOI was
-56±16 ms; with MPP was -42 ± 17 ms; and with MPP-FOI was -58±14 ms;
omnibus P <0.001. The differences in QRS shortening
between SPP-FOI and MPP-FOI were not significant (P = 0.69, with
a difference between groups of 2 ± 7 ms).
The pacing configuration at discharge is summarized in Figure
3 . The shortest QRS duration was achieved using SPP-FOI in 9 patients
(28%), MPP in 1 patient (3%), and MPP-FOI in 22 patients (69%). Among
the latter two groups combined, 12 out of 23 (52%) patients were not
candidates for chronic MPP because of either (1) the pacing thresholds
exceeded 3.5 V/0.4 ms at the distal (4, 17%) or proximal (6, 26%)
cathodes or (2) incorrigible PNS (2, 9%).
In the SPP configuration, the left ventricular cathode was D1 in 20
patients (62%), M2 in 6 (19%), M3 in 5 (16%), and P4 in 1 (3%). For
the MPP configurations, the two selected LV vectors were D1/P4 in 12
patients (37%), D1/M3 in 14 (44%), and M2/P4 in 6 (19%).