6.4. Heart Failure with Narrow QRS and PR Prolongation
A less studied but significant indication is the application of HBP in
heart failure patients with narrow QRS and atrio-ventricular
dyssynchrony, namely an extensive PR prolongation. Except for
inter-ventricular dyssynchrony, caused by RV pacing, the long
prolongation of the atrial emptying phase also drives to non-optimal
ventricular filling and, therefore, non-optimal application of the
Frank-Starling law. Especially in heart failure patients, that is
important not only for symptoms but also for their adequate cardiac
function, affecting their mortality. After all, in addition to the
simultaneous activation of the two ventricles, the benefit of
biventricular pacing is also due to PR interval
optimization.45
And for this indication of HBP, the data is limited. The randomized,
crossover HOPE-HF trial (His Optimized Pacing Evaluated for Heart
Failure Trial), which is still conducting, includes 160 patients with PR
prolongation (≥200 msec), impaired LVEF ≤40%, and either narrow QRS
≤140 msec or RBBB. The clinical impact of HBP on reducing the PR
interval is studied.55 As primary endpoint is
considered the change in exercise capacity. Secondary endpoints include
changes in LVEF, QoL scores, B-type natriuretic peptide values, and
daily patient activity levels. In another recently published study,
Strocchi et al. (2020), in 24 LBBB heart failure patients recruited for
CRT upgrade (96% males, mean LVEF 34% ± 10%), have compared HBP with
LBBAP, LV septal pacing, biventricular endocardial and biventricular
epicardial pacing, regarding ventricular activation changes. HBP showed
clear superiority over the other pacing methods in ventricular
synchrony, while noteworthy is that for left bundle pacing, AV delay
optimization resulted in a reduction of RV activation
times.56 Undoubtedly, for these studies, as well as
for all the above related to HBP, the lack of large RCTs that would
relate the impact of these findings on hospitalizations or mortality is
a disadvantage and should be investigated in the coming years.