Hemodynamic evaluation
Based on the hemodynamic evaluation, the best univentricular pacing was LV pacing for all 85 patients presenting with left bundle branch block or nonspecific block and for one patient presenting with right bundle branch block. The best LV pacing site was in a lateral or posterior vein rather than the anterior vein (29). When pacing at the selected pacing sites with the best AV delay (mean 119 ± 32 ms), the aortic pulse pressure increased an average of 9.9 ± 11%, and the LV maximum positive pressure rate change increased 19.9 ± 20%.
Implantation
Thirty-four patients were implanted with an ICD and 52 patients were implanted with a pacemaker. All 86 patients were implanted with a LV pacing lead; 61 patients received an epicardial lead and 25 received a transvenous lead. Transvenous lead implantation was successful in 93% of patients (25 successes of 27 attempts).
Randomization
The 86 implanted patients were randomized to the two treatment sequences with a nearly equal distribution of long and short QRS group patients in each sequence (Table 1). There were no significant differences in baseline characteristics between patients assigned to different sequences (Table 1).
Safety
Seventeen patients did not complete the two crossover periods. Three patients were withdrawn immediately after randomization. One had misplaced leads; another received an elective left ventricular assist device (LVAD); and the third was implanted with an ICD device plus a pacemaker.
Five patients dropped out during an active pacing period. Two patients without an ICD had a sudden cardiac death. One patient developed a left-sided pleural effusion related to the epicardial lead implantation. Two patients were unwilling to comply with the study protocol.
Nine patients dropped out during an inactive pacing period. Three patients died (two of them without an ICD by sudden cardiac death). Three patients developed acute HF decompensation (two of them were prematurely switched to active pacing), and the third received a LVAD. One patient developed ventricular tachyarrhythmia and had a replacement biventricular ICD implanted. One patient developed untreatable atrial tachyarrhythmia. One patient developed bronchitis requiring frequent hospitalization.