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.